-

■

THE

RAY SOCIETY

INSTITUTED MDCCCXLIV

This volume (No. 131 of the Series) is issued to the Subscribers to the
Ray Society for the Two Years 1944 and 1945, and at a price of

45/- to the Public.

LONDON

MCMXLVII

06

THE TREMATODA OF
BRITISH FISHES

BY

BEN DAWES, D.Sc., A.R.C.S., D.I.C., F.L.S.

(Reader in Zoologj^ University of London, King's College)

LONDON
PRINTED FOR THE RAY SOCIETY

SOLD BY

BERNARD QUARITCH, LTD.
11, Grapton Street, New Bond Street, London, W. 1

1947

To My Mother

Made and printed in Great Britain by

Adlard & Son, Ltd.,

at their works, Bartholomew Press, Dorking.

PREFACE.

In writing this monograph, my aim has been to describe the trematodes
of British fishes more fully than was possible in my book, The Trema-
toda (Cambridge University Press, 1946), but not to presume to treat
the subject exhaustively. Because of their inconstant shape, indeter-
minate growth and structural variability, trematodes are not easy to
describe or to arrange systematically. Several British zoologists have
collected fish trematodes and listed their names without describing
them. The literature contains a few good descriptions, but also some
very inadequate records, and we owe much of our knowledge of the
trematode parasites of fishes to continental and American zoologists.
The distribution of trematodes is sporadic, their discovery fortuitous,
and it will be evident that more work remains to be done than can be
done by a single zoologist before our systematic plan of fish trematodes
can be completed. I have made some additions to our knowledge,
but there is plenty of scope for further work.

Some of the forms mentioned in the following pages have not been
collected as yet in Britain, and it can be argued that these do not
therefore belong to the British fauna. British marine fishes are not
confined to British waters, however, and it would be illogical not to
include, for instance, forms that occur in some of our commonest fishes
caught off the coast of France or Belgium and in other localities not
very distant from our shores. In some instances it has been difficult
for me to decide where an imaginary line should be drawn and what
forms should be included in or excluded from the list, but I have tried
to include all the forms we can reasonably expect to turn up in British
waters sooner or later. The hosts have been denoted by their common
names in order to save space, but the corresponding scientific names
are listed on pp. 339-43.

I am indebted to several zoologists for encouragement and assis-
tance, but particularly to Professor C. M. Yonge, F.R.S., in whose
Department of Zoology at Bristol much of the work was done. Dr.
W. T. Caiman, F.R.S., gave me some friendly advice and criticism,
and Dr. H. A. Bay lis has been kind enough to check the names of the
trematodes. Several persons have allowed me to examine specimens,
and appropriate acknowledgments have been made in the text.
Most of my own specimens were collected in the Marine Biological
Laboratory, Plymouth, and I am grateful for the assistance given to
me by the staff there. I wish also to thank the printers for the con-
sideration they have shown me and the care they have taken over the
production of my book.

BEN DAWES.

King's College,
London, W.C. 2 ;
July 25, 1946.

CONTENTS

Preface ...........

I. The Phylum Platyhelminthes and the Class Trematoda
II. The Three Orders of the Trematoda ....

III. The Morphology of the Monogenea ....

a. External Structure —

(a) General ........

(b) The Prohaptor ......

(c) The Opisthaptor ......

b. Internal Structure — ■

(a) The General Musculature and Parenchyma .

(b) The Components of the Raptors and their Mode of Action

(c) The Nervous System and Receptors

(d) The Digestive System

(e) The Excretory System

(f ) The Reproductive Systems

IV. The Morphology of the Aspidogastrea

V. The^Morphology of the Digenea .

i. The Sub-order Gasterostomata .
n. The Sub-order Prosostomata

a. External Structure .

B. Internal Structure —

(a) The General Musculature and Parenchyma .

(b) The Nervous System ....

(c) The Digestive System ....

(d) The Excretory System ....

(e) The Reproductive Systems

VI. Trematodes of the Order Monogenea ....
Key to the Families and Higher Groups of the Monogenea

VII. Trematodes of the Order Digenea ....

Key to the Families of Digenea Parasitic in European Fishes

VIII. List of Literature .......

Alphabetical List of Hosts ......

List of Hosts and Their, Parasites ....

General and Systematic Index .....

PAGE
V

1

2
3

6

7
7
8
8
8

10

12

12
13

14

15
16
17
17

18

22
23
146
147
311
339
345
357

753

Abbreviations Used in the Figures.

A. — ab, retracted ecsoma ; as, anterior sucker ; av, accessory vitelloduct

connecting the vaginae.
B. — b, brain ; bs, buccal sucker.
C. — c, caecum ; ca, copulatory apparatus ; eg, cephalic glands ; eg', caudal

glands ; ci, cirrus ; cm, closing muscles of haptorial valves.
E. — e, eye ; e', egg ; e", embryo ; eb, ejaculatory bulb ; ec, excretory canal ;

ed, ejaculatory duct ; egg, shelled-egg ; ep, excretory pore ; eu, eggs

in utero.
G. — ga, genital atrium ; gic, genito -intestinal canal ; gl, lamella of gill ; gp,

genital pore.
H. — hd, hermaphrodite duct.
I. — i, intestine.
L. — 1, terminal process or lappet ; lc, large clamp ; Lc, Laurer's canal ; Ip,

process of lip.
M. — m, mouth ; mc, muscular crest ; my, myoblast.
O. — o, ovary ; ce, oesophagus ; oo, ootype ; om, opening muscles of haptorial

valves ; os, oral sucker ; ov, oviduct.
P. — p, pharynx ; pg, prostate glands ; pr, prostatic vesicle ; pra, anterior

prostatic vesicle ; prp, posterior prostatic vesicle.
R. — ro, " ring-organ " ; rs, receptaculum seminis.
S. — s, larger sucker ; s', small sucker ; sg, shell glands ; sq, squamodisk ; sv,

seminal vesicle.
T. — t, testes.
U. — u, uterus.
V. — v, vitellarium ; va, vagina ; vd, vas deferens ; vg, vagina ; vn, ventral

nerve ; vp, vaginal pore ; vs, ventral sucker.
Z. — zo, zone of the ovary ; zt, zone of the testes.

&>\CAi

THE TREMATODA OF
BRITISH FISHES

I. THE PHYLUM PLATYHELMINTHES AND THE CLASS

TREMATODA.

The phylum Platyhelminthes comprises four well-defined classes,
the Turbellaria, Temnocephalida, Trematoda and Cestoda. These
types of flatworm differ notably among themselves. They may be
monoecious or dioecious, covered with cilia or a cuticle, having or
lacking a gut and special organs of attachment, and they may have
very different modes of life and life -histories. Yet they agree in being
bilaterally symmetrical, triploblastic, accelomate Metazoa devoid of
a blood vascular system, having a well-developed muscular system,
a spongy parenchymatous investment to the internal organs, and a
protonephridial excretory system in which the flame -cell is the funda-
mental unit. The great majority of Platyhelminthes are herma-
phrodite.

Adult Trematoda (flukes) and Cestoda (tapeworms and their
allies) differ from almost all other Platyhelminthes in their parasitic
mode of life. A few exceptional Turbellaria habitually associate with
Mollusca and Echinodermata, and some are parasitic in echinoids and
holothurians, but the vast majority live in freedom. Temnocephalida
are passengers, not parasites, because while living attached to fresh-
water Crustacea they devour insect larvae, rotifers and other small
creatures, and are thus self-supporting. Adult Trematoda and Cestoda
habitually nourish themselves at the expense of a host animal. Some
trematodes attach themselves to superficial parts of the host and are
called ectoparasites ; others, and all Cestodes, penetrate into the interior
of the host and five in one of the internal organs, thus being endo-
parasites. Cestodes can be distinguished from trematodes by the
absence of a gut, feeding in these worms being by the absorption of
predigested nutriment through the integument. Detached pro-
glottides of some cestodes may five independently for a short period
in the intestine of their hosts, a location in which trematodes also
occur, and they may be mistaken for flukes by the unwary zoologist,
but the absence of a gut invariably betrays their true identity. Trema-
toda, therefore, are ectoparasitic or endoparasitic Platyhelminthes
having a cuticle and an alimentary canal.

^ THE TREMATODA OF BRITISH FISHES

II. THE THREE ORDERS OF THE TREMATODA.

Zeder (1800) first attempted a systematic classification of parasitic
worms of all kinds and referred to flukes as " sucking worms."
Rudolphi (1808) invented the name " Trematoda," which is now in
general use. During the early part of the 19th century the study of
trematodes made much progress, and in 1856 two schemes of classi-
fication were proposed independently : Burmeister divided the
Trematoda into Malacobothrii, Pectobothrii and Aspidobothrii (groups
roughly represented by forms now known as distomes and holostomes,
Polystomids, and Aspidogastrids respectively) ; Leuckart divided
them into the " Distomea " and " Polystomea," endo- and ecto-
parasites respectively. Carus, in 1863, renamed Leuckart's groups
Digenea and Monogenea (the "Trematodes Digeneses" and "Trema-
todes Monogeneses" of v. Beneden, 1858). On the whole, Leuckart's
scheme has been the more popular, although in 1892 Monticelli
attempted to revive the three groups of Burmeister under the new
names Heterocotylea (monogenetic forms), Malacocotylea (digenetic
forms) and Aspidocotylea (Aspidogaster) . Faust and Tang (1936)
made further efforts of this kind, reminding us that while Aspidogaster
combines the characters of both Monogenea and Digenea, it (and its
allies) cannot rightly be included in either group because of the equi-
vocal nature of the life -history, which in some instances is completed
in a single host, but in others seems to require two. Aspidogastrids
occur in fishes, chelonians and molluscs, but do not seem to have been
found in fishes in Britain (though it is likely that they occur here).
In spite of the fact that they form a very small group they will be
regarded here as of equal standing with Monogenea and Digenea,
forming the third order, the Aspidogastrea.

The three main types of Trematoda can be recognized in a general
way by superficial characters, the nature of the organs of adhesion
and the positions of various apertures on the surface of the body. In
Digenea the adhesive organs are generally two comparatively simple,
more or less hemispherical, muscular suckers, unaccompanied by
accessories. One encircles the mouth and is called the oral sucker,
the other is situated somewhere on the ventral surface of the body
and is called the ventral, if far back the posterior sucker. In Mono-
genea adhesion to the host is facilitated by various structures, generally
more complicated suckers or clamp-like structures, often having a
more or less complex system of skeletal supports, and accessories
such as hooks and hooklets, sometimes glands which produce a sticky
secretion. Price (19346) proposed the term haptor (Gk. haptein, to
fasten) to denote an organ of attachment without having any morpho-
logical implication ; I have proposed (Dawes, 1946) to designate the
haptor near the anterior extremity the prohaptor, that near the
posterior extremity the opisihaptor. In Aspidogastrids the prohaptor
is sometimes absent, and the opisthaptor comprises either a single
row, or three or four rows of suckerlets of a distinctive type {alveoli),
the whole arrangement sometimes forming an organ which is as
conspicuous as the " foot " of a gastropod mollusc.

THE MORPHOLOGY OF THE MONOGENEA 3

The mouth is almost invariably near the anterior extremity in
both Monogenea and Digenea, but in one family of the latter (the
Bucephalidae) it is central, as in some Turbellaria. A second opening,
the common genital pore, is generally situated a short distance behind
the mouth, but in Bucephalids it is near the posterior extremity. A
few trematodes have separate male and female pores which are not
far apart. Other openings are diagnostic. In Monogenea there is a
pair of antero -lateral excretory pores, in Digenea a single posterior
pore. In some Monogenea there is a single, median ventral vaginal
pore, or a pair of more or less lateral pores, or a dorsal pore ; in Digenea
there is a single postero-dorsal pore, the opening of Laurer's canal.
Laurer's canal, which leads into the female reproductive system, is
absent in Monogenea, and vaginae never occur in Digenea.

The three orders of the Trematoda are decidedly unequal in the
numbers of their families, the Digenea containing more than 60
(about one-third of them confined to fishes) as well as numerous
unclassified genera, the Monogenea 16 and the Aspidogastrea the
solitary family Aspidogastridse. Only one family of the Monogenea is
absent from Europe, but a number of families of the Digenea which
parasitize fishes elsewhere have not been recorded in this continent.
Aspidogastrids have been found in Europe, notably in the Volga delta
and the Don, and also in the Caspian Sea and elsewhere.

III. THE MORPHOLOGY OF THE MONOGENEA.

In this section an attempt will be made to give a detailed impression
(based on my previous account, see Dawes ; 1946) of the external and
internal structure of Monogenea, so as to render fully intelligible the
abbreviated diagnoses to be given later. For the most part, internal
structure has not been studied in the same detail as the external,
perhaps because taxonomic importance has been attached to superficial
characters, but also because heavy pigmentation sometimes obscures
the internal organs, even in the living trematodes. If this sketch
indicates greater variety in the superficial organs of the Monogenea
than in their deeper parts, however, it is perhaps because the latter
are the more stereotyped.

a. External Structure.
(a) General.

Most Monogenea are less than 10 mm. long, but some attain a
length of 20 or 30 mm., and in shape they are lanceolate, elliptical or dis-
coidal, sometimes of rather rugged outline. When the body is elongate
it is often almost cylindrical ; when discoidal it is flat, but sometimes
convex dorsally and concave ventrally. The lateral margins may
turn inwards ventrally. The anterior region which bears the mouth is
generally very mobile, at one moment drawn out into a tapering
process, but at another strongly contracted, even retracted into the
body, and it makes frequent exploratory movements. The entire

4 THE TREMATODA OF BRITISH FISHES

body is in some measure extensile and contractile, so that the shape is
anything but fixed. Carefully preserved specimens generally provide
what might be called the mean shape and show corresponding uni-
formity internally, but the absence of a fixed form necessarily implies
greater variability in the topographical relations of the internal organs
than would be encountered in animals of constant shape.

The entire body is covered with a cuticle which is rarely as thick
or as spinous as that of the Digenea, in which greater protection
against the secretions of the host would seem to be needed, and where
spines provide purchase during locomotion in crevices and at the same
time a superficial roughness that assists adhesion under such circum-
stances. The cuticle of Monogenea is not invariably smooth, however,
sometimes having a generous sprinkling of spines dorsally and laterally
in the anterior region. In the absence of spines, sometimes in their
presence, the cuticle may be raised into papillae. Spines may also
be localized on disk-like plates called squamodisks posteriorly. The
cuticle may be continued into the terminal parts of the digestive and
reproductive systems, and it both covers the haptors and lines their
cavities. Subcuticular cells are generally sparse, suggesting that the
cuticle might be a cuticularized epithelium, but alternative modes
of origin undoubtedly prevail. The cuticle is frequently termed
" chitinous," but specific tests have not confirmed the presence of
chitin (see Remley, 1942) and the term should be avoided.

(b) The Prohaptor.

, In some Monogenea the prohaptor is a cup- shaped muscular organ
encircling the mouth, an oral sucker essentially similar to that of
Digenea, but more feebly developed and less sharply set off from the
underlying parenchyma. More often, this haptor comprises a pair of
saucer-like suckers situated some distance from the mouth at the
lateral margins of the somewhat truncated anterior extremity. These
anterior suckers are sometimes frilled by a pleated membrane. Less
conspicuous suckers, called buccal, occupy the lateral walls of the
prepharynx in many Monogenea, and may be so small as to be evident
only in sections. Otherwise the prohaptor may be ill-defined and not
sucker-like, and represented by various structures which have received
nearly as many names. There may be two symmetrical suctorial
grooves, one on either side of the anterior extremity, or lateral expan-
sions of this region called head-lappets, or papilla-like outgrowths of
more concise shape known as head-organs with associated multicellular
head-glands which secrete a viscid substance and extrude it through
special ducts on the surface here. Head- organs vary in number,
and they provide characters of taxonomic importance ; there may be
one or two pairs, three pairs, several pairs, or numerous scattered
individuals. Some Monogenea with neither head-lappets nor head-
organs have numerous glands opening on lateral glandular areas,
which may co-exist with anterior suckers. In a few instances a pro-
haptor is absent, but the mouth may be encircled by a somewhat

THE MORPHOLOGY OF THE MONOGENEA 5

membranous structure called a pseudosucker. Whatever its structure,
the prohaptor brings about the application of the mouth to the sub-
stratum whilst feeding is in progress, and it may also serve for tem-
porarily maintaining adhesion while the opisthaptor gains a fresh hold
on the host during locomotion.

(c) The Opisthaptor.

The simplest kind of opisthaptor is just a ventral disk-like out-
growth of the posterior region, which is generally muscular and may
be unarmed, or provided with large hooks and much smaller hooklets
which serve as grapnels. Special muscles cause the recurved tips of
the hooks and hooklets to bite into the tissues of the host, other
muscles abstracting them again. The hooks may be supported by two
transverse cuticular bars, one dorsal and the other ventral, or by a
single bar. The hooklets are carried over into the adult from the
larval stage, and are so small as to have been overlooked by many
investigators, though Price (19376) has reported their presence in
numerous genera of the Capsalidse and they are well known to occur
in other families. They number 14-16 as a rule and they persist for
varying periods when not permanent. They are frequently referred
to as marginal hooklets because of the usual position, but this qualifi-
cation is unnecessary and it may be misleading.

This comparatively simple opisthaptor is characteristic of the
sub-order Monopisthocotylea, in various families of which certain
modifications are found. From the simplest type of all, a mere
eminence bearing hooks and hooklets, a series can be arranged in which
the opisthaptor becomes sucker-like, but still simple, then septate to
varying degrees, the ventral surface becoming divided up by slightly
raised and more or less radial septa into a number of sectors or loculi,
each with a sucker-like function of its own. The numbers of septa
and loculi are 6-7, 8 or 10, and the radial symmetry may be disturbed
by the incompleteness of some of the septa and the fusion of others,
or may even give way to bilateral symmetry in instances where two
or more series of loculi are arranged tangentially to the margin of the
haptor, some members of the series being larger than others. The
simplest modification is the development of one central loculus and a
small number of peripheral loculi. A third set of loculi may be
interposed between the central and peripheral, and bilaterality is
evident when the posterior loculus is much larger than the others.
Mention must be made of a modification of another kind, in which the
haptorial disk of the larva fails to enlarge during growth and is sup-
planted by a large secondarily developed disk or pseudohaptor bearing
radial rows of spines. In this type of opisthaptor the true disk persists
as a rudiment, still bearing the hooklets, on the posterior margin of the
functional pseudohaptor.

In the other sub-order, Polyopisthocotylea, the opisthaptor shows
a higher grade of organization, comprising one pair to four pairs of
muscular, cup-like suckers or clamp-like organs set on a disk or

6 THE TREMATODA OF BRITISH FISHES

cotylophore, or on the ventral surface of the body. In rare instances
asymmetrical arrangements have been recorded. The number of
pairs of such structures has been used to distinguish various families
of the sub-order, but the validity of this is questionable. The terminal
part of the opisthaptor is subject to further modification, the most
posterior pair of suckers sometimes being of much reduced size and,
in one family, set near the tip of an elongate dorsal outgrowth or
appendage of the disk. Where the opisthaptor has become compli-
cated in this way, the haptorial armature, consisting of hooks and
hooklets, has become simplified, though not invariably, or propor-
tionately. In particular, the bar-like supports for the hooks have
disappeared. There may be one pair of large hooks, or several pairs of
smaller ones, some of which may overlie others. In some Polyopistho-
cotylea cuticular structures of the most fantastic shapes simulate
hooks, but are really deeply situated layers of cuticular materials
which serve as supports for the suckers and as a firm basis for the
insertion of the muscles which work them. Other cuticular skeletal
structures (sclerites) reach the climax of complexity in the family
Diclidophoridse ; their nature and arrangement will be considered in
the diagnoses for the various members of this family.

b. Internal Structure.
(a) The General Musculature and Parenchyma.

Immediately beneath the cuticle, several layers of muscular fibrils
support the integument of the body and bring about the general
movements of the animal. The fibrils of the outermost layer extend
tangentially to the surface in the transverse plane, collectively forming
a circular layer, which is absent in a few instances. Beneath it, as a
rule, other fibrils are arranged diagonally and longitudinally in turn,
the longitudinal layer being relatively thick. These layers of muscles
function in a complementary manner, the transverse fibrils contract-
ing when the longitudinal relax, and vice versa, to produce lengthening
and attenuation of the body at one time, shortening and thickening
at another. The diagonal muscles mainly augment the effects due
to the other layers. Additional muscles traverse the parenchyma
dorso-ventrally and by their contraction flatten the body somewhat.

The muscular layers are not of uniform thickness, though care
must be taken in determining their thicknesses lest local contractions
falsify the determinations. In Hexostoma extensicaudum, the super-
ficial layer of diagonal fibrils is thinner anteriorly than posteriorly.
In this trematode the thick longitudinal layer is divided into two
subsidiary layers separated by parenchyma ; both layers are thicker
dorsally than ventrally and posteriorly than anteriorly, and the deep
layer is 4-7 times as thick as the more superficial. Deep and super-
ficial components of the longitudinal muscle layer play different parts
in the action of the opisthaptor, and the greater thickness of the former
is explained by the fact that adhesive action of the suckers depends

THE MORPHOLOGY OF THE MONOGENEA 7

on it, release being due to the superficial components (see Dawes,
1940a).

The parenchyma is composed of loosely packed cells and fibrils
which fill the available space around the internal organs. The simplest
condition is that in which polygonal cells form a tissue binding these
organs with the integument, but in some instances ecto- and endo-
parenchyma are differentiated, the former comprising masses of fibrils
secreted by cells, the latter cellular masses. In some Monogenea the
parenchyma is a true syncytium which enters into the composition
of the ducts of various internal organs, here being fibrillar and devoid
of nuclei. Fibrillar protoplasm invariably stiffens the ends of the body
and other parts in which rigidity is required.

(b) The Components of the Haptors and their Mode of Action.

From what has been said already about the haptors of the Mono-
genea it will be evident that haptorial action varies considerably.
Unfortunately this subject has not been studied in detail, so that a
comparative account cannot be given. I have already (Dawes, 1940a,
1946) explained it in Hexostoma extensicaudum, but have to admit that
many other modes probably exist which would repay serious study.
Where the haptors comprise suckers, the action may be due to intrinsic
muscles, but in many Monogenea the suckers are fibrous, not muscular,
and extrinsic muscles which are inserted in the skeletal supports alter
the degree of concavity to produce, increase or decrease the suction.

(c) The Nervous System and Receptors.

Although difficult to demonstrate, the nervous system is not com-
plex, consisting of two anterior clusters of nerve cells and several
bundles of fibres. The ganglia are connected by a transverse com-
missure, forming a rudimentary " brain," from which the nerves issue
to various regions of the body. The anterior region is well provided
with nervelets, and three pairs of nerves generally extend posteriorly
in the dorsal, ventro-lateral and ventral regions. The ventral nerves:
are the most prominent, and are so metimes linked by transverse com
missures forming a kind of network in this region. They give off
nervelets to the opisthaptor, and the prohaptor and pharynx are other
organs having a rich innervation, though not from the same source.
The ventro-lateral nerves are invariably smaller than the ventral and
the dorsal nerves are well developed in some forms, absent in others.
Most of the nerves are motor in function, as might be expected from
the feeble development of sense organs, which are more important
than in Digenea, however, in accordance with the more variable con-
ditions in the environment. The chief sense organs are paired eye-
spots, which may have an accessory lens-like structure, or may be
absent. Tristoma has been credited with a rudimentary kind of
" taste -org an," but such inferences are hardly justified. In most
Monogenea, however, numerous sensory nerve-endings exist at the
base of the integument, particularly near the anterior extremity and

8 THE TREMATODA OF BRITISH FISHES

in the kaptors. Apart from the eyes, these may be regarded as the
principal receptors.

(d) The Digestive System.

The alimentary canal is divisible into three parts, pharynx, oeso-
phagus and intestine. In some Monogenea a prepharynx is interposed
between the mouth and the pharynx, but this is often a transitory
structure, being obliterated by movements of the anterior extremity.
When it is permanent, buccal suckers may be situated in its walls.
When these are absent, the pharynx may serve as a sucker. This
part of the gut may be protrusible, and there may be even closer
resemblance to the Turbellaria when the pharynx is enclosed in a
pouch. In Capsala the pharynx has a distinctive central constriction,
and it is sometimes beset with papillae. The intestine is sometimes
simple and saccular, a condition which may be modified by the develop-
ment of fenestrations in the region of the gonads, but generally it
bifurcates near the posterior end of the pharynx. The two caeca thus
formed may be simple and unbranched, or the crura may unite pos-
teriorly to form a ring-like intestine. Often the caeca give off median
and lateral diverticula, and these may have dendritic terminations or
may form anastomoses. In some Monogenea with a discoidal opist-
haptor an intestinal trunk may extend into it from a median anasto-
mosis farther forward, giving off ramifying branches. Where the
opisthaptor is further complicated by the development of a dorsal
appendage, branches of the caecal stem may extend into this almost
to its tip. Differences of a histological nature also exist. The lining
of the intestine may be a continuous epithelium of cubical or cylindrical
cells, or the continuity may be broken. Alternatively, cells may be
absent, the lining apparently consisting of fibrils secreted by the
parenchyma. Much scope exists for the histological study of this and
other systems of organs.

(e) The Excretory System.

Our knowledge of this system is scanty, but it is built up of flame-
cells and collecting vessels. The latter may form a network, but
generally they unite to give rise ultimately to a pair of longitudinal
canals which are situated in the lateral regions, beginning anteriorly
as fine vessels, widening and turning about near the opisthaptor and
extending to the level of the pharynx, where each enters a small
spherical vesicle which is connected with the exterior by a short,
straight canal. This general arrangement is never met with hi the
Digenea, the paired vessels and pores being distinctive.

(f) The Reproductive Systems.

Some Digenea are dioecious, but all Monogenea are androgynous.
The male system comprises a single testis in some instances, but more
often there are two, three or numerous testes, which occupy the space

THE MORPHOLOGY OF THE MONOGENEA 9

between the caeca, tending to fill it when numerous, and generally
situated behind the ovary. Vasa efferentia unite ultimately to form a
vas deferens leading to the copulatory organ, which is sometimes quite
simple, but may be complicated by cuticular accessories of somewhat
doubtful function. It may be protrusible and eversible (i.e. a cirrus)
or only protrusible (i.e. a penis), and it generally projects into a shallow
ventral pit or genital atrium which also receives the terminal parts of
the female system. When the male and female pores are separate
they may be median, but are sometimes lateral. The vas deferens is
sometimes distended to form a seminal vesicle, and the terminal part
of the male system, or ejaculatory duct, frequently has a cuticular
lining and glands may open into one part of it, the pars prostatica. In
a few Monogenea a copulatory organ is absent, but in others it is
conspicuous and sometimes equipped with hooklets that assist
copulation. This end may be served, alternatively, by hooklets in
the wall of the genital atrium.

In the female system the ovary is rarely globular, as in the Digenea,
but is generally elongate and much folded, sometimes lobed as well.
Ova mature in the terminal part and pass into a short oviduct, the
first part of which may form a chamber, the ovicapt, which can be
closed at either end by a sphincter and spaces out the ova into a
steady stream. In a special region of the oviduct, the ootype, the ova
are fertilized and encapsulated. At this point several ducts converge ;
they are the vagina or vagince, the vitelloducts, the uterus and the
genito -intestinal canal. The vagina is not invariably present, and its
absence is a negative character of some taxonomic importance. When
a vaginal system is present it may consist of a single tube, or of separate
tubes forming a pair, or a pair of tubes which merge to form at single
canal at some point along their length, three conditions which are
made use of by systematists. The median or lateral positions of the
vaginal pores have been commented on already. The canals, which
are sometimes lined with sculptured cuticle, serve as conduits for
spermatozoa received in copulation and retained till required in a
chamber, the receptaculum seminis, conveniently near the ootype.
Where the vagina? are continuous with the lateral vitelloducts they
possibly serve also as conduits for the removal of unwanted portions
of shell materials. The vitelloducts are extensive paired canals from
the vitellaria, follicular organs extending along the lateral regions of the
body and sometimes encroaching on the median space between
the caeca. Their main terminal parts extend transversely inwards,
meeting in a median vitelloduct or a vitelline reservoir. They serve
for the transference of vitelline cells loaded with droplets of shell
substance to the ootype. In rare instances the vitellaria are absent ;
in a few the follicles are associated with the ovary, forming a germ-
vitellarium, as in some Turbellaria. The uterus is a wide tube which
receives the shelled eggs and conducts them to the genital atrium.
Its terminal part, the metraterm, may be muscular, like the vagina,
and provided with a cuticular lining and structures superficially
resembling hooks. The remaining canal of the four mentioned, the

10 THE TREMATODA OF BRITISH FISHES

genito -intestinal canal, connects some part of the oviduct with the
right caecum, rarely the left. It is not represented in the Monopistho-
cotylea, and one possible function of the canal is the removal of super-
fluous shell fragments deposited in or near the ootype during the
process of shell-formation. The eggs of Monogenea are relatively
large and generally provided with polar filaments, or a filament at one
pole only. In some instances the egg is ovoid, in others the poles end
in knob-like processes. Otherwise, one pole may have a small thicken-
ing, the other a long, twisted filament, or one pole a short, hooked
process, the other a long, straight filament. In rare instances both
poles are drawn out into very long filaments fifty times as long as the
capsule, and the filaments may be contiguous so that the eggs are
laid in chains. All these departures from a regular ovoid form are
indications that the egg-shell was formed from liquid material, some
of which was drawn out into a viscid thread prior to hardening. In
all Trematoda the bulk of this material originates in the vitelline cells,
which convey it to the ootype, the mould in which the capsule takes
shape. No doubt the details of egg-formation vary slightly in different
Monogenea, but I have described elsewhere (Dawes, 19406, 1946) the
process in Hexostoma extensicaudum. Unicellular glands situated just
outside the wall of the ootype secrete a thin liquid, but not in sufficient
amount to account for all the egg-shells formed, so that the name
shell-glands is misleading. Several possible functions have been
suggested for this liquid — that it is a nutrient for ova and spermatozoa,
or a lubricant ensuring the smooth passage of the eggs into the uterus,
or a hardening agent — but all seem to fall short of the truth. I have
suggested (19406) that it may form a thin layer upon which shell-
forming materials from the •■vitelline cells are laid down from the inside,
and (1946) that it possibly contains agents (electrolytes, for instance)
which bring about the rapid extrusion of these materials at an appro-
priate instant. Polar filaments are no doubt formed as rivulets of
shell material which overflow from the ootype, and their common
occurrence in Monogenea is an indication that a greater excess of
material exists than in Digenea. This is probably due to the great
development of the vitellaria and the smaller numbers of eggs produced.

IV. THE MORPHOLOGY OF THE ASPIDOGASTREA.

The order Aspidogastrea (family Aspidogastridae) contains only nine
genera, but these have a world-wide distribution and are variously para-
sites of fishes, chelonians, Gastropod and Lamellibranch Mollusca and the
larger Crustacea. The most familiar form, Aspidogaster conchicola, (Fig.
29 A, p. 150) inhabits various locations in freshwater mussels of the genera
Anodonta and Unio, but especially the pericardial cavity, where 20-30
individuals may be crowded together near the internal opening of the
kidney. This species occurs in the New World as well as the Old, and
in China. Faust (1922) discovered it in snails and in the alimentary
canal of a turtle. Juveniles sometimes occur in the intestine of
lamellibranchs, occasionally encysted in the pericardial gland. In

THE MORPHOLOGY OF THE ASPIDOGASTREA 11

America parasitized Unionida) ingested by fishes, frogs and turtles
liberate their worms, which continue to live in the new hosts, so that a
second host is annexed to the otherwise simple life-cycle (Williams,
1942). Aspidogaster conchicola forcibly fed to the turtle, Pseudemys
troosti, has continued to live in the stomach for periods up to fourteen
days (Van Cleave and Williams, 1943). The most complete descrip-
tion of this trematode was given by Stafford (1896), and I have recently
(1946) given an account of it, drawing attention to several points in
the anatomy which would bear closer study. Williams (loc. cit.) made
a few general remarks concerning the structure of the adult, but he
was concerned primarily with the larvae and the life history.

It is unnecessary here to deal with the detailed morphology of
Aspidogaster conchicola,* but a few points may be noted before passing
on to other species and genera. The adult worm is about 3 mm. long
and 1 mm. in maximum breadth, although much smaller specimens
may be found to have matured. The body is anvil-shaped, the upper
part containing the viscera, the lower forming an enormous cotylo-
phore bearing numerous transverse and three longitudinal septa,
which divide the lower surface into alveoli. At the margin of the
disk near the indentations which lie opposite the transverse septa
there are papilla-like marginal organs, which Diesing (1845) described
as pores, Voeltzkow (1888) as retractile sense organs. Several zoo-
logists have stated than an oral sucker is not present in the adult, but
Williams affirmed its presence and it occurs in the adults of other
species, e.g. A. decatis and A limacoides (see Fig. 29 B, C, p. 150).

The genus Aspidogaster is characterized by the four rows of alveoli,
a single testis and the absence of papillae on the central part of the
cotylophore and of lip-like processes near the mouth. Various species
of the genus differ in the number of alveoli, which are generally far
fewer than in A. conchicola. According to I. and B. Bychowsky
(1934) the numbers of alveoli do not form very reliable criteria of
specific distinction, but A. conchicola has 28-42 in the middle rows, A.
limacoides 12-18 and A. decatis 9-10.

It is unnecessary to enumerate the various genera of Aspidogastrea,
a key to which has been given (Dawes, 1941, 1946), but three of them
must be mentioned because their species are parasitic in fishes in
Europe. They are Macraspis Olsson, 1868, Stichocotyle Cunningham,
1884, and Cotylogaster Monticelli, 1892. The first two have a single
row of alveoli, the last three rows. In Macraspis the suckers
are borne on a disk, marginal organs are present, the mouth is
terminal and there is a single testis. The type species, M . elegans
Olsson, 1868, was discovered in the gall-bladder of the rabbit-fish
in the Skagerrak. In Stichocotyle a disk is wanting, the alveoli
appearing as separate suckers, marginal organs are absent, the
mouth is not quite terminal and there are two testes. The type
species, 8. nephropis Cunningham, 1884, as originally described, was
a larval form from the Norway lobster in the Firth of Forth, and

* See Fig. 29 A (p. 150) for a diagram of the reproductive organs.

12 THE TREMATODA OF BRITISH FISHES

Monticelli thought it possibly a form of Macraspis, but Odhner (1898)
discovered the adult, which inhabits the bile-ducts of various rays
and may be expected to occur in Britain. Nickerson (1902) also
found the larva in the American lobster, Homarus americanus. Cotylo-
gaster is further distinguished by the marginal organs, the terminal
mouth with its oral suckers, and two testes. The type species, C.
michcelis Monticelli, 1892, was found in the intestine of Cantharus
vulgaris at Trieste, a second species, C. occidentalis Nickerson, 1899,
in the same location of Aplodinotus grunniens in North America.
Another form, at one time included in the genus Aspidogaster, but
later referred by Eckmann (1932a) to a new genus, Lobatostoma, occurs
in fishes in North America. The occurrence of the European species
mentioned in British waters is not improbable, but they would be
readily recognizable by the generic characters should they appear.

V. THE MORPHOLOGY OF THE DIGENEA.

Only about one-third of the families of Digenea exist in fishes, so
that by confining our attention to parasites of this class of hosts we
shall overlook much of the variety of structure which characterizes
the Order. The Digenea of fishes are by no means stereotyped, but
by comparison with the wealth of forms parasitic in higher vertebrates
they are comparatively uniform. The body is rarely flat and leaf-like,
but generally elongate and with tapering or rounded extremities, and
circular or oval in cross section. Two main types of structure exist
representing the two sub -orders of the Digenea, namely, the Gastero-
stomata and the Prosostomata. In the former the mouth is situated
at or near the middle of the body and the haptor is anterior to it ; in
the latter this opening is near the anterior extremity, and what might
be regarded as the main haptor, the ventral sucker, lies behind it.

i. The Sub -order Gasterostomata.

This group occurs only in fishes and contains one family, the
Bucephalidse (syn. Gasterostomidse Braun). Adult gasterostomes
inhabit the alimentary canal, while larvse occur in Mollusca and encyst
in various parts of the central and peripheral nervous system of fishes,
notably in the brain and ear, or on the course of the cranial or spinal
nerves. Bucephalopsis gracilescens, a common parasite in the pyloric
caeca of Lophius, is a typical representative of the group. It is about
6 mm. long, colourless, except for the brown tinge due to eggs in utero,
and covered with delicate spines. The mouth is situated about one-
quarter of the distance along the body and is encircled by a globular,
muscular organ about 0'3 mm. in diameter that is commonly called an
oral sucker ; but the fact that the organ lies beneath the integument
shows it to be a pharynx. A slightly larger sucker about 0'4 mm. in
diameter occupies the anterior tip of the body and is thus well in
front of the mouth. In other genera this anterior holdfast is of a
different nature, a sucker having retractile tentacles in Bucephalus,
a fan-like hood in Rhipidocotyle, a protrusible rostellum or rhynchus in

THE MORPHOLOGY OF THE DIGENEA 13

Prosorkynchus. Along with other characters it provides a means of
distinguishing the different genera. Other characters are fairly
constant, but the topography of the internal organs may vary some-
what. The chief organs are a simple sac-like intestine, a prominent
and undivided excretory vesicle having a posterior pore, and a set of
hermaphrodite reproductive organs opening by a posterior common
genital pore. The male reproductive system includes a pair of
globular testes and of vasa efferentia, a short vas deferens, a large
cirrus pouch containing an elongate and spinous cirrus, a seminal
vesicle and numerous prostate glands. The female system comprises
a globular ovary, which is smaller than either of the testes, a short
oviduct, an ootype, and the ducts which occur in all Digenea, namely
the vitelloducts, uterus and Laurer's canal. The vitellaria are coarsely
follicular and anterior in position, and they are sometimes arranged in
the form of a bow, their ducts converging on the ootype. Even before
the eggs are formed the uterus has developed two or three limbs and
extends far forward before passing back to the genital pore ; in the
gravid condition it may develop other, rather indeterminate folds also.
The encysted juvenile Bucephalopsis gracilescens occurs most
commonly in the haddock. The cysts, which are easily recognized
by their oval or pear shape and are about 0*6 mm. long, sometimes
occur in the skin, but more often in the central canal of the nerve cord
or on the auditory or spinal nerves. The young individuals which
occupy the cysts singly may be up to 25 mm. in length and already
they have most of the characteristic organs of the adult.

ii. The Sub -order Prosostomata.

Several distinctive types of Prosostomata parasitize vertebrates
and have long been known by common group-names such as Amphi-
stomes, Monostomes, Holostomes, Distomes, Echinostomes and
Schistosomes, which are adequately dealt with in text-books on
helminthology. Of these general types only the Distomes are repre-
sented in fishes in Europe, though certain close relatives of other types
occur in this class of vertebrate. Amphistomes parasitize all classes of
the Vertebrata, but not in Britain. Mesometra, a genus of what might
be called Monostomes probably closely related to the Notocotylidae,
was discovered in Box salpa in Mediterranean waters. Aporocotyle,
a blood parasite related to the Schistosomatidse, is a parasite of certain
teleosts, notably flatfishes. Echinostomes are parasites of birds and
mammals, but certain near relatives, the Acanthostomatidse, occur in
fishes. Holostomes also parasitize the two highest classes of verte-
brates, but their larvae occur in fishes, e.g., " Diplostomum volvens " in
the eye or lens capsule of the Trout and other fishes. The corre-
sponding adult, Diplostomum spathaceum (Rudolphi, 1819), is an intes-
tinal parasite of various gulls which feed on the intermediate hosts.
Distomes form a very large group, and more than a dozen of the 40 or
more families occur in British fishes. They are easily recognized by
the two conspicuous suckers, the oral surrounding the mouth and the

14 THE TREMATODA OF BRITISH FISHES

ventral situated somewhere on the ventral surface of the body, but
not at the posterior end. Not all Prosostomata are included in these
general terms, but few other types are important for the present
purpose. One family deserves special mention, however, the Didy-
mozoidae, thread-like cyst-dwellers, some of which lack suckers. Two
species of the type genus, Didymozoon, have been found in this country,
where other genera probably exist, although only one genus, Kollikeria,
has been found so far.

a. External Structure.

Prosostomatous Digenea are mostly 5-10 mm. long, though some
attain a length of 20-30 mm. and thread-like forms become much
longer. The cuticle is generally thicker than in Monogenea and spines
are more common. When spineless, the cuticle may be wrinkled, and
in some instances it is differentiated into narrow transverse zones
which give it a serrated profile. I have previously (Dawes, 1946)
outlined theories regarding the nature of the cuticle, which seems to
have several modes of origin, being in some instances a metamorphosed
epithelium, in others a secretion produced by cells which afterwards
sink into the parenchyma. Gland cells sometimes exist in the
parenchyma, particularly near the mouth, and are said to be of ecto-
dermal origin. They open by minute ducts which pierce the cuticle.
Similar glands sometimes open into the anterior part of the gut,
generally the oesophagus, and possibly produce secretions that assist
digestion. On the other hand, some glands to which such a function
has been ascribed are probably part of the apparatus used by the
cercaria for effecting an entry into the second intermediate or final
host. Such penetration-glands may be particularly noticeable in
juveniles, and they are generally lost before the adult stage is reached.

Nothing further need be stated at this point about the apertures
on the surface of the body, and little about the suckers, which vary
very little and consist largely of radial fibrils sharply marked off from
the underlying parenchyma, a character which contrasts with that
seen in the haptors of the Monogenea. Equatorial and meridional
fibrils occur near the rim of the sucker and form a sphincter. The
cavities of the suckers are invariably lined with cuticle. The oral
sucker may have a coronet of large spines and sometimes has a number
of short fleshy processes. Sensory papillae may occur along the margin
of the ventral sucker.

In some Hemiuridae the body is divided into two regions, the pos-
terior part forming an appendage which can be retracted into the
anterior part, undergoing considerable folding in the process. The
two regions have been called " body " and " tail," " soma " and
" abdomen," and " soma " and " ecsoma " respectively. The ecsoma
has been called the " appendix," the anterior part of the soma the
' presoma." The ecsoma was once supposed to be a modified tail
such as occurs in cercariae. Wagener (18606) opposed this view, but
Monticelli later (1891) revived and defended it. Looss (1896) contested

THE MORPHOLOGY OF THE DIGENEA 15

the opinion once more, and later (1907) supported Pratt (1898) in
regarding the ecsoma as nothing more than a modified part of the
excretory bladder. Looss observed that an ecsoma occurs in Hemi-
uridse which inhabit the stomach of the host, not in those which live in
the oesophagus (e.g. Aponurus, Aphanurus) or intestine (Leciihaster) ,
and that it is present in the larger forms, but not in the smaller, and
best developed in the largest. He suggested that parasites of the
stomach require a thick cuticle in order to resist the acidic action of
the gastric juice, and that such a protective layer would tend to interfere
with other functions of the surface of the body, possibly with nutrition
and respiration. The thinner cuticle of the ecsoma would permit
such functions to be carried out, and retraction of the organ into the
soma when a high degree of acidity developed in the stomach would
afford protection. This tentative opinion has never been discarded,
although some facts tell against it. The functions attributed to the
integument are doubtful, but in any case the ecsoma may be extended
or retracted in Hemiurids collected from the stomach of a fish when
gastric digestion is at its height. Also, the cuticle of the soma and
that of the ecsoma in several species of Hemiuridse do not show any
appreciable difference in thickness (Lloyd, 1938), although the staining
reactions may be different, the ecsoma taking on a sharp and brilliant
coloration with cytoplasmic stains, the soma an altogether duller and
less decided tone. This may indicate different physical or chemical
properties, or merely different external influences during the life of
the trematode.

Needless to say, the appearance of the same species of trematode is
very different when the ecsoma is extended and when it is retracted.
In the former condition the fluke has a long, tapering posterior end
similar to that of most other Digenea ; in the latter the posterior end is
truncated, and the illusion of an additional organ is created by the
arborescent space (a portion of the external world) which is now
included in the body. Intermediate stages in the retraction of the
ecsoma provide additional appearances in which some folding is more
or less evident.

Looss also commented at length on alterations of the form and
topography of the organs in the posterior part of the soma which are
brought about by retraction of the ecsoma, emphasizing that structural
characters in the anterior region or "pre -soma" are less variable and
thus more reliable in taxonomy. One character of some Hemiurids
in this region is a small, sucker-like ventral pit a short distance in
front of the ventral sucker. In Looss' opinion the identification of
species of Hemiuridae which have soma and ecsoma is possible so long
as the anterior region of the soma is well preserved.

b. Internal Structure.

(a) The General Musculature and Parenchyma.

Some Prosostomata are decidedly muscular, the parenchyma being
almost filled with contractile fibrils, but others have feebler muscles

16 THE TREMATODA OF BRITISH FISHES

and an altogether more delicate texture. Three muscle layers (circular,
diagonal and longitudinal) are generally arranged in the form of a tube
beneath the cuticle. Sometimes an additional layer of circular fibrils
exists beneath the typical layers, and there may be a layer of deep
longitudinal fibrils separated from the superficial ones by a wide zone
of parenchyma, as in Cestoda. Dorso- ventral muscles traverse the
parenchyma in most instances, especially in the lateral regions, which
are not complicated by the presence of internal organs, but these are
ill developed when the form of the body is cylindrical. The muscle
fibrils rarely show the histological characters of other types of
muscle, but are striated in some cercariae. Giant cells called myo-
blasts, having a number of processes each inserted in a muscle fibril,
sometimes occur beneath the general musculature, but are more
numerous in the vicinity of the suckers. They may themselves be
arranged in small groups which seem to be syncytial. Special arrange-
ments of muscles exist in some parts of the body, e.g. near the genital
pore, where the copulatory organ is operated by extrinsic retractors
and protractors. The main musculature of the body is generally
thicker ventrally than dorsally.

The parenchyma of Prosostomata is more open than that of
Monogenea, the cells and fibrils forming a loose network of irregular
spaces filled with liquid and forming a rudimentary " lymph system."
The general appearance recalls to mind the mesenchyme in early
embryos of Vertebrata. In juvenile Digenea embryonic cells wander
through this network to establish in appropriate situations the rudi-
ments of organs such as the gonads. Other wandering cells resemble
lymphocytes, and may play a part in the distribution of nutrients and
other substances about the body.

(b) The Nervous System and Receptors.

The nervous system, like that of Monogenea, consists of paired
ganglia, a supra- oesophageal commissure and paired nerves. The
" brain " may He far forward, but it gives origin to several nerves
which extend to the anterior region, numerous branches passing to the
oral sucker and the integument, and also to three pairs of unequally
developed longitudinal nerves that extend posteriorly. The ventral-
most longitudinal nerves are best developed and they may be con-
nected by commissures to produce a nerve network beneath the
integument. This may be extended when other commissures link the
ventral with the lateral, and even the dorsal nerves. From the main
nerves or the commissures, or both, numerous fibrils extend peri-
pherally, branching everywhere underneath the integument. They
are mainly motor nerves, sense-organs being even less developed than
in the Monogenea. The miracidia and sporocysts of some Digenea
possess a pair of eye-spots, and in a few instances a third eye is present,
but such organs are generally absent in adults, although vestiges of
them may persist for a time. Pyriform cells and fine hair-like pro-
cesses commonly exist in the integument and may serve as receptors,

THE MORPHOLOGY OF THE DIGENEA 17

like the papillae at the margins of the suckers. Other organs of this
kind which lie close to the mouth have been called " taste -organs,"
but there is no proof that this is their true nature.

(c) The Digestive System.

This system is not dissimilar to that of Monogenea, although
generally bifurcate and unbranched in the Prosostomata of fishes. It
comprises a muscular pharynx, an oesophagus of variable length and
a pair of caeca, which may be so short as scarcely to reach the ventral
sucker, even when this is decidedly anterior, or so long as almost to
touch the posterior extremity. The pharynx may be rudimentary or
absent, likewise the oesophagus, which otherwise may be very long
in ribbon-like Digenea. The oesophagus may be lined with epithelial
ectoderm or with cuticle, though it is generally fibrillar and homo-
geneous ; its walls may contain transverse and longitudinal muscles,
and the ducts of glands may penetrate it. In very elongate Digenea
this anterior part of the gut may be lengthened by the presence in
front of the pharynx of a narrow prepharynx, which is absent in oval
forms.

The caeca, or intestinal crura, are generally simple and unbranched,
and they may merge to form a ring-like intestine. In Hemiuridae a
special region of the gut, the gland- stomach, is interposed between
them and the oesophagus. In a few Digenea two anterior extensions
of the caeca pass along the sides of the oesophagus, imparting an H-
shape to the intestine, and the main crura or the anterior diverticula,
or both, may possess short lateral outgrowths. In one family there
is a single median caecum, as in the Bucephalidae — a condition which
may also arise secondarily when only one caecum develops to the
full size. In a few instances the intestinal crura do not end blindly,
but communicate with the exterior by way of the terminal part of the
excretory system, so that the excretory pore is strictly a cloacal
aperture. Sometimes there is a true anus, or a pair of anal apertures,
but this is not common, although more frequent than was at one time
supposed. Such characters are exceptions to the general rule and
not important in taxonomy, as their presence or absence in related
forms shows. Circular and longitudinal muscles may occur in the
wall of the intestine, which may also have a simple epithelial lining.
The free ends of the epithelial cells sometimes have thread-like or
brush-like processes which project into the lumen.

(d) The Excretory System.

The usual position of the excretory pore in Prosostomata is pos-
terior and terminal, though exceptions occur and miracidia and rediae
have a pair of postero-lateral pores, and the same may be true of
cercariae which have not yet developed a tail. As the rudiment of the
tail grows out the two primary pores are carried with it, the two main
excretory canals coming to lie side by side near the tail-stem. Here
fusion occurs later on, and the final shedding of the tail at the end of

2

18 THE TREMATODA OF BRITISH FISHES

cercarial life not only preserves a single posterior pore, but destroys
all evidence of the paired origin of the excretory vesicle. This generally
receives a pair of canals, which pass directly into it or into a pair of
cornua near its anterior end. The vesicle may be small and spherical
or long and tubular, according to the degree and extent of fusion of
the paired vessels of the early larvae. When the lateral canals are
prominent, the main vessels form a characteristic Y- or V- shape
according to the length of the median stem. The former shape is
characteristic of some families, the latter of others, but neither can
be accepted without reserve as a familial character.

Finer canals open into the main excretory vessels, which form a
pair of longitudinal trunks extending to a level near the pharynx,
where they may unite, or turn about and extend separately back
towards the posterior extremity. Each recurring loop generally
receives tributary canals formed by the fusion of small and still smaller
factors, the finest of which end each in a flame-cell. The mode of
branching seen in this part of the system, and the numbers of flame-
cells which are involved in various groupings, are matters of taxonomic
importance and can be represented by a shorthand expression, the
flame-cell formula. The method by which the formula is applied
was outlined in connexion with the Aspidogastrea in my previous
work (Dawes, 1946) and need not be repeated here, though it will be
as well to mention that the number of tributary canals arising from the
longitudinal trunks is indicated by the number of terms in the expres-
sion (each term denoting the number of branches formed at a division),
and that the power to which each term is raised represents the number
of times branching occurs. As each terminal twig of the system ends
in a flame-cell, the total number of such units can easily be calculated
from the formula, which takes account of the duplication due to
bilateral symmetry. The patterns of flame- cells and ducts provide
important means of diagnosis, especially for larvse, in which compara-
tive simplicity prevails ; the chief drawback in the case of adults is
the difficulty with which the details can be made out, even in living
trematodes if they are fleshy.

From this brief statement it will be evident that the excretory
system is protonephridial, as in Turbellaria. The flame- cell is a
cellular unit possessing elongate cilia that project into the blind
terminal capillary and by their movements produce a flickering effect,
as the name implies. Sometimes the capillaries are cellular or syn-
cytial, and from certain cells, or parts of the syncytium, tufts of cilia
may project into the lumen. The way in which flame-cells produce a
flow of liquid is unknown, and any study of the mechanics of the flow
would be welcomed by helminthologists. The action of the flame-
cells prevents stagnation in the terminal canals and the deposition of
solids which might otherwise occur there.

(e) The Reproductive Systems.

Mention has been made already of the dioecious nature of some
trematodes, but previous remarks might be amplified slightly here.

THE MORPHOLOGY OF THE DIGENEA 19

Schistosomes, many of which exhibit sexual dimorphism, have their
sex determined in the earliest stages of development, the sporocysts
giving rise to cercarise that will develop into males or females, but
not both, so that a definitive host which is infected with cercarise
that came from the same sporocyst has flukes of one sex only. Male-
producing cercarise develop in the blood vascular system, becoming
adult in about 40 days, but female-producing cercarise may remain
immature in the absence of males for periods up to 9 months, attaining
only one-fifth of the normal definitive size, and having an undeveloped
ovary and rudimentary vitellaria. In the presence of males, however,
maturity is reached in about two months, and anomalous females
complete their development if male-producing cercarise are introduced
into the blood vascular system of their host. The development of the
female thus seems to be conditioned by a substance or substances
secreted by the male.

Sexual dimorphism may arise out of hermaphroditism, as seems to
be the case in Didymozoidse, a series of which can be arranged to show
all stages in its development. Didymozoon scombri and D. faciale,
parasites of the mackerel, have normal male and female organs of
unusual thread-like or tubular pattern. Species of Wedlia consist of
females which develop only the rudiments of the male organs, and males
which have a non-functional ovary, vitellaria, shell-glands and recep-
taculum seminis. Nematobothrium filarina is characterized by indi-
viduals of different thicknesses, the thicker ones forming numerous
eggs of a golden colour, the thinner ones only a few colourless eggs.
We know practically nothing about the determination of unisexuality
and sexual dimorphism in such forms, our knowledge of the general
anatomy being deficient, except for a few forms which have been
described fairly recently. Apart from these two main sets of examples,
Prosostomata are regularly hermaphrodite, the genital organs showing
a greater variety of structure than in Monogenea, particularly the
terminations of the genital ducts. The male and female systems
generally open to the exterior close together in a shallow genital
atrium, but some Prosostomata of fishes have a deep, tubular atrium
which resembles a hermaphrodite duct and the terminal part of the
entire atrium of other forms. The common genital pore is generally
situated in the median plane between the suckers, but may occupy a
lateral or even a dorsal position. It may be situated relatively very
far forward near the mouth, but in the great majority of Prosostomata
it is just in front of the ventral sucker.

The male reproductive system comprises a pair of testes and vasa
efferentia, a vas deferens, seminal vesicle and cirrus, as well as a
number of accessories which are not invariably present, a cirrus pouch,
glandular pars prostatica and ductus ejaculatorius. It generally
develops before the female system (protandry). Occasionally there is
a single testis, or numerous testes, but generally there are two and they
may be spherical or ovoid, rarely lobed or branched, and situated
behind or in front of the ovary, or one on either side of it. The sperma-
tozoa are thread-like bodies of variable length (0*02-0*2 mm. long)

20 THE TREMATODA OF BRITISH FISHES

which are sometimes enclosed in spermatophores, as in Prosorhynchus
and some rhabdoccele Ttirbellaria. They pass along the vasa efferentia,
sometimes by the agency of cilia, into the vas deferens and finally the
seminal vesicle, a dilated region of the male duct in which they are
stored temporarily. Their ultimate ejaculation during copulation is
brought about by reflex contraction of the vesicle.

Some of the modifications of the copulatory organs are of taxonomic
importance. The typical organ is a cirrus provided with both cir-
cular and longitudinal muscles, although these may be ill developed.
Spinelets may arise from the internal wall, to be erected when the
organ is protruded and thus to help to maintain a firm union with the
terminal parts of the female system during copulation. Some spine-
like structures found in this situation, however, are probably less
rigid than the term indicates and more hair-like. The retracted cirrus
is generally lodged in a cirrus pouch, which also encloses the pars
prostatica, i.e. that part of the male duct which is perforated by the
ducts of prostate glands, whose secretion nourishes the spermatozoa,
and also the seminal vesicle. Sometimes the vesicle lies outside the
cirrus pouch, when it is called a vesicula seminalis externa, though
the type interna is the more usual, and both may exist. Sometimes the
cirrus pouch is small and the pars prostatica terminates in the paren-
chyma outside, or the pouch is absent, rarely the cirrus as well. When
a true cirrus is wanting, a protrusible muscular organ which takes its
place is formed by fusion of the male and female ducts, and is thus
homologous with the genital atrium of other Prosostomata. The
organ is sometimes enclosed in a pouch similar to the cirrus pouch, and
variously known as a "false cirrus sac", "false cirrus pouch" or
" sinus sac." A rather fine distinction is sometimes drawn when this
has continuous muscular walls and is said to be " complete," or has
sparse and discontinuous muscles and is said to be " incomplete."

The components of the female reproductive system are similar to
those of the Bucephalidae, namely, an ovary, oviduct, ootype, uterus,
Laurer's canal, receptaculum seminis, vitellaria and vitelloducts. The
ovary is generally smaller than either of the testes and globular,
though it may be lobed or branched, but is rarely follicular or tubular.
Generally, it is displaced towards the right, but may occur almost as
often on the left. Ripe ova travel along a short section of unmodified
oviduct to the ootype, assisted by a ciliary current. Here they meet
clusters of vitelline cells which have travelled down the vitelloducts
and spermatozoa previously stored in the receptaculum seminis, and
become fertilized and encapsulated. The ootype is a modified part of
the oviduct which is conveniently situated in relation to other ducts,
and receives the secretion formed by numerous unicellular shell-glands
situated immediately outside its wall. The receptaculum seminis
occurs at the base of Laurer's canal, or in some other situation, but
never far removed from the ootype. In its absence sperms may
aggregate in the proximal part of the uterus, which then forms a
receptaculum seminis uterinum. The uterus varies in length and
degree of folding, sometimes having a descending limb which extends

THE MORPHOLOGY OF THE DIGENEA 21

towards the posterior extremity, then recurring as an ascending limb.
Both limbs may be intensely folded, the folds filling what space is
available. Otherwise, the uterus may consist of an ascending limb
which follows a sinuous course towards the genital atrium. The
terminal part of the uterus, or metraterm, often has a cuticular lining,
and may have muscular walls and a lining provided with enigmatic
structures resembling hooklets. Glands similar to the prostate glands
may open into the metraterm, which functions as a vagina in most
Prosostomata, although Laurer's canal has been observed to serve this
purpose in some. The way in which the eggs receive their shells is
essentially the same as in the Monogenea, though the formation of an
operculate egg calls for some modification of the process. According
to Ujiie (1936a) the peripheral wall is formed first, then the posterior
end, and finally the operculum. This writer (19366) also suggested
that two types of shell-glands exist in Digenea, but the use of criteria
based on differential staining reactions in formulating this opinion has
been adversely criticized (Dawes, 19406). The shell-glands produce
a thin secretion, and may contribute to the gelatinous envelopes with
which the eggs of Pleurogenes and some Haploporidse are provided, but
they do not form the bulk of the egg-shell. The most plausible hypo-
thesis is that the secretion causes rapid extrusion of droplets of shell-
forming substance from vitelline cells which have travelled from the
follicles of the vitellaria to the ootype. The vitellaria of Prosostomata
are rarely as well developed as in Monogenea, and when we take into
consideration also the larger number of eggs produced, this implies
a more economical use of shell-forming materials, thus explaining the
rarer occurrence of polar filaments in Digenea. The vitellaria are
generally lateral and follicular, but they may be compact and are
sometimes fused into a minute single mass. Some trematodes with
reduced vitellaria produce fewer eggs with thinner shells, but this is
not invariably so, implying perhaps an unusually great capacity to
secrete which compensates for a small size. This point requires
investigation.

Laurer's canal extends from a pore on the postero -dorsal surface
to a point near the ootype. In some instances it has a muscular wall
and it may have a ciliated hning. The receptaculum seminis is generally
situated at its base, but is absent in some families. Laurer's canal is
absent in Derogenes, and although it has been observed to function
as a vagina in a few Digenea, it probably serves in most as a conduit
for unwanted fragments of shell-forming substance, thus maintaining
the ootype in a fit condition for the work it has to do.

Processes of the eggs are rare in Prosostomata, but a few parasites
of birds and of fishes have eggs with one or two filaments. Generally,
the eggs are ovoid and operculate, although opercula are lacking in
some families, in which case the capsule must split before the mira-
cidium can emerge. The shape, size and colour of the eggs, as well
as the presence or absence of polar filaments, are characters of some
taxonomic importance. Some eggs are very much larger than others —
a fact which is overlooked when they are not seen side by side unless

22 THE TREMATODA OF BRITISH FISHES

careful measurements are made. Perhaps size has been unduly-
stressed as a taxonomic aid, and in some recent determinations a very
wide range of sizes has been found in a single species. But the size
of the eggs must take its place along with other characters, the ensemble
of which decides specific identity.

In conclusion, mention may be made of situs inversus, which occurs
infrequently in regard to asymmetrical organs, but is not of particular
importance in taxonomy. Malformations are more likely to mislead
us, but these also seem to be infrequent. Instances are known of
the atrophy of one testis, or one vitellarium, and such abnormalities
may be more common than the literature indicates. Perhaps arti-
facts due to bad fixation are more important, because more common,
and sometimes misleading about the natural limits of variability in
a species. Alterations of the proportions of a trematode during growth
may also, if neglected in a taxonomic study, make specific limits more
difficult to determine. Many species of Trematoda have been erected
unnecessarily because sufficient allowance has not been made for the
rather wide range of variability to be expressed in a group of animals
which have neither a definite shape nor a definitive size.

VI. TREMATODES OF THE ORDER MONOGENEA.

Odhner (1912) divided the order Monogenea into two sub-orders,
the Monopisthocotylea and the Polyopisthocotylea, characterized
respectively by the absence or presence of a genito-intestinal canal,
i.e. a tubular connection between the oviduct and the right caecum,
rarely the left. Most writers have concurred, but Fuhrmann (1928)
proposed an alternative tripartite division of the order into the Mono-
pisthodiscinea, Monopisthocotylinea and Polyopisthocotylinea, the first
two groups representing subdivisions of Odhner's Monopisthocotylea
based on a number of characters, but mainly on the absence or presence
of a sucker-like opisthaptor. Price (1937a) indicated that this scheme
offers little taxonomic advantage, and Odhner's scheme will be adopted.
Unfortunately, the genito-intestinal canal is a rather delicate object
which is not easily discernible in the rather opaque and sometimes
pigmented body, so that it is a character of doubtful practical value.
Amongst the correlated characters, however, the nature of the opis-
thaptor is distinctive and permits easy diagnosis. If this organ com-
prises a number of suckerlets or clamp-like structures, the fluke belongs
to the Polyopisthocotylea ; if instead it is a disk-like structure,
whether an indubitable sucker or merely a region of the body which
bears hooks, the fluke can be referred to the Monopisthocotylea.

A complete classification of the Monogenea has not been accom-
plished in a modern sense, although Price (1936 ; 1937a-c ; 1938a, b ;
1939a, 6 ; 1940a ; 1942 ; 1943a, 6) has made very substantial progress
with a scheme of his own, firmly establishing a number of super-
families, families and lower taxonomic units. It is doubtful if some
of the super-families have any phylogenetic significance, but they are
serviceable units in diagnosis. Perhaps before an ideal scheme can

TREMATODES OF THE ORDER MONOGENEA 23

be propounded we shall need to consider life -histories and growth
cycles in greater detail. Little is known about changes in the pro-
portions of Monogenea during growth, a closer study of which would
enable us better to assess variability in the relative sizes of organs
and parts within a species. In dealing also with the shapes and struc-
ture of various kinds of cuticular hooks, hooklets and sclerites we have
probably been misled by differences more indicative of the processes
of growth than of phylogenetic distinction. But in lieu of information
concerning the growing trematode we have to depened on the characters
of the adult, which have been put to good use by Price, whose work
has been liberally drawn on in setting out the scheme which follows.
Useful suggestions have been made by Sproston (in litt.), particularly
regarding the Mazocraeidae, a family with which Price has not yet dealt
in detail, and to her also my thanks are due.

Key to the Families and Higher Groups of the Monogenea.

I. Opisthaptor a postero-ventral outgrowth bearing 1-3 pairs of hooks
and 12-16 hooklets, or a sucker-like disk with or without radial
septa on the ventral surface and having hooks and hooklets or not.
Genito-intestinal canal absent . . . MONOPISTHOCOTYLEA.

1. Opisthaptor having hooks and transverse supports

O Y ROD ACT Y WIDE A .

a. Habit viviparous ...... Gyrodactylidje.

b. Habit oviparous :

(a) Anterior extremity devoid of head lappets Dactylogyrid^c.

(b) Anterior extremity having conspicuous head lappets

CALCEOSTOM ATIDiE .

2. Opisthaptor unarmed or having hooks without supports

CAPSALOIDEA.

a. Prohaptor a pair of anterior suckers or glandular depressions :

(a) Intestine simple and sac-like . . . Udonellid^:.

(b) Intestine bifurcate :

(i) Genital pores nearly together . Capsalidje.

(ii) Genital pores not nearly together Acanthocotylidje.

b. Prohaptor not a pair of anterior suckers or glandular depressions :

(a) Opisthaptor equipped with hooks . Monocotylid^e.

(6) Opisthaptor not equipped with hooks MiCROBOTHRnD^:.

II. Opisthaptor comprising few or many suckerlets or clamps arising from
a discoidal outgrowth or from the naked postero-ventral surface of
the body. Genito-intestinal canal present . POLYOPISTHOCOTYLEA.

1. Prohaptor generally an oral sucker, never a pair of buccal suckers ;

opisthaptor comprising one pair or three pairs of cup-like
suckers, never clamps . . . P0LY8T0MAT0IDEA.

a. Opisthaptor having an appendix-like prolongation

Hexabothriid^.

b. Opisthaptor lacking an appendix . . Polystomatid^.

(Not represented in British fishes ; parasites of am-
phibians and reptiles.)

2. Prohaptor a pair of buccal suckers ; opisthaptor comprising four

or many pairs of clamps, or few suckers, each organ having
cuticular skeletal supports or sclerites . DICLIDOPHOROIDEA.

24 THE TREMATODA OF BRITISH FISHES

A. Clamps of the opisthaptor each having two valves which
grip by a pincer-like action ; sclerites arranged as —

(a) a semicircular marginal piece in each valve and a uni-

lateral basal piece, sometimes a rudimentary middle
piece ...... Mazocrjeidje.

(b) a pair in each valve combined into a semicircle and a

well developed and semicircular middle piece

MlCROCOTYLIDiE.

(c) as in (b), but modified, the lateral pieces fused, or the

ventral pieces segmented near the middle, the middle
piece massive, sometimes thickened . Discocotylid^;.

(d) as in (6), but modified differently from (c) ; the lateral

pieces joined without fusion, one pah - being spurred,

the middle piece meeting additional pieces which

make a pair .... Gastrocotylidje.

b. Clamps or suckers of the opisthaptor having a more or less

constant circular or oval opening ; sclerites arranged as :

(e) eight pieces of complicated shapes, the middle piece

in two segments, and sometimes numerous minute
pieces arranged in rod-like chains to form a sheet

DlCLIDOPHORJDiE.

(/) three pieces in each sucker, their shapes variable, but
the middle piece largest and somewhat X-shaped

Hexostomatidje .

Sub-order MONOPISTHOCOTYLEA Odhner, 1912.

(Monocotylea Blainville, 1828; Tricotylea and Calicotylea Diesing, 1850;

Tristomeae Taschenberg, 1879 ; Oligocotylea Monticelli, 1903 ; Mono-

pisthodiscinea and Monopisthocotylinea Fuhrmann, 1928.)

Prohaptor absent, or a feeble oral sucker, or a pair of anterior
suckers, or two elongate antero-lateral depressions receiving the duct
of numerous unicellular glands, or one or more pairs of head-organs
receiving the ducts of the cephalic glands. Opisthaptor discoidal, its
ventral surface sometimes partitioned by septa into loculi, never
subdivided into distinct suckers or clamps, generally having 1-3 pairs
of hooks and 12-16 hooklets, the hooks often supported by transverse
cuticular bars. Eyes and a vagina present or absent. Genito -intestinal
canal absent (except, possibly, in the Protogyrodactylidae, a family of
Australian Monogenea).

Super-family GYRODACTYLOIDEA Johnson & Tiegs, 1922.

Prohaptor absent, or represented by at least one pair of head-
organs, receiving the ducts of cephalic glands arranged in two groups,
one on either side of the pharynx. Opisthaptor discoidal or wedge-
like, bearing 1 pair or 2 pairs of hooks and 1 or 2, rarely 3, cuticular
supporting bars. Intestine simple and sac-like, or bifurcate and with
or without short diverticula. Genital pore in or near the median
plane. Cirrus simple, cuticularized, sometimes having complex
cuticular accessories. Vagina present or absent. Genito -intestinal
canal rarely, if ever, present. Habit oviparous or viviparous.

GYRODACTYLIDiE 25

Family GYRODACTYLUXE Cobbold, 1864.

Amphibdellidse Carus, 1885, in part ; Gyradactylidse Monticelli, 1888.)

r

Size small. Shape elongate. Head-organs one pair. Opisthaptor
well developed, generally having 1 pair of hooks and 15-16 hooklets.
Intestine bifurcate, the crura not uniting posteriorly and being devoid
of diverticula. Eyes absent. Cirrus armed with a row of spinelets,
generally equipped with a triangular cuticular plate. Ovary V-shaped
or lobed and situated behind the testis. Vagina absent. Vitellaria
absent or compounded with the ovary to form a germ-vitellarium.
Habit viviparous, the parent containing two or three generations of
embryos one inside another. Hosts cephalopods, fishes and amphibians.

Two sub-families can be separated easily : in the Gyrodactylinse
(parasites of fishes and amphibians) the opisthaptor has 1 pair of
hooks and 16 hooklets, and the anterior extremity is bilobed, each lobe
bearing a head organ : in the Isancistrinse (parasites of cephalopods)
the opisthaptor has 15 hooklets, but no hooks, and the anterior
extremity is truncated.

Sub-family Gyrodactylin^e Monticelli, 1892, sensu Johnston & Tiegs,

1922.

Genus GYRODACTYLUS Nordmann, 1832.

This genus has the characters of the sub -family as stated above.

About 14 species occur in Europe and about 10 elsewhere, although

some of the species are unnamed and others are of doubtful validity.

Gyrodactylus elegans Nordmann, 1832. (Figs. 1 A, B, 2 Ba, Ca.)

Hosts : three-spined stickleback, ten-spined stickleback.

Location : gills.

Bradley (1861, pp. 209-10) found numerous specimens of this
species on sticklebacks in the Hampstead ponds, scattered over the
surface of the body and attached at one end, " while the other floated
freely." When fully extended the specimens were about 1 mm. long
and one -tenth as broad, tapering from the middle towards both ends,
the anterior end much narrower and bifid, each division having a
retractile, brush-like extremity which was used "as a tactile organ
and also for progression." The " disk " was said to be horseshoe
shape, the curved margins having 16 lobes each with powers of
independent movement. Through the centre of each lobe runs a
tendinous cord associated with a hooklet, and in the disk there are 2
recurved hooks back to back, connected by a ring by which and their
bases they are freely held in situ. When the bases are " cupped " the
hooks are erected. Bradley also recognized the pharynx as a spherical
cavity and behind it a " germ sac " containing the next generation.
He often found two young ones inside the body of the parent and noted
that they closely resemble this in form. Bradley and his colleague
Bowerbank observed the young tear the envelope and free itself,

26

THE TREMATOPA OF BRITISH FISHES

noting that inside it was a young one of a third generation. In some
specimens still immature the " germ sac " simply contained a number
of " vesicular corpuscles."

Houghton (1862, p. 77) first saw specimens on the pectoral fins
and tail of young sticklebacks of the smooth-spined variety (" Gastero-
steus leirus ") hatched from a nest of eggs brought from a ditch on
the Eyton moors (Shropshire). The father fish was literally covered

Fig. 1. — A, Gyrodactylus elegans; B, hooks and tran verse bar of G. elegans.
C, hooks of Ancyrocephalus paradoxus. D, Amphibdella flavolineata;
and E, one of the hooks of the same. F, hooks and transverse bar of
Tetraonchus monenteron. G, Amphibdelloides maccallumi, and H, hooks
and bar of the same. (B, C, F, after Luhe, 1909 ; A, after Bychowsky,
1933 ; D, E, G, H, after Price, 1937a.)

with two to three hundred specimens, and when it died the " gills "
were also found to be " full of them." Examining other three -spined
and also ten-spined sticklebacks from another ditch Bradley found
most of them infested with moderate number of the parasites.

Cobbold (1862) also found specimens on the tails of sticklebacks,
and writing later (1864) about these worms from " the Serpentine,
Regent's Park," gave an account of the " birth " of the young indi-
viduals, also mentioning the opinions of other writers. The " daughter
first showed itself externally as a slight bulge on the centre of the
parent's body, where the integument yielded in a way suggestive of

GYRODACTYLID^ 27

a vaginal opening. As the young one struggled to free itself, there
was no sign of injury to the parental tissues. The flexed middle
region of the body first emerged, followed by the anterior extremity,
some time elapsing before the broad posterior extremity became free.
The opening in the parent's body was immediately sealed, all that
remained being a small cavity inside the body. The whole process of
" birth " took about five minutes. Comparing the " parent " with
the " daughter," Cobbold could " scarcely aver that the former was
the larger of the two," but the similarity of size was perhaps more
apparent than real, the young individual becoming extended as it
moved about actively, the parent contracting in a quiescent posture.
Johnstone (1912, p. 47, Fig. 4) has referred to this species specimens
found on the dorsal and ventral fins of a plaice taken from Morecambe
Bay, but not on the caudal fin, skin and gills. They were not seen
in a satisfactory condition, but were 0-4 mm. long and 0-05 mm.
broad, with 2 recurved hooks about 0-05 mm. long and "6 or 7
pairs " of smaller marginal hooks (13 indicated in the figure).
Most of the specimens contained embryos. The record is puzzling, and
Johnstone had some doubt in identifying the worm as O. elegans,
though he regarded it as near this species, which has been found in
various parts of Europe (R. Rhine, Lake Constance, Lake of Lucerne)
and in America, and occurs on various other freshwater fishes as well,
notably the bream, tench, loach, crucian carp, minnow and pike, and
has also been recorded as a parasite of brackish water fishes such as
the common goby, and marine fishes such as the lumpsucker. Several
brief descriptions are available (Nordmann, 1832, pp. 106-8, PL 10,
figs. 1-3 ; Wagener, 1860, pp. 768-93, Pis. 17, 18 ; Gamble, 1896, p. 61,
fig. 29 ; Benham, 1901, p. 53, fig. Ill, 6-8) ; and Liihe, 1909, p. 11,
fig. 6). The diagnostic characters of the species seem to be : Size :
0*5-1-0 mm. long. Shape spindle -like, with a median notch between
the head-organs. Opisthaptor disturbing the smooth contour of the
body posteriorly. Basal parts of the 2 hooks having an outer
margin which curves ventrally to form a space or groove accommo-
dating the cuticular supports. Main supporting bar almost Y-shaped,
having a pair of anterior processes with short dorsal lobes and a median
posterior plate covering the hooks ventrally ; subsidiary bar a delicate
transverse connection between the dorsal lobes of the main bar.
Gut : pharynx having 8 short processes, which project into the
prepharynx and can be protruded through the mouth.

Gyrodactylus medius Kathariner, 1894.

Host : minnow.
Location : gills.

Baylis (1928) recorded the occurrence of this species near Edin-
burgh. It has been found also on the continent of Europe in the
common carp and bream as well, and it occurs in Canada. It is
supposed to combine the characters of pharyngeal processes such as
occur in G. elegans, with two simple and unlobed transverse supports

28 THE TREMATODA OF BRITISH FISHES

for the hooks, but Johnson and Tiegs (1922) thought it possible that
the two forms might be identical. For the original description see
Kathariner (1894, p. 129, PL 7, figs. 3, 8 ; PI. 8, figs. 9-16 ; PL 9,
figs. 17-24).

For a fist of other species of Gyrodactylus, none of which have been
found in Britain, see Dawes (1946, p. 108). The sub-family Isan-
cistrinse Fuhrmann, 1928, contains only one genus, Isancistrum de
Beauchamp, 1912, with the solitary species 7. loliginis de Beauchamp,
1912, which is not a parasite of fishes, but occurs on the gills of Loligo
media L., and thus may turn up in sea-water aquaria. It is a small,
squat form about 0-2 mm. long, which, like Gyrodactylus elegans, may
contain several generations of embryos at the same time.

Family DACTYLOGYRIDiE Bychowsky, 1933.

(Gyrodactylidse Cobbold, 1864, in part ; Amphibdellidse Cams, 1885,

in part.)

Size small. Shape elongate. Head-organs two or more pairs.
Cephalic glands lateral, sometimes encroaching on the median region
in front of the mouth. Opisthaptor fairly well developed, possessing
or lacking squamodisks, but having 1 pair or 2 pairs of hooks and
14 hooklets. Ovary globular or elongate and curved, situated in
front of the testis . Vagina present or absent . Vitellaria well developed .
Habit oviparous.

The three sub -families can be distinguished by the numbers of
hooks and the presence or absence of squamodisks. The opisthaptor
has only 1 pair of hooks in the Dactylogyrinse, but 2 pairs in the
Tetraonchinse and Diplectaninae, squamodisks occurring only in the
latter, where they are dorsal and ventral in the posterior region.

Sub-family Dactylogyrin^: Bychowsky, 1933.

{Gyrodactylince Monticelli, 1892, in part.)

In this group the opisthaptor is well developed, equipped with
pair of hooks, 1 or 2 supporting bars and 14 hooklets, but lacks
squamodisks. The crura of the gut unite posteriorly, forming a
ring-like intestine, eyes are present, the gonads are globular, and the
ovary situated in front of the testis, and the vagina has or lacks cuti-
cular skeletal supports. In the genus Dactylogyrus the hooks are
supported by a single bar, in Neodactylogyrus by two similar or dis-
similar bars.

Genus DACTYLOGYRUS Diesing, 1850, sensu Price, 1938.
(Fig. 2 A, Bb, Cb, Da, b.)

Dactylogyrus auriculatus (Nordmann, 1832) Diesing, 1850.

Gyrodactylus auriculatus Nordmann, 1832 (pp. 108-9, PI. 10, figs. 4-9 ;
G. auricidaris of Wedl, 1857.

This species has not appeared in Britain, but occurs attached to
the gills of the bream and carp on the Continent. It was originally

DACTYL0GYRIDJ3

29

described as a very small fluke of the same size as Gyrodactylus elegans,
and Dujardin (1845, p. 480) gave the length as 0-25 mm., Beneden
(1858, p. 66, PL 7, figs. 9-11) as 20-25 mm., obviously omitting the
decimal points. The latter writer first found the trematode attached
to Diplozoon paradoxum on the gills of the bream. According to
Luhe (1909, p. 18) the old descriptions and figures are insufficient for
the identification of the species, and many species have since been
erected, evidently without reference to the type. None has appeared,
in Britain, although some of them probably occur here, so that it is

Fig. 2. — A, diagram of the principal organs of Dactylogyrus, B, copu-
latory apparatus of Gyrodactylus (a) and Dactylogyrus (b). C, hooklets
of Gyrodactylus (a), Dactylogyrus (b) and Tetraonchus (c). D, copulatory
apparatus (a) and lateral cuticular structure (b) of Dactylogyrus chrani-
lowi. (After Bychowsky, 1933.)

pertinent to mention the opinion of Nybelin (1937), according to whom
many trematodes allocated to "D. auriculatus Nordmann " are either
unintelligible, or under suspicion of belonging to other species, just
as Dujardin's " G. auriculatus" was distinct from Nordmann's and
justifiably renamed dujardinianus by Diesing. Several characters
specified in the original description leave no doubt that "auriculatus
Nordmann " really belongs to the genus Dactylogyrus sensu lato,
notably the presence of 4 processes at the anterior extremity, of
4 eyes and well developed vitellaria. Other characters specified
are enigmatical, particularly the presence of 20 hooklets arranged
in a double coronet of 12 and 8 on the outer and inner rows,

30 THE TREMATODA OF BRITISH FISHES

which Nybelin regarded as an error of observation. After examining
a number of species which occur in Sweden, five of them new, Nybelin
concluded that D. sp. Wegener, 1910, and D. wunderi Bychowsky,
1931, which were regarded as identical, most closely approach " D.
auriculatus Nordmann " in general structure. Accordingly, he pro-
posed to regard both as synonyms of the type-species, but unfor-
tunately, Price (1938a, p. 49) transferred D. wunderi to Neodactylo-
gyrus because the hooks are supported by two transverse bars. All
five of Nybelin's new species belong to this genus, and as he was dealing
with forms having two bars, it was natural for him to infer that the
second bar was overlooked in Nordmann's description of auricidatus,
although his description in an addendum of a sixth new species, D.
cordus, was of a form with only one bar, and a number of species
previously described undoubtedly have this character. We must
conclude, therefore, that as D. sp. Wegener and D. wunderi Bychowsky
are identical with one another, neither can be synonymous with G.
auriculatus Nordmann, and both belong to the genus Neodactylogyrus.
It may be impossible to decide in some early descriptions which of
these two genera are under consideration, because the distinguishing
characters make no allowance for the possible oversight by earlier
writers of one of the transverse bars. Thus D. falcatus (Wedl) was
credited by Liihe (1909) with one bar and was retained in the genus
Dactylogyrus by Price (1938a), although Nybelin figures two bars
(Fig. 10). As I have already given a list (Dawes, 1946, p. 112) of the
European " species " of Dactylogyrus nothing further need be added
here, except to state that the specific characters include the shapes,
sizes and various arrangement of the cuticular structures of the
opisthaptor and the nature of certain cuticular accessories of the
copulatory apparatus.

Genus NEODACTYLOGYRUS Price, 1938.

(Dactylogyrus Nordmann, 1832, in part.)

Hooks of the opisthaptor supported by 2 transverse cuticular
bars ; other characters as in Dactylogyrus.

Neodactylogyrus megastoma (Wagener, 1857) Price, 1938.

Dactylogyrus megastoma Wagener, 1857 (a, p. 57, PI. 14, fig. 5 ; PI. 36a, fig. 2).

The locality in which this trematode was originally found was not
stated, although Braun (1879-93) gave it as Middle Europe. A
diagnosis of this trematode, which occurs on the bitter ling carp
(Rhodeus amarus) and white bream, but has not appeared in Britain,
was given by Liihe (1909, p. 13, fig. 14). The opisthaptor has hooks
with sickle-like points and double roots set at right angles, the smaller
continuing the base of the point, the longer diverging from it. The
transverse bars are fairly similar, the dorsal having notched extremi-
ties, the ventral being the more strongly recurved. The marginal
hooklets are said to number 14.

DACTYLOGYRID^: 31

About 21 " species " of Neodactylogyrus occur in Europe, but none
has appeared in Britain. About 16 other " species " occur in America.
For a list of the European species see Dawes (1946, p. 113).

Sub-family Tetraonchinje Monticelli, 1903.

Cuticle devoid of scales or spines. Opisthaptor lacking squamo-
disks, but bearing 2 pairs of hooks and 12-16 hooklets. Intestine
sac-like or bifurcate. Eyes present or absent. Gonads generally-
globular, not lobed. Vagina present or absent. Price (1937a) gave
a key to 20 genera, mainly American. One other genus which
belongs to the sub-family is Linguadactyla. Of the European genera,
Amphibdella has hooks which are not supported by transverse bars ;
Ancyrocephalus and Haplocleidus have 2 bars, but the hooks are of
equal and unequal sizes respectively. Four other genera have only
1 transverse bar and two of them have hooks of equal sizes, Tetra-
onchus having a single caecum and Amphibdelloides a pair of caeca.
The remaining two have hooks of unequal sizes, the opisthaptor being
lobed and pedunculate in Dactylodiscus, but not in Linguadactyla.

Genus TETRAONCHUS Diesing, 1858.

(Gyrodactylus of Wedl, 1857 ; Dactylogyrus of Wagener, 1857, in part ;
Monocoelium Wegener, 1910 ; Ancyrocephalus of Luhe, 1909, in part.)

Head-organs numbering two or several pairs and bearing the open-
ings of the cephalic glands. Opisthaptor fairly well differentiated,
with 2 pairs of hooks supported by a large bar and 16 marginal
hooklets. Intestine a simple caecum devoid of diverticula. Eyes
present. Gonads situated near the middle of the body, vagina absent.

Tetraonchus monenteron (Wagener, 1857) Dies., 1858. (Figs. 1 F, 2 Cc.)

Dactylogyrus monenteron Wagener, 1857 (a, pp. 63-7, 69-73, PI. 13, fig. 1 ;
PI. 36a, fig. 3/) ; Gyrodactylus cochlea Wedl, 1857 (pp. 258-74, PL 3, figs. 32-
7) ; Ancyrocephalus monenteron (Wagener) of Luhe, 1909 (p. 19, figs. 27, 30).

Host : pike.
Location : gills.

This species occurs in various parts of Europe (Italy, Lake Con-
stance), and was found by Van Cleave and Mueller (1934, p. 184, PL 28,
figs. 1-3) in pike at Oneida Lake, New York. According to Sproston
(in litt.) it also occurs in Britain. Size : 1-2 mm. long. Shape :
elongate and of uniform girth, tapering slightly posteriorly. Eyes :
two pairs, the anterior and posterior nearly together. Opisthaptor :
large and broader than long, the breadth sometimes exceeding that
of the body. Hooks each having a narrow and sickle-like blade
and a broad and plate-like base having a stump-like process ;
transverse supporting bar flattened and dumbbell- or butterfly- shaped ;
hooklets as indicated in Fig. 2 Cc. Gut : pharynx large and spherical,
intestine long and sac-like. Reproductive systems : genital pore situated

32 THE TREMATODA OF BRITISH FISHES

behind the pharynx ; genital hooklets long and slender ; support of the
copulatory organ arranged spirally around its tip. Gonads compact
and situated in the median plane, the ovary in front of the testis.
Vitellaria extensive laterally and composed of numerous coarse
follicles. Vagina absent. [Note : — the only other species is T. alas-
kensis Price, 1937, a parasite of Salmonidse in Alaska.]

Genus ANCYROCEPHALUS Creplin, 1839.
(Diplectanum of authors ; Tetraonchus Diesing, 1858, in part.)

Head-organs generally numbering 3 pairs and bearing the openings
of the cephalic glands. Opisthaptor less distinct than in Tetraonchus,
the 2 pairs of hooks supported by 2 transverse bars ; 14 hooklets
present. Gut bifurcate, the caeca discrete. Eyes present. Gonads
situated as in Tetraonchus, vagina present.

Ancyrocephalus paradoxus Creplin, 1839. (Fig. 1 C.)

Dactylogyrus unguiculatus Wagener, 1857 (p. 61, pp. 64-5) ; Tetraonchus
unguiculatus (Wagener) Diesing, 1858 (pp. 380-1).

Host : perch.
Location : gills.

This species is well known on the Continent (at Griefswald,
Vienna, Gedani) and occurs in Britain, a single specimen in my
collection having been obtained in southern England. According to
Luhe (1909, p. 18, fig. 28) the trematode is 3-4 mm. long, and the
elongate body tapers to a small opisthaptor bearing hooks with sickle-
like points and 2 basal processes, one plate -like and the other knob-
like, each pair being connected by a beam-like transverse bar. My
specimen has the following characters : — Size : about 0-8 mm. long
and 0-23 mm. broad in the middle, but only 0-17 mm. at the level of
the pharynx. Shape : tapering to a greater extent posteriorly than
anteriorly and truncated at the anterior extremity. Cephalic glands
arranged in two groups and slightly behind the pharynx ; head-organs
ill defined. Opisthaptor about 0-12 mm. broad and somewhat longer,
its anterior boundary ill-defined ; large ventral hooks fairly similar,
the base about 0-04 mm. long and 0-02-0-025 mm. broad across the
wide lobe proximal to the point, which is about 0-02 mm. long, and
one of which is curved while the other is straight. Smaller dorsal
hooks slightly smaller, the base about 0-03 mm. long and 0-025 mm.
broad across the corresponding but knob-like lobe ; points about the
same size and gently curved. Eyes : those of the anterior pair the
smaller, 0-046 mm. apart and 0-032 mm. from the anterior extremity,
those of the posterior pair 0-057 mm. apart and 0-056 mm. from the
extremity. Pharynx 0-06 mm. diameter, its anterior border situated
between the eyes of the two pairs. Reproductive systems : genital
pore near the pharynx, cirrus cuticular and about 0-07 mm. long, its
distal part slightly bulbous. Testis longitudinally ovoid, 0-09 mm.
long and 0-07 mm. broad, the hinder boundary at the middle of the

DACTYLOGYRIDJE 33

body. Ovary transversely ovoid, measuring 0-06 X 0-045 mm.,
situated just in front of and contiguous with the testis. Vitellaria
well developed laterally, extending from the level of the pharynx to
the base of the opisthaptor, the follicles more numerous and densely
arranged posteriorly. Vaginal pore situated on the right margin of
the body just in front of the level of the ovary ; vagina cuticular and
apparently forming a short spiral. Eggs absent.

Genus HAPLOCLEIDUS Mueller, 1937.

Hooks of the opisthaptor unequal in size, those of the ventral pair
only about half as large as those of the dorsal. Cirrus long and spirally
coiled, or having a spiral fin, generally an accessory piece as well.
Vagina opening on the left margin of the body.

The type and two other species of this genus occur in America,
two species in Europe, one of them H. monticellii (C. de Martiis, 1925)
Price, 1937, which was described as a species of Ancyrocephalus taken
from an American catfish (Haustor catus) in Italy, the other H. siluri
(Zandt, 1924) Price, 1937, which was also originally regarded as
Ancyrocephalus and occurs in the sleat-fish, Silurus glanis, in Lake
Constance and in the Vistula, Poland. I have already given a short
diagnosis of the latter species (Dawes, 1946, p. 116), which is unlikely
to appear in British waters, although the host descends into brackish
or salt water and was once recorded as a Scottish river fish.

Genus AMPHIBDELLA Chatin, 1874.
(Tetraonchus of Monticelli, 1903.)

Head-organs numbering 3 pairs. Opisthaptor lobed and clearly
differentiated, having 2 pairs of hooks of similar sizes which are not
supported by cuticular bars and 14 hooklets. Gut bifurcate, the
caeca discrete. Eyes absent. Gonads situated in the anterior region,
the ovary extending lateral to the caecum of its side. Vitellaria
extensive laterally, vagina cuticular and lateral.

Amphibdella flavolineata MacCallum, 1916. (Fig. 1 D, E.)

Host : torpedo.
Location : gills.

This species was discovered on a torpedo (Tetranarce occidentalis)
and a " sting ray " at Woods Hole and was found by Pees & Llewellyn
(1941) at Colwyn Bay. British specimens have not yet been described,
but Price (1937a, pp. 151-3, figs. 1-4) described American specimens.
Size : 3-8-43 mm. long and 051-068 mm. broad. Head-organs :
3 pairs, situated near the anterior extremity, receiving the ducts
of lateral cephalic glands situated in front of the pharynx. Opist-
haptor lobed, 0-425-0-475 mm. broad, provided with 2 pairs of
hooks 0-15-0 "16 mm. long and 14 marginal hooklets about 0-01 mm.
long, one to each lobe. Blade of each hook lacking a shoulder-like

34 THE TREMATODA OF BRITISH FISHES

lobe near the base and tapering gradually from base to point. Gut :
mouth median ventral and 0- 19-0*23 mm. from the anterior extremity ;
pharynx globular and 0-13-0-15 mm. diameter ; oesophagus very short
and associated with a pair of clusters of unicellular glands ; caeca simple
and discrete, extending to the posterior ends of the vitellaria. Repro-
ductive systems : genital pore median near the bifurcation of the gut ;
cirrus tubular and about 0-1 mm. long, having a complicated cuticular
accessory ; seminal vesicle S-shaped and conspicuous. Testis small and
situated on the left, largely hidden by vitelline follicles ; ovary elongate
and curved, overreaching the caecum laterally. Vitellaria a long
series of very coarse follicles lateral to the caeca extending from an
anterior level near the ootype nearly to the posterior extremity.
Vagina situated just in front of the ovary on the right side of the bod}^
associated with a large receptaculum seminis. Ootype situated just
in front of the gonads, slender and having gland cells clustered around
its base. Eggs not observed.

The type-species, A. torpedinis Chatin, 1874, has been found at
Naples and elsewhere in the Mediterranean, on the gills of the torpedo.
According to Price, this species differs from A. flavolineata in the
nature of the copulatory apparatus and in the size and shape of the
hooks, each of which has a slender blade which widens before meeting
the biramous root to produce a shoulder-like process. Chatin gave
the length of the hooks as 0-085 mm., i.e. only half that of A. flavo-
lineata.

Genus AMPHIBDELLOIDES Price, 1937.

(Amphibdella Chatin, 1874, in part.)

Closely resembling Amphibdella, but opisthaptor not lobed and
hooks having only a single supporting bar.

Amphibdelloides maccallumi (Johnston & Tiegs, 1922) Price, 1937.

(Fig. 1 G, H.)

Amphibdella torpedinis Perugia & Parona, 1890, nee Chatin, 1874 ; A. tor-
pedinis MacCallum, 1916, nee Chatin, 1874 ; A. maccallumi Johnston &
Tiegs, 1922.

Host : torpedo (Torpedo nobiliana ; T. marmorata in the Mediter-
ranean).

Location : gills.

This species was described by Perugia & Parona (1890, p. 24,
PL 1, figs. 12, 13 ; PI. 2, figs, 14-18) and redescribed by Price (1937a,
pp. 153-4, figs. 5-8). It has been found, but not described, by Rees
and Llewellyn (1941) at Colwyn Bay. The Italian specimens were
comparatively large, 3-5 mm. long and 0-42 mm. broad, the opis-
thaptor 022 mm. diameter and the hooks 0-14 mm. long, their support
0-084 mm. long. American specimens are sometimes much smaller.
Size : 1-1-3-5 mm. long and 0-25-0-48 mm. broad. Eyes absent.

DACTYLOGYRID^ 35

Head-organs : 3 pairs situated near the anterior tip of the body,
receiving the ducts of numerous cephalic glands, which form a trans-
verse band in front of the pharynx and extend back on each side
nearly to the level of the genital pore. Opisthaptor not lobed and 0-21-
0-42 mm. broad, having 2 pairs of hooks 0-13-0*17 mm. long
which taper gradually from base to point and 14 hooklets about 0-01
mm. long. Supporting bar of the hooks slightly curved, the anterior
margin concave, 0-064-0-095 mm. long and 0-019 mm. broad. Gut :
mouth median ventral and 0-13-0-17 mm. from the anterior extremity.
Pharynx globular and 0-075-0-095 mm. diameter. (Esophagus long.
Reproductive systems : genital pore median and situated near the
bifurcation of the gut. Cirrus tubular and about 0-17 mm. long, equipped
with two accessory pieces about 0-13-0-16 mm. long, one having a
single curved tip and the other a trifurcate tip or five or more points
(see Perugia & Parona, 1890, PI. 1, fig. 13). Testis median and very
elongate, extending almost to the ends of the cseca. Ovary much
smaller, but also elongate and situated in front of the testis. Vitel-
laria comprising two lateral arrays of fairly large follicles, which merge
in a narrow transverse band behind the testis and extend anteriorly
nearly to the anterior end of the ovary. Vaginal pore situated on the
right margin of the body near the middle of the ovary ; vagina slender
and cuticular opening into a large receptaculum seminis lying alongside
the anterior half of the ovary and on its right. Eggs not observed.

Genus LINGUADACTYLA Brinkmann, 1940.

Opisthaptor indistinct, but equipped with 2 pairs of curved
hooks, those of one pair (dorsal ?) larger than the others, a middle
piece of oval shape and 12 (? 14) hooklets set in the narrow pos-
terior region of the body. Gut including 2 separate caeca having
branched lateral diverticula. Young specimens having 1 pair of
eye-spots and hooks which are only slightly smaller than those of the
adult. Gonads situated near the middle of the body ; copulatory
apparatus comprising 2 cuticular pieces, one of them pointed and
the other forked ; vagina absent.

Linguadactyla molvae Brinkmann, 1940.

Host : blue ling.
Location : gills.

This species was discovered at Bergen, Norway, and described in
great detail by Brinkmann (1940, p. 7, Pis. 1-4, figs. 1-17). Adults
are permanently attached, and the epithelium of the gill reacts to the
irritation set up by the opisthaptor by proliferation, which forms an
annular pad around the posterior end of the parasite. The parasite,
which is likely to appear in Britain, thus seems to protrude from a
cyst-like structure on the gills. Size : mature when 2-6 mm. long
and then rather less than half as broad. Shape : elliptical or tongue -
shaped, sometimes narrower posteriorly, slightly concave dorsally and

36 THE TREMATODA OF BRITISH FISHES

ventrally. Colour : yellowish white, the vitellaria forming dark
lateral stripes. Prohaptor : cephalic glands apparently absent. Opis-
thaptor : large and small hooks 0*12 and 0-06 mm. long, in immature
specimens 1-2 mm. long, in adults 5 mm. long. Large hooks 0-143 mm.
long and strongly curved, tapering gradually from base to point, each
with one short and one longer bifurcate root. Small hooks 0-07 mm.
long and just as curved, each having a single root, the two roots being
linked by a short triangular or oval cuticular bar. Gut : mouth not
quite terminal, bordered by a conspicuous dorsal and a less prominent
ventral lip. Pharynx large. (Esophagus absent. Caeca fairly long, ex-
tending to the posterior one-third of the body. Diverticula of the caeca
branched and lined with columnar epithelium. Reproductive systems :
genital pore median and just behind the bifurcation of the gut. Testes
numerous, mainly situated between the caeca in the second quarter
of the body. Vas deferens curving round the left caecum near the
ovary and continuing diagonally forward, dilated to form a seminal
vesicle. Prostate gland cells well developed. Copulatory organ
equipped with two cuticular pieces, one tubular and pointed and
resting in a groove in the other, which is forked. Ovary pyriform
and situated just in front of the testes. Ootype median and tubular ;
uterus short and straight, also median. Vitellaria lateral to the main
caeca and extending forward to the level of the pharynx ; lateral vitello-
ducts connected by a transverse vessel in front of the ovary ; main
unpaired duct arising asymmetrically from the left lateral duct opposite
the ovary.

Genus inq. DACTYLODISCUS Olsson, 1893.

Opisthaptor lobed and pedunculate and having 2 pairs of hooks,
those of the dorsal pair the larger, and a middle piece of peculiar shape.
Eyes present. Gonads rounded and situated near the middle of the
body, cirrus simple.

Olsson (1893, pp. 7-8, PL 1, figs. 7-10) described the only species
of this genus, D. borealis, a parasite about 2 mm. long on the gills of
the grayling and gwyniad in Sweden. Johnston and Tiegs (1922)
regarded Dactylodiscus as a sub -genus of Ancyrocephalus , but Price
(1937a) preferred to retain it as a genus till more information about the
structure of D. borealis is forthcoming. We know practically nothing
about the head- organs, cephalic glands, hooklets, vagina and other
important structures.

About 15 other genera of the Tetraonchinae are known outside
Europe. Seven of them occur in North America : Actinocleidus
Mueller, 1937 ; Anchoradiscus Mizelle, 1941 ; Cleidodiscus Mueller,
1934 ; Diplectanotrema Johnston & Tiegs, 1922 ; Rhabdosynochus
Mizelle & Blatz, 1941 ; Urocleidus Mueller, 1934 ; and Tetrancistrum
Goto & Kikuchi, 1917, the last-named occurring also in Japan and
the Philippines. Four others occur in Australia : Anchylodiscus
Johnston & Tiegs, 1922 ; Daitreosoma Johnston & Tiegs, 1922 ;
Empleurosoma Johnston & Tiegs, 1922 ; and Murraytrema Price,

DACTYLOGYRIDiE 37

1937. The remaining genera are found in Japan ; Anchylodiscoides
Yamaguti, 1937 ; Ancyrocephaloides Yamaguti, 1938 ; Haliotrema
Johnston & Tiegs, 1922 ; and Parancyrocephaloides Yamaguti, 1938.
Many of these genera have been reviewed by Price (1937a).

Sub -family Diplectanin^: Monticelli, 1903.

(Lepidotreminse Johnston & Tiegs, 1922.)

Opisthaptor equipped with dorsal and ventral squamodisks, or
plates of cuticle covered with scale-like spines arranged in charac-
teristic rows, and 2 pairs of hooks, 2 supporting bars and 14 hooklets.
Vagina present or absent.

Genus DIPLECTANUM Diesing, 1858, sensu Price, 1937.

(Dactylogyrus of Wagener, 1857, in part ; Acleotrema Johnston & Tiegs,
1922 ; Lepidotes Johnston & Tiegs, 1922 ; Squamodiscus Yamaguti, 1934.

Dorsal and ventral squamodisks having concentric rows of scale-
like spines, but not spine-like hooks. Hooks of the opisthaptor sup-
ported by 3 transverse bars. Vagina present or (?) absent.

According to various writers (Johnston & Tiegs, 1922 ; Fuhrmann,
1928 ; Van Cleave & Mueller, 1932 ; Sprehn, 1933) this genus was
regarded as being identical with Ancyrocephalus , but Price (1937a)
upheld its validity. It was proposed by Diesing for two species
named by Wagener (1857a) and later (18576) briefly characterized,
namely Dactylogyrus cequans and D. pedatum. Price has shown that
although Diesing did not designate a type of the genus Diplectanum,
the former of these species may be taken as such. It was originally
found on the gills of the bass, and Price accepts as members of the
same species specimens from the same species of host described under
the name D. cequans by Beneden & Hesse (1863), Stossich (1896) and
Maclaren (1904). The outstanding generic character is the squamo-
disks, which are lacking in Ancyrocephalus.

Diplectanum sequans (Wagener, 1857) Diesing, 1858 (p. 381).

(Fig. 3 A-G.)

Dactylogyrus cequans Wagener, 1857 (p. 99, PI. 15, fig. 14).

Host : bass.
Location : gills.

This species has been found in the Irish Sea, off the coast of Belgium
and in the Mediterranean, where three other species occur on other
hosts. British descriptions of this species are very inadequate. A.
Scott (1904, p. 35 ; 1906, p. 49, PL 10, fig. 4) merely stated that the
trematode was plentiful in the Irish Sea. According to the stated
magnification of his figure the specimen he considered was about
2*1 mm. long and 0-5 mm. broad, the squamodisks measuring about
0-13 X 0-20 mm. Three antero-lateral papillae shown probably

38

THE TREMATODA OF BRITISH FISHES

carried the openings of the cephalic glands. T. Scott (1905, p. 117,
PL 6, fig. 24) described the species in three or four lines, obviously
confounding the anterior and posterior extremities. The dorsal and
ventral squamodisks were not noted, a fault in other accounts also ;
the length was given as about 2 mm. and the illustration indicated
three pairs of indistinct head-organs. The same writer later (1912)
repeated the previous mistake, asserting that the " head " is armed
with two hooked spines on each side of a cleft occupied by a process

Fig. 3. — Diplectanum cequans. A, entire trematode ; B, anterior end,
showing the head-glands (solid black), " brain " (in outline) and mouth
(dotted line) ; C, a squamodisk, showing the arrangement of rows of
spines ; D skeletal bar for support of the hooks ; E, posterior end,
showing the skeletal bar in situ, also the hooks, caudal-glands and
squamodisk ; F, one of the hooks ; G, schematic diagram of the repro-
ductive systems. (After Maclaren, 1904.)

thickly covered with minute " prickles." Maclaren found the species
common on the bass at Trieste, one-third of the fishes examined being
infested with two to four specimens each, and he gave a good descrip-
tion (1904, p. 574, figs. A, B, C 1-5 ; PI. 20, figs. 1-12 ; PI. 21, figs.
13-22). Size: 5-1*5 mm. long and about one-quarter as broad.
Colour : difficult to see because of the same colour as the gills, beneath
the filaments of which the parasite lies hidden. Shape : elongate and
fusiform, but flattened and tapering posteriorly from the level of the
genital pore. Cuticle bearing numerous small papilla?. Cephalic

CALCEOSTOMATlDiE 39

glands forming a large group on either side of the anterior extremity
and opening by numerous pores, the individual cells pyriform. Caudal
glands similar to the cephalic, but situated between the squamodisks
posteriorly, arranged in two pairs, one behind the other. Opisthaptor :
squamodisks broader than long, measuring 0-13 x 0-15 mm., each
having small spines arranged in regular rows which are transverse
posteriorly, become concave near the middle and are U-shaped an-
teriorly. Hooks : two on each side of the body postero-lateral to the
squamodisks, each recurved at the tip and having two unequal roots.
Transverse supporting bars forming a pair meeting in a joint in the
median plane, curving in the lateral regions to meet the roots of the
hooks. Gut : mouth a ventral slit not quite terminal and provided
with lips having short lobes which are somewhat extensile. Pharynx
prominent. (Esophagus short. Caeca long and unbranched. Eyes :
two pairs, located in front of the pharynx and mouth. Reproductive
systems : genital pore displaced to the right just behind the bifurcation
of the gut. Cirrus 0-2 mm. long and cuticular, also on the right.
Ejaculatory duct long and muscular, the ejaculatory bulb having two
chambers, the distal one the larger. Pars prostatica constricted, the
smaller posterior part surrounded by gland- cells. Testis slightly
lobed, median and slightly behind the middle of the body. Ovary
reniform and situated on the left just in front of the testis. Uterus
short and fairly straight, the receptaculum seminis at its base small
and globular, the ootype situated nearby. Vagina extending forward
and to the left to open on the ventro-lateral surface of the body,
thick-walled and muscular, but having a cuticular lining, its opening
unarmed. Vitellaria comprising numerous follicles extending from
the level of the pharynx, where they are most abundant, to the ends
of the caeca, where they are sparse. Transverse vitelloducts asym-
metrical, the right anterior to the left, at the level of the ootype.
Eggs unobserved.

Four of nine other species of Diplectanum occur in Europe, and
Price (1937a) regarded all as inadequately described, although pro-
bably valid. They are D. sciceno3 (Beneden & Hesse, 1863), originally
described as a species of Epibdella parasitic on the surface of the
meagre on the coast of Belgium ; D. aculeatum Parona & Perugia,
1899, found on Corvina nigra ; D. echeneis (Wagener, 1857), found on
the gilt-head and Couch's sea bream ; and D.pedatum (Wagener, 1857),
found on a wrasse. The last three occur in the Mediterranean, and
Maclaren (1904) gave diagnoses of the first two, and also of D. scicence.

Two other genera of Diplectaninae occur in Australia, one genus
in U.S.A.

Family CALCEOSTOMATID.E Parona & Perugia, 1890, emend.
Poche, 1926, sensu Fischthal & Allison, 1941.

Prohaptor generally comprising head-lappets at the expanded
anterior extremity, which has numerous scattered cephalic glands.
Opisthaptor sucker-like, but not markedly muscular, having or lacking

40 THE TREMATODA OF BRITISH FISHES

hooks and hooklets. Eyes present or absent. Intestine with or with-
out short diverticula. Testis single. Cirrus simple, but cuticular.
Vagina present or absent.

Sub-family Calceostomatin^: Monticelli, 1892, emend.

With the characters of the family. The two European genera can
be distinguished by the nature of the prohaptor ; in Calceostoma it
comprises head-lappets, but in Anoplodiscus a pair of pseudosuckers.

Genus CALCEOSTOMA Beneden, 1858.

Anterior extremity expanded to form conspicuous ventrally-
curled head-lappets, pseudosuckers absent. Opisthaptor cup-like,
having hooks and hooklets or (?) not. Eyes present. Testes elongate,
ovary branched, vagina absent.

Calceostoma calceostoma (Wagener, 1857) Johnston & Tiegs, 1922.

Dactylogyrus calceostoma Wagener, 1857 (p. 99) ; Calceostoma elegans Beneden,
1858 (pp. 60-3, PL 7, figs. 1-8).

Host : meagre.
Location : gills.

This species has not been found in Britain, but probably occurs
here, having been found off the coast of Belgium. It was inadequately
described, but has the following general characters. Size : up to
10 mm. long. Prohaptor : head-lappets large, taking up one-fifth of
the length of the body proper. Opisthaptor terminal and discoidal,
about one -third as broad again as the body, supposedly bearing a
single centrally situated hook, but the second hook and other cuticular
accessories probably lost. Eyes not observed, but probably present.

Another European species, C. inerme Parona & Perugia, 1889 (p.
747), was discovered on Corvina nigra and the umbrina (Umbrina
cirrosa) at Genoa and has not appeared in Britain. As the name
implies, hooks and hooklets are lacking on the opisthaptor, but may
have been overlooked. The only other species, C. glandulosum John-
ston & Tiegs, 1922, a parasite of Scicena antarctica in South Queens-
land, is about 5 mm. long, has 2 pairs of eyes, 2 large hooks and
certain haptorial accessories, and has been fully described.

Genus ANOPLODISCUS Sonsino, 1890.

Prohaptor a pair of pseudosuckers situated at the anterior extremity.
Opisthaptor cup-like and devoid of accessories. Eyes present. Cirrus
having a cuticular lining and an accessory piece. Testis situated in
front of the middle of the body, the ovary in front of it. Vagina
present.

The type-species, A. richiardii Sonsino, 1890, occurs on the gills

MONOCOTYLID.E 41

of Couch's sea bream in the Mediterranean. Sonsino regarded it as
related to both Gyrodactylids and Tristomids, but Monticelli (1891,
p. 108 ; 1095, pp. 65-8, figs. 1-3) extended the meagre description,
and subsequently the species has had a chequered taxonomic career,
having been referred at different times to several families (Gyro-
dactyhdae, Monocotylidae, Microbothriidae, Udinellidae) . Its present
position is due to Fischthal & Allison (1941). The only other species,
A. australis Johnston, 1930, was discovered on one of the fins of Sparus
australis in Sydney Harbour. Other genera of the Calceostomatidse
occur in America (see Dawes, 1946, p. 120).

Super-family CAPSALOIDEA Price, 1936.

Prohaptor absent, or a feeble oral sucker, or a pseudosucker, or
two lateral glandular grooves. Head organs present or absent.
Opisthaptor generally a prominent muscular disk partitioned by septa
on the ventral surface to form loculi and sometimes having hooks,
but never cuticular supporting bars. Gut : intestine simple and sac-
like or bifurcate, sometimes having median and lateral diverticula.
Genital pore median or lateral. Cirrus sometimes cuticular, but never
equipped with accessories. Testes : sometimes few, or only one testis.
Vagina present or absent.

Family MONOCOTYLIDiE Taschenberg, 1879.

Shape flattened, the outline oval or elliptical. Prohaptor a weak
oral sucker, or two or more anterior suckers supplied with a sticky
secretion by the cephalic glands. Opisthaptor a disk having a septate
ventral surface, generally equipped with 1 pair of hooks and 14
hooklets. Eyes present or absent. Gut : mouth ventral, not quite
terminal ; pharynx large ; oesophagus short or absent ; caeca simple and
long ; intestine sometimes ring-like. Genital pore typically median.
Cirrus generally cuticular. Testes rarely 3 or many, generally only
a solitary testis. Ovary curved and sometimes looped round the right
caecum. Vaginal generally paired, but sometimes a single vagina or
none.

The three sub-families which are represented in Europe can be
distinguished from one another by the nature of the haptors and the
vagina. In two of them the prohaptor is a feeble oral sucker and
the opisthaptor has no more than 8 loculi, the Monocotylinae having a
single vagina, the Calicotylinae a pair of vaginae ; in the Merizocoty-
linae the prohaptor consists of head- organs and cephalic glands and
the opisthaptor has more than 8 loculi.

Sub-family Monocotylinae Gamble, 1896.

Of the two European genera, Heterocotyle has a feeble oral sucker,
Monocotyle only a membranous pseudosucker.

42 THE TREMA.TODA OF BRITISH FISHES

Genus MONOCOTYLE Taschenberg, 1878.
Opisthaptor having its ventral surface divided by septa into 8
equal loculi and equipped with 1 pair of hooks, probably hooklets
also. Prohaptor sometimes fringe-like and papillate. Eyes absent.
Testis single. Opening of the uterus marginal.

Monocotyle myliobatis Taschenberg, 1878.

This species occurs on the gills of the eagle ray at Naples and
Trieste, but has not appeared in Britain. According to the descriptions
of Taschenberg (1878, p. 574) and Perugia & Parona (1890, p. 18,
PL 1, figs. 4, 5 ; PI. 2, figs. 6, 7) it is 5 mm. long and 2 mm. broad,
elongate, broadening posteriorly and whitish in colour. The opis-
thaptor is 1-5 mm. diameter, has 8 radial septa, two in the longi-
tudinal axis of the body and the remainder equally spaced three on
each side. The hooks are borne on the most posterior lateral septa,
are 0-46 mm. long, have very unequal roots and an outwardly directed
point bent at right angles to the shaft. The prohaptor is 0-53 mm.
diameter and forms a fleshy fringe-like lip bearing numerous papillae.
The pharynx is large, 0-29 mm. long and 0-24 mm. broad, and the
reproductive organs are imperfectly known, certain details illustrated
by Perugia & Parona being unacceptable. The egg has a long and
spirally- wound filament at one pole.

Genus HETER0C0TYLE T. Scott, 1904.

{Monocotyle of authors ; Trionchus MacCallum, 1916 ; Monocotyloides

Johnston, 1934.)

Ventral surface of the opisthaptor having a central depression
bounded by a ridge from which 8 septa radiate to form peripheral
loculi, and bearing 1 pair of hooks and 14 hooklets. Prohaptor
a weak oral sucker. Eyes present or absent. Testis undivided, cirrus
slender and cuticular, vagina probably always present.

Heterocotyle pastinacae T. Scott, 1904. (Fig. 4 A.)

Host : sting ray.

Location : gills.

Several specimens on which this species are based were found in
Dornoch Firth and described briefly by T. Scott (1904, p. 279, PL 17,
fig. 14 — wrongly given as 15 in the descriptions of the plates) and again
mentioned by this writer in 1912 (PL 27, fig. 9). Size : 1-44 mm. long
and about one-third as broad. Shape : ovate to elongate, tapering
anteriorly, but truncated at the extremity and narrowed just in front
of the opisthaptor, much flattened. Prohaptor smaller than the
pharynx. Opisthaptor broader than long in the ratio 13/11 and
apparently broader than the body in the ratio 4/3, its margin slightly
crenate, the ventral surface divided by radial septa into eight loculi
which meet in a small and central diamond-shaped depression repre-
senting the point of attachment of the whole haptor to the body.

MONOCOTYLIDiE

43

The two posterior loculi, slightly larger than the four anterior, but
smaller than the two lateral, which are about twice as large as the ones
in front of them, and like the posterior loculi, are divided into proximal
and distal portions by a "circular line " as shown in the figure. Hooks
relatively small and approximately spanner- shaped, inserted into the
haptor in the septa separating the postero-lateral and the most posterior
loculi, one on either side. Other characters not determined, but pharynx
shown very large and oval in outline, lateral bands of vitelline follicles
extending from its lateral margins to the opisthaptor.

Fig. 4. — A, Heterocotyle pastinacce. B, Thaumatocotyle concinna. C, T.
dasybatis ; D and E, an egg and a hook of the same. F. Calicotyle kroyeri ;
G an egg of the same ; H, a hook, and I, the opisthaptor. (A, B, after
Scott, 1904 ; C-E, after Price, 1938 ; F, after Lebour, 1908a ; G, H, I,
original.)

Two other species occur in America and a third in Australia.
Price (19386, p. 113) re-examined MacCallum's specimens of H.
minima, which occurs on the gills of the sting ray and piked dogfish
at Woods Hole, concluding that it is closely related to and possibly
identical with H. pastinacw. Brinkmann (1940, p. 76), apparently
unaware of Price's work, compared the original descriptions and
reached the same conclusion. In suggesting that Heterocotyle is a
synonym of Monocotyle, Brinkmann (loc. cit., p. 80) is at variance with
Price, who, perhaps because the latter genus has been imperfectly
defined, chose to regard the two genera as distinct. It is doubtful
if the slightly different nature of the prohaptor is sufficient to warrant
the recognition of two genera, but further study of the gill-trematodes of

44 THE TREMATODA OF BRITISH FISHES

sting rays is necessary before the difficulties can be removed and the
issue decided.

Sub-family Calicotylinje Monticelli, 1903.
Genus CALICOTYLE Diesing, 1850.

Nybelin (1941, p. 16) proposed the division of this genus into three
sub-genera, Calicotyle, Calicotyloides and Gymnocalicotyle, the characters
of which I have previously given (Dawes, 1946, p. 127). This procedure
is unnecessary and might be misleading, because the six species which
have been assigned to the genus have not been established beyond
question. Two species occur in Britain, namely, C. kroyeri and
C. affinis, C. stossichi occurs in the Mediterranean, two others, C.
australis Johnston, 1934, and C. inermis Woolcock, 1936, are Australian,
and the sixth species, C. mitsuhurii Goto, 1894, occurs in Japan.

Calicotyle kroyeri Diesing, 1850. (Fig. 4 F-I.)

Hosts : starry ray, skate, thornback ray, shagreen ray, sandy ray,
spotted ray, long-nosed skate, cuckoo ray, painted ray (in West
Sweden, the first four of these hosts) .

Location : cloaca, rarely the rectum, very rarely the gills.

T. Scott (1902) found this species on the starry ray caught about
sixty miles south-east of the Shetlands, as well as on specimens of the
same species of host caught off Aberdeen and in the Clyde, and men-
tioned his son's finding it on the same host caught in Beaumaris Bay,
A. Scott (1904) recording its occurrence also in the thornback ray in
the Irish Sea. Lebour (1908a) found specimens in the cloaca of the
starry ray, invariably in females, not in males as generally recorded.
She also found specimens in the uterus (sic) and on the gills of this
host. Nicoll (1914) found the species on the sandy ray, spotted ray
and thornback ray at Plymouth, Little (1929a) on the sandy ray at
Gal way, Baylis and Idris Jones (1933) on the spotted ray at Plymouth,
Baylis (1939) also recording its occurrence on " skate " at Durham.
Rees and Llewellyn (1941) noted several hosts, the spotted ray at
Newquay and the long-nosed skate, cuckoo ray, shagreen ray and
painted ray on the Irish Atlantic Slope. I have found the trematode
on the thornback ray at Plymouth, and several times in skate from
unknown localities which were dissected in the laboratory. The
species was discovered by Kroyer on the starry ray caught in the
Kattegat, although Beneden and Hesse (1864) wrongly named the skate
as the original host, and Beneden (1871) found it on this host off the
coast of Belgium. It has also been recorded at Naples and Trieste,
and it has been described by several zoologists, including Wierzejsky
(1877, p. 550, PL 31) ; Monticelli (1891, p. 108, PI. 6, figs. 33-5) ;
T. Scott (1902, pp. 299-300, PL 13, fig. 30) ; Lebour (1908a, pp. 39-40,
PL 5, fig. 1). Size : up to 5 mm. long and nearly as broad. Shape

MONOCOTYLID^E 45

variable, the outline sometimes almost circular, but tapering anteriorly
and having a median indentation at the extremity, the oral sucker
protruding a little, sometimes triangular and pointed in front, invari-
ably much flattened. Colour white or pale yellow. Prohaptor an oral
sucker up to about 0-7 mm. diameter. Opisthaptor a circular disk
up to about 2 mm. diameter (1-0 mm. in specimens 2-8 mm. long and
2-7-3-1 mm. broad) and approximately one-third to two-fifths as long
as the body proper, typically not projecting beyond the body, but
sometimes overlapping it by more than half its diameter, presumably
by extension of the short attachment. Ventral opening of the opis-
thaptor much smaller than the diameter (0-7 mm. broad and 0-6 mm.
long in a disk 1 mm. diameter), its margin forming a rather delicate
and inturned fringe, ventral surface having seven radial septa extending
from a central circular space towards the periphery. Hooks about
0-3 mm. long from base to the curve of the point and 0-1 mm. in
greatest breath on a disk 1 mm. diameter, largely imbedded in the
tissue of the two most posterior septa, directed diagonally forward and
inward towards the anterior end of the posterior loculus, the points
turning sharply outwards to underlie the antero-lateral margin of the
same (not of the shape or having the orientation shown in Diesing's
figure (1858a, PL 1, fig. 18), or Lebour's (1908a, PL 5, fig. 1). Out:
pharynx almost spherical and up to 0-4 mm. diameter. (Esophagus
very short. Caeca fairly long and thick- walled, shaped like an inverted
question-mark, but sometimes more divergent anteriorly and puckered
considerably. Excretory system : main canals lateral to the caeca.
Reproductive systems : genital pore median just behind the bifurcation
of the gut. Cirrus and ejaculatory bulb lined with cuticle, the former
curved and about 0-3 mm. long and equipped with a short cuticular
piece curved into the shape of a figure 9, sometimes sharply pointed,
but otherwise terminating in a triangular spade-like expansion.
Testes numerous, filling the region between the curved hinder ends
of the cseca. Ovary elongate and folded, situated on the right in
front of the testes. Oviduct extending towards a median receptaculum
seminis situated near the cirrus. Vaginae arranged nearly in the trans-
verse plane, their openings ventro-lateral, their terminal parts glan-
dular. Vitellaria well developed, the follicles filling the parenchyma
of the lateral regions from the level of the pharynx to the opisthaptor.
Egg (Fig. 4 G) large and triangular in optical section, about 0-10 mm.
long and 0-11 mm. broad, having a short filament 0-035 mm. long at
the posterior pole.

Calicotyle affinis T. Scott, 1912. Sp. inq.

Host : rabbit-fish.

Location : cloaca, rarely on the skin or gills, but sometimes in the
rectum.

This species was found and very inadequately described by T. Scott
(1912, p. 68, PL 7, fig. 1), but described in detail by Brinkmann (1940,
p. 62, PL 12, figs. 46-8 ; PL 13, figs. 50-2 ; PL 14, fig. 56 ; PL 15,

46 THE TREMATODA OF BRITISH FISHES

figs. 57, 58d), who found specimens at Bergen. Scott's specimens
were taken from a fish caught in the North Sea and were said to be
larger than C. kroyeri, attaining a length of 9 mm., and of somewhat
different shape. The prohaptor was overlooked, and the opisthaptor
had a central space of transversely elongate, not circular shape. Other
information given is scanty, but Brinkmann supplied sufficient to
form a good diagnosis. Size: up to 7 mm. long, measured to the point
of attachment of the opisthaptor, and 3 mm. broad, mature when
2-3-2-9 mm. long. Shape : oval outline and broadest near the middle
of the body, acutely pointed anteriorly and broadly pointed posteriorly,
slightly flattened, but convex dorsally and concave ventrally. Colour
yellowish -white to orange-red. Cuticle smooth. Prohaptor an oral
sucker. Opisthaptor similar to that of C. kroyeri, but the central
loculus elongate in the transverse plane and the hooks 0-4 mm. long,
excluding the curved points. Gut : pharynx elliptical, oesophagus
absent, a pair of clusters of unicellular glands occupying the space
between the pharynx and the anterior ends of the caeca, which are
fairly long and extend back to a level midway between the testes and
the opisthaptor, their lining being formed of columnar cells. Excretory
system : vesicles lacking, lateral canals situated one on either side
of the body and opening dorsally at the level of the pharynx. Repro-
ductive systems : genital pore median and near the bifurcation of the
gut. Cirrus equipped with a long and cuticular accessory arranged in
three coils. Vas deferens situated on the left side of the body and
extending in front of the cirrus, here dilating to form a seminal vesicle.
Testes numerous and situated between the caeca in the middle of the
body. Ovary very elongate, situated just in front of the testes and
formed into a transverse U-shaped loop embracing the right caecum,
its blind end globular. Oviduct very short. Ootype divisible into a
fertilization chamber flanked by shell-glands which debouch in two
groups and a more anterior pyriform chamber continuous with a very
short uterus. Receptaculum seminis globular, situated in the median
plane just in front of the ovary. Vaginae extending diagonally outward
from a point near the receptaculum seminis, into which it opens, to
the pores, which are situated anterior to the genital pore and beneath
the anterior parts of the caeca on the ventral surface. Eggs of the
same shape as in C. inermis Woolcock, 1936 (but not described by the
writer thus named). Vitellaria as in C. kroyeri.

Brinkmann based his opinion of the specific identity of C. affinis
on the shape of the body and of the opisthaptor, the zoological status
of the host and the openings of the vaginae into the receptaculum
seminis. Neither the first nor the second criteria are of great impor-
tance, and the last criterion rests on a negative finding after the
reconstruction of C. kroyeri from serial sections, this species being
said to have a receptaculum seminis with antero-lateral horns into
which the vaginae open. The species of Scott is thus not established
beyond reasonable doubt, but stands as a species inquirenda.

Calicotyle stossichi Braun, 1899 (pp. 80-2, 1 fig.) was found in the
rectum of a smooth hound taken from the Mediterranean to the Berlin

MONOCOTYLIDiE 47

Aquarium. It has characters in which it resembles C. affinis. The
lateral margins of the body are almost parallel and the central space
between the loculi of the opisthaptor is transversely elongate, but like
C. affinis and other species recognized at the present time, it may
ultimately become a synonym of C. kroyeri.

Sub-family Merizocotylinje Johnston & Tiegs, 1922.

Two European genera can be distinguished by the nature of the
opisthaptor, which has 4 loculi bordering a central space in Thau-
matocotyle, but 7 in Merizocotyle.

Genus MERIZOCOTYLE Cerfontaine, 1894.
(Meristocotyle Rossbach, 1906.)

Head-organs numbering 3 pairs. Opisthaptor discoidal, the ventral
surface having a central circular or oval depression surrounded by 7
loculi, in addition to which there are 18 marginal loculi, the posterior
being the largest. Hooks and hooklets present. Eyes absent. Testis
single.

Merizocotyle diaphana Cerfontaine, 1894.

Merizocotyle minor Cerfontaine, 1898.

Hosts : skate, long-nosed skate.
Location : gills.

This species occurs at Roscoff and off the coast of Belgium, but
has not been recorded in Britain, although almost certain to occur
here. It was very completely described by Cerfontaine (1895, pp.
936-46, figs. 1-6 ; 18986, pp. 329-57, figs. 1, 3, 5, 8-11, PI. 13 ; figs.
1-9, PI. 14). Size : 6 mm. long and about 1-5 mm. broad. Other
characters (see Dawes, 1946, p. 129). The form " M. minor " was
discovered in the second host named above and was described by
Cerfontaine (18986, pp. 357-61, figs. 2, 4, 6, 7, PI. 13) as a smaller
trematode 3 mm. long and 1 mm. in greatest breadth with a relatively
large opisthaptor half as long as the body proper, not one-third as
long, a relatively small and centrally- situated testis and a slightly
different uterus, differences which do not warrant the specific distinc-
tion. The only other species of the genus, M . pugetensis Kay, 1942,
occurs in America.

Genus THAUMATOCOTYLE T. Scott, 1904.

(Pseudomerizocotyle Kay, 1942.)

Head-organs numbering 3 pairs. Opisthaptor discoidal, the ventral
surface having a central depression surrounded by 4 loculi, in addition
to which there are 13 marginal loculi, the posterior being the largest.
Hooks and hooklets present. Eyes present. Testis single.

48 THE TREMATODA OF BRITISH FISHES

Thaumatocotyle concinna T. Scott, 1904. (Fig. 4 B.)

Host : sting ray.
Location : nasal fossa?.

This species was found on a fish caught in Dornoch Firth and
described very inadequately by T. Scott (1904, pp. 278-9, PL 17,
fig. 15 — wrongly given as 14 in the descriptions of the plates) and
again mentioned and figured by this writer in 1912 (PL 12, fig. 1).
Size about 3 mm. long and one -fifth as broad. Shape elongate, the
margins of the body nearly parallel, the anterior extremity approxi-
mately triangular, but notched in the median plane. Head-organs :
3 pairs of small disks arranged along the abruptly tapering margins
of the anterior region, probably receiving the openings of cephalic
glands. Opisthaptor discoidal, its length and breadth apparently
about 0-29 and 0-27 body-length ; outline nearly circular but slightly
indented opposite the peripheral radial septa, the ventral surface
divided up into loculi which show bilateral, but not radial symmetry.
Peripheral loculi numbering 13, the most posterior larger than
the others and shaped like an equilateral triangle with a blunt apex
reaching more than half-way to the centre of the haptor. Other
marginal loculi of nearly equal size and " subquadrate " shape, cut
off from the central part of the haptor by a tangential septum ; central
loculi not described, but shown arranged as in Fig. 4 B. Hooks of
slender rod-like shape, long and straight except at their inwardly
curved tips, situated slightly lateral to the radial septa of the large
posterior loculus. Internal organs not described, but pharynx
apparently very large, its length and breadth about 0-2 and 0-12
body-length. Testis slightly smaller than the pharynx and situated in
the posterior half of the body. Vitellaria mainly lateral and extending
from the opisthaptor to the pharynx, the follicles encroaching on the
median plane behind and in front of the testis and behind the pharynx.
According to Price (19386) and Brinkmann (1940), the American
trematode T. dasybatis (MacCallum, 1916) Price, 1938, which is
parasitic on the olfactory organs and gills of the same host and other
hosts at Woods Hole, may be identical with T. concinna. According
to the re-description by Price (19386, pp. 117-19, figs. 11-14) this form
(Fig. 4 C) is 1-5-2-6 mm. long, has two pairs of eye-spots, a long and
cuticular cirrus, paired vaginae with ventral apertures underlying the
caeca near the middle of the body, and a triangular egg about
0-100 mm. broad with a long and slender filament projecting from
the apex.

Family MICROBOTHRIID^ Price, 1936.
(Dermophagidae MacCallum, 1926 ; Labontidse MacCallum, 1927.)

Prohaptor sucker-like or absent. Opisthaptor small and discoidal,
lacking septa and hooks. Eyes absent. Intestine bifurcate, the caeca
with or without diverticula. Male and female pores side by side,
sometimes debouching into an atrium. Cirrus cuticular or muscular,

MICROBOTHRIIDiE 49

and provided with a cuticular ejaculatory duct. Vagina single, rarely
double. One testis or two testes in the Microbothriinse, numerous
testes in the Pseudocotylinse.

Sub-family Microbothriin^: Price, 1938.

(Dermophaginse MacCallum, 1926 ; Labontinae MacCallum, 1927 ; Para-
cotylinae Southwell & Kirshner, 1937.)

Three European genera can be distinguished by the nature of the
gut and the vagina. In Leptocotyle the caeca are devoid of lateral
diverticula, which are present in the other genera, Leptobothrium
having a double vagina and Microbothrium a single vagina. Ano-
plodiscus has been placed in this group, but is probably better placed
in the Calceostomatida? {q.v.).

Genus MICROBOTHRIUM Olsson, 1869.

(Pseudocotyle Beneden & Hesse, 1863 ; Dermophagus MacCallum, 1926,
nee Dejean ; Philura MacCallum, 1926 ; Labontes MacCallum, 1927.)

Prohaptor a pair of sucker-like organs in the wall of the pre-
pharynx. Opisthaptor simple and discoidal or elliptical, and having a
prominent and ventral groove lined with cuticle. Mouth slit-like and
not quite terminal. Caeca long and having diverticula with dendritic
endings. Genital pore median ; cirrus long and muscular ; ejaculatory
duct lined with cuticle. Testis situated near the middle of the body.
Vagina a single tube.

Microbothrium apiculatum Olsson, 1869. (Fig. 5 D, E.)

Pseudocotyle apiculatum (Olsson) Braun, 1890 (p. 530) ; Philura ovata
MacCallum, 1926 ; Dermophagus sguali MacCallum, 1926.

Host : piked dogfish.
Location : skin.

This species occurs in the Skagerrak, the Arctic, Canada and U.S.A.,
and was found in an unspecified locality (probably off the west coast
of Ireland) by Gallien (1937), so that it is of likely occurrence in British
waters. American specimens have been described by Price (19386,
p. 184, figs. 1, 2), and I have already given a diagnosis (Dawes, 1946,
p. 131).

Microbothrium centrophori Brinkmann, 1940.

Host : Centrophorus squamosus.
Location : caudal fin.

This species was described in detail by Brinkmann (1940, p. 19,
Pis. 5-7, figs. 18-22 ; PI. 8, figs. 23, 24, 27-28), and I have noted (Dawes,
1946, p. 132) the chief differences from M . apiculatum, with which it
may prove to be identical.

4

50 THE TREMATODA OF BRITISH FISHES

Genus LEPTOBOTHRIUM Gallien, 1937.

(Pseudobothrium Gallien, 1937, nee Guiart, 1935.)

Prohaptor a pseudosucker encircling the not quite terminal mouth.
Opisthaptor small and unarmed. Caeca discrete and having a few
(8 or 9) broad and digitate lateral diverticula. Eyes absent.
Testis situated between the caeca. Cirrus simple. Ovary small and
anterior to the testis . Vagina dividing into two branches, both of which
open into the genital atrium. Other characters as in Microbothrium.
The genus was re-named because Pseudobothrium Guiart, a genus of
cestodes, was preoccupied.

Leptobothrium pristiuri (Gallien, 1937) Gallien, 1937. (Fig. 5 A, B.)
Pseudobothrium pristiuri Gallien, 1937.

Host : black-mouthed dogfish.
Location : skin of the dorsal surface.

This species was found in the Atlantic west of Ireland and was
described by Gallien (1937, p. 10, fig. 1, PI. 1, fig. 3). It has not been
found in British waters, but probably occurs therein. According to
the original description it is up to 1-6 mm. long and 1 mm. broad, but
the flat and broadly lanceolate shape and these dimensions are modified
by muscular movements. The prohaptor takes the form of two
circular lips situated in the antero -ventral region, and was illustrated
as comparatively large buccal suckers and labelled " ventouse " on
one side, but they are not true suckers, but pseudosuckers. For other
characters see Fig. 5 A, B, and Dawes (1946, p. 132).

Genus LEPTOCOTYLE Monticelli, 1905.

(Paracotyle Johnstone, 1911.)

Prohaptor a feeble oral sucker. Caeca not provided with lateral
diverticula. Other characters as in Microbothrium.

Gallien (1937, p. 13) and Price (19386, p. 186) discussed the taxo-
nomy of the genus and corrected several errors which have arisen.
The name was first used by Monticelli for a sub-genus of Pseudocotyle
including his P. minor, Tagliani first using it in the generic sense.
Tagliani showed that the genus Paracotyle is identical with Leptocotyle,
but he omitted Monticelli's species from the genus. E. I. Jones (1933)
re-described " Paracotyle caniculce " and, overlooking Leptocotyle minor,
regarded it as a species of Microbothrium, A. Scott (1906) having
considered it a species of Epibdella. Gallien regarded both " Para-
cotyle caniculoz " and " Microbothrium caniculm " as synonyms of
Leptocotyle minor, and Price concurred.

MICROBOTHRIID.*:

51

P iZh ^ e f tobothr ^ m P r \^rt ; B, the genital apparatus of the same.
Snfp^ % J? min0r '< r D ' ^«7*o*^» a^fatom ; E, an egg of the
F^fw V e ?§o° Le P t0 ™ tyle : mn0r - < A ' B ' after Galli en, 1937 ; D,
fq'33 ^ C6 ' ' Johnstone, 1911 ; F, after E. I. Jones

52 THE TREMATODA OF BRITISH FISHES

Leptocotyle minor (Monticelli, 1888) Monticelli, 1905. (Fig. 5 C, E.)

Pseudocotyle minor Monticelli, 1888 (p. 16) ; 1890 (p. 191, fig. 4) ; Leptocotyle
minor Monticelli, 1905 (p. 70); Epibdella sp. A. Scott, 1906 (p. 192, PI.
9, fig. 1) ; Paracotyle caniculce Johnstone, 1911 (p. 16, figs. 1-4 ; Pis. 1, 2,
figs. 1—7) ; Microbothrium caniculce (Johnstone) Idris Jones, 1933 (p. 329,
figs. 1-3), and of Baylis and Idris Jones, 1933.

Host : rough hound.

Location : skin of the head just behind the eye, sometimes the
dorsal fins.

A. Scott (1906) found several specimens about 2 mm. long on fish
caught south of the Calf of Man, and gave a recognizable drawing but
practically no other information about them. Johnstone described
these specimens, and mentioned that in two years numerous other
specimens were found on dogfishes kept in the Aquarium tanks at
Port Erin, but no mature specimen was seen. Little (1929a) found
specimens on the gills and in the buccal cavity of the same host at
Galway, and the mature specimens found by Baylis & Idris Jones and
described by E. I. Jones occurred at Plymouth. The species has also
been found in the Mediterranean. There are several points of variance
in the descriptions of Johnstone (1911) and E. I. Jones (1933), notably
in regard to the structure of the terminal parts of the male reproductive
system, and to judge by specimens from Liverpool kindly lent to me
by Professor Daniel, Johnstone's account seems to be the more
accurate, but some of the observations of E. I. Jones are here shown in
parentheses. Size : 2 mm. long and 1-2 mm. broad (up to 3-2 mm.
long and 1-5 mm. broad). Shape : elliptical or oval in outline, pointed
anteriorly and flattened. Prohaptor : an oral sucker, not quite
terminal and slightly transversely oval, 0-14 mm. broad. Opisthaptor
a small and almost terminal discoidal sucker only slightly raised from
the general surface of the body in the posterior region, lacking hooks,
booklets and septa and about 0-3 mm. diameter. Gut : prepharynx
short. Pharynx 0-23 mm. diameter. (Esophagus absent (very short),
caeca long and without diverticula, extending along a sinuous course
to a level just in front of the opisthaptor, lined with epithelial cells.
Excretory system : vesicles ovoid and situated one on either side of
the pharynx, pores lateral at the level of the oesophagus. Reproductive
systems : genital pore median and situated just behind the bifurcation
of the gut. Cirrus pouch thick- walled and muscular, containing the
cirrus, ejaculatory duct and bulb (also a pars prostatica). Testis
transversely ovoid, median and just behind the middle of the body.
Ovary globular or transversely elongate, situated just in front of the
testis. Vitellaria extensive dorsal and lateral to the caeca, merging in
the median plane behind the testis, the follicles coarse and pyriform.
Vaginal pore a longitudinal slit on the left of the genital pore ; vagina
club-shaped and muscular, but having a cuticular lining, its connec-
tions with other organs undetermined. Genito- intestinal canal
apparently absent. According to E. I. Jones the only egg observed
was large (0-0144 mm. long — an obvious misprint for 0-144 mm.) and

MICROBOTHRIIDxE 53

oval, with pointed extremities and a long filament at one pole. I found
two specimens having one egg each and they were of very variable
lengths, dimensions of the capsules 0-114-0-145 x 0-042-0-045 mm.,
filaments 0-27-0-32 mm. long.

Sub-family Pseud ocotylinje Monticelli, 1903.
Genus PSEUDOCOTYLE Beneden & Hesse, 1865.

Prohaptor absent. Opisthaptor small and sucker-like, devoid of
accessories. Eyes absent. Genital pores median and nearly together ;
testes numerous. Vagina double and separate from the genital atrium.

Pseudocotyle squatinse Beneden & Hesse, 1865. (Fig. 6 G.)

Host : monk-fish.
Location : skin.

This species has been found in monk-fish caught in the North Sea,
off the coast of Belgium, at Roscoff and in the Mediterranean. The
only British record is that of Nicoll (1914, p. 497), who found specimens
at Plymouth, but did not describe them. The original description
(4th Appendix, 1865, pp. 11-18, PI. 2, figs. 1-7) was more complete
than most descriptions by the same writers, and concerned specimens
5 mm. long and 3 mm. broad of oval and flattened form, but notched
posteriorly and slightly indented anteriorly. According to one of the
figures there were about 53 testes, and the eggs were said to be large
and oblong, truncated at the ends and devoid of filaments. I have
two specimens obtained from the same host taken from an unknown
locality and they are of closely similar size and very uniform. Size :
4-6 mm. long and 2-6 mm. broad near the midbody (2-0 mm. in the
narrower specimen). Shape : outline oviform, the posterior end
slightly truncated, the anterior end having a median notch, dorso-
ventrally flattened. Prohaptor absent. Opisthaptor a small, sucker-
like disk 0-32 mm. diameter situated on a short peduncle at the posterior
extremity, sometimes sunk in a slight indentation on the truncate
posterior margin. Hooks and hooklets absent. Gut : mouth very
narrow, sunk in the anterior indentation, pharynx ovoid (or heart-
shaped), 0-32 mm. long and 0-28 mm. broad, situated at the base
of a capacious mouth-tube (prepharynx) . (Esophagus very short
(practically absent). Caeca long, discrete, and having long lateral
diverticula which branch twice or thrice, the most anterior pair (which
Beneden & Hesse were inclined to regard as the " brain ") directed
forward at the sides of the pharynx and branching only once or twice.
Excretory system : vesicles large, having dense parenchymatous and
much-folded walls situated opposite the origins of the anteriorly-
directed caeca and slightly behind the pharynx. Reproductive systems :
genital pore situated near the median plane just behind the bifurcation

54

THE TREMATODA OF BRITISH FISHES

of the gut. Cirrus and ejaculatory duct cuticular, contained within
a slightly muscular cirrus-pouch. Testes numerous (about 64),
occupying an oval zone 1-8 mm. long and 0-95 mm. broad, a little
behind the midbody. Ovary globular, hollow, about 0-38 mm.
diameter, situated immediately in front of the testes and slightly
lateral. Receptaculum seminis almost as large as the ovary and
postero-lateral to it on the opposite side of the median plane. Vitel-
laria very well developed, occupying broad lateral zones 0-75 mm. wide,
bounded on the median side by the caeca and enveloping the diverticula,

0-5

Fig. 6. — A-F, Udonella caligorum : A, the egg ; B, C, hatching individuals ;
D, E, young forms ; F, the adult. G, Pseudocotyle squatince. (A-F,
after Price, 19386 ; G, original.)

extending from the level of the pharynx almost to the opisthaptor,
leaving only triangular anterior and posterior regions and an oval
central region devoid of follicles. Vitelloducts profusely branched,
the main lateral ducts situated slightly median to the caeca, the trans-
verse ducts immediately in front of the ovary and the receptaculum
seminis. Vaginal pores slightly lateral, immediately in front of the
lateral ends of the transverse vitelloducts, the vaginae extending
inwards parallel with the latter. Eggs few (only one seen) and of
irregular ovoid shape, more convex on one side than on the other,
about 0-156 mm. long and 0-08 mm. broad.

UDONELLID^E 55

Pseudoeotyle lepidorhini Guiart, 1938.

Host : " Lepidorhinus squamosus"
Location : skin.

I have been unable to consult the original description of this species,
which was found off Finistere and has fewer testes and no oesophagus.

Family UDONELLID.E Taschenberg, 1879.

Shape cylindrical or spindle -like. Prohaptor, when present, two
small sucker-like organs augmented by cephalic glands. Opisthaptor
sucker-like and devoid of septa and hooks. Pharynx large and pro-
trusible. Intestine sac-like, but sometimes fenestrated near the gonads.
Genital pore median or slightly lateral. Cirrus absent. Testis median.
Ovary median and situated in front of the testis. Eggs oval or elongate,
having one polar filament. Udonella having a pharynx devoid of
hooks or stylets, other genera (inquirenda) a pharynx provided with
two hooks (Echinella) or numerous stylets (Pteronella) .

Genus UDONELLA Johnston, 1835.

(Amphibothrium Frey & Leuckart, 1847 ; Nitzschia Baer, 1826, in part ;
Lintonia Monticelli, 1904 ; Calinella Monticelli, 1910.)

Prohaptor a pair of sucker-like organs. Opisthaptor terminal,
discoidal and unarmed. Gut having an unarmed bulbous pharynx
and a simple sac-like intestine, which may be fenestrated in the vicinity
of the gonads.

Udonella caligorum Johnston, 1835. (Fig. 6 A-F.)

Udonella lupi Beneden & Hesse, 1863 (1864, p. 92, PI. 8, figs. 11-14) (on the
wolf-fish) ; U. merlucii B. & H., 1863 (p. 93) (on the hake) ; U. rnolvce
(B. & H., 1863) (as Pteronella ; 1864, pp. 94-5, PI. 8, figs. 20-23) (on
the ling) ; U. pollachii B. & H., 1863 (1864, pp. 90-1, PI. 8, figs. 1-8)
(on the pollack) ; U. scicence B. & H., 1863 (1864, p. 93, PL 8, figs. 15-16) (on
the shadow-fish) ; U. triglce B. & H., 1863 (1864, p. 92, PI. 8, figs. 9, 10)
(on Trigla sp.) ; Nitzschia papillosa Linton, 1898 (p. 508, PI. 40, figs. 1-6) ;
Lintonia papillosa (Linton) Monticelli, 1904 (p. 117) ; Udonella socialis
Linton, 1910 ; U. sp. Monticelli, 1889 (on Caligus on the flounder) ; Cali-
nella myliobati Guberlet, 1936 ; Phylline caligi Kroyer, in Beneden, 1858
(p. 13 ; see 1861, p. 13) ; Amphibothrium krceyeri Frey & Leuckart, 1847
(pp. 147-8, PL 2, fig. 2).

Hosts : Caligus spp. on the halibut, cod, pollack, wolf-fish, ling,
hake, flounder. Free -swimming Caligus rapax and C. curtus. Anchor -
ella uncinata on cod. For some other hosts see Dawes (1946, p. 120).

Location : mainly on the egg-sacs of the female copepod.

This species was found off the west coast of Scotland by T. Scott
(1901), and occurs off the coast of France (near Brest) and Belgium, in
the North Sea, in Canada and various localities in U.S.A. (Woods
Hole, Tortugas, Monterey Bay). The forms described by Beneden &
Hesse seem to have got their names from the hosts of the Caligus on

56 THE TREMATODA OF BRITISH FISHES

which they were found. Price (19386, p. 194, figs. 12-17) compared
British specimens collected at Plymouth by Baylis & Idris Jones
(1933) with American specimens and found that they showed no
essential differences. But size seems to be somewhat variable ; the
specimens of Johnston (1835, p. 497, fig. 45 a-c) were about four
" lines " long, those of Beneden (1858, p. 13) 5-6 mm. long, other
specimens described being much smaller. Size : 1-1-1-4 mm. long
and one-quarter or one-fifth as broad (0-25 mm.) at the level of the
ovary. Shape elongate, almost cylindrical. Cuticle puckered near
the anterior extremity to simulate annulations. Prohaptor a pair of
retractile sucker-like organs 0-04-0-06 mm. wide, apparently bearing
the openings of cephalic glands. Opisthaptor discoidal, 0-19-0-21 mm.
diameter, devoid of septa, hooks or hooklets. Caudal glands arranged
somewhat laterally as a pair of groups immediately in front of the
opisthaptor. Gut : mouth median and not quite terminal ; prepharynx
present; pharynx ovoid, 0-15 mm. long and 0-085-0-095 mm. wide,
somewhat protrusible ; intestine simple and sac-like, extending back
almost to the opisthaptor. Eyes absent. Sensory, papillce : one pair
anteriorly. Excretory system : vesicles lateral at or slightly behind
the level of the end of the pharynx. Reproductive systems : genital
pore beneath the left group of cephalic glands. Cirrus apparently
absent, ejaculatory duct slender, seminal vesicle at its base and near
the ootype on the right. Testis median, globular, 0-075-0-095 mm.
diameter, near the midbody. Ovary 0-133 mm. diameter, median
and immediately in front of the testis. Vitellaria comprising a few
large follicles in the lateral regions and extending from the pharynx
to within a short distance of the opisthaptor. Vagina absent. Ootype
large and vesicular, having unicellular glands clustered round its base.
Metraterm very short. Eggs pyriform, measuring 0-133 x 0-042 mm.,
each having a long and slender filament tipped by an adhesive disk.
Note : the eggs measured were mounted in balsam and wrinkled ;
possibly living eggs are somewhat larger. Life-history : when newly
hatched the worm is almost mature, but of small size. The smallest
individual observed by Price was 0-21 mm. long and 0-057 mm. broad.
During growth the relative sizes of the ovary and testis vary, the former
being invariably smaller than the latter in juveniles, but not adults.
The life-history is as outlined by Beneden (1858, pp. 16-17).

Genus inq. ECHINELLA Beneden & Hesse, 1863, nee Swains, 1840.

This genus was erected for a species, E. hirundinis Beneden &
Hesse, 1863, which was found on C aligns parasitic on the yellow
gurnard near Brest. According to the original description (1864,
p. 94, PI. 8, figs. 17-19) it is 2-3 mm. long, elongate and cylindrical
with an annulated cuticle, a prohaptor represented by two tentacle-like
organs, a large and sucker-like opisthaptor and a pharynx equipped
with two cuticular hooks. The colour of this trematode, which is
possibly identical with Udonella caligorum, was said to be pale rose,
and the eggs were credited with the same colour and one filament.

ACANTHOCOTYLID^ 57

Genus inq. PTERONELLA Beneden & Hesse, 1863.

This genus was erected for a species, P. ?nolvce Beneden & Hesse,
1863, which was found on C aligns parasitic on the ling near Brest.
According to the original description (1864, pp. 94-5, PL 8, figs. 20-3)
it is 2-3 mm. long, spindle-like, annulated when young, having a
ciliated wing-like membrane at the anterior extremity, a large sucker-
like opisthaptor and a pharynx equipped with numerous cuticular
stylets. The colour was said to be white, and the dark-green eggs are
laid in clusters with the single filaments joined. This species is also
probably identical with Udonella caligorum.

Family ACANTHOCOTYLID^ Price, 1936.

(Anisocotylidse Tagliani, 1912, in part.)

Prohaptor : two retractile sucker-like organs surrounded by the
pores of the cephalic glands. Opisthaptor generally minute and having
two centrally situated and fourteen marginal hooklets, supplemented
by a large pseudodisk equipped with radial septa or radial rows of
spinelets or cuticular concretions, sometimes well developed and
without a pseudodisk. Genital pores separate, the male pore almost
median, the female pore marginal. Testes numerous, sometimes one
testis present. European sub -families distinguished by the nature
of the opisthaptor, the Enoplocotylinae having a large true haptor
and no pseudodisk, the Acanthocotylinae a vestigial true haptor and a
large pseudodisk.

Sub-family Enoplocotylinje Tagliani, 1912.
Genus EN0PL0C0TYLE Tagliani, 1912.

Prohaptor comprising two weak suckers surrounded by the openings
of the cephalic glands. Opisthaptor large and discoidal, equipped
with a pair of centrally-situated hooks and 14 marginal hooklets, each
of which occupies an oval loculus.

This genus was erected for a species, E. minima Tagliani, 1912,
which occurs on the skin of the murry in the Mediterranean and has
not appeared in Britain.

Sub-family Acanthocotylinje Monticelli, 1903.
Genus ACANTH0C0TYLE Monticelli, 1888.

Prohaptor a pair of sucker-like organs surrounded by the openings
of the cephalic glands. Pseudodisk large and equipped with radial
rows of irregular spinelets. Gut including caeca devoid of lateral
diverticula.

I have given (Dawes, 1946, p. 136) a provisional key for the separa-
tion of five European species of this genus, and a statement about four

58 THE TREMATODA OF BRITISH FISHES

American species and about the only other genus of the Acantho-
cotylinse, Lophocotyle Braun, which has a naked pseudodisk. The
European species can be distinguished by the numbers of testes and
differences in the opisthaptor, although their validity is by no means
properly established. Acanthocotyle borealis has about 266 spines
arranged in 32 rows, but in all other instances there are about 20 rows,
A. elegans and A. oligoterus having about 150 spines, A. lobianchi and
A. monticellii more than 200. The last-named species differs from
others in having a smooth cuticle and a pseudodisk with a smooth
margin, A. elegans also having a cuticle of the same kind, but a
pseudodisk with a crenulate margin.

Acanthocotyle monticellii T. Scott, 1902.

Acanthocotyle branchialis Willem, 1906 ; A. concinna T. Scott, 1902.

Hosts : thornback ray, spotted ray.
Location : gill- chamber.

T. Scott (1902, pp. 300-2, PL 13, figs. 31, 32, 32 A, 33) gave a very
cursory description of the single specimen found on the thornback ray
obtained at Aberdeen fish-market, not even specifying the size, which
seems to have been about 6-6 mm. long and 1-3 mm. in greatest breadth.
Monticelli examined the specimen and regarded it as a valid new species,
later describing it (1905), pp. 74-5, figs. 4, 5. Willem (1906, p. 599,
PL, figs. 1-10) collected ten specimens of what he regarded as a new
species from the mucus in the gill- chamber of a spotted ray bought in
the market at Gand and fished off the coast of Belgium. Brinkmann
(1940, p. 50) gave good reasons for considering this form identical with
A. monticellii and it is recorded here as a synonym, although Price
(19386, p. 190) regarded both as valid species. Brinkmann counted
the numbers of spines shown in the various rows in Scott's figure and
found them to compare very closely with the figures provided by
Willem, being significantly different in only one row, whereas the
Belgian specimens themselves showed variability in this respect in
several rows. Willem also seems to have settled the question about
the lateral position of the uterine pore. Size : 5-6-5 mm. long and
about one -fifth as broad. Prohaptor a pair of anterior suckers and
associated cephalic glands, not head-organs as indicated in Scott's
fig. 31. Opisthaptor : pseudodisk about one-fifth as broad again
as the body, bearing 20 rows of spine-like concretions, mainly
12-14 in a row and totalling about 224-50, the approximate numbers in
individual rows starting anteriorly and proceeding back along one
side 10-14, 11-14, 10-13, 12-14, 12-14, 11-14, 12-14, 12-13,
9-11 and 7-8. In each row the most central spines are implanted per-
pendicular to the surface and well spaced, but more crowded peri-
pherally. True disk borne on a short peduncle attached to the
slightly indented posterior margin of the pseudodisk, bearing 1 pair
of centrally-situated hooklets and 14 hooklets in a marginal position,
each situated on a pyramidal eminence. Reproductive systems :

ACANTHOCOTYLID^E 59

testes numbering about 28, situated between the caeca in the pos-
terior two-thirds of the body proper ; ovary small and ovoid, situated
just in front of the most anterior testes. Vitellaria made up of
numerous coarse follicles lateral to the caeca and in that part of the
body occupied by the gonads. Eggs fusiform, operculate and equipped
with a filament about as long as the capsule and terminating in a disk.

Acanthocotyle oligoterus Monticelli, 1899. (Fig. 7 A-E.)

Hosts : thornback ray, " Raja punctata"
Location : skin.

This species occurs at Naples and was described by Monticelli
(1899a, pp. 115-17, PI. 1, figs. 2, 9 ; PL 2, figs. 12, 14, 20, 24,25c, 27,
29 ; PI. 3, fig. 48). I have four specimens obtained from an unknown
British locality which have characters more in conformity with this
than with other species, although only one of them shows any signs
of a tuber culate integument. In this instance the tubercles are very
few and may represent mere wrinkles in the cuticle, which are evident
as such in other specimens. Size : body proper 3-8-5-0 mm. long
and 1-0-1-5 mm. in greatest breadth posteriorly. Cephalic glands
numerous, extending from the prohaptor to a level behind the pharynx.
Prohaptor a pair of anterior suckers 0-12 mm. diameter in smaller
specimens, 0-17 mm. broad, and 0-21 mm. deep in the largest, situated
0-28-0-39 mm. apart. Opisthaptor : pseudodisk oval and attached
terminally so that more than one-half of the surface area projects
beyond the end of the body proper, measuring 1-3-1-5 x 1-2-1-25 mm.
Spines arranged in twenty more or less radial rows and totalling
140-6, the numbers in the individual rows, starting in front and pro-
ceeding backwards, 7, 7-8, 7-8, 7-8, 8-9, 7-9, 7-8, 7-8, 5-6, 5-6.
(Note. — The numbers in the last four rows imply counting from before
backwards, and including in one row all the spines which fit it and
excluding those counted even when they fit in more posterior rows,
when these are dealt with.) True haptor transversely oval in outline,
situated on a short peduncle in a notch on the posterior border of the
pseudodisk, 0-055-0-062 mm. broad and 0-040-0-058 mm. long,
and bearing 16 hooklets each about 0-007 mm. long, 14 of them
near the periphery having their hooked points directed inwards, the
central ones on right and left having their points directed forwards and
inwards. Gut : mouth minute, situated on the ventral surface about
0-38 mm. from the anterior extremity. Prepharynx very small or
absent. Pharynx pyriform, and not more than 0-33 mm. long or
0-29 mm. broad. (Esophagus absent. Caeca long and devoid of
diverticula, along most of their courses dividing the body into approxi-
mately equal longitudinal one-thirds. Excretory system : vesicles sac-
like, situated just in front of the vitellaria, opening to the exterior each
by a short and straight canal. Reproductive systems : male pore median
just behind the pharynx. Uterine pore at the same transverse level,
or slightly anterior to it on the right margin of the body. Testes not
very numerous (26-32), and arranged in a paired series between the

60

THE TREMATODA OF BRITISH FISHES

caeca extending from the opisthaptor almost to the anterior ends of
the vitellaria. Ovary globular and situated just in front of the
receptaculum seminis, which is pyriform and anterior to the testes.
Ootype and a bilobed glandular mass situated immediately in front
of the transverse vitelloduct. Vitellaria comprising numerous very
coarse follicles lateral to the caeca and between the excretory vesicles
and the opisthaptor, the lateral vitelloducts just median to the follicles
and lateral to the caeca. Eggs (one seen in each of three specimens)

ss

fS>

*m<m<h^ *«®e

0-05

Fig. 7. — Acanthocotyle oligoterus. A, entire trematode (details of the
opisthaptor omitted) ; B, the pseudohaptor, and C, some representative
spines from the same ; D, the true haptor, showing the hooklets ; E,
the egg. (Original.)

rounded at one pole, pointed and having a short filament at the other,
0- 15-0- 17 mm. long.

A. Scott (1906, p. 192, PI. 9, figs. 2-4) described very briefly as
Acanthocotyle sp. a specimen about 1-8 mm. long which was found in
washings from trawl refuse from Fishguard Bay and which resembles
this more than other species. Unfortunately no diagnostic characters
were given, but according to the figure this rather contracted specimen
had a very large pseudodisk 0-7 mm. diameter, bearing 20 rows
of spines totalling about 136 and a true haptor of triangular shape
equipped with 2 central and 14 marginal hooklets. The testes cannot
be counted in the figure, being obscured by a large bouquet of about
31 eggs which must have exceeded 0-3 mm. in length, but they would
seem to have been fewer than 30.

ACANTHOCOTYLIDiE 61

Acanthocotyle borealis Brinkmann, 1940.

Host : starry ray.

Location : skin, of the ventral surface.

This species was found near Herdla, north of Bergen, Norway, and
was described by Brinkmann (1940, p. 34, Pis. 9-11, figs. 29-45). Size:
about 4 mm. long and 1-1 mm. in greatest breadth. Shape : elongate
oval outline, convex dorsally and concave ventrally, truncated
anteriorly, narrowing posteriorly to the attachment of the opisthaptor.
Prohaptor : three or four tongue-shaped lobes at the antero- lateral
angles of the body and associated cephalic glands. Pseudodisk slightly
broader than the body and attached to it by a short peduncle, having
a thin membranous border and spines arranged in 32 curved radial
rows which reach the periphery, but not the centre. Taking the
rows on one side in order antero -posteriorly the spines in them
number 8, 9, 9, 9, 10, 8, 9, 9, 9, 9, 10, 8, 8, 7, 6 and 5, and are therefore
most numerous in the fifth and eleventh rows, the numbers variable,
but never by more than a single spine in any row. Each spine con-
sisting of a basal plate and a point directed towards the row in front of
it, the centrally- situated spines smallest and roughly triangular in
shape, more peripheral ones larger and curved, and the most peripheral
ones somewhat smaller than the curved ones and straight. True
haptor discoidal, 0-1-0-12 mm. diameter, attached by a short peduncle
and equipped with 2 central and 14 marginal hooklets having sickle-
shaped points. Other characters : pharynx 0-17-0-20 mm. long
and 0-10 mm. broad, internally and externally triangular in section.
(Esophagus absent. Cseca long and simple and lined with an epithelium.
A group of unicellular glands postero-dorsal to the pharynx opening
into its lumen. Male pore situated on a small papilla just behind the
pharynx and slightly on the right side ; the uterine pore on the right
margin of the body a little farther back. Testes numerous (but
described as a testicle with a number of lobes) ; cirrus small ; cirrus
pouch present. Seminal vesicle bipartite ; sperms filiform and about
one quarter as long as the mature ovum. Ovary somewhat globular.
Eggs yellowish and club-shaped, 0-5 mm. long and 0-07 mm. broad,
tapering to a narrow stalk terminating in a plate at one end, apparently
laid in bundles of four.

Acanthocotyle lobianchi Monticelli, 1888.

Host : thornback ray.
Locution : skin dorsally.

This species was first found in the Gulf of Naples and was described
on several occasions by Monticelli (1888, p. 13 ; 18906, p. 190, 1891 ;
PI. 5, figs. 9, 10, PI. 6, figs. 36-39 ; 1899a, pp. 111-13, PI. 1, figs. 1,
3-6, 10, PL 2, figs. 11, 15, 16, 18, 21, 22, 25, 26, 31, 33, PL 3, figs.
34-43, 46-7, 49-58). It is 3-6 mm. long and is supposed to differ from

62 THE TREMATODA OF BRITISH FISHES

the preceding species in having a tongue-shaped true haptor bearing
8 marginal hooklets with their straight roots directed radially
inwards, but this shape was not consistently illustrated by Monticelli.
T. Scott found a specimen " in some material from the Firth of Clyde "
which he thought might belong to this species.

Acanthocotyle elegans Monticelli, 1890.

Host : thornback ray.
Location : skin dorsally.

This species was also found at Naples and described several times
by Monticelli (18906, p. 191, fig. 3 ; 1899a, p. 108, PI. 1, figs. 7, 8,
PL 2, figs. 13, 17, 19, 23, 256, 28, 29, 32, PL 3, figs. 44, 45 ; 1905, p. 73).
It is supposed to be a small species 2-4 mm. long and, like A. oligoterus,
was said to have 15 hooklets on the true haptor, although Brinkmann
proved that the latter species has 14 peripheral and 2 central hooklets
and thought it very probable that A. elegans has the same number.

Family CAPSALID^ Baird, 1853.

(Phyllinidse Johnston, 1846 ; Tristomidse Cobbold, 1877 ; Tristomatidae
Gamble, 1896; Encotyllabidae Monticelli, 1888.)

Shape oval or elliptical and flat, constricted anteriorly to form a
cephalic lobe. Cuticle smooth, or papillate, or spinous dorso-laterally.
Prohaptor a pair of suckers, or glandular areas, or suckers and glandular
areas situated on the margins of the cephalic lobe. Opisihaptor
discoid al and sucker-like, sometimes having its ventral surface formed
into loculi, equipped with at least 1 pair and sometimes as many as
3 pairs of hooks and 14 hooklets. Gut : mouth ventral, never
encircled by an oral sucker ; caeca having median and lateral
diverticula which may have dendritic terminations. Eyes : 2 pairs.
Excretory pore dorso-lateral at or near the level of the pharynx. Genital
pores somewhat lateral, opening into an atrium or not. Gonads :
ovary median and situated in front of two or more testes. Vagina
present or absent. In the Encotyllabinse the opisthaptor has a stout
peduncle, in other sub-families it is sessile. In two sub-families septa
and loculi exist, in the other two they do not. Loculate forms may
have 2 testes as in Trochopodinse or many as in Capsalinse, and
non-loculate forms fall into the sub-families Benedeniina3 and Nitz-
schiinae on the basis of the same characters.

Sub-family Encotyllabinje Monticelli, 1892.

(Encotyllabidse Monticelli, 1888.)

Genus ENCOTYLLABE Diesing, 1850.

(Cheloniella Beneden & Hesse, 1863 ; Tristoma of Taschenberg, 1878.)

Lateral margins of the body turned ventralwards. Prohaptor
sucker-like, muscular, elliptical, encircled by a wide pleated membrane.

CAPSALIDiE 63

Opistkaptor bell-like, pedunculate and septate, and equipped with
2 pairs of hooks (one pair massive) and 14 (?) hooklets. Genital
pore somewhat lateral, genital organs arranged as in Trochopus.

Encotyllabe nordmanni Diesing, 1850 (p. 428).

Tristotna excavatum of Nordmann, MS. ; T. nordmanni (Diesing) Taschenberg,
1878 ; Encotyllabe normanni Braun, 1900 (p. 550).

This species was found in the nostrils of Ray's bream, Brama
mediterranea and Heliaster chromis, in the Mediterranean, and the original
description merely states " Longit. corp. \\" ; latit. \" ; longit.
pedic. acet. §*," but some more rather scanty information was given
later (Diesing, 1858a, p. 70, PL 1, figs. 11-15; 18586, p. 364) and a
figure was given by Fuhrmann (1928, fig. 6, p. (2) 6).

Encotyllabe pagelli Beneden & Hesse, 1863.

Tristoma pagelli (Beneden & Hesse, 1863) Taschenberg, 1878 (p. 569).

Host : common sea bream.
Location : buccal cavity.

This species was originally found near Brest and has appeared off
the west coast of Ireland. According to the original description
(1864, pp. 80-1, PI. 7, figs. 1-11) the living trematode is very lively
and the movements include the modification of the lateral expansions
of the body, which are continually being brought together and sepa-
rated again. Colour straw yellow with a narrow border of rose, the
peduncle of the opisthaptor pale like the body, but roseate in the
middle region. Shape narrow oval, the outline wrinkled, slightly
convex dorsally and concave ventrally, the posterior extremity of the
body proper somewhat pointed. Prohaptor 2 anterior suckers of
medium size, each bordered by a thin pleated membrane and having
a V-shaped cavity. Opisthaptor relatively small and very convex,
surrounded by a large pleated membrane and bearing in the depths of
its cup 2 stout curved hooks the points of which cross one another.
Peduncle thick, circular in section, very contractile, slightly annulated,
enlarging near its union with the haptor. Gut bifurcate, mouth
circular. Reproductive systems : genital hooklets 5 in number and
arranged in a coronet with the points inwardly directed. Eggs dark
chestnut brown and of bizarre shapes, some having 2 or 3 filaments,
as well as a filament of great length and flexibility by which each is
moored.

Other Species.

Monticelli (1907) described two species found in Italy, E. paronaz
(on Crenilabrus pavo) and E. vallei (on the gilt-head). Four species
occur outside Europe, E. lintoni Monticelli, 1909, on Calamus calamus
in Bermuda, E. pagrosoma MacCallum, 1917, in U.S.A. and two (E.
masu Ishii & Sawada, 1938, and E. spari Yamaguti, 1934) in Japan.

64 THE TREMATODA OF BRITISH FISHES

Sub-fainily Trochopodin^ Price, 1936, emend Dawes, 1946.

Two genera must be considered, and in Trochopus there are 10
septa dividing up the ventral surface of the opisthaptor, in Megalo-
cotyle only 6 or 7.

Genus TROCHOPUS Diesing, 1850.

( Capsa la of Nordmann ; Tristoma of Diesing, 1836; Placunella Beneden

& Hesse, 1863, in part.)

Prohaptor a pair of disk-like, almost sessile organs of medium size
and varying form and appearance. Opisthaptor discoidal, almost
sessile, provided with a marginal membrane, the ventral surface
divided by 10 septa into loculi and bearing 3 pairs of hooks and
14 marginal hooklets. Genital pore just behind the prohaptor on
the left ; genital atrium long ; cirrus pouch curved, its basal part
passing over the median plane to the right side of the body. Testes
numbering 2, ovoid in shape, side by side and contiguous or slightly
separated, generally at or in front of the middle of the body. Ovary
globular and situated in front of the testes. Vagina slender, its pore
situated just behind the common genital pore.

Trochopus gaillimhe Little, 1929. (Fig. 8 A-F.)

Host : yellow gurnard.
Location : gills.

This species was found at Galway and described in great detail
by Little (19296, p. 107, figs. 1-8 ; Pis. 9-11, figs. 1-14), who noted its
brisk movements over the gills by muscular activity and the use of
the haptors. Size up to 585 mm. long, a specimen 5-03 mm. long
being 2-78 mm. broad. Shape broad oval or subrectangular outline,
broadly rounded posteriorly and notched in the median plane, taper-
ing, but truncate anteriorly. Colour translucent, milky-white and
faintly roseate. Prohaptor a pair of sessile saucer-like suckers 0-45-
0-50 mm. diameter provided with a semi-membranous frill containing
numerous mucous glands arranged in regular radial rows. (The frill
is subject to shrinkage during fixation and its width was therefore
undetermined.) Opisthaptor discoidal, convex dorsally, 1*8 mm.
diameter, having a pleated membranous frill and bearing 12 septa
and 3 pairs of hooks. Four anterior septa form a group, 3 lateral
septa on each side two additional groups. These 10 main septa
converge on the middle of the haptor, forming a space of horse -shoe
shape with its open end posteriorly. Two additional short septa
occur in the posterior space, one on either side of the middle line ;
they barely reach half-way to the middle of the haptor. Marginal
frill scalloped, each pleat overlapping the next, except posteriorly,
where about 8 pleats are separate and distinct. Hooks of the first
pair situated at the junction of the postero-lateral septa, their points
directed towards the middle of the haptor, 0-1 mm. long and each

CAPSALID.E

65

comprising a long cylindrical " handle " and a minute recurved point.
Hooks of the second and third pairs much stouter than those of the
first and 0-30-0-35 mm. long, situated close together and mainly
embedded in the tissues of the most posterior complete septa, the
hooks of the second pair the more median. Hooks of the second pair
having 4-5 condylar processes for the attachment of muscles and 4-5
rows of serrated ridges distally. Hooks of the third pair tapering
gradually from a broad base, each having a strong, recurved point.
Gut : mouth ventral, 0-75 mm. from the anterior extremity, being a

Fig. S.—Trochopus gaillimhe. A, dorsal view showing the gut and
gonads ; B, the reproductive organs ; C, the anterior suckers ; D, the
opisthaptor ; E and F, hooks of the 1st and 2nd (E) and 3rd (F) pairs.
(After Little, 19296.)

transverse slit 0-60 mm. wide bordered by prominent anterior and
posterior lips. Pharynx ovoid, 0-78 X 0-40 mm., its lining bearing
numerous granular papillate structures. (Esophagus short (0-10 X 0-05
mm.), caeca having about a dozen lateral and half as many median
diverticula, all of which tend to branch more than once. Caeca and
diverticula lined with amoeboid cells with prominent nuclei. Eyes :
2 pairs, one behind the other, slightly in front of the mouth, those
of the anterior pair 0-14 mm. apart and 0-44 mm. from the anterior
extremity, those of the posterior 0-28 mm. apart. Reproductive
systems : male and female pores opening one behind the other into a
shallow common genital atrium immediately behind the left anterior
sucker. Cirrus-pouch membranous, epithelial and lined with thin
cuticle. Cirrus very long, narrow and folded, encased in cuticle, con-

66 THE TREMATODA OF BRITISH FISHES

taining two ducts (a) and (6), each lined with cuticle ; (a) is the con-
tinuation of the pars prostatica, i.e. the ejaculatory duct, which may
be packed with spermatozoa ; (b) is smaller, and contains a gelatinous
substance derived from a large accessory sac (0-45-0-60 mm. long)
situated beneath the cirrus and pars prostatica. Vas deferens swollen
at its base to form a W-shaped seminal vesicle. Testes globular,
0-45-0-55 mm. diameter, but only 028 mm. thick, side by side and
almost confluent near the midbody. Ovary spherical, 0-40 mm.
diameter, median, in front of and between the testes. Oviduct short,
almost at once receiving the unpaired vitelloduct, which extends from
the vitelline reservoir antero -lateral to the ovary ; beyond this point
slightly folded to the ootype, which is ovoid and 0-11-0-12 mm. in
greatest width. Uterus very short, metraterm straight. Vitellaria
comprising numerous follicles occupying the available space above and
beneath the caeca throughout the whole extent of the body. Vagina
0-9-1-2 mm. long, wide at the base, but narrowing towards the external
opening, which is situated near the genital pores. Receptaculum
seminis globular or ovoid (0-17 x 0-14-0-17 mm.) and situated at the
base of the vagina. Eggs pyriform, very large (0-163-0-197 x 0-100-
0-142 mm.), dark yellow, and having a twisted filament 0-39 mm. long
attached to the posterior pole. Only one egg found in utero at any
time, situated either in the ootype or the metraterm.

Other Species, their Hosts and Distribution.

Trochopus brauni Mola, 1912 (miller's thumb : Italy).

T. differens Sonsino, 1891 (black sea bream : Mediterranean).

T. diplacanthus Massa, 1903 (Placunella pini of A. Scott, 1901)
(yellow gurnard : Mediterranean, Irish Sea) .

T. lineatus T. Scott, 1901 (streaked gurnard : in the Clyde, Scot-
land) .

T. micracanihus Massa, 1903 (yellow gurnard : Italy).

T. onchocanthus Massa, 1906 (unidentified fish : Italy).

T. pini Beneden & Hesse, 1863 (red and yellow gurnards : Brest.
Also Trigla corax : Italy).

T. tubiporus (Diesing, 1835) (Tristoma tubiporum Diesing, 1835 ;
Trochopus longipes Diesing, 1850) (yellow gurnard, red gurnard,
Cantharus lineatus : Irish Sea, Italy, North- West France) .

Most of these species are ill defined and the British records very
doubtful. According to T. Scott (1901, pp. 143-4, PL 8, fig. 18 ; 1905,
p. 118; 1912, PL 27, fig. 3) Trochopus lineatus is about 3 mm. long,
broad oval in outline, and has a discoidal opisthaptor with 12
radiating septa spaced out at fairly regular intervals, the posterior
2 having their inner ends free, the remaining 10 merging with an
almost central ring-like septum. The same writer (1912) mentioned
only 1 small hook on each of the penultimate rays, and 2 other
pairs of hooks were either overlooked or missing from the specimens,
which had 2 pairs of eye-spots. A. Scott (1904) claimed to have
found T. pini (as Placunella) on the yellow gurnard in the Irish Sea, but

CAPSALID^E 67

the only characters mentioned were 8 distinct and 2 indistinct " rays "
in the " posterior sucker." Some information concerning most of
the species is available in the later paper by Massa (1906).

Genus MEGAL0C0TYLE Folda, 1928.

(Trochopus of Mola, 1912, and Massa, 1903, in part; Placunella Beneden

& Hesse, 1863, in part.)

Opisthaptor having 6 or 7 septa, other characters as in Trochopus.
The type-species, M . marginata Folda, 1928, is a parasite of Sebastodes
nebulosus in North America. Three other species were discovered in
Europe, but have not appeared in Britain.

Megalocotyle zschokkei (Mola, 1912) Price, 1939.

Trochopus zschokkei Mola, 1912.

Host : miller's thumb.
Locality : unspecified.

According to the original description — Size : 2*65 mm. long.
Shape : elliptical, if the haptors are left out of account. Colour pale
rose. Prohaptor a pair of cup-shaped anterior suckers 0*35 mm.
diameter situated relatively close together. Opisthaptor discoidal,
0*9 mm. broad, having ventrally 7 radiating septa which merge
centrally, those of the most posterior pair bearing 3 pairs of hooks
which are set close together and are similar except in size (0'24 mm.,
017 mm., and 06 mm. long in the outer, middle and inner pairs
respectively).

Megalocotyle hexacantha (Parona & Perugia, 1889) Price, 1939.

Placunella hexacantha Parona & Perugia, 1889 (p. 740, fig. 1). Trochopus
hexacanthus (Parona & Perugia) Massa, 1906 (pp. 59-60, PI. 2, figs. 15-17 ;
PL 3, figs. 28, 36).

Host : dusky perch (at Genoa).

Megalocotyle rhombi (Beneden & Hesse, 1863) Price, 1939.

Placunella rhombi Beneden & Hesse, 1863 (1864, p. 72, PI. 5, figs. 9-18).
Trochopus rhombi (Beneden & Hesse) Massa, 1903 (p. 255) (see also Massa,
1906, pp. 58-9, PI. 2, fig. 1).

Host : turbot (near Brest).

Sub-family NiTZSCHUKa: Johnston, 1931.

Genus NITZSCHIA Baer, 1826, nee Denny, 1842, nee Beneden, 1858,

nee Linton, 1898.

(Hirudo Abildgaard, 1794; Nitychia and Nityschia Nordmann, 1833;
Nitschia Haswell, 1892; Nitzchia Beneden, 1858.)

68 THE TREMATODA OF BRITISH FISHES

Nitzschia sturionis (Abildgaard, 1794) Kroyer, 1852 (p. 777).

Hirudo sturionis Abildgaard, 1794 (pp. 55-6, PI. 6, fig. 1) ; Nitzschia elegans
Baer, 1826 (pp. 125-6) ; N. elongata of Monticelli, 1909 ; Tristoma sturionis
of Cuvier, and Blainville, 1847 (pp. 329-30) ; T. elegans of Beneden &
Hesse, 1864 (pp. 64, 77) ; T. elongatum of Nitzsch, 1826 (pp. 150-1).

Host : sturgeons.

Location ; gills.

This species occurs widely in Europe (North Sea, Baltic Sea,
Mediterranean) and possibly in America, although Price (19386) was
of the opinion that N. superba MacCallum, 1921, is the only American
species. It has been described by Abildgaard (1797, p. 135, PL 3,
figs. 3-5), MonticeUi (1891, p. 106, PI. 6, fig. 32) and Liihe (1909, p.
5, fig. 1). Size : 12-23 mm. long. Shape : elongate, broadening
slightly at the anterior end, tapering slightly towards the opisthaptor.
Prohaptor : two sucker-like grooves of elongate oval shape diagonally
arranged at the anterior extremity. Opisthaptor : discoidal and sucker-
like, with a delicate marginal membrane, but lacking septa and papilla.
Hooks arranged in 3 pairs, their sizes approximately equal, mar-
ginal hooklets numbering 14. Gut bifurcate, pharynx relatively
large. Reproductive systems : genital pore median or slightly to the
left of the middle line near the bifurcation of the gut. Ovary compact,
situated in front of the testes, which number up to 27, perhaps
more, and occupy the space between the caeca in the posterior half
of the body.

Price (1939a) proposed the erection of a new species, N. monticellii,
for the " forma giovane " of N. elongata (= N. sturionis of Monticelli,
1909), claiming that two species were represented in Monticelli's
specimens, this form having hooks of unequal lengths on the opisthaptor.

Sub-family Capsalinje Johnston, 1929, emend Price, 1939.
(Tristominae Braun, 1893 ; Tristomatinae Gamble, 1896.)

Two European genera are readily distinguished, Capsala by the
transversely constricted pharynx and testes which sometimes over-
step the caeca laterally, and Tristoma by the unconstricted pharynx
and testes which are confined between the caeca. The genus Cap-
saloides Price, 1936, resembles Tristoma in these characters, but can
be separated from it by the distal bifurcation of the posterior rays
of the opisthaptor and the claw-like tips of the hooks. Two species
of this genus occur in America, another in Japan, and a fourth species,
C. perugiai (Setti, 1898), was discovered on Tetrapterus belone at
Spezia, but has not appeared in Britain.

Genus CAPSALA Bosc, 1811.

(Phylline, Oken, 1815, in part ; Tristoma Cuvier, 1817, in part ; Trico-
tyle Guiart, 1938 ; Tristomella Guiart, 1938 ; Capsala of Guiart, 1938,

in part.)

Opisthaptor having posterior septa which are not bifid distally and
hooks which, when present, do not have claw-like tips. Dorsal

CAPSALIDJE 69

marginal spines present or absent. Pharynx having a marked con-
striction at or slightly behind the middle. Testes generally numerous,
sometimes extending lateral to the caeca.

Capsala martinieri Bosc, 1811 (pp. 384-5). (Fig. 9 A, B.)

Phylline diodontis Oken, 1817 (p. 182, PI. 10, fig. 3 ; based on Martiniere,
1787, pp. 207-8, figs. 4, 5) ; P. coccinea of Schweigger, 1820 (p. 474) ;
Tristoma maculatum Rudolphi, 1819 (pp. 123, 430, PI. 1, figs. 9, 10) ;
T. coccineum of Rudolphi, 1819 (pp. 123, 428), and authors ; T. cephala
Risso, 1826 (p. 262) ; T. aculeatum of Couch (quoted by St. Remy) ; T.
molce Blanchard, 1847, of Guiart, 1938; T. rudolphianum Diesing, 1850, of
Johnston, 1865 (p. 330) ; Capsala maculata (Diesing) of Nordmann, in
Lamarck, 1840 ; C. rudolphiana (Diesing) of Johnston, 1865 (p. 33) ; C.
sanguinea Blainville, 1828, and Nordmann, in Lamarck ; C. cephala (Pvisso)
of Johnston, 1929 ; C. molce (Blanchard) of Johnston, 1929.

Host : sun-fish.
Location : gills.

This species is widespread in Europe and occurs on both the Atlantic
and Pacific coasts of America. It has been described concisely by
Price (1939a, p. 79, figs. 19-21), and I have already given a brief
diagnosis (Dawes, 1946, p. 138), mentioning also unusually large
specimens collected by Professor Yonge near Bergen. An up-to-date
diagnosis based on the two sets of specimens can now be given. Size :
15-28-5 mm. long and 16-30 mm. broad. Shape : almost circular in
outline, but deeply notched posteriorly, concave ventrally and convex
dorsally. Cuticle smooth dorsally except near the margins of the
body, where there is a relatively broad longitudinal band of irregu-
larly-disposed spines, most of them having 4 cusps, the ventral
surface covered with numerous minute papillae. Prohaptor a pair of
large sucker-like organs 1-4 to more than 2 mm. diameter, sometimes
slightly ovoid. Opisthaptor discoidal and 8 to nearly 14 mm. diameter,
encircled by a pleated membrane 0-4-0-5 mm. wide, the ventral surface
bearing numerous papillae and having a central depression of hep-
tagonal shape and 7 radiating septa peripheral to it. Hooks
absent, hooklets present. Out : mouth median just behind the pro-
haptor ; pharynx 2-2-5 mm. long and 1-2-2 mm. broad, having a
distinct constriction at the second third of its length. Reproductive
systems : genital pore just behind the left anterior sucker. Cirrus pouch
club-shaped, its base in the median plane just behind the pharynx ;
testes very numerous, and occupying most of the central region of the
body and extending to within 1-5 mm. of the margin behind the
pharynx. Ovary lobed, 1-5-2-7 mm. long and 2-3-7 mm. broad, situated
in front of the testes about 2 mm. behind the pharynx. Vitellaria
comprising numerous follicles occupying most of the space throughout
the body and extending into the cephalic lobe, but leaving a clear
lateral zone about 1 mm. wide on each side of the body. Vitelline
reservoir up to 0-6 mm. diameter, situated in front of the ovary on the
left. Vagina slender, its pore 0-37-0-45 mm. postero-lateral to the

70

THE TREMATODA OF BRITISH FISHES

genital pore. Ootype ovoid and situated just behind the cirrus pouch.
Eggs not found.

Other species of Capsala which have been recorded in Europe
include C. cutanea (Guiart, 1938), C. grimaldii{ Guiart, 1938), C. inter-

Fig. 9. — Capsala martinieri. A, entire trematode ; B, part of the
margin of the body, showing the marginal spinelets. (Original.)

rupta (Monticelli, 1891), C. onchidiocotyle (Setti, 1899), C. pelamydis
(Taschenberg, 1878) and G. thynni (Guiart, 1938). None of these
species has been found in British waters.

CAPSALID^ 7 1

Genus TRISTOMA Cuvier, 1817.
(Capsala Bosc, 1811, in part.)

Opisthaptor having posterior septa which are not bifid distally and
hooks which, when present, do not have claw-like tips. Dorsal mar-
ginal spines, when present, arranged in numerous short transverse
rows of similar or dissimilar spines. Pharynx nearly globular and
never constricted at or near the middle. Testes numerous and con-
fined between the caeca.

Tristoma coccineum Cuvier, 1817 (pp. 42-3, pi. 15, fig. 10 ; PI. 36 bis,
figs. 1-3).

Tristoma papillosum Diesing, 1836 (pp. 313-16, PL 17, figs. 13-16); Capsala
papillosa (Diesing) of Nordmann, in Lamarck, 1840.

Hosts : sword-fish, hammerhead shark.
Location : gills.

This species occurs in various parts of the Mediterranean (Genoa,
Naples, Palermo, Messina), and in Canada and U.S.A. Price (1939a)
showed that Cuvier included two species under this name, one from
the sword-fish and the other from the sun-fish, the latter being the
form later known as T. molce Blanchard, 1847, and now considered to
be one of the synonyms of Capsala martinieri. Diesing (1836) re-
described forms from both these hosts, but his " T. coccineum " was
the form from the sun-fish. The remaining form from the sword-fish
was described as T. papillosum and bore dorsal tubercles, for this
reason being referred by Price to the species under consideration, which
is not completely host-specific, one of a number of American specimens
being found on the hammerhead shark. According to Price (1939a, p.
84, figs. 29-32) it is 10-12 mm. long and nearly four-fifths as broad ;
the cuticle has prominent dorsal papillae and 43-54 rows of 2 to 4
marginal spines, the innermost having 1 cusp, the second and third
2 to 7 cusps, while the outermost are comb -like. The anterior
suckers are about 1-3-1-7 mm. diameter, the opisthaptor about 1-8-
2-4 mm. and its margin 0-17-0-36 mm. wide. The large hooks are
straight and 0-13-0-15 mm. long, the hooklets 0-015 mm. long. The
globular pharynx is 1-1-3 mm. long and 1-1-1-5 mm. broad. The eggs
are fairly large, more or less triangular and with 4 prolongations,
their dimensions 0-114 x 0-095 mm.

Tristoma integrum Diesing, 1850 (p. 429).

Tristoma coccineum Cuvier, 1817, in part ; T. coccineum Cuvier of Taschen-
berg, 1879 (a, p. 59 and c, p. 296) and authors ; T. rotundum Goto, 1894
(pp. 245-8, PI. 24, figs. 6-9).

Host : sword-fish.
Location : gills.

This species occurs in various parts of the Mediterranean (Genoa,
Naples, Venice, Messina) and in U.S.A. and Japan. According to

72 THE TREMATODA OF BRITISH FISHES

Price (1939a, pp. 86-8, figs. 33-35) the outstanding differences between
this and the previous species lie in the arrangement and morphology of
the dorsal marginal spines, which are numerous (upwards of 300 on
each side of the body) in this species and not dissimilar in different
rows. Further details can be found in the paper by Price, and two
good figures occur in that by Taschenberg (1879c, PL 1, figs. 1,2), these
having been merged to form one admirable illustration by Braun
(1893, PI. 8, fig. 1).

Two other species of Tristoma have been recorded in the Mediter-
ranean and elsewhere — T. levinsenii Monticelli, 1891 (pp. 101, 122,
PI. 6, fig. 21) (on Thynnus sp.), and T. uncinatum Monticelli, 1889
(Boll. Soc. Nat. Napoli, 3, pp. 117-19, PI. 4, figs. 1-7) (on the halibut
and Pleuronectes sp.).

Sub-family Benedeniin^e Johnston, 1931.

(Encotyllabinse Monticelli, 1892, in part ; Ancyrocotylinse Monticelli,
1903 ; Tristominse Braun, 1893, and of Monticelli, 1892, in part.)

Three European genera can be separated by the nature of the
caeca and prohaptor. The caeca of Ancyrocotyle lack diverticula ; those
of other genera have median and lateral diverticula, and Benede?iia
has a pair of anterior suckers, Entobdella a prohaptor comprising
glandular areas only.

Genus BENEDENIA Diesing, 1858, nee Schneider, 1875.

{Epibdella Beneden, 1856, in part ; Phylline Oken, 1815, nee Abildgaard,
1790, in part ; Tristoma Cuvier, 1817, in part.)

Prohaptor a pair of suckers or sucker-like disks. Opisthaptor
discoidal, lacking septa, but equipped with 3 pairs of dissimilar
hooks and 14 hooklets. Testes 2 in number, side by side, and
confluent. Vas deferens generally not forming a loop in front of the
ovary, which is anterior to the testes and not separated from them by
a wide belt of vitelline follicles. Vagina present or absent.

Benedenia sciaenae (Beneden, 1856), Linstow, 1903 (p. 355).

Epibdella sciaenae Beneden, 1856 (pp. 502-8, PI., figs. 1-4) ; Benedenia elegans
Diesing, 1858 (p. 364) ; Phylline scicence (Beneden) Sonsino, 1878 (p. 263) ;
Tristoma scicence (Beneden) Taschenberg, 1878 (p. 568).

Host : meagre (in the North Sea, near Ostend and in Italy).

The original description of this species has not been available to
me, but MacCallum (1927, p. 298) gave such details as — Size : 18-20
mm. long and 10-12 mm. broad. Prohaptor a pair of rounded anterior
suckers. Opisthaptor bearing papillae and short spine -like hooks.
Cirrus pouch simple and thin- walled. Vaginal pore situated near the
genital pore. Eggs ovoid, each having one polar filament. Beneden
(1858, pp. 23-37) specified the length and breadth of the body as 24 x
12 mm. and the diameter of the opisthaptor as 5 mm., and gave a long
account of the anatomy unaccompanied by figures. Three hooks

CAPSALID^E 73

were mentioned, but only two pairs briefly described. The " tubercles "
on the opisthaptor were said not to show the regularity seen in Ento-
bdella hippoglossi. For other accounts of this worm, see Goto (1894,
p. 233 ; 1899, pp. 269-70, PI. 20, figs. 8, 9) and Monticelli (1891, pp.
105, 107, 120, 125, 126, PL 6, fig. 23).

Benedenia monticellii (Parona & Perugia, 1895), Linstow, 1903.

Phylline monticellii Parona & Perugia, 1895 (p. 2) ; Epibdella monticellii
(Parona & Perugia) Parona, 1896 (p. 1).

Host : golden grey mullet (at Trieste).

According to the original description 6 mm. long and 2-5 mm. broad.

Prohaptor comprising a pair of large and deep anterior suckers (the
dimensions of which are given as 0-056 x 0-049 mm.). Opisthaptor
1-8 mm. diameter, lacking papillae and bearing 2 pairs of hooks,
respectively 0-016 mm. and 0-011 mm. long. Gut having a triangular
" oesophageal bulb." [Note. — Price (1939, p. 65) has already pointed
out that the original description is barely generic, the eyes, vagina,
eggs and other organs being undescribed, and that the opisthaptor
probably bears 3 pairs of hooks, not 2, the sizes of which are
possibly ten times as great as was stated (perhaps as a result of mis-
prints) .]

Other Species of Benedenia.

About 16 species other than those mentioned are distributed in
various parts of the world (U.S.A., Mexico, Chile, Eastern Russia,
Japan and elsewhere), but none is known to occur in Europe.

Genus ENTOBDELLA Blainville, in Lamarck, 1818.

(Epibdella Blainville, 1828; Phylline Oken, 1815, nee Abildgaard, 1790,
in part ; Phyllonella Beneden & Hesse, 1863.)

Prohaptor a pair of elongate glandular areas bordering the cephalic
lobes. Opisthaptor discoidal and provided with hooks as in Benedenia.
Vas deferens forming a loop in front of the ovary, which is generally
separated from the testes by a wide zone of vitelline follicles. Other
characters as in Benedenia.

Entobdella hippoglossi (Muller, 1776), Johnston, 1856 (p. 32).

(Fig. 10A-C.)

Hirudo hippoglossi Muller, 1776 (p. 220 ; 1788, p. 138, PI. 54, figs. 1-4) ;
Phylline hippoglossi (Muller) of Oken, 1815 (p. 371) ; Epibdella hippoglossi
(Muller) of Blainville, 1828 (p. 567) ; Tristoma hamatum Rathke, 1843
(pp. 238-42, PI. 12, figs. 9-11) ; Nitzschia hippoglossi (Muller) of Taschen-
berg, 1878 (p. 568) ; Phyllonella hippoglossi (Muller) of Goto, 1899, Pratt,
1900, and MacCallum, 1927 ; Epibdella bumpusii of Canavan, 1934.

Host : halibut.
Location : skin.

T. Scott (1901, p. 142) stated that this trematode is sometimes very
common on halibut landed from the steam line-fishing boats at the

74

THE TREMATODA OF BRITISH FISHES

fish market, Aberdeen, but lie gave only a few very general characters
and neither measurements nor a figure. The trematode is widely
distributed, having been recorded in the Skagerrak, Denmark, the
Arctic (Greenland), as well as in Alaska, Canada (Nova Scotia) and
U.S.A. (Woods Hole ; Swans Island, Me.). Price (1939a, pp. 69-71,
figs. 1, 7) and Linton (1940, p. 6, PL 14, figs. 164-9) described American
specimens which agree in all essential details of structure with those
described by earlier writers, and I have already given a diagnosis
(Dawes, 1946, p. 144), mentioning four specimens of my own found in

Fig. 10. — Entobdella hippoglossi. A, the entire trematode; B, some papillae
from the opisthaptor. C, posterior end of the opisthaptor, showing the
hooks and papillae (a, b, c represent hooks of the 1st, 2nd and 3rd
pairs). (Original.)

British waters. These are rather small, 10-15 mm. long and 7-8-5
mm. broad, and one of them is figured here for the first time. I have
since acquired a specimen which is quite as large as the largest American
specimen dealt with by Price, and here modify the diagnosis to include
my own small specimens. Size : 10-18 mm. long and 7-0-8-5 mm.
broad (American forms seem to be rather narrow*), but according to
various writers up to 24 mm. long and 13 mm. broad. Shape : ellip-
tical, decidedly flattened, slight lateral constrictions marking oft' the
cephalic lobe. Prohaptor a pair of elongate glandular areas. Opis-
thaptor discoidal, very thin and sucker-like, 4-5-7-5 mm. diameter,*

* Price may be in error regarding the breadth of the body and the size of
the opisthaptor. He gave the measurements 13-18 mm. and 3-6-4-8 mm. for

CAPSALID.dE 75

encircled by a marginal membrane up to 0*17 mm. wide, its ventral
surface concave, the posterior half bearing radiating rows of papilla?
about 0-2 mm. broad at the base and 0-2 mm. long, provided with
3 pairs of hooks and 14 marginal hooklets. Hooks of the first
pair having the shape of a spear-head, 0-51-0-84 mm. long and
with a slightly curved median margin ; hooks of the second pair
slender and with recurved tips, 0-8-1-6 mm. long ; hooks of the third
pair 0-09-0-16 mm. long, their tips slender and recurved, hooklets
about 0-02 mm. long. Gut : mouth ventral near the posterior limit of
the cephalic lobe. Pharynx broader than long, measuring 0-58-0-85 x
0-85-1-1 mm., the caeca having much- branched lateral diverticula.
Reproductive systems : common genital pore situated at the posterior
end of the cephalic lobe on the left margin of the body. Cirrus pouch
club-shaped, its base slightly on the right and midway between the
ovary and the pharynx. Testes globular or ovoid and situated side
by side near the middle of the body, dimensions 1-00-1-32 x 0-92-
1-16 mm. in my small specimens, 1-7-2 mm. diameter in the larger
American specimens. Ovary transversely ovoid, 0-6-0-7 x 0-85-1-2
mm., separated from the more anterior testes by a band of vitelline
follicles 0-25-0-35 mm. wide. Vitellaria filling up the available space
throughout the body, but absent from the cephalic lobes and the
parenchyma immediately around the genital ducts. Vagina slender,
its pore situated behind and median to the genital pore. Ootype
ovoid and situated in the median plane behind the cirrus pouch.
Metraterm slender. Egg (absent from my specimens) tetrahedral,
about 0-228 mm. broad and having a long slender filament.

Entobdella soleae (Beneden & Hesse, 1863), Johnston, 1929.

(Fig. 11 A-F )

Phyllonella solece Beneden & Hesse, 1863, and of Little, 1929a ; Epibdella
solece (Beneden & Hesse, 1863) of Monticelli, 1892, and authors ; E. producta
(Linstow, 1903) Odhner, 1906.

Hosts : sole, sand sole.
Location : skin.

This species was found by Beneden near Brest and later (1871) off
the coast of Belgium. T. Scott (1901, pp. 142-3, PL 8, fig. 17) twice
found it in the Clyde and gave a very short and general description
of a specimen 6-7 mm. long. A. Scott (1904) recorded its occurrence
in the Irish Sea, Southern (1912) west of Ireland. Bay lis & Idris
Jones (1933) found it at Plymouth, where I have also obtained speci-
mens, and Little found it very abundant (60 out of 100 soles infected
with 2 to 5 and sometimes as many as 8 specimens each) at
Galway and gave a detailed description (1929c, pp. 324-37, figs. 1-10 ;

length and breadth and, taking small figures together, this gives a breadth equal
to 0-27-0-28 body-length. But his Fig. 1 illustrates a breadth which is 0-63 or
0-77 body-length, according to whether or not we exclude the opisthaptor from
the statement of length. The opisthaptor was stated to be 3-6-4-8 mm. diameter,
i.e., of the same breadth as the body, yet his figure clearly shows its breadth to
be less than half that of the body, at most four-ninths.

76

THE TREMATODA OF BRITISH FISHES

Pis. 15-17, figs. 1-13). My specimens are fairly small, and I have
included a few details about them in parentheses in the following

mJ 0-1

Fig. 11. — Entobdella solece. A, contracted individual showing the gut and
gonads ; B, extended individual, showing the gonads and vitellaria ;
C, hooks of the 2nd pair ; D, those of the 1st pair ; E, the genital
organs ; F, the opisthaptor. (After Little, 1929c.)

description. Size : 2-1-5-9 mm. long and 1-05-2-9 mm. in greatest
breadth (2-85 x 1-30 mm.), according to Scott (1901, p. 142) up to

CAPSALID^ 77

6-7 mm. long. Shape oval and much flattened, the two extremities
bluntly rounded, each with a slight median notch. Colour trans-
lucent, whitish with a pale lemon tinge, milky -white after death.
Prohaptor a pair of elongate glandular areas, marked off posteriorly
by a slight constriction (together 0-25 mm. long and 0-41 mm. broad).
Opisihaptor sucker-like, 1-54 mm. long and 1*4 mm. broad in a specimen
5-93 mm. long (0-92 x 0-82 mm.), with a frilled membrane broadest
anteriorly, where it is 0-23 mm. wide (0-16 mm.). Two main septa
originating close together slightly in front of the middle of the sucker,
diverging towards the bases of the hooks of the first pair, then extend-
ing along the courses of the hooks of the second pair, terminating at
the posterior margin of the haptor. These septa are connected by a
transverse septum between the bases of the first hooks. In front of
them there is a ridge of horse-shoe shape, not very evident in cleared
preparations, and possibly representing the points of insertion of
muscles. Hooks numbering three pairs [not two, as stated or figured
by Beneden and Hesse (1864), Cunningham (1890) and T. Scott (1901,
1912.) Southern (1912) seems to have first recorded the correct
armature of the haptor.] Hooks of the first pair in the position stated,
0-28 mm. long (0-145 mm., not allowing for curvature), half embedded
in the tissue, consisting of a bifid condylar process and a large recurved
point. Hooks of the second pair in the position stated, 0-65 mm. long
(0*42 mm.), almost completely embedded, consisting of a slightly
curved shaft and a terminal, recurved point. Hooks of the third
pair small, 0-121 mm. long (0-12 mm.), situated slightly lateral to the
points of the hooks of the second pair. (Note. — Not having two shafts
apiece as in "Epibdella producta" according to Linstow.) Eyes :
2 pairs, the posterior pair slightly the larger and 0-26 mm. apart
(0-11 mm.) ; anterior pair 0-14 mm. apart (0*8 mm.) and 0-37 mm.
from the anterior extremity (0-23 mm.). Gut : mouth ventral, 0-40
mm. from the anterior end of the body (0*25 mm), a wide transverse
or crescentic slit bordered by prominent anterior and posterior lips.
Pharynx 0-70 mm. broad (much smaller ; about 0-2 mm.), having
large multicellular papillae projecting into its cavity. (Esophagus
practically absent. Caeca long, uniting slightly in front of the opist-
haptor, provided with numerous dendritic lateral diverticulae and a
few median branches, especially behind the testes. Caeca and diver-
ticula lined with large amoeboid cells. Excretory system : main longi-
tudinal ducts roughly parallel to the lateral vitelloducts, expanding
somewhat anteriorly, lined with cuticle. Reproductive systems :
common genital pore as in E. hippoglossi, behind the left glandular
area of the prohaptor. Cirrus elongate, 1-05 mm. long in a specimen
5-93 mm. long and 0-21 mm. wide basally near the hind end of the
pharynx, where it is free in the pouch, traversed by two ducts of equal
size, (a) and (b) : (a) small, the ejaculatory duct ; (b) large, connected
with a large, oval accessory sac measuring 0-25 x 0-18 x 023 mm.,
but variable in size, adjacent to the base of the cirrus and median.
(Note. — According to Little the accessory sac contains a granular
secretion of large cells on either side of the ootype which is assembled

78 THE TREMATODA OF BRITISH FISHES

in the sac by way of afferent ducts ; the secretion is supposed to play
a part in the emission of spermatozoa.) Seminal vesicle 0*04 mm.
diameter (? sectional), close to the left margin of the ootype, elongate
and folded. Pars prostatica Z-shaped, penetrating the postero-dorsal
end of the cirrus, to continue as the ejaculatory duct. Testes ovoid,
0-53 x 0-37 x 0*21 mm., side by side and almost contiguous slightly
behind the midbody. Ovary ovoid, its dimensions 0-28 x 0-37 x 0-28
mm., median, the longest axis transverse, slightly in front of the testes
and just in the posterior half of the body. Oviduct almost immediately
receiving the median vitelloduct. Receptaculum seminis comprising
three spherical chambers 0-075-0-147 mm. diameter in front of the
ovary. Ootype ovoid, 0-189 mm. in greatest width when distended,
0-110 mm. when contracted, situated slightly in front of the recep-
taculum seminis. Metraterm 1-0 mm. long, passing obliquely to the
left parallel with the cirrus, thin- walled. Vitellaria comprising
numerous follicles above and beneath the caeca and diverticula, filling
the median region of the body at and behind the levels of the gonads.
Mam vitelloducts lateral, closely following the courses of the excretory
canals ; transverse ducts forming a large vitelline reservoir, measuring
0-143 X 0-253 X 0275 mm. immediately in front of the ovary. Eggs
pyramidal in outline, having the apex directed posteriorly in the
ootype and prolonged into a long, slender, and twisted filament 0-44
mm. long. Egg-capsule proper very large, measuring 0-143 x 0-143
mm. and dark yellow. Vagina enlarged basally to form a receptaculum
seminis, apparently ending blindly (?) near the anterior end of the
vitelline reservoir, its pore slightly lateral at the level of the ootype
and thus far behind the common genital pore.

Two other species of Entobdella occur in Europe — E. diadema
(Monticelli, 1902), which occurs on Trygon violacea in Italy, and E.
steingroveri (Cohn, 1916), which was found on an unidentified fish.

Genus ANCYR0C0TYLE Parona & Monticelli, 1903.

(Placunella Beneden & Hesse, 1863, in part.)

Prohaptor a pair of muscular suckers situated on fleshy pads.
Opisthaptor sucker-like and with a marginal membrane, 3 pairs
of hooks and 14 hooklets, the hooks of the third pair lateral to those
of the second. Gut bifurcate, the caeca devoid of diverticula. Testes
2 in number and situated behind the ovary, sometimes (?) a single
testis situated in front of it. Vagina present.

Ancyrocotyle vallei (Parona & Perugia, 1895) Parona & Monticelli,
1903.

Placunella vallei Parona & Perugia, 1895 (a, pp. 3-4).

Host : pilot-fish.

Location : gills.

This species has been found at Trieste and Genoa, but not in Britain.
According to the very brief original description it is 3 mm. long and
0-42 mm. broad, the suckers of the prohaptor 0-028 mm. diameter and

CAPSALIDiE 79

the opisthaptor 0-056 mm. diameter. The lengths of the hooks are
0-035 mm., 0-003 mm. and 0-004 mm., and the dimensions of the eggs
0-014 x 0-007 (misprinted as 0-07) mm. I have been unable to consult
the redescription by Parona & Monticelli (1903, pp. 117-21, PI. 3,
figs. 1-6), but Price (1934a, pp. 1-3) has drawn attention to notable
features of the anatomy, the presence of only two pairs of hooks on
the opisthaptor and of a single testis situated in front of the ovary —
characters by which the species can be identified.

The only other species of Ancyrocotyle is A. bartschi Price, 1934,
which was discovered on the gills of the pilot-fish in the West Indies
and was based on two immature specimens. In describing these
specimens Price (1934a, pp. 1-2, PI. 1, figs. 1, 2) considered the possi-
bility of their identity with A. vallei, but noted certain differences,
notably the presence of two testes, which are situated behind the
ovary, and the structure of the hooks of the second pair. In view of
the possible identity we can note the characters briefly. Size : 0-83-
0-97 mm. long and 0-25-0-27 mm. broad. Shape elongate and rectan-
gular. Prohaptor a pair of sucker-like organs 0-08 mm. diameter,
situated near the hind ends of pads of tissue. Opisthaptor sucker-like
and nearly sessile, fringed by a narrow membrane and equipped with
3 pairs of hooks and 14 marginal hooklets. Hooks of the first
pair straight and 0-020-0-023 mm. long ; hooks of the second pair
0-068-0-076 mm. long and situated just behind the first, their tips
recurved ; hooks of the third pair 0-025-0-028 mm. long and broad and
flat with slender recurved tips, situated lateral to the second. Hooklets
0-01 mm. long. Gut : mouth 0-15 mm. from the anterior extremity.
Pharynx nearly globular, 0-10 mm. long and 0-12 mm. broad. (Eso-
phagus very short or absent. Caeca very long and unbranched.
Reproductive systems : common genital pore situated on the left of
the pharynx. Cirrus pouch arranged diagonally, 0-16 mm. long and
0-04 mm. broad, its base crossing the median plane. Testes elongate
oval and side by side near the middle of the body, dimensions 0-18 x
0-08 mm. Ovary ovoid and situated just in front of the testes,
ootype a little farther forward. Vagina short, its pore near the
inner margin of the left caecum about 0-06 mm. behind the pharynx.

Sub-order POLYOPISTHOCOTYLEA Odhner, 1912.

(Polycotyla Blainville, 1828; Octobothrii E. Blanchard, 1847; Eupoly-
cotylea Diesing, 1850; Polycotylea Diesing, 1850, in part.)

Prohaptor an oral sucker, or 2 buccal suckers, or 2 ventral grooves
or bothria. Opisthaptor very variable, but always comprising suckers
or clamps with or without hooks. Eyes rarely present. Vagina present
or absent. Genito -intestinal canal invariably present.

Super-family POLYSTOMATOIDEA Price, 1936.

Prohaptor a terminal or slightly ventral oral sucker. Opisthaptor
comprising a cotylophore which generally bears 3 pairs of cup-like

80 THE TREMATODA OF BRITISH FISHES

suckers and 1-3 pairs of hooks. Suckers sometimes provided each
with a hook, which is large in Hexabothriidse, but small in Poly-
stomatidge. Gut comprising a short pre -pharynx, a spherical pharynx,
a short oesophagus and a pair of caeca with or without diverticula or
anastomoses. Eyes generally absent. Genital pores debouching in
an atrium on the ventral surface of the body. Testis single, but
numerous testes sometimes present. Ovary situated anterior to the
testis or testes. Vagina double, the openings lateral. Hosts : Amphibia,
Reptilia and Fishes, rarely Mammalia. Type family : Polystomatidae
Gamble, 1896, parasites of amphibians and reptiles.

Family HEXABOTHRIID^ Price, 1942.

(Onchocotylidse Monticelli, 1903.)

Prohaptor a fairly well developed oral sucker, or two ventro-
lateral grooves or bothria. Opisthaptor a circular or rectangular
disk bearing 3 pairs of suckers, each of which has a large crescentic
hook and an appendix bearing 1 pair of small terminal suckers and
1-3 pairs of hooklets. Eyes generally absent, but present in the
Diclybothriinae. Genital pore median and ventral. Cirrus generally
devoid of hooklets or spinelets. Testes numerous. Ovary relatively
large, elongate and folded, the folds situated in front of the testes.
Vagina double. Hosts fishes, particularly Selachii. In Diclybothriinae
the appendix of the opisthaptor has 3 pairs of large hooks, in other
sub -families only 1 pair of small hooks. In Rajonchocotylinse the
vaginae form a median duct, which enters the vitelline reservoir ; in
Hexabothriinse they are discrete and open separately into this chamber.

Sub-family Hexabothriin^ Price, 1942.

(Onchocotylinae Cerfontaine, 1899 ; Diaphorocotylinte Monticelli, 1903,

in part.)

Prohaptor an oral sucker. Opisthaptor comprising a somewhat
rectangular cotylophore bearing 3 pairs of suckers and a relatively
long appendix having 1 pair of small and almost terminal muscular
suckers and 1 pair of hooks. Roots of the large hooks not abruptly
narrowed at the base of the blade. Vaginas, entering the vitelline
reservoir separately. Eggs each having a process at one pole or both
poles, but lacking meridional ridges.

In Hexabothrium the cirrus is equipped with spinelets, in other
European genera it is not, but according to Price (1942) the extension
of vitelline follicles into the appendix of the opisthaptor distinguished
Neoerpocotyle from Erpocotyle, in which they do not. This does not
seem to be a reliable criterion of generic distinction, and Neoerpocotyle
is probably a synonym of Erpocotyle.

HEXABOTHRIIDJE 81

Genus HEXABOTHRIUM Nordmann, 1840.

(Onchocotyle Diesing, 1850 ; Acanthonchocotyle Cerfontaine, 1899.)

Hooks on the opisthaptor proper of about equal size. Cirrus
equipped with spinelets. Vitellaria not extending into the appendix.
Eggs with one polar prolongation.

Hexabothrium appendiculatum (Kuhn, 1829), Nordmann, 1840 (p. 601).

Polystoma appendiculatum Kuhn, 1829 (pp. 460-3, PI. 11, figs. 1-3) ; Oncho-
cotyle appendiculata (Kuhn) of Diesing, 1850 (p. 419) and authors ; Acan-
thonchocotyle appendiculata (Kuhn) Cerfontaine, 1899 (pp. 461-2, PI. 19,
figs. 6, 14a).

Host : nurse hound.
Location : gills.

This species occurs in the Mediterranean and at Roscoff. Accord-
ing to Price (1942, p. 40, footnote) the specimens found in Britain
and referred to this species by T. Scott (1901, p. 151, PL 8, figs. 30-31 ;
1912, PI. 27, figs. 11, 12) probably belong to the genus Baj onchocotyle,
because parasites of the skate and thornback ray, while specimens
found by Lebour (1908a, p. 44, PL 5, figs. 9-12) belong to Erpocotyle.
In neither case can precise allocations be made, the descriptions being
incomplete. Price claimed that the distinguishing characters were
established by Cerfontaine, who examined a single specimen from what
is regarded as the type-host, the original and a later description by
Nordmann (1832) alike being insufficient for specific diagnosis. Accord-
ing to Cerfontaine this species has the following characters, although
Olsson (1875, p. 11) found specimens 8-10 mm. long : — Size : 6-7 mm.
long. Opisthaptor not strictly rectangular, but rounded towards the
base of the appendix. Hooks of the third pair of suckers smaller than
those of the first two pairs. Reproductive systems : genital armature
comprising numerous hooklets which are spike -like and larger than
those of H. canicula (q.v.), their bases also being larger relative to the
points.

Hexabothrium canicula (Cerfontaine, 1899) Price, 1942. (Fig. 12 I.)

Onchocotyle appendiculata (Kuhn) of Stossich, 1877 ; Acanthonchocotyle cani-
cula Cerfontaine, 1899 (p. 462, PI. 19, figs. 5, 13, 146, c).

Hosts : rough hound, nurse hound.
Location : gills.

This species occurs off the coast of Belgium, at Roscoff, Naples
and Trieste. According to Cerfontaine the opisthaptor is rounded
posteriorly and the hooks of the suckers of the third pair are smaller
than the others, their claws very small. Reproductive systems : genital
armature consisting of numerous spike-like hooklets of a feebler nature
than those of the previous species, their bases less marked off from the
points. Vagina double, but the two canals very short. Eggs each
having a single polar filament several times the length of the capsule,
which is about 0-160 mm. long and 009 mm. broad.

6

82

THE TEEMATODA OF BRITISH FISHES

Fig. 12. — A-F, Neoerpocotyle catenulata : A, entire trematode ; B, diagram
of the genital organs, snowing the long and convoluted oviduct ; C, a
chain of three eggs ; D, the hooklets borne on the appendage of the
opisthaptor ; E, the hooks from the large suckers on one side ; F, the
claw and part of the shaft of a hook. G-H, Erpocotyle Icevis : G, the claw
and part of the shaft of a hook ; H, two eggs of slightly different form.
I, the egg of Hexabothrium canicula. J, the egg of Erpocotyle borealis.
(J, after Beneden, 1853 ; remainder after Guberlet, 1933.)

HEXABOTHRIID^] 83

Guberlet (1933, p. 327, PL 4, fig. 6) found this species on the gills
of both hosts at Naples. His specimens were relatively small (3-4-5
mm. long) and not very evident on the host when alive, lacking con-
trast with the colour and texture of the branchial filaments, but they
were readily recognizable by the characters specified by Cerfontaine,
especially the size and shape of the hooklets surrounding the genital
pore and the egg with its single polar filament (Fig. 12 I).

Other Species.

The only remaining species of Hexabothrium is H. musteli (Mac-
Callum, 1931) Price, 1942 (Acanthonchocotyle musteli MacCallum,
1931 ; Onchocotyle musteli (MacCallum) Dollfus, 1937), a parasite on
the gills of Mustelus canis in U.S.A. (Woods Hole). It has curved
genital hooklets.

Genus ERPOCOTYLE Beneden & Hesse, 1863.

(Squalonchocotyle Cerfontaine, 1899 ; Erpetocotyle of Fuhrmann, 1928.)

Cirrus devoid of hooklets or spinelets. Vitellaria not extending
into the appendix. Eggs each having two polar prolongations. Other
characters as in Hexabothrium.

Erpocotyle laevis Beneden & Hesse, 1863. (Fig. 12 G, H.)

Polystomum appendiculatum Thaer, 1850 (pp. 602-3, Pis. 20-22, figs. 1-45),
nee Kuhn, 1829, in part ; Squalonchocotyle vulgaris Cerfontaine, 1899 (pp.
457-8, PI. 18, figs. 3, 4, 9 ; PI. 19, fig. 1 ; PI. 20, figs. 5, 8-11 ; PI. 21, figs.
3, 5, 7, 9).

Hosts : smooth hound.
Location : gills.

This species was found near Brest and occurs elsewhere on the
continental coast (Roscoff) and in the Adriatic. I have found two
specimens on the smooth hound at Plymouth. According to Price
(1942, p. 41) it cannot be identified from the original description (see
Beneden & Hesse, 1864, pp. 87-9, PI. 7 bis, figs. 1-9), but more or less
circumstantial evidence enables the identity of the species to be estab-
lished and the genus to be revived. This conclusion is reached in view of
the degree of host specificity shown by Monogenea. Price was satisfied
that this species is congeneric with species allocated by Cerfontaine
(1899) to the genus Squalonchocotyle and, taking two of these (vulgaris
and catenulata) into consideration, concluded (on the basis of an
assumption that the distribution of the vitelline follicles into the
appendix of the opisthaptor, or only to the end of the body proper, is
a valid character of taxonomic importance) that the form which most
closely resembles Erpocotyle lozvis is Squalonchocotyle vulgaris, which is
regarded as a synonym of Beneden & Hesse's species, so that the
genus Erpocotyle can be recognized and utilized.

According to Cerfontaine (1899, p. 457) for "Squalonchocotyle
vulgaris " (my observations, based on two specimens, shown in paren-
theses) : — Size : about 12 mm. long, but very extensile to three times

84 THE TREMATODA OF BRITISH FISHES

the normal length, then forming a slender cylinder (9-2 mm. long
and 1-05 mm. broad). Colour dark brown. Cuticle bearing small
tubercles, which approach the opening of the bell-like oral sucker, but
do not occur in its cavity (very insignificant). Opisthaptor (T85 mm.
long, the appendix measuring 1-18 x 0-30 mm.). Claw of each large
hook bent in a right angle (confirmed), its base clearly separated from
the shaft and of smaller girth (respective breadths 0-043 mm. and
0-029 mm.). Hooklets (0*06 mm. long, neglecting curvature) each
having very unequal roots, the ventral long (0*040 mm.) and curved,
the dorsal shorter (0-018 mm.) and narrower (tips of the roots 0-04 mm.
apart). (Suckers 0-40-0-45 mm. diameter, suckerlets 0-25 mm. long
and 0-16 mm. broad, constricted near the base.) Gut : intestinal
crura having median and lateral diverticula along their entire length
(a single median diverticulum extending into the appendix almost to
the suckerlets). Reproductive systems : (genital pore median, close
behind the pharynx and 0-88 mm. from the anterior extremity.)
Vaginal pores slightly behind the level of the genital pore and at the
lateral margins of the body (confirmed ; position about 0-1 mm. behind
the level of the genital pore). Cirrus short and more or less globular
when evaginated (about 0-11 mm. diameter). Uterus following a
straight course between the ootype and the genital atrium (confirmed).
Eggs each having two short and straight polar filaments which are
about as long as the capsule, i.e. 0-200 mm. long (overall length of egg
and filaments about 0-52 mm., capsule about 0-24 mm. long, anterior
and posterior filaments 0-11 mm. and 0-17 mm. respectively).

Guberlet (1933, p. 327, PL 4, figs. 3, 5, 9) found several specimens
of this species associated with Neoerpocotyle catenulata on the gills of
Mustelus Icevis at Naples. They were 10-12 mm. long and 0-8-1-4
mm. broad and the suckers of the opisthaptor were of different sizes,
those of the third pair smaller than the rest and having hooks 0-87
mm. long as against 1-2 mm. This was not so in my specimens, the
suckers being about 0-40 mm., 0-45 mm. and 0-45 mm. diameter
respectively, the mean length of the hooks (for the two sides) 0-71 mm.,
0-98 mm. and 0-82 mm. Guberlet also observed that the cuticular
tubercles tend to disappear in preserved specimens, and that the spine -
lets on the shafts of the hooks near the claw vary both in different
suckers of the same individual and in different specimens, numbering
6-10. He determined the size of the egg as 0-22 x 0-06 mm., the
filaments being 0-13 mm. long.

Erpocotyle abbreviata (Olsson, 1876) Price, 1942.

Onchocotyle abbreviata Olsson, 1876 (p. 12, PI. 2, figs. 27, 28) ; Squalonchocotyle
abbreviata (Olsson) of Cerfontaine, 1899 (p. 375, PI. 19, fig. 3).

Host : piked dogfish.

Location : gills.

This species has been found in the Skagerrak and at Roscoff, but
not in Britain. According to Cerfontaine (1899) it shares some
characters with E. canis, but is 7-8 mm. long and has distinctive large

HEXABOTHRIID^ 85

hooks, the claw being relatively long, distinct from the shaft, bent at
a right angle, but having a straight point. Hooklets having straight
roots. Caeca with median and lateral diverticula, the former not
well developed. Cirrus long and cylindrical ; seminal vesicle clearly
differentiated. Uterus more or less convoluted ; vaginal pores as in E.
cants ; eggs about 0-100 mm. long and with two long polar filaments.

Erpocotyle canis (Cerfontaine, 1899) Price, 1942.

Squalonchocotyle canis Cerfontaine, 1899 (pp. 458-9, PI. 18, figs. 1, 2, 7, 12 ;
PI. 19, fig. 2 ; PI. 20, fig. 12 ; PL 21, figs, 2, 6, 10) ; Onchocotyle appendi-
culata of Beneden, 1858, nee Kuhn, 1829).

Host : tope. .

Location : gills.

This species has been found off the coast of Belgium and at Roscoff ,
but not in Britain. According to Cerfontaine it has the following
characters : — Size : 7-8 mm. long. Cuticle bearing tubercles, which
occur also in the cavities of the haptors. Opisthaptor having large
hooks of distinctive shape, the claw bent in a right angle, the curve
continuing to the tip, the base of nearly the same girth as the shaft.
Large suckers having fleshy rims. Hooklets having short roots, the
space between these shallow, so that whole shape is triangular, the
points having two sharp bends. Gut : caeca having median and lateral
diverticula. Reproductive systems : oviduct displaying several con-
volutions. Vaginal pores situated just behind the level of the genital
pore and midway between the median plane and the margin of the
body. Cirrus long and cylindrical, seminal vesicle having a valve
at its base. Eggs about 0-100 mm. long, each having two very long
filaments, but in some instances only one filament, both kinds of egg
occurring in the same specimen.

Erpocotyle borealis (Beneden, 1853) Price, 1942. (Fig. 12 J.)

Onchocotyle borealis Beneden, 1853 (pp. 59-68, figs. 1-11) ; Squalonchocotyle
borealis (Beneden) of Cerfontaine, 1899 (pp. 456-7, PI. 18, fig. 13 ; PL 19,
fig. 7 ; PL 20, figs. 13, 14 ; PL 21, fig. 16).

Host : Greenland shark.
Location : gills.

This species has been found near Greenland, in the Skagerrak and
off the coast of Belgium, but not in Britain. According to Cerfon-
taine it is 20 mm. long, but Beneden's specimens were 25-30 mm. long
and 3-4 mm. broad. The claw of each large hook is regularly curved,
its base continuing the shaft, and the hooklets have a dorsal root
opposite the point which is longer and more delicate than the ventral,
the two being separated by a fairly deep space, which Beneden failed
to observe. The caeca have lateral diverticula which do not anastomose
throughout their length, but median diverticula of small size only
anterior to the gonads. Reproductive systems : vas deferens very long
and convoluted. Vaginal pores a little behind the level of the genital
pore and halfway between the median plane and the margin of the

86

THE TREMATODA OF BRITISH FISHES

Fig. 13. — A-C, Erpocotyle galeorhini (Sq. abbreviata form A of Dollfus,
1937) : A, anterior region ; B, a group of eggs ; C, one of the hooks.
D-G, Erpocotyle eugalei (Sq. abbreviata form B of Dollfus) : D, anterior
region, showing a chain of eggs leaving the body ; E, one of the hooks ;
F, a hooklet ; G, region of the body containing the female reproductive
organs, showing especially the long and convoluted oviduct. H-K,
Erpocotyle dollfusi (Sq. abbreviata form D of Dollfus) : H, entire animal
in ventral view ; I, one of the hooks ; J, the anterior region ; K, the
region of the body containing the reproductive organs. (After Dollfus,
1937.)

HEXABOTHRIIDiE 87

body. Eggs very large, about 0-250 mm. long, and equipped with
two short polar filaments, which are not longer than the capsule and
are sometimes folded down on it.

A number of other species of Erpocotyle occur outside Britain.
Dollfus (1937) recognized four forms of Squalonchocotyle abbreviate
(Olsson) which, according to Price (1942), form separate and distinct
species. All these forms were found on Selachii near the coast of
Morocco. E. galeorhini Price, 1942 (form A of Dollfus, 1937, p. 402,
figs. 1-3 ) (Fig. 13 A-C) , on the smooth hound near Rio de Oro ; E. eugalei
Price, 1942 (form B of Dollfus, 1937, p. 405, figs. 7-12) (Fig. 13 D-G),
on the tope near Agadir ; E. torpedinis Price, 1942 (form C of Dollfus,
1937, p. 410, figs. 13-18) ; on the torpedo (T. marmorata) on the Atlantic
coast of Morocco ; and E. dollfusi Price, 1942 (form D of Dollfus, 1937,
p. 411, figs. 19-24) (Fig. 13 H-K), on the spinous shark at Rabat.
These forms — they are hardly likely to remain valid species — differ
particularly in size, the shapes of the hooks and the form of the eggs
(Fig. 13). Five other species occur in North America and one in Japan.

Genus NE0ERP0C0TYLE Price, 1942.

(Squalonchocotyle Cerfontaine, 1899, in part.)

Vitellaria extending into the appendix of the opisthaptor. Other
characters as in Erpocotyle.

Neoerpocotyle grisea (Cerfontaine, 1899) Price, 1942.

Onchocotyle appendiculata Taschenberg, 1879 (pp. 24-7, PI. 3, figs. 1-3 ; PI. 4,
figs. 1, 3-6; Squalonchocotyle grisea Cerfontaine, 1899 (p. 376, PI. 19, fig. 8).

Host : 6-gilled shark.

Location : gills.

This species has been found at Naples and Trieste and also off the
west coast of Ireland. According to Cerfontaine (1899, p. 461) it is
about 15 mm. long. The claws of the hooks are not clearly marked off
from the shaft and are curved at a right angle to it. The hooklets are
Y-shaped, the roots and point being of about equal size, and the ventral
root bent towards its own side and terminating in a minute knob.
The vaginal pores are situated near the genital pore at the level of the
excretory pores, and the eggs have two short filaments only half as
long as the capsule, which is about 0-175 mm. long and gradually
tapers towards the poles.

Neoerpocotyle catenulata (Guberlet, 1933) Price, 1942.

(Fig. 12 A-F.)

Squalonchocotyle catenulata Guberlet, 1933 (p. 328, PI. 4, figs. 1, 2, 4, 7, 8, 10) ;
Poly stoma appendiculatum Thaer, 1850, nee Kuhn, 1829, in part.

Host : smooth hound.
Location : gills.

This species was discovered at Naples, where Guberlet found four
out of six hosts parasitized, one with more than fifty worms, most of
which were immature, but clearly recognizable. It is 7-11 mm. long

88 THE TKEMATODA OF BRITISH FISHES

and 1-5 and 1 mm. in greatest breadth and thickness ; the oral sucker
is 0-5 mm. diameter and the suckers of the rectangular opisthaptor
are arranged in two parallel rows, those of the most posterior pair
being slightly the smallest. Each hook has a smooth shaft with a
slight lateral ridge and a long and sharply-bent claw, and the hooks
of the most posterior pair are smaller than the remainder, 1-64 mm.
long instead of 1-80 mm. The appendix is almost cylindrical, about
2 mm. long and 0-75 mm. thick, its two curved hooklets 0-07-0-08 mm.
long, each of them having two roots. The internal anatomy was
described in great detail, which must be neglected here, although
essential details can be made out in the figure. The distal part of
the oviduct is notably relatively very long and convoluted, and the
vaginal pores are situated in the same transverse plane as the genital
pore and midway between it and the margins of the body, the vaginae
being long and straight, their girth uniform as they extend back to
meet the anterior ends of the main vitelloducts. The eggs are pale
brown, measure 0-127-0-141 x 0-052-0-066 mm. and each has two
very long filaments 0-3-0-7 mm. long, which are continuous with those
of adjacent eggs. The eggs are discharged in groups of 10-65, appearing
in chains of 35 or more, one worm being observed to lay 140 eggs in
three masses at one time.

One other species of this genus is N. licha (Rees & Llewellyn, 1941),
which was found on the gills of Scymnorhinus licha on Porcupine Bank
(Atlantic seaboard), but has not been described. Five other species
are known, all of them occurring in North America.

Sub-family Rajonchocotylin^ Price, 1942.

Opisthaptor a circular disk bearing 3 pairs of large suckers and
a postero-dorsal appendix having 1 pair of small suckers. Ovary
situated in front of the middle of the body. Vaginal joining to form a
single duct before entering the vitelline reservoir. Eggs devoid of
polar filaments, but provided with meridional ridges. The two genera
Eajonchocotyle and Bajonchocotyloides are distinguishable, according to
Price (1942), by the extension of the vitellaria into the appendix in the
latter, but not in the former. It is likely that the latter genus will
ultimately fall as this character is unreliable.

Genus RAJ0NCH0C0TYLE Cerfontaine, 1899.

Opisthaptor circular. Ovary in the anterior half of the body.
Vaginae forming one duct entering the vitelline reservoir, vitellaria
excluded from the opisthaptor.

Rajonchocotyle batis Cerfontaine, 1899. (Fig. 14 N-P.)
Onchocotyle appendiculata Olsson, 1867, nee Kuhn, 1829.
Host : skate.
Location : gills.

This species occurs in the Skagerrak and off the coast of Belgium,
also off the West coast of Ireland (Irish Atlantic Slope and Porcupine

HEXABOTHRIIDiE 89

Bank ; see Rees & Llewellyn, 1941), at Plymouth and elsewhere round
our coast. According to Cerfontaine (1899, pp. 462-3, PI. 19, figs. 11, 12 ;
PI. 21, fig. 12) it is 12-15 mm. long. The disk is circular and the
suckers very large. The hooks are distinctive, the shaft tapering
sharply in a straight chamfer near the base of the claw, the surfaces of
contact being of equal girth. The hooklets each have 3 delicate
branches, that carrying the claw being very short and having a hump
on the dorsal and more convex side, the others being the roots. The
vaginal pores are situated far behind the level of the genital pore and
not far from the median plane, the median vaginal canal being long.
The eggs have a small tubercle at one pole and are about 0-175 mm.
long.

Rajonchocotyle alba Cerfontaine, 1899. (Fig. 14 F-J.)

Host : burton skate.
Location : gills.

This species was discovered at Roscoff and, according to Cerfon-
taine (1899, pp. 463-4, PI. 18, figs. 5, 6, 8 ; PI. 19, fig. 9 ; PI. 20, figs.
1-3, 6, 7 ; PI. 21, figs. 1, 4, 8, 11, 13-15) is 8-9 mm. long, the hooks
long and of uniform girth and tapering near the base of the claw, but
not in a straight chamfer as in the previous species. Hooklets with
unequal roots, the dorsal the more massive, and a shallow cleft between
them. Vaginal pores situated behind the genital pore and midway
between the median plane and the margins of the body, the median
vagina short. Eggs having a tubercle at one pole and about 0-180
mm. long.

Rajonchocotyle prenanti (Saint-Remy, 1890) Cerfontaine, 1899.

(Fig. 14 K-M.)

Onchocotyle prenanti St Remy, 1890 (pp. 41-3) ; O. borealis Stossich, 1885
(p. 162), nee Beneden, 1853.

Host : long-nosed skate.
Location : gills.

This species has been found at Trieste and at Roscoff, but not
in Britain. According to Cerfontaine (1899, p. 464, PI. 18, figs. 10,
11 ; PI. 19, fig. 10 ; PI. 20, fig. 4) it is 8-9 mm. long, the large hooks
are shorter and of more uniform girth than in the previous species,
but the tapering of the shaft near the base of the claw is very marked.
The hooklets have roots between which there is a deep notch. The
eggs have a tubercle at either pole and are very large, about 0-220 mm.
long.

Rajonchocotyle miraletus Rees & Llewellyn, 1941.

This species was recorded on the gills of the cuckoo ray at Porcupine
Bank, but has not been described.

90 THE TKEMATODA OF BRITISH FISHES

Genus RAJONCHOCOTYLOIDES Price, 1940.

Vitellaria extending into the appendix. Other characters as in
Rajonchocotyle.

Rajonchocotyloides emarginata (Olsson, 1876) Price, 1940.

(Fig. 14 A-E.)

Onchocotyle emarginata Olsson, 1876 (pp. 11-12, PI. 2, figs. 23-26) ; O. appen-
diculata Sonsino, 1891, nee Kuhn, 1829.

Host : thornback ray.
Location : gills.

Price (1940a, p. 76, fig. 1) redescribed this species from a specimen
sent from Britain and forming part of the collection made at Plymouth
by Baylis & Idris Jones (1933). Olsson's description was also based
on a single specimen, which seems to have been mutilated, having
an opisthaptor with 2 instead of the usual 6 large suckers. It was
unusual also in having vitellaria which extended into the appendix of
the opisthaptor, but agreed with the British specimen in this, so that
Price felt justified in erecting a new genus on account of this character.
That the two specimens belonged to the same species was assumed on
this account and because they were found on the same host species.
The following characters were determined by Price, but my deter-
minations for six specimens found at Plymouth are given in paren-
theses. Size : body 5 mm. long (2-5-4-2 mm.) and 1-8 mm. broad
(0-55-1-10 mm.). {Note.— Olsson (1865, p. 11) gave the length as 12
mm., the breadth as 0-9 mm., so that his specimen was much more
elongate than those under consideration ; see also PL 2, fig. 23.)
Shape : body tapering from its posterior part to an acute point
anteriorly (not as fusiform, more truncated anteriorly). Prohaptor
an oral sucker about 0-285 mm. diameter (transversely oval, 0-29-
0-31 mm. broad and 0-20-0-23 mm. long) (0-4 mm. in Olsson's specimen).
Opisthaptor about 2-5 mm. diameter (1-35-1-75 mm., the cotylophore
itself about 0-60-0-75 mm.), having 6 suckers arranged in a circle
and an appendix 1-36 mm. long and 0-51 mm. wide (1-15-1-20 x 0-28-
0-48 mm.) terminating in a pair of muscular suckers (which may be
more deeply situated on account of a superficial invagination) . Large
suckers about 0-595 mm. diameter (0-35-0-40 mm. diameter in
small specimens, 0-50 X 0-45 mm. in larger), each containing one
large hook about 1-14 mm. long (0-68-1-08 mm.). Suckers of the
appendix about 0-322 mm. long and 0-15 mm. broad (0-16-0-28 x
0-11-0-17 mm.), constricted at the proximal end (lined with deeply-
staining material, probably thick cuticle). Small hooks of the
appendix situated between the small suckers and about 0-04 mm.
long (up to 0-04 mm. long and 0-02 mm. wide between the bases
of the roots). Gut : pharynx 0-15 mm. long and 0-115 mm. broad
(0-11 x 0-095 mm.-0-12 mm. diameter). (Esophagus very short.
Intestinal crura provided with median and lateral diverticula and
uniting posteriorly, giving off several short diverticula in the opis-

HEXABOTHRIID^

91

thaptor and sending a single stem into the appendix almost to the level
of the small suckers (confirmed). Reproductive systems : genital pore
situated near the bifurcation of the intestine and 0-475 mm. from the
anterior extremity (sometimes closer to it). Testes numerous, occupy-
ing the space between the intestinal crura in the posterior half of the
body proper (generally extending into the forebody). Ovary looped

Fig. 14. — A-E, Rajonchocotyloides emarginata : A, entire trematode ; B,
a small hook ; C, the tip, and D, the whole of a large hook. E, the
egg. F-J, Rajonchocotyle alba : F, the female organs ; G, the egg ; H
and I, the whole and the tip of a large hook ; J, a small hook. K-M,
Rajonchocotyle prenanti : K, the egg ; L, the tip of a large hook ; M,
a small hook. N-P, Rajonchocotyle batis : N, the tip of a large hook ;
O, the egg ; P, a small hook. (A-E, after Price, 1940 ; F-P, after
Cerfontaine, 1899.)

several times and situated on the right at or slightly in front of the
midbody anterior to the testes (sometimes considerably in front of the
midbody). Receptaculum seminis large and situated on the left near
the ovary. Vitefiaria extending from the level of the genital pore to
near the tip of the appendix, the follicles following the course of the
intestine (present in the appendix to very variable extent). Vitelline
reservoir elongate and situated in front of the ovary. Uterus long
(forming a few small folds between the gonads and the genital pore).
Eggs Rugby-football- shaped and very large, measuring 0-170-0-197 x
0-080-0-097 mm. (0-183-0-219 x 0-067-0-086 mm.), also provided with
meridional bands.

92 THE TREMATODA OF BRITISH FISHES

Sub-family DiCLYBOTHRiiNiE Price, 1936.

Prohaptor 2 ventro- lateral bothria. Opisthaptor : 3 pairs of
suckers, each having a large hook, and a posterior lobe bearing 1
pair of small suckers and 3 pairs of large hooks, two of them similar
to those of the two large suckers. Eyes present.

Genus DICLYBOTHRIUM Leuckart, 1835.

(Diplobothrium Leuckart, 1842.)

Diclybothrium armatum Leuckart, 1835. (Fig. 15 A-G.)

Diclibothrium armatum Leuckart, 1835 (p. 764) ; Diklibothrium crassicau-
datum Leuckart, in Kollar, 1836 (p. 219) ; Diplobothrium armatum Leuc-
kart, 1842 (pp. 13-18, PI. 1, fig. 6 a-f) ; Hexacotyle elegans Nordmann,
1840 (p. 597) ; Polystoma (Hexacotyle) armatum (Leuckart) of Dujardin,
1845 (p. 319) ; ? Erpocotyle circularis Linstow, 1904 (pp. 493-4, figs. 18-20
[in some offsets pp. 17-18, figs. 1-3]) ; ? Diclibothrium circularis (Linstow)
of Skwortzoff, 1928 (pp. 563-73, figs. 4-13).

Hosts : various sturgeons.
Location : gills.

This trematode has been found in Russia and elsewhere in Europe
and occurs in Canada and U.S.A., and was recently described by Price
(1942, pp. 53-4, figs. 1 M, N ; 2 O, P ; 3 M), who was unable to decide
with certainty whether all the forms which have been found in stur-
geons are distinct or belong to the same species, study of specimens
from European sturgeons being the only means of settling the problem.
This species has not been recorded in Britain, but it is likely to turn
up and for that reason a brief diagnosis must be given, the data for
D. circularis of Skwortzoff being given in parentheses. Size : 2-5-13
mm. long and 0-22-1-1 mm. broad (3-25-5-88 x 0-41-0-85 mm.).
Shape elongate and elliptical in section. (Eyes : 2 pairs situated
dorso -lateral to the pharynx.) Prohaptor : 2 ventral bothria 0-08-
0-15 mm. wide. Opisthaptor circular or rectangular, 0-32-1 mm. long
and 0-32-0-8 mm. wide (0-55 x 0-57 mm.), having 6 nearly or quite
sessile suckers each provided with a large hook, and with a triangular
posterior appendix 0-22-0-32 mm. long (0-14 mm. ventrally ; 0-2 mm.
dorsally) and 0-12-0-24 mm. wide bearing 1 pair of small muscular
suckers and 3 pairs of hooks. Suckers of the main part of the
opisthaptor 0-20-0-37 mm. diameter (0-21-0-22 mm.), hooks 0-40-0-47
mm. long. Suckers of the appendix about 0-06 mm. long ; hooks of
the outer pair 0-44—0-54 mm. long (0-32 mm.), directed postero-
ventrally ; hooks of the second pair similar to the outer and 0-34-
0-35 mm. long (0-25 mm.), directed postero-dorsally ; hooks of the
third pair straight and 0-10-0-12 mm. long (0-08 mm.) and situated
near the tip of the lobe and directed antero-ventrally. Gut : mouth
ventral and 0-14-0-40 mm. from the anterior extremity. Pharynx
ovoid, 0-06-0-10 mm. long and 0-06-0-10 mm. broad (0-1 X 0-08 mm.)

HEXABOTHKIIDiE

93

(oesophagus practically absent, caeca long and united posteriorly).
Excretory system : pores dorso-lateral at the same level as the posterior
end of the cirrus. Reproductive systems : genital pore median and
0-24-0-68 mm. from the anterior extremity (cirrus pouch 0-21 mm.

Fig. 15. — A-C, " Diclibothrium circularis " : A, the entire trematode (ventral
view) ; B, the appendix of the opisthaptor (ventral view) ; C, the same
as B, in side view. D-G, Diclybothrium armatum : D, the entire tre-
matode (ventral view) ; E, the egg ; F, a hook from one of the suckers ;
G, hooks from the appendage of the opisthaptor. In B-G, a, b, c repre-
sent hooks of the 1st, 2nd and 3rd pairs. (A-C, after Skwortzoff, 1928 ;
D-G, after Price, 1942.)

long and 0-12 mm. broad), cirrus muscular and 0-16-0-32 mm. long
(0-05 mm.) and 0-05-0-16 mm. broad, its eversible tip armed with
short and thickly- set spines extending about 0-04 mm. behind the
point. Seminal vesicle pyriform, measuring 0-10-0-24 x 0-08-0-18
mm. (0-14-0-16 mm. long), connected to the base of the cirrus by a

94 THE TREMATODA OF BRITISH FISHES

narrow region. Testes very numerous (300 or more), ovary tubular
and much convoluted, situated near the end of the first one-quarter
of the body. Vitellaria lateral (extending ventrally and dorsally)
between the vaginal pores and the posterior end of the body proper
(ending a short distance in front of the opisthaptor). Receptaculum
seminis elongate and 0-2 mm. long, situated on the left of the ovary.
Vaginal pores slightly dorsal and 0-45-1-5 mm. from the anterior
extremity. Ootype and shell glands situated in front of the ovary.
Uterus long and sinuous in the median plane. Eggs very large,
measuring 0-208-0-224 x 0-088-0-140 mm. (0-11-0-14 mm. long),
polar processes absent. (Note. — Infection with this trematode may be
heavy. Skwortzoff found 1-11 specimens per host and noted a 70%
infection of sterlets.)

Super-family DICLIDOPHOROIDEA Price, 1936.

Prohaptor a pair of buccal suckers. Opisthaptor a cotylophore
bearing a paired series of suckers or clamps, or similar structures
arising from the ventro -lateral surface of the body, sometimes pedun-
culate, typically 8 in number, but sometimes numerous, each
having a rather complicated cuticular skeleton of rib-like supports
numbering 3-8, their arrangement providing familial characters.
Terminal hooklets present in the larva sometimes persisting in the
adult. Terminal region sometimes comprising a languet which may
be equipped with 1-3 pairs of hooklets. Gut comprising a prepharynx,
bulbous pharynx, short oesophagus and intestinal crura which may
merge posteriorly and are provided with median and lateral diverticula,
sometimes with anastomoses. Reproductive systems generally open-
ing by a common genital pore. Cirrus sometimes equipped with
hooklets. Ovary generally elongate and folded, situated in front of
the testes, but sometimes having some of the testes in front of it.
Vaginal present and generally opening dorsally, or absent. Eggs
generally provided with filaments. Location : the gills of fishes, rarely
the skin of fishes or their crustacean parasites.

Family DICLIDOPHORID^ Fuhrmann, 1928.
(Choricotylidae Rees & Llewellyn, 1941 ; Dactylocotylidae Brinkmann, 1942.)

Opisthaptor : 4 pairs of suckers or clamps, generally peduncu-
late, each organ having 8 cuticular bars of complex shapes, charac-
teristically arranged ; 4 bars border the opening of the sucker or
clamp ventrally ; 2 others are bent at right angles, one part of each
bordering the opening of the sucker dorsally, the other being directed
towards its centre ; the remaining 2 bars occur in the dorsal wall
of the organ, one being T-shaped and the other continuing the stem of

the T beyond the upper limbs (thus, T), the whole arrangement being
cruciform. The stem of the T-piece has a lamellar extension and with
its fellow supports the concavity of the organ. The dorsal walls of

DICLIDOPHOMDiE 95

the suckers are further supported by two fan-like systems of very small
rods, each comprising 6 or 7 concentric arcs in which the numbers
of elements vary. The base of the sucker is formed of a muscular
cup. Terminal hooks or hooklets invariably absent in adults. Cirrus
generally equipped with a circlet of curved and grooved (but not
necessarily bifurcate) hooklets. Beceptaculum seminis generally
present. Testes numerous. Ovary elongate and folded, generally
situated in front of the testes. Vagina present or absent. Two sub-
families can be separated by the characters of the opisthaptor, which
consists of cup-luce suckers in the Cyclocotylinse, but pincer-like
clamps in the Diclidophorinse.

Sub-family Diclidophorin^ Cerfontaine, 1895, sensu Price, 1943

In Diclidophoroides the opisthaptor is sharply marked off from the
rest of the body ; in other genera it is not, but in Octodactylus the testes
are situated exclusively behind the ovary, while in Diclidophora some
occur in front of it.

Genus DICLIDOPHORA Diesing, 1850.

(Dactycotyle Beneden & Hesse, 1863 ; Dactylocotyle Marschall, 1873 ;
Dactylocotyle " Parona & Perugia, 1899 " of Brinkmann, 1942a, in part.)

Opisthaptor not sharply set off from the body and comprising 4
pairs of pedunculate clamp-like organs. Testes numerous and located
both in front of and behind the ovary. Eggs having polar filaments.

Diclidophora merlangi (Kuhn, in Nordmann 1832) Kroyer [1851 ?]

(p. 606). (Fig. 16 A-C.)

Octostoma merlangi Kuhn, in Nordmann, 1832 (pp. 78, 82) ; Octobothrium
platygaster Leuckart, 1842 (p. 30) ; Diclidophora longicollis Diesing, 1850
(p. 417) ; Octoplectanum longicolle Diesing, 1859 (p. 443) ; Octobothrium
merlangi (Kuhn) of Beneden, 1856, 1858, Monticelli, 1888, Scott, 1900,
Lebour, 1908 ; Dactylocotyle merlangi (Kuhn) of Cerfontaine, 1895 (b, pp.
922, 939, 942-3, PI. 1, figs. 4, 8).

Host : whiting.
Location : gills.

This common trematode was found by Beneden (1870) in whiting
caught off the coast of Belgium, and it has been found by T. Scott
(1901) in Scotland, by A. Scott (1904) in the Irish Sea, by Lebour
(1908a) at Cullercoats, by Nicoll (1914) and Baylis & Idris Jones (1933)
at Plymouth, where I have found it myself, at Galway by Little (1929a)
and at Aberystwyth by Rees & Llewellyn (1941). It is safe to say
that it may be found on whiting caught anywhere on our coasts, and
it occurs in the Mediterranean. Cerfontaine (1895 ; 1898a, pp. 324-5)
found one hundred specimens, all of which came from the most anterior
gills and gave a brief diagnosis of them. They were 8-10 mm. long,
but apparently up to 15 mm. long after death, specimens previously

96

THE TREMATODA OF BRITISH FISHES

studied by Beneden (1858, p. 49) being 14-15 mm. long. Beneden
observed that the eggs of this trematode have at each pole a filament
slightly shorter than the capsule itself. Lebour (1908a, pp. 40-1, PI.
5, fig. 2) found specimens in 75% of the whiting she examined at

Fig. 16. — A-C, Diclidophora merlangi : A, entire trematode ; B, the genital
hooklets ; C, one of the clamps. D-F, Octodactylus palmatus : D, the
entire trematode ; E, the egg ; F, one of the clamps. (Original.)

Culler coats, generally two or three specimens on a host, but sometimes
as many as six. Her specimens were about 11 mm. long and 4 mm.
in greatest breadth. She indicated the position of the genital pore
immediately behind the bifurcation of the gut (Cerfontaine did not
mention it) and gave the number of genital hooklets as 12-14. She
was unable to observe the testes and was misled by Beneden to regard

mOLTDOPHORTD/E 97

tliem as a single organ, although they were left out of the figure. She also
saw the pale yellow egg and supported Beneden's observation regarding
polar filaments. My own specimens are almost exactly of the shape
indicated by Cerfontaine. Size : 6-8-10-2 mm. in total length, 2-1-
2-65 mm. in greatest breadth at the level of the testes. Narrow
anterior region 2-1-2-9 mm. long and 0-9-1-0 mm. broad, where it
merges with the wider region. Prohaptor a pair of buccal suckers
0-10-0-13 mm. long and 0-08 mm. broad, situated with their centres
0-125-0-135 mm. from the anterior extremity. Opisthaptor : Cotylo-
phore triangular, 1-7-1-8 mm. long, the breadth along anterior and
posterior margins being 2-1-2-5 mm. and 0-35-0-45 mm. Peduncles
equally spaced along the lateral margins of the cotylophore, of about
equal length (0-5-0-65 mm.), those of the most posterior pair slightly
longer than the rest, tapering slightly towards the clamps, each con-
taining a diverticulum of the intestinal crus. Clamps also of about
equal size, 0-33-0-37 x 0-24-0-27 mm., sclerites as in Fig. 16. {Note. —
In the interesting specimen figured, one of the clamps of the second pair
is of abnormally small size, suggesting malformity, but the sclerites
show the usual arrangement, though they too are smaller and more
slender.) Gut : pharynx about 0-22 mm. diameter (i.e. much larger
than the buccal suckers), generally elongate oval in outline, sometimes
broader than long, caeca having diverticula. Reproductive systems :
genital pore median and situated 0-50-0-57 mm. from the anterior
extremity. Genital hooklets numbering 16, each strongly curved and
deeply grooved, but having a single sharp point. Testes numerous,
mainly confined between the caeca and behind the ovary, but extending
laterally to the level of the receptaculum seminis, which is bipartite
and situated immediately in front of the ovary near the median plane.
Ovary elongate and folded. Uterus and vas deferens median and little
convoluted. Vitellaria abundantly developed, the follicles extending
from just behind the genital pore to the posterior extremity, a few
entering the base of each peduncle. Eggs not observed.

Diclidophora denticulata (Olsson, 1876) Price, 1943.

(Fig. 17 F-K ; 18 A-H.)

Octobothrium denticulatum Olsson, 1876 (p. 10, PI. 1, figs. 13-17) ; Dactylo-
cotyle denticulatum (Olsson) of Cerfontaine, 1895 (pp. 923-38) ; D. car-
bonarii Cerfontaine, 1895 (pp. 929, 931, PI. 1, figs. 1, 5, 9, 10, 11 ; PI. 2,
figs. 12-20.

Hosts : coal-fish, poor cod, hake.
Location : gills.

This species has been recorded several times from fishes in British
waters, by Nicoll (1915) in the coal-fish at Aberdeen, by Little
(1929a) in the same host at Galway, by Bay lis & Idris Jones (1933) in
the hake at Plymouth, where I have found it in the poor cod, and
by Rees & Llewellyn in the coal-fish on the Irish Atlantic Slope.
It was originally described from specimens found on coal -fish caught
in the Skagerrak, and it occurs in Canada (Nova Scotia) and U.S.A.

7

98

THE TREMATODA OF BRITISH FISHES

DICLIDOPHOKIDJE - 99

(Woods Hole). The original specimens were 7 mm. long and 2 mm.
broad, and the description by Olsson broadly and clearly represented
the species but contained several errors, notably the supposition that
the gonads are compact and spherical. Cerfontaine (1895) found two
to three specimens on each individual host, noting that they are
generally attached to the second or third gills. His grey specimens
were 6-13 mm. long and ripe eggs in utero gave the specimens a brown
tinge. Cerfontaine's description of the action and structure of the
clamps of the opisthaptor must be considered in detail, such excellence
being a rarity in the literature. The worm applies its ventral surface
to the surface of the gill lamella with the posterior extremity directed
towards the branchial arch, and the clamps grasp groups of filaments
on the internal and external surfaces (Fig. 18 A). When the worm is
detached from the host the form is subject to change, the clamps
curving on their peduncles towards the ventral surface of the body.
Cerfontaine described the cuticular skeletal supports of the clamps
in some detail. Each clamp has two valves, one dorsal and the other
ventral, but during attachment the whole clamp undergoes torsion
through an angle of about 90°, so that the valve which is anatomically
ventral becomes topographically anterior so long as adhesion is main-
tained. The rather complicated skeletal structures which support the
clamp are best understood by reference to the following parts :

Anterior valve : facing towards the anterior end of the worm during
adhesion (anatomically the ventral valve).

Posterior valve : turned towards the posterior extremity (anatomi-
cally dorsal).

Each valve may be regarded as possessing an external and an
internal surface, the latter bounding the cavity, and four sides, (i) distal,
bordering the opening, (ii) proximal, near the hinge, (iii) internal, facing
the body of the worm, and (iv) external, facing outwards. Fig. 18 B
represents a transparent whole mount of the most posterior clamp on
the right (though all have fundamentally the same skeletal structure),
with the anterior valve uppermost. We can consider the sclerites of
the two valves separately.

Anterior valve has a central curved sclerite, convex in front, (a),
which is prolonged on the internal side into a cuticular plaque (b)
occupying the internal half of the valve and terminating internally
and below in a thick margin (c). The external half of this valve
contains a sclerite (d), which is symmetrical with the margin (c) of the
plaque (b) and extends along the distal margin of this region. Cen-
trally, the external half of the valve bears numerous (about 30) small,
cuticular teeth (e), which occupy a prominent superficial position and
are directed obliquely in a medio -anterior direction. Each tooth has
a thick base and a conical point.

Posterior valve has 7 cuticular pieces or sclerites of diverse shapes.
The most prominent, curved, median sclerite (f) is convex in a pos-
terior direction. Two much smaller pieces (g, g) articulate with its
distal extremity and extend along the corresponding margin of this
valve, one along the internal, the other along the external part of the

100

THE TREMATODA OP BRTTJSH FISHES

Fig. 18. — Diclidophora denticulata. A, longitudinal section passing
through a gill-lamella of the host and the opisthaptor of the trematode,
showing the mode of attachment ; B, one of the clamps of the opis-
thaptor as seen in a whole mount, the anterior valve towards the
observer ; C, D, E, F, section passing through the clamp respectively
along the planes indicated by the lines CC, DD, EE and FF ; G, the
male organ, showing the genital hooklets ; H, the egg (a and b, the
ends of the short and long polar filaments respectively). For an ex-
planation of the arrangement of the sclerites a-e in the anterior valve
and f-k in the posterior valve see the text on p. 99. (After Cerfon-
taine, 1895.)

DICLIDOPHORID^ 101

margin. A large sclerite (h) articulates with the proximal extremity
of the median sclerite (f ) and extends along the internal, and slightly
towards the external side at the proximal end of the valve. A small
sclerite (i) occurs near the internal extremity of (h) and is more or
less parallel with the median sclerite (f). Finally, two other sclerites
extend along the external half of this valve, one (k) following the
external margin, the other (1) articulating with the proximal end of (k)
and passing obliquely in a medio-posterior direction.

A number of narrow cuticular bands which vary in form and
arrangement occur on the internal surface of the posterior valve.
Similar structures occur on the internal surface of the anterior valve.
The opening of the clamp is a large gap at the distal extremity, extend-
ing some distance along the internal and external margins. During
attachment the gill filaments of the host project through this aperture
and are gripped by the distal extremities of the two valves (Fig. 18 A).

Cerfontaine stressed the difficulty of gaining a comprehensive idea
of the skeletal structures of a clamp when the organ is mounted whole
as a transparency. His sections greatly assist comprehension and
are reproduced in Figs. 18 C-F, the planes of section of the whole
clamp being indicated by corresponding letters, CC-FF in Fig. 18 B
and topographical aids being added.

Various muscles are responsible for opening and closing the valves
of the clamps, but their arrangement has not been worked out in
sufficient detail. Some of them are indicated in the figures, o.m.
representing the opening muscles, cm. the closing muscles.

Price (1943), p. 46, figs. 2, 3) gave a detailed description of American
specimens 7 mm. long and 1-6 mm. broad at the level of the ovary.
My own specimen is clearly recognizable from his account and has the
following characters : — Size : total length 5-9 mm., greatest breadth
at the level of the ovary 1-75 mm. Cuticle slightly wrinkled. Shape
tapering gradually from the level of the ovary anteriorly, the bluntly
pointed anterior extremity constricted at the level of the buccal
suckers, tapering sharply to the origin of the opisthaptor, about 3-5
mm. from the anterior end. Prohaptor : buccal suckers ovoid, 0*21
mm. long and 0-15 mm. broad. Opisthaptor : cotylophore narrowing
posteriorly (to about 0-9 mm. from 1-4 mm.) ; clamps uniform in size
and shape, borne on short, stout peduncles, their dimensions about
0-8 x 0-5 mm. Sclerites as indicated in Fig. 17 G, H. {Note. — The
plaque on the internal side of the anterior valve is very well developed
in the clamps of the first three pairs, but is not evident in the clamps
of the 4th pair (in a preparation counter-stained with light green, which
renders the sclerites very obvious) . The cuticular supports of clamps
of the 4th pair are rather more delicate than the others.) Gut : pharynx
about 0-2 mm. diameter, caeca having numerous lateral diverticula,
one at least passing into each peduncle. Reproductive systems : male
genital pore about 0-5 mm. from the anterior extremity. Genital
hooklets numbering 13, each deeply grooved on the outer side. Testes
distributed within the cotylophore, as well as the posterior part of the
body. Ovary far back in the body. Vitellaria tending to fill the

102 THE TREMATODA OF BRITISH FISHES

cotylophore as well as the posterior half of the rest of the body. Follicles
progressively less numerous to the level of the male genital pore and
a few entering the base of each peduncle. Female genital pore about
1 mm. behind the male. Egg spindle-shaped, measuring 0-295 x
0-08 mm., and having a curved filament much shorter than the capsule
at the anterior pole and a long filament (length about 0-8 mm.) at the
posterior (only part of which is shown in Olsson's fig. 14).

Diclidophora luscae (Beneden & Hesse, 1863) Price, 1943.

Dactycotyle Iusccb Beneden & Hesse, 1863 (1864, pp. 111-12) ; Dactylocotyle
luscce (Beneden & Hesse) of Cerfontaine, 1895 (p. 922) ; Octobothrium
luscce (Beneden & Hesse) of Taschenberg, 1879 (a, p. 27).

Hosts : bib, poor cod.
Location : gills.

The earlier records of this trematode concern specimens found near
Brest and at Roscoff, but Little (1929a) found the trematode in the bib
at Galway. The original description was very imperfect and had no
accompanying figure, conveying the impression that there is little to
distinguish this species from D. pollachii. The length was given as
6-7 mm. ; the genital hooklets were said to have single points, and the
eggs two short polar filaments. For some time Cerfontaine (18956)
failed to find the trematode, but later found it twice at Roscoff and
described it very clearly (1898a, pp. 315-22, PL 12, figs. 1-5). Size :
4r-7 mm. long. Shape as in D. pollachii, but more squat, the anterior
extremity attenuated, but very short, enlargement to maximum
breadth occuring sharply near the origins of the peduncles of clamps
of the first pair. Colour clear grey, the gut dark brown, the eggs in
utero imparting a brownish-yellow colour. Opisthaptor : cotylophore
trapezoidal and broadest anteriorly, the peduncles robust, each bearing
a characteristic clamp, the ventral valve of which has irregular nodules.
Chit : pharynx spherical. (Esophagus fairly long. Bifurcation of the
intestine near (behind) the level of the male pore (far in front of the
female pore). Median and lateral diverticula not numerous. Anasto-
moses very evident in the region of the receptaculum seminis, ovary
and ootype (the relatively posterior positions of which are regarded
as characteristic of the species) and in the cotylophore, the ramifica-
tions passing into the peduncles. Intestine lined with squamous
epithelium. Reproductive systems : male pore conspicuously anterior
to the female pore. Testes numerous, occupying the spaces between
the ramifications of the intestine. Vas deferens short, median and not
very sinuous, dilating to form a vesicula seminalis near its junction
with the male organ. Genital hooklets generally numbering 10,
each having a short and straight base and a strongly curved blade.
Ovary situated at the transverse level of the peduncles of the first pair,
folded into an N-shape. Oviduct short and straight and median,
ootype club-shaped, its expanded portion directed posteriorly and
situated behind the ovary. Vitellaria as in other species. Recep-

DICLIDOPHORIDJE 103

taculum seminis situated in front of the ovary and transverse vitello-
ducts and on the right. Vagina short and opening ventrally. Eggs
each having a crozier-shaped filament shorter than the capsule itself at
one pole and a long filament terminating in a funnel-like structure with
a milled margin at the other. Crozier-shaped filaments directed
anteriorly in utero and eggs grouped in bunches because of the entangled
posterior filaments.

Diclidophora pollachii (Beneden & Hesse, 1863) Price, 1943.

Dactycotyle pollachii Beneden & Hesse, 1863 (1864, pp. 110-11, PI. 11, figs.
23-30) ; Dactylocotyle pollachii (Beneden & Hesse) of Cerfontaine, 1895 (6,
pp. 938, 941, PI. 1, figs. 2, 6) and 1898 (a, p. 324) ; Octobothrium pollachii
(Beneden & Hesse, 1863) Taschenberg, 1879 (a, pp. 246-7.)

Host : pollack.
Location : gills.

This species was originally found near Brest, and Cerfontaine 's
specimens were obtained at Roscoff. T. Scott (1901, p. 150, PL 8,
figs. 28, 29) found specimens on pollack caught in salmon-nets at Bay
of Nigg, near Aberdeen, T. Scott (1904, p. 116) in the same host in the
Irish Sea, and Little (1929a) has found it at Galway. T. Scott gave
practically no description, merely giving the length as 10 mm., but he
mentioned minute " prickles " or " spines " on the anterior valve of
the clamps, and these could hardly have been the well -developed
" teeth " of D. denticulate/,, and must have been nodules such as were
seen by Cerfontaine. According to the original description, the length
of the trematode is 5 mm., but other details are scarcely discernible,
although the genital hooklets were said to be bifurcate and the egg
was credited with a filament slightly longer than the capsule at one
pole and a much longer and crozier-like process at the other. Cerfon-
taine, who found the worms on the third gills more often than else-
where, gave a clear diagnosis. Size : 8-13 mm. long. Shape : pointed
anteriorly, but broadening rather abruptly in the anterior half of the
body and of uniform breadth farther back. Colour clear dark grey,
the ramifications of the gut appearing brown. Opisihaptor : the
clamps and their peduncles not as robust as in D. denticulata, but larger
than in D. merlangi, and having irregular nodules on the ventral valves.
Gut : oesophagus shown longer than in D. denticulata and D. mer-
langi, the crura of the intestine having far fewer median and lateral
diverticula, particularly in the anterior region, and a few anastomoses
in the vicinity of the haptorial disk. Reproductive systems : genital
hooklets generally numbering 14, rarely 11, 10 or even only 9. Testes
numerous and arranged in groups amidst the ramifications of the
intestine, many of them lateral to the crura of the intestine. Ovary
situated far back in the body, only a short distance in front of the
origins of the haptorial peduncles of the most anterior pair. Eggs
each having 2 polar filaments, that at the anterior pole the shorter
and shaped like a crozier, but of a more irregular shape than that seen

104 THE TKEMATODA OF BRITISH FISHES

in the egg of D. denticulata. (Note. — Cerfontaine also regarded the
genital pores of D. pollachii as distinct and separate, like those of D.
denticulata, but unlike those of D. merlangi.)

Genus OCTODACTYLUS Dalyell, 1853.

(Pterocotyle Beneden & Hesse, 1863.)

Opisthaptor not sharply set off from the rest of the body. Testes
situated entirely behind the ovary. Eggs devoid of polar extensions.

Octodactylus palmatus (F.S. Leuckart, 1830) Price, 1943, etnend.

(Fig. 16D-F.)

Octobothrium palmatum Leuckart, 1830 (p. 612) ; Octodactylus inhcerens
Dalyell, 1853 (pp. 262-3, PL 36, figs. 1, 2) ; Octobothrium digitatum Rathke,
1843 (pp. 242-4, PL 12, figs. 13-15) ; Diclidophora palmata (Leuckart)
Diesing, 1850 (pp. 417-18) ; Octoplectanum palmatum (Leuckart) Diesing,
1858 (p. 443); Dactylocotyle molvce Cerfontaine, 1895 (p. 944, PL 1,
figs. 3, 7) ; Pterocotyle palmata of Beneden & Hesse, 1863 (1864, p. 107,
PL 11, figs. 1-13), and Lebour, 1908a (p. 41, PL 5, fig. 3) ; Dactylocotyle
palmata of Cerfontaine, 1895.

Host : ling.
Location : gills.

This trematode is widely distributed in northern European waters,
occurring off the coasts of Iceland, Norwav, Sweden, Belgium and
France. T. Scott (1901, p. 149, PI. 8, fig. 27 ; 1912, PI. 27, fig. 8)
found specimens about 20 mm. long on ling in the Moray Firth and in
the Clyde, and they have been found on this host at Culler coats by
Lebour (1908a), at Galway by Little (1929a), on the Irish Atlantic
Slope by Rees & Llewellyn (1941) and at Plymouth by myself. Early
descriptions are of little use and sometimes misleading. Dalyell repre-
sented the trematode upside down. Beneden and Hesse gave a wrong
impression even of the shape, and gave little useful information
other than the presence of 16 genital hooklets and wrongly described
the eggs as pointed at each pole, representing them in figures as
pointed at one pole, but more or less rounded at the other. Olsson
(1876, p. 9, figs. 9-12) gave several erroneous characters, notably
the compact and globular form of the gonads. Dalyell removed 29
worms from part of the gills of a single host ; Cerfontaine found as
many as 11, fairly uniformly distributed on right and left, and
generally attached to the ventral side of the gills of the most posterior
pair. He gave a useful diagnosis of specimens 10-20 mm. long (dead
individuals up to 30 mm. long) with an opisthaptor of characteristic
palmate shape and pedunculate clamps of a robust nature, those of
the most posterior pair nearly together. He showed clearly that the
crura of the intestine have numerous median and lateral diverticula,
but relatively few anastomoses, that the genital pore is situated just
behind the pharynx, the testes are numerous, the genital hooklets

DICLIDOPHORID^E 105

16 in number and the eggs devoid of polar filaments. Lebour
(1908a, p. 41, PL 5, fig. 3) dealt with three solitary specimens, and gave
the length and breadth as 12-5 x 2 mm., the number of genital
hooklets as 16 or 17 and the dimensions of the eggs as 0-20 x
0-08 mm. She showed clearly the characteristic arrangement of
uterine folds full of eggs just behind the bifurcation of the gut, but
gave a wrong impression of the shape of the ovary and omitted the
testes.

A specimen of my own, taken from the ling, outstrips the size-
limit specified by Cerfontaine. Size : 22-5 mm. long, 4-2 mm. broad
near the midbody, 2-3 mm. broad between levels 0-2 and 0-45 mm.
from the anterior extremity, about 2-75 mm. broad at the origin of
the opisthaptor. Shape tapering gradually from the midbody to a
level 0-45 mm. from the anterior end, then of uniform girth to within
0-2 mm. from the anterior end, beyond which the body tapers to a
blunt point. Body tapering also towards the opisthaptor. Pro-
haptor a pair of buccal suckers, diagonally oval in outline, 0-18 mm.
long and 0-14 mm. broad. Opisthaptor : cotylophore indistinct, about
2 mm. long, tapering posteriorly to a breadth of about 0-55 mm.
Clamps uniform in size and shape, measuring about 0-6 X 0-4 mm.,
their peduncles 0-6-0-8 mm. long and 0-5 mm. broad, those of the
most posterior pair slightly the longest. Sclerites in general similar
to those of Diclidophora, arranged as indicated in Fig. 16 F. Gut :
mouth transversely oval, 0-18 mm. wide, situated 0-1 mm. from the
anterior extremity. Pharynx longitudinally oval (0-3 X 0-23 mm.).
(Esophagus very short. Intestine bifurcate, having lateral diverticula
and in the posterior region (zone of the testes) anastomosing median
branches, one main branch passing into each peduncle. Reproductive
systems : genital pore median, 0-4 mm. behind the pharynx and about
1 mm. from the anterior extremity. Genital hooklets numbering 18,
each having plate -like roots and strongly curved points, which are
deeply grooved, but not bifurcate. (Note. — It is easy to get an erroneous
impression that they are forked and have two closely situated prongs.)
Testes very numerous (more than 300), extending from a level in front
of the midbody to the opisthaptor, confined to a median zone between
the intestinal crura. Ovary elongate, but folded (N-shaped), situated
immediately in front of the testes in the median plane. Vitellaria
extremely well developed, mainly lateral to the testes in the posterior
half of the body, but following the courses of the intestinal anasto-
moses, extending anteriorly in a pair of broad lateral bands to the
posterior end of the mass of uterine folds, a few follicles on either side
extending forward to the midpoint of the narrow anterior region.
Uterus having a few folds in the narrowing anterior region and many
folds which almost fill the narrow region itself, but are largely confined
to the region between the intestinal crura. Eggs very large and very
numerous (more than 200 in utero), yellow, having an inner lining
with internally-directed protoplasmic processes about 0-08-0-016 mm.
long (mainly on one side), devoid of polar filaments and measuring
about 0-220 x 0-090 mm.

106 THE TREMATODA OF BRITISH FISHES

Octodactylus minor (Olsson, 1876) Price, 1943, emend. (Fig. 17 A-E.)

Octobothrium minor Olsson, 1876 (p. 10) ; Dactylocotyle minus (Olsson) of
Gallien, 1937 (p. 146, figs. 7-9 ; PL 1, fig. 1) ; Octobothrium palmatum
forma minor Olsson, 1868 (PL 4, figs. 70, 71.

Hosts : poutassou, whiting.
Location : gills.

Olsson obtained 48 specimens of this species from 15 specimens
of the poutassou at Bergen. It was found on the whiting south-
west of Ireland and described by Gallien, and was recorded on the
same host on the Irish Atlantic Slope by Rees & Llewellyn (1941).
The description by Gallien is concise and clear. Size up to 5-2 mm.
long and 1-1 mm. broad at the middle of the body. Colour brown.
Shape elongate and very flat, tapering towards the extremities. Pro-
haptor a pair of typical buccal suckers. Opisthaptor : cotylophore
one-tenth as long as the body and not sharply set off from it, bearing
four pairs of pedunculate clamps with 2 distinct valves and a ter-
minal languet. Each clamp having 10 sclerites and a muscular cup
with a well-developed dorsal wall. Gut : pharynx bulbous. (Eso-
phagus very short. Intestinal crura long, uniting in the cotylophore
and sending a branch into each peduncle, and having numerous irregular
median and dendritic lateral diverticula. Intestine lined with columnar
cells filled with brown pigment. Excretory system : vesicles at the
level of the pharynx, pores slightly dorsal. Nervous system : brain
giving off one pair of anterior and two pairs of posterior nerves, the
latter comprising a relatively short lateral nerve and a longer median
nerve on each side of the body. Median nerves uniting in the cotylo-
phore and sending a trunk into each peduncle. Reproductive systems :
genital pore just behind the pharynx. Cirrus equipped with 12
sickle-shaped hooklets. Vas deferens long and sinuous. Testes not
very numerous, situated in the posterior region (not the anterior as
Olsson stated) between the ca3ca. Ovary folded (N -shaped) and
situated in front of the testes near the middle of the body. Arrange-
ment of various ducts (oviduct, genito-intestinal canal, vitelloducts,
uterus) very similar to that in Cyclocotyla pagelli {q.v.), the vagina not
distinctly seen, but joining the receptaculum seminis and opening
ventrally in the median plane. Vitellaria comprising numerous
follicles which tend to fill the parenchyma of the whole body. Uterus
containing a single fusiform egg having two short polar prolongations,
total length 0-109 mm. (? given as l-900fx).

Octodactylus morrhuae (Beneden & Hesse, 1863) Price, 1943.

Pterocotyle morrhuae Beneden & Hesse, 1863 (1864, pp. 106-7) and of Scott,
1901 (pp. 149-50, PL 8, fig. 25) ; Dactylocotyle morrhuce (Beneden & Hesse)
of St. Reray, 1898 (p. 551).

Hosts : cod, whiting.
Location : gills.

This species was discovered near Brest, but subsequently found in
both hosts in Aberdeen Bay by T. Scott (1901), and on the cod at

DICLIDOPHORIDiE 107

Gal way by Little (1929a). According to the very incomplete original
description, which had no figure, it is 14-15 mm. long and has clamps
which are borne on long peduncles of different sizes, the anterior
shortest and the most posterior longest. The clamps of right and left
sides are separated by a deep cleft, as in 0. palmata, and the eggs are
similarly devoid of filaments. The authors considered the possibility
of identity with this species, but thought both of them distinct, basing
this conclusion on the size and colour of the body and the way in which
the peduncles of the clamps are arranged, only the last character
having any significance. T. Scott's specimen was 8'5 mm. long and
3-5 mm. in greatest breadth. The body was said to be uniformly
very broad posteriorly, but tapering sharply anteriorly. The posterior
extremity was truncated, but a moderately broad prolongation carries
two clamps on short peduncles and two other pedunculate clamps
occur nearly together at its base. The remaining two pairs of clamps
are situated on the lateral parts of the truncated posterior region and
are sessile, although longitudinal folds on the ventral surface of the
posterior region simulate peduncles. The description is certainly
that of a very odd specimen and the figure suggests considerable
flaccidity, apart from which resemblance to 0. macruri is closer than
to any other species of Octodactylus . We may conclude, therefore,
that the identity of this species is very doubtful ; in some respects it
resembles both 0. palmata and 0. macruri, but has been described so
vaguely that no reliable impression of its structure can be gained.

Octodactylus macruri (Brinkmann, 1942) Dawes, 1946.

(Fig. 19 A-E.)

Dactylocotyle macruri Brinkmann, 1942 (a, p. 1, figs. 1-8).

Host : Macrurus rupestris (=Coryphcenoides rupestris).
Location : gills.

This species was found in the Skagerrak and was fully described
by Brinkmann. Considering the wide distribution of other species
of this genus, we may conclude that it is a likely member of the British
fauna and must consider its diagnostic characters. Size : 1-25-3-5 mm.
long (mean 2-25 mm.) and 0-5-0-75 mm. in greatest breadth immediately
in front of the opisthaptor. Shape : tongue- or lancet-shaped,
tapering anteriorly, broadest posteriorly. Prohaptor a pair of ovoid
buccal suckers 0-065 mm. in greatest length. Opisthaptor : cotylo-
phore broad, merging imperceptibly with the rest of the body and
bearing 4 pairs of uniform clamps on short peduncles laterally.
(Note. — In the living animal the lateral halves of the opisthaptor
are bent ventralwards and to some extent brought nearer together,
thus embracing the gill filaments of the host.) Peduncles very
flexible, the clamps capable of some rotary movement. Each clamp
comprising anterior (anatomically ventral) and posterior (dorsal)
valves, both of which are elliptical and hinged onone another trans-
versely to the long axis. Cuticular sclerites of the two valves

108

THE TREMATODA OF BRITISH FISHES

ill defined, merging gradually into the musculature and connective
tissue. Anterior valve (ventral) having 3 sclerites (a, b, c, Fig. 19
C, D), 2 of them (a, c) near the periphery, the third (b) diagonal to
the median line of the clamp, its base directed towards (c), and con-
nected with (a) along its entire length by a fine cuticular membrane.
Posterior (dorsal) valve having 6 sclerites (d-i, Fig. 19 E), 4 of them
(d, e, g, h) near the periphery, more or less paired (e-g, d-h), another,
the largest, (f), meeting (e) and (g) distally and extending diagonally
towards the proximal end of (h). Between the proximal ends of (f)

Fig. 19. — Octodactylus macruri. A, entire trematode ; B, diagram of the
reproductive organs ; C, diagram showing the arrangement of sclerites
in one clamp of the opisthaptor, which is also shown for the ventral
(anterior) and dorsal (posterior) valves in D and E respectively, (a, b,
c are sclerites in the ventral valve ; d, e, f, g, h and i those in the dorsal
valve.) (After Brinkmann, 1942a.)

and (d) is the sixth sclerite (i), which thus extends parallel with the
hinge of the clamp. Delicate rod-like sclerites extend in arcs across
the posterior valve. Gut : pharynx about 0-1 mm. long. Reproduc-
tive systems : common genital pore median, close behind the pharynx.
Testes numerous (about 20), situated in the fourth one-sixth of the
body and confined between the caeca. Vas deferens extending in
a straight line anteriorly, underlying the ovary and ootype, widening
near the genital pore into a pyriform seminal vesicle with thick
walls. Cirrus bulbous, about 0-06 mm. broad and equipped with 10 to 14
ventrally directed hooklets forming a circlet with the points directed

DICLTBOPHORTD.T] 109

laterally. Ovary situated in front of the testes and folded into an
N- or W-shaped mass, the blind end postero- ventral and on the right,
the short oviduct emerging anteriorly and on the left. Arrangement
of the genital ducts as shown in Fig. 19 B. Receptaculum seminis
ventro -lateral to the closed end of the ovary, genito -intestinal canal
opening into the right caecum. Ootype longitudinally elongate and
situated mainly between the ovary and the testes. Uterus straight
and parallel to the vas deferens. Vitellaria very extensive, their
follicles occupying all the available space in the body, overlying the
testes, but not the ovary and ootype, which are surrounded by clear
parenchyma. Vitelline follicles very large, as few as four taking up
the entire breadth of the body anteriorly, but smaller posteriorly.
Eggs not observed.

Genus DICLID0PH0R0IDES Price, 1943.

Opisthaptor sharply set off from the rest of the body. Testes
situated behind the ovary. Other characters as in Octodactylus.

Diclidophoroides phycidis (Parona & Perugia, 1889).

Dactylocotyle phycidis Parona & Perugia, 1889 (pp. 743-4, fig. 5) ; Dactycotyle
phycidis Rees & Llewellyn, 1941.

Host : greater fork-beard.
Location : gills.

This species was originally found in the greater fork-beard at Genoa,
but was found on the same host by Rees & Llewellyn (1941) on the
Irish Atlantic Slope. Price (1943a) was diffident about the inclusion
of this species in the genus Diclidophoroides, so imperfect was the
original description. British specimens have not yet been described.

Other Diclidophorince.

Scott (1901, p. 147, PI. 8, fig. 22) found a trematode about 4 mm.
long and 2 mm. in greatest breadth on the gills of a Norway pout
caught about sixty miles south-east of Sumburgh Head, Shetland,
recording it as " Octobothrium (?) esmarkii (sp. nov.)." So incomplete
was the description that this form cannot be rightly assigned to a
particular genus, but it belongs either to Diclidophora or to Octodactylus.
The best guess that one can make would be to consider it possibly
identical with Diclidophora luscae.

Sub-family Cyclocotylin^: Price, 1943.

(Diclidophorinse Cerfontaine, 1895, in part.)

Two European genera, Cyclocotyla and Diclidophoropsis , can be
distinguished by the absence or presence of vaginae. Two other genera
occur in Japan only and two in America only. One other genus which
has been referred to this group is Neoheterobothrium Price, 1943, which
contains two North American species. Price thought it might possibly

110 THE TREMATODA OF BRITISH FISHES

contain " Octobothrium leptogaster Leuckart, 1830," which is the type-
species of Chimcericola, a genus of the Discocotylidse.

Genus CYCL0C0TYLA Otto, 1823.

{Octostoma Otto, 1823, nee Kuhn, 1829 ; Cyclostonia Otto, 1823, nee

Lamarck, 1799 ; Cyclobothrium Cerfontaine, 1895, in part ; Choricotyle

Beneden & Hesse, 1863 ; Diclidophora Diesing, of Goto, 1894, in part ;

Mesocotyle Parona & Perugia, 1889.)

Opisthaptor sharply set off from the rest of the body, the component
suckers pedunculate or almost sessile and fairly equally spaced out.
Genital atrium not muscular, cirrus armed with hooks. Testes located
behind the ovary. Vitellaria extending into the opisthaptor. Vaginae
absent.

The type species, Cyclocotyla bellones Otto, 1823 (p. 300, PI. 41,
fig. 2a-c) was discovered on the dorsal surface of a " Hornhecht "
(Belones acus) at Naples and has not appeared in this country. Two
of the other European species, C. chrysophryi (Beneden & Hesse, 1863)
and C. pagelli (Gallien, 1937), have appeared in Britain and one, C.
charcoti (Dollfus, 1922) off the coast of Spain. C. labracis (Cerfontaine,
1895) (Diclidophora labracis Cerfontaine, 1895 (pp. 126-42, PL 3, figs.
1-15)) was discovered on the bass at White Bank in the North Sea.
The remaining two European species are C. squillarum (Parona &
Perugia, 1889) (Mesocotyle squillarum Parona & Perugia, 1889 (pp.
76-80, 1 PL, figs. la-3a)), a parasite on Bopyrus squillarum at Trieste,
and C. taschenbergii (Parona & Perugia, 1889) (Diclidophora taschen-
bergi Parona & Perugia, 1892 ; Dactylocotyle taschenbergi of Stossich,
1898 (pp. 12-13)). All these combinations were made by Price (1943,
p. 49). Regarding the last-named species, which was discovered on
Sargus rondeletii at Genoa and redescribed by Parona & Perugia
(1892, p. 95, PL 2, fig. 4 ; PL 3, figs. 13, 14), some doubt exists, Llewellyn
(1941, p. 425) having suggested that the worm should be transferred
(from Choricotyle, where he tentatively placed it) to the genus Diclido-
phoropsis, because Cerfontaine (1896, p. 517) believed it to have two
vaginal pores, situated near the genital atrium. If this conclusion
was justified, the worm cannot be retained in Cyclocotyla and must be
placed in Diclidophoropsis.

Cyclocotyla chrysophryi (Beneden & Hesse, 1863) Price, 1943.

(Fig. 20 D-F.)

Choricotyle chrysophryi Beneden & Hesse, 1863 (1864, p. 109, PI. 11, figs. 16-
22), and of Llewellyn, 1941 (a, pp. 397-405, figs. 1-7) ; C. chrysophrii
(Beneden & Hesse) Cerfontaine, 1898 (a, p. 303) ; C. chrysophris (Beneden
& Hesse) Monticelli, 1888 (pp. 11, 16).

Hosts : gilt-head, common sea bream.
Location : gills.

This species was discovered near Brest and has been recorded by
Rees & Llewellyn (1941), who found it on the common sea bream
on the Irish Atlantic Slope, and described in detail by Llewellyn

DICLIDOPHORIDiE

111

112 THE TREMATOBA OF BRITISH FISHES

(1941a). The original description was a very general and incomplete
account of large specimens 6 mm. long. Size : about 5 mm. long and
1 mm. in greatest breadth. Colour brown. Shape as in my Fig. 20 D.
Prohaptor a pair of buccal suckers 0-10 mm. diameter. Opisthaptor
four pairs of pedunculate, cup-like suckers, having circular or oval
apertures, and a terminal languet 0-11 mm. long and 0-03 mm.
broad. Peduncles decreasing in length from before backwards,
respective length being 1-0, 0-75, 0-50 and 0-46 mm., the most anterior
directed forwards, the most posterior backwards and intervening ones
showing an intermediate orientation. Origins of the most anterior
peduncles separated by the entire breadth of the body. Sclerites
eight in number, arranged as in my Fig. 20 E, and supplemented by
systems of small rods as also shown. The base of each sucker is
composed of a muscular cup. Muscular system including transverse
muscle bands connecting the peduncles of the same pair and bundles
from each pair of peduncles which originate in a powerful median
ventral muscle band. Gut : mouth not quite terminal and transversely
oval (0-22 x 0-10 mm.) ; pharynx 0-10 mm. diameter, its lumen only
about 0-007 mm., oesophagus very short, intestine comprising two
crura with median and lateral diverticula. The crura unite at the
end of the body proper, the median trunk entering the opisthaptor
sending a main diverticulum into each peduncle. Nervous system :
brain dorsal to the oesophagus and giving off a pair of anterior and
two pairs of posterior nerves. Of the latter the internal are stouter
and longer than the external, continuing into the opisthaptor, where
they are connected by a transverse commissure, beyond which they
give off paired nerves to the peduncles of the first three pairs and are
connected by a second commissure, behind which the nerves to the
peduncles of the fourth pair arise. Reproductive systems : common
genital pore median, beneath the posterior end of the oesophagus and
0-37 mm. behind the mouth. Testes numbering about 30, all situated
between the crura of the intestine in the posterior part of the body
proper. Vas deferens and seminal vesicle somewhat sinuous. Penis
spherical, 0-03 mm. diameter, generally bearing 8 bifid hooklets,
rarely 9. Ovary folded and slightly in front of the testes. Recep-
taculum seminis very large, situated in front of the ovary. Note :
the female system includes an enigmatic ring-organ, a ring 0-066 mm.
diameter encircling the oviduct near the ootype. It consists of homo-
geneous secretion and is of unknown function, though it is suggested
that it may act as a valve preventing retrogression of the eggs, though
the latter were unobserved.

Cyclocotyla pagelli (Gallien, 1937) Price, 1943. (Fig. 20 A-C.)

Diclidophora pagelli Gallien, 1937 (p. 22, figs. 5, 6 ; PI. 1, fig. 4).

Host : common sea bream.

Location : gills.

This species was erected for one specimen found on a host caught
off West Ireland. Size : 3-4 mm. long and 1 mm. broad. Shape

DICLIDOPHORID^ 113

broadly rounded anteriorly, gradually narrowing posteriorly, thick
and fleshy. Muscles and parenchyma little developed. Prohaptor
a pair of rounded, muscular, cup-like buccal suckers. Opisthaptor :
cotylophore elongate, 0-9 mm. long, broader proximally than distally,
bearing 4 pairs of suckers on thick lateral peduncles, which become
progressively smaller in a posterior direction. Suckers deeply concave,
globular, 0-35 mm. diameter, each having a skeletal framework of the
type shown (Gallien's fig. 5, my Fig. 20 B), composed of relatively
thick sclerites (thicker than in Diclidophoropsis) , the median pieces
(1 and 2 in Gallien's nomenclature) describing a pronounced arc which
gives the entire organ great depth. The base of the organ comprising
a thick, muscular cup. Gut : mouth slightly ventral ; prepharynx
short, pharynx small and spherical, oesophagus very short, practically
absent ; intestinal crura long and irregular, having numerous branched
lateral and uneven median diverticula, uniting in the cotylophore and
sending a branch into each peduncle. Intestine lined by epithelium
containing much brown pigment. Excretory system : vesicles and
pores lateral at the level of the pharynx. Nervous system : brain
giving off 1 pair of anterior and 2 pairs of posterior nerves, of the
latter one pair (the interval) well developed and entering the cotylo-
phore, sending twigs into each peduncle. Reproductive systems :
genital pore located near the level of the pharynx. Testes numerous,
situated in the space between the caeca in the posterior half of the body
proper. Vas deferens long and straight, dilated to form a seminal
vesicle in the anterior region. Cirrus muscular, but ill developed,
0-06 mm. diameter ; hooklets present, but not precisely determined in
the whole animal (8 reconstructed in serial sections of the specimen).
Ovary formed into short longitudinal folds (W-shape), close in front
of the testes, the medianmost fold containing oocytes. Oviduct
receiving the short duct of the receptaculum seminis near the anterior
end of the ovary and the genito-intestinal canal slightly beyond this,
then continuing in a posterior direction to the ootype, which is situated
behind the ovary. Vitellaria very well developed, the follicles prac-
tically filling the rest of the body, transverse vitelloducts at the level
of the receptaculum seminis, here forming the long, straight median
duct which enters the oviduct near the ootype. Vagina absent
(confirmed). Eggs not observed.

Cyclocotyla charcoti (Dollfus, 1922) Price, 1943. (Fig. 21 A-F.)

Cyclobothrium charcoti Dollfus, 1922 (a, p. 287, figs. 1-3 ; 6, p. 348, figs. 1-4) ;
Choricotyle charcoti (Dollfus) of Llewellyn, 1941 (6, p. 424) ; Diclidophora
sp. Fuhrmann, 1928 (p. (2) 4, fig. 5).

Hosts : horse mackerel, bogue.

Location : on Cymothoa oestroides parasitic in the buccal cavity.

This species was found in the former host near Gijon (Oviedo)
and in the harbour of Musel, and in the latter at Monaco. Size :

114

THE TREMATODA OF BRITISH FISHES

smaller of two specimens about 3 mm. long and 2-5 mm. in greatest
breadth, larger about 4-7 mm. long. Shape as in Fig. 21 A, D,
flattened, convex dorsally and concave ventrally. Cephalic lobe
very variable in shape, about 0-65 mm. long in the smaller specimen,
but when fully extended up to two-fifths of total length. Opisthaptor :
peduncles of the suckers short (up to 0-5 mm. long) and inconspicuous
when fully contracted. Sclerites 8 in number, arranged as in Figs. 21

Fig. 21. — Cyclocotyla charcoti. A, a specimen in which the cephalic lobe
is contracted ; B and C, sclerites of the suckers of the 3rd pair, right
and left respectively, seen in ventral view ; D, specimen having the
cephalic lobe well extended ; E, anterior end of D ; F, anterior end of
a specimen having a contracted cephalic lobe ; G, the egg. (After
Dollfus, 1922a and b.)

B, C, representing the supports of R. and L. suckers of the third pair.
Internal organs incompletely known, but hooklets on the penis number-
ing 6 and eggs measuring 0-354-0-375 x 0-062-0-076 mm., each having
a short filament at either pole (Fig. 21 G).

Genus DICLID0PH0R0PSIS Gallien, 1937.

Suckers of the opisthaptor pedunculate. Genital atrium not
muscular ; cirrus equipped with hooklets. Testes situated behind the
ovary. Vitellaria extending into the peduncles of the opisthaptor.
Vaginae present.

DICLIDOPHORIDiE

115

Diclidophoropsis tissieri Gallien, 1937. (Fig. 22 A-D.)

Host : Macrurus Icevis (=Malacocephalus Icevis).
Location : skin near the gills, but not on them.

Gallien (1937, p. 15, Figs. 2-4 ; PL 1, fig. 2) obtained about 20
specimens of this species on 13 hosts, some of which had 5 apiece, off
West Ireland. Size : 6-7 mm. long when fairly extended and 1 mm.

Fig. 22. — Diclidophoropsis tissieri. A, entire trematode ; B, diagram of
the genital organs ; C, a genital hooklet ; D, one of the suckers. (After
Gallien, 1937.) For numbering of the sclerites in D see the text on p. 1 16.

broad, but young individuals 3-5 mm. long and 0-7 mm. broad found
on the same host. Colour white with yellow margins, more translucent
centrally. Shape elongate and much flattened, gradually narrowing
anteriorly. Prohaptor a pair of oval buccal suckers of cup-shape
(dimensions 0-25 X 0-175 mm.) composed largely of muscular fibrils

116 THE TREMATODA OF BRITISH FISHES

set perpendicular to the surface. Opisthaptor a small cotylophore
bearing 4 pairs of pedunculate suckers radially arranged. Peduncles
long and narrow, extensile and variable (in some instances the suckers
are lost, all that remains after the accident being the severed peduncles) .
Each sucker circular in outline, slightly extended in the main axis of
the peduncle, about 0-75 mm. diameter and having a rigid skeletal
framework composed of 8 slender sclerites arranged in the form of a
cross with a circle around it, which serves to keep the sucker perma-
nently open. Details of the sclerites : continuing the longitudinal axis
of the peduncle are two arched sclerites, the basal (No. 1) being longer
than the distal (No. 2) and with forked extremities. From the distal
ends of piece 1 near the centre of the sucker, two sclerites (Nos. 3 and
4) extend towards the margin and, bending through an angle of 90°,
follow this to the proximal end of piece 1 . On each side of the distal
end of piece 2 two other sclerites (Nos. 5 and 6) extend along the
margin of the sucker through an arc of about 45°, and continuing to
the flexures of pieces 3 and 4, two more (Nos. 7 and 8). The 8 sclerites
are more slender than in some genera. At the base of the sucker
there is a muscular cup, into which are inserted extrinsic muscles
which extend along the peduncles and are lost (?) in the parenchyma
of the posterior part of the body. Gut : prepharynx and pharynx well
developed, oesophagus very short, intestinal crura widely divergent
and long, bearing numerous short and irregular diverticula, confluent
posteriorly in the cotylophore and sending an irregular branch into
each peduncle. Intestine lined with an epithelium. Excretory system :
pores slightly dorsal near the vaginal pores. Vesicles large and
elongate, situated near the anterior ends of the caeca. Lateral canals
continuing posteriorly to the level of the cotylophore. Nervous system:
brain well developed, situated above the anterior end of the pharynx,
giving off 2 anterior and 4 posterior nerve trunks. Of the latter
one pair is lateral, shorter and less developed, the other ventral,
joining in the cotylophore and sending a nerve into each peduncle.
Reproductive systems : genital pore close behind the oesophagus. Cirrus
muscular, fleshy, armed with 128 (± 5) simple hooklets 0-025 mm. long
and flexed into an obtuse angle. Testes numerous, filling the median
space between the caeca in the posterior half of the body proper. Vas
deferens long and slightly folded. Ovary folded in front of the testes
in the anterior half of the body. First part of the oviduct convoluted,
forming a receptaculum seminis uterinum, receiving the long, narrow
and straight median vagina and median vitelloduct near the hinder
border of the ovary. Ootype extending dorso-ventrally close behind
the ovary. Uterus wide and straight, situated ventrally. Vitellaria
well developed, the follicles being arranged about the caeca, merging
in the cotylophore and sending a cord into each peduncle. Transverse
vitelloducts immediately in front of the ovary ; geni to -intestinal canal
near its hinder end, joining the oviduct between the median vitelloduct
and vagina. Lateral vaginae extending transversely, their pores
slightly behind the level of the genital pore. Eggs not observed.

Some other genera of the Cyclocotylinae which occur outside

MICROCOTYLTDiE ] 1 7

Europe have been mentioned already. It remains to mention another
trematode of uncertain systematic position, Platycotyle gurnardi
Beneden & Hesse, 1863, which was found on the gills of the grey
gurnard near Brest and was only very inadequately described (see
Beneden & Hesse, 1864, pp. 108-9, PL 11, figs. 14, 15). It forms the
type of the genus Platycotyle Beneden & Hesse, 1863, which is charac-
terized by a rectangular opisthaptor bearing 4 widely separated suckers
set on peduncles and by the lack of terminal hooks (see also Pratt,
1900, pp. 656-7, fig. 27).

Family MICROCOTYLID^] Taschenberg, 1879.

Opisthaptor generally comprising numerous clamps (not less than
16 in the adult), each having 2 pairs of curved lateral half-hoops
which articulate either with a single median piece or with basal pieces,
the dorsalmost piece being spurred. Testes numerous. Ovary elongate
and folded, situated in the middle third of the body, in front of the
testes. Eggs having polar filaments.

Sub -family Microcotyun^: Monticelli, 1892.

(Axininse Nicoll, 1915, in part.)

With the characters of the family. Differences in the opisthaptor
serve to distinguish the genera. In Microcotyle the cotylophore is
almost symmetrical and bears numerous small clamps in a paired
series ; in two other genera it is asymmetrical, the clamps more
numerous on one side than on the other, which may lack them, its
terminal region being spatulate and bearing 2 pairs of hooks in
Pseudaxine, but of a different shape and without hooks in Axine.

Genus MICROCOTYLE Beneden & Hesse, 1863.

Cotylophore more or less set off from the rest of the body or forming
a kind of frill along its tapering posterior margins, generally symmetrical
but sometimes having more clamps on one side than on the other,
frequently with its anterior end projecting from and extending parallel
to the ventral surface of the body, occasionally set at an angle to the
main axis of the body. Clamp-like suckers very numerous, hooklets
absent. Genital atrium sometimes very complex, having an anterior
or several lateral, or paired posterior outgrowths, sometimes unarmed,
or having one type or several types of hooklets or spines. Vaginal
pore equipped with hooklets or not, sometimes associated with a pair
of dorsal sucker-like pits each with a tongue-like process which can
be protracted and retracted. In addition to the type-species, M.
donavini Beneden & Hesse, 1863, this genus contains nearly 70 species.
At least 16 species have been recorded in Europe, only 5 of them in
Britain, 22 in Japan, about 20 in North America, 6 in Australia, and
single species in Egypt, Java, the Philippines and the Galapagos
Archipelago. G. A. & W. G. MacCallum (1913, p. 223) reviewed

118 THE TREMA.TODA OF BRITISH FISHES

30 species, compiling scanty data about them from the works of Parona
& Perugia (1890-1), Goto (1894, 1899), Vogt (1878), Lorenz (1878),
and Ariola (1899). Many of the species they dealt with are very
imperfectly described, and it is very unlikely that all of them and some
species since erected are valid.

Microcotyle donavini Beneden & Hesse, 1863 (1864, p. 114, PL 12,
figs. 1-11).

Microcotyle canthari Beneden & Hesse, 1863 (1864, pp. 113-14) ; M. chryso-
phryii Beneden & Hesse, 1863 (1864, p. 148) ; M. erythrini Beneden &
Hesse, 1863 (1864, pp. 115-16) and probably others.

Hosts : comber, ballan wrasse.
Location : gills.

T. Scott (1905, pp. 116-17, PI. 6, fig(s). 21 (and 22)) obtained
specimens assigned to this species from the ballan wrasse in the Moray
Firth and from the same host in the North Sea. Scott merely stated
that the specimen figured was 5-3 mm. long and had about 34 pairs
of clamps, and he again represented it in 1912 (PL 27, fig. 4). The
trematode has also been found near Brest, at Roscoff, and by Sproston
at Plymouth. The original description of this species is very inadequate.
The main characters recorded were a relatively very large mouth
surrounded by a fleshy lip having a median incision, numerous genital
hooklets of flat and triangular shape, an oval cotylophore bearing an
unspecified number of clamps (24 pairs indicated in fig. 1), and fusiform
eggs of reddish colour each of which had a delicate pointed filament
about as long as the capsule at one pole, and a slightly longer and
stouter process shaped like a crozier at the other. Microcotyle canthari
was said to have 30-40 genital hooklets with curved points, the only
character in the original description which may be said to challenge
the relegation of the species to synonymy with M . donavini. The
same kind of genital hooklets was described for M. chrysophryii, and
this form was admitted to be similar to M. canthari, differing only in
the characters of the mouth and the buccal suckers, which hardly
merit the specific distinction. Microcotyle erythrini, also described
without a figure, is certainly identical with the type-species, having
similar genital hooklets and eggs. The first of these three forms was
found on the black sea bream in Italy, the second on the gilt-head in
Italy, and the third on the pandora near Brest and the bogue and
axillary bream in Italy.

Microcotyle labracis Beneden & Hesse, 1863.

Host : bass.
Location : gills.

T. Scott (1905, p. 117, PL 6, fig. 23— not 21 as stated in the heading)
assigned to this species specimens from an unstated locality which he
obtained from his son, basing his diagnosis on a general resemblance
to M. donavini, but twice as many clamps (the figure shows 68 on one

MICROCOTYLID^E 119

side and 67 on the other), and an oesophageal bulb of different structure.
A. Scott (1906, p. 49, PI. 10, fig. 3) mentioned under this name a
" large " form of unstated size (it must have been about 7-9 mm. long
and 1-3 mm. broad) from a bass caught in the Irish Sea. The most
that can be made out from the figure is that it had about 113 clamps
(55 on one side arid 58 on the other), the entire opisthaptor taking up
about one-third of the length of the body. According to the original
description (1864, p. 112, PI. 12, figs. 12-18) the genital hooklets
have triple points of unequal size, and the reddish eggs a simple filament
at one pole and at the other a peculiar process about as long as the
capsule, terminating in a large anchor-like structure perforated near
the middle. Specimens assigned to this species have been found
outside Britain at Brest, at Roscoff and in Italy.

Microcotyle centrodonti Brown, 1929. (Fig. 23 D, E.)

Host : common sea bream.
Location : gills.

This species was discovered on hosts in the Aquarium of the
Zoological Society, London, the hosts suffering asphyxiation as a
result of excessive mucus-production by the gills. In the same tank
with the fatally-infected fishes were specimens of the Mediterranean
sea bream, which showed an immunity to the trematode, which was
described in detail by Brown (1929, pp. 67-83, figs. 1-6). (My figures
were prepared from a specimen kindly presented to me by Miss Brown.)
Size : 2-5-4-5 mm. long. Shape elongate, tapering towards the
extremities, the anterior end truncated and the posterior acutely
pointed. Colour : translucent and off-white. Cuticle thin, but the
subcuticle thicker and faintly striated. Prohaptor a pair of transversely
ovoid buccal suckers. 0-06 mm. long. Opisthaptor : cotylophore
longer than the rest of the body, when fully extended twice as long,
its anterior end projecting some distance antero-laterally from the
point of origin, which is marked by a slight constriction, bearing 60
to 80 pairs of clamps (73 pairs commonly in large specimens) of oval
shape. Anterior clamps 0-08 mm. broad, those near the posterior
end only 0-03 mm. broad. Sclerites of the clamps 5 in number,
namely paired laterals in both the dorsal and the ventral valve, those
in one valve spurred near the hinge, and a U-shaped middle piece
with unequal parts about the hinge, the shorter broader than the
longer and relatively less expanded at its end. Gut : prepharynx
funnel-like ; pharynx small and spherical ; oesophagus of medium length ;
caeca terminating behind the testes near the cotylophore and having
numerous median and lateral diverticula, the former the smaller.
Reproductive systems : common genital pore near the bifurcation of
the gut at the anterior end of a genital atrium measuring 0-07 x 0-05
mm. Copulatory organ a conical fibrous papilla ; vas deferens slightly
convoluted ; testes numerous (14-23) and situated in the posterior
one -quarter of the body ; spermatozoa filiform. Ovary elongate and
coiled, situated just in front of the testes. Uterus wide and straight,

120

THE TREMATODA OF BRITISH FISHES

narrowing distally. Vitellaria lateral and slightly median to the caeca.
Vaginal pore mid-dorsal a short distance behind the level of the genital

Fig. 23. — A-C, Gastrocotyle trachuri : A, entire trematode ; B, one of the
clamps ; C, the terminal languette, showing the 3 pairs of hooks. D.
Microcotyle centrodonti ; E, one of the clamps. (Original.)

atrium ; vagina narrow and lacking hooklets. Eggs small, measuring
0-05 x 0-015 mm., each having a very long and much-convoluted

MICROCOTYLID/E 121

filament terminating in a point at one pole, and a much shorter filament
rather longer than the capsule and terminating in a knob having
8 curved points at the other. " Dorsal suckers ": two slightly lateral
sucker-like dorsal pits which form a pair, each with a protractile and
retractile central " tongue " having 12 simple spines at its free edge.
(Note. — It was suggested that these organs help to maintain adhesion
during copulation. They are situated antero -lateral to the vaginal
pore and occur also in M . alcedinis and M. canthari (?).)

Microcotyle draconis Briot, 1904 (pp. 126-7).

Host : greater weever.

Location : gills.

Nicoll (1914, p. 497, fig. 6) found two specimens of Microcotyle at
Plymouth and assigned them to this species, but did not describe
them, merely mentioning that they had seven " suckers " on each side.
The specimen figured was found on the same host at Aberdeen, and had
11 pairs of clamps and about 17 testes.

Microcotyle fusiformis Goto, 1894 (pp. 192-3, PL 2, fig. 3 ; PL 4, fig.
6 ; PL 5, fig. 1).

Host : butter-fish.
Location : gills.

Crofton (1940, pp. 318-19) recorded the occurrence of this species
on the host named at Culler coats.

Genus AXINE Abildgaard, 1794, nee Oken, 1835.

(Heter acanthus Diesing, 1836.)

Body externally and internally asymmetrical. Prohaptor a pair of
buccal suckers. Opisthaptor extending along one postero-lateral
margin of the body, and bearing numerous small clamps arranged
obliquely to the longitudinal axis of the body. Intestine bifurcate,
the caeca having long median and lateral diverticula. Genital pore
median near the origins of the caeca. Testes numerous and situated in
the posterior half of the body ; ovary curved and elongate farther
forward. Vagina unarmed and generally opening by a pore on the
left side of the body.

Axine belones Abildgaard, 1794 (6, pp. 59-60, PL 6, fig. 3a, b).

Axine triglce Beneden & Hesse, 1863 (1864, p. 117) ; Heteracanthus pedatus
Diesing, 1836 (pp. 310-13, PL 17, figs. 1, 2) ; Axine orphii Beneden & Hesse,
1863 (1864, pp. 116-17, PL 12, figs. 19-27).

Hosts : gar-fish ("A. triglce " on the yellow gurnard).
Location : gills.

Specimens of this species obtained from the gar-fish in the North
Sea were described so briefly by T. Scott (1912, pp. 69-70, PL 7, figs.

122 THE TREMATODA OF BRITTSH FTSHES

6, 7) that hardly any information, is available except the length of
8-10 mm., and the hatchet-like shape of a cotylophore bearing 52
clamps. Nicoll (1914, p. 496) found specimens on the same host at
Plymouth, but did not describe them. According to Beneden &
Hesse specimens of "A. orphii " 5 mm. long have numerous clamps
(42 shown in their fig. 19), the median sclerite being bifurcate at the
tip of the long arm, but trifurcate at the tip of the other, and the genital
hooklets total 26-7, but " trois groupes, places sur une ligne verticale,
allant en augmentant de nombre." Four groups are represented in
their fig. 20, a short anterior row of 10, a larger and curved posterior
row of 18, and two lateral rows with 11 and 12 respectively, similar
groups in fig. 21 indicating the corresponding numbers 10, 20, 11 and
13. The eggs were said to be " fusiformes, termines, a leur extremite,
par une tige mince et courte," but shown in fig. 27 with two long
polar filaments at least twice as long as the capsule. The same writers
(1864, p. 117) claimed that " Axine triglce" which was described
without a figure, differs from "A. orphii " mainly in the general shape,
colour and size, although the size is unspecified, as well as in the
disposition of the opisthaptor, which occurred on the left instead of
on the right. Lorenz, who gave a detailed description of this trematode
(1878, p. 3, Pis. 1, 2, figs. 1-18), was categorical about the identity
of "Axine orphii " with A. belones, and A. triglce is equally certainly
synonymous with this valid species. Size : 4-8 mm. long. Shape :
very elongate, tapering gradually from the opisthaptor to the anterior
extremity. Colour milky white, grey laterally. Opisthaptor : cotylo-
phore terminal, but obliquely set (the left margin being the more
anterior), bearing a single row of 50-70 small clamps. (Note. — Lorenz
showed Beneden & Hesse to be mistaken in regarding them as
suckers.) Median sclerite having unequal limbs, the shorter on the
left, marginal sclerites numbering 4 on each side (two in each valve
being of about equal length and adjacent on each side), supplemented
by a small " Spange " (probably a process of one of the lateral marginals
on each side. Left valve more " muscular " (fleshy ?) than the right.
Gut : pharynx ovoid, smaller than the buccal suckers and situated
slightly behind and between them. (Esophagus and caeca long, the
latter extending to the cotylophore and bearing numerous short
median and lateral diverticula along its entire length. Excretory
system : main lateral canals dorsal to the caeca and alongside the
oesophagus and uniting anteriorly ; terminal canals situated in the first
quarter of the body ; pores located on small porso-lateral papillae just in
front of the genital pore. Reproductive systems : genital pore median
and slightly anterior to the bifurcation of the gut ; genital atrium
muscular, its lining bearing two lateral groups of 12-20 hooklets
arranged in a double row and a ventral hemispherical elevation pro-
vided with a small circlet of 8-12 hooklets. Cirrus fusiform and
muscular, having a thick basal annulus bearing 16-24 hooklets ventrally
and laterally. Vas deferens long and convoluted ; seminal vesicle not
far from the base of the cirrus. Testes (described as a testis) numerous,
filling the space between the caeca and behind the ovary, i.e., the pos-

GASTROCOTYLTDyE 123

terior half of the body. Ovary J -shaped and situated on the left, the
long limb being continued as the oviduct, which receives the vitello-
ducts and vagina near the receptaculum seminis and then turns
posteriorly, to recur near the ootype, this organ being situated on the
recurrent (anteriorly- directed) limb. Uterus thick- walled, almost
median, opening into the genital atrium dorsal to the cirrus. Vagina
displaying three regions, the basal having thick, muscular walls to a
point near the junction with the oviduct, the middle capacious and the
terminal trumpet-shaped. Vaginal pore situated near the left lateral
margin of the body, but on the dorsal side slightly behind the level
of the seminal vesicle. Vitellaria restricted to the lateral regions,
extending from the level of the middle segment of the vagina to the
cotylophore near the caeca and their diverticula. Eggs each having
two polar filaments, the shorter sometimes represented by a knob-like
process, and occurring singly in utero.

Family GASTROCOTYLID.E Price, 1943.

(Microcotylidae Taschenberg, 1879, in part ; Axininae Nicoll, 1915, in part.)

Opisthaptor comprising numerous small clamps arranged in a
unilateral series along the margin of a very large and asymmetrical
cotylophore occupying the posterior two-thirds of the body. Clamps
having sclerites in general similar to those of Microcotylidse, but
stouter and including an additional pair of submarginal pieces in one
of the valves. Testes not numerous, occupying the posterior region.
Ovary elongate and folded, situated in front of the testes. Eggs each
having two pointed filaments.

Genus GASTROCOTYLE Beneden & Hesse, 1863.

In erecting this genus, Beneden & Hesse (1864, p. 117) specified
that the anterior half of the body is narrow, the posterior wide and
equipped with minute suckers arranged unilaterally along its entire
length. An additional character is the nature of the sclerites men-
tioned for the family.

Gastrocotyle trachuri Beneden & Hesse, 1863. (Fig. 23 A-C.)

See Beneden & Hesse, 1864, p. 96, pp. 117-18, PL 13, figs. 1-8.

Host : horse mackerel.
Location : gills.

Idris Jones (1933e, pp. 227-32, figs. 1-4) found at Plymouth and
described the only six specimens which have appeared in Britain,
although the trematode is known to occur near Brest and elsewhere in
the Eastern Atlantic, in the Mediterranean and in Japan. According
to the original description the genital pore is equipped with very small
and closely-set hooklets, the cotylophore is situated on the right side
of the expanded posterior region and bears 32-38 small clamps and 4

124 THE TREMATODA OF BRITISH FISHES

bifurcate hooks, those of the external pair the larger, and the fusiform
eggs have two rather straight filaments about as long as the capsule,
one at either pole. British specimens have the following characters : —
Size : 4-7 mm. long and 1-2 mm. broad posteriorly. Shape elongate,
the posterior two -thirds broad, the anterior one -third narrower and
tapering to a point. Prohaptor a pair of buccal suckers 0-023 mm.
long and 0-015 mm. broad. Opisthaptor : cotylophore situated along
the left side of the broad region of the body, bearing a single series of
32-40 small clamps 0-08 mm. diameter, as well as a stump-like process
with 3 pairs of dissimilar terminal hooks, those of the most lateral
pair much larger than the others. Gut : mouth terminal and very
small ; pharynx 0-046 mm. long, and 0-030 mm. broad ; oesophagus
well developed and about 0-2 mm. long, its walls provided with pouches ;
intestine bifurcate, the crura having numerous median and lateral
diverticula and anastomozing near the posterior extremity. Repro-
ductive systems : genital pore situated in the median ventral line
beneath the posterior part of the oesophagus, its lips bearing 12 long
and narrow hooklets, each having a bifurcate root and a straight
shaft, but a sharply- curved tip. Genital atrium muscular and 0-023
mm. diameter. Testes comprising a compact mass of lobules situated
in the most posterior region of the body. Ovary elongate and folded
into the shape of an inverted U, situated in front of the testes, but in
the posterior half of the broad region. Uterus wide and thin-walled,
extending along a straight course and opening into the base of the
genital atrium. Vitellaria very well developed, the follicles scattered
throughout the body between the hind end of the oesophagus and the
posterior extremity and extending into the cotylophore. Vaginal pore
situated in the middle dorsal line just behind the level of the genital
pore. Eggs not present. Note : E. I. Jones stated that the " arma-
ture " of the " suckers " is very different from that described by
Beneden & Hesse, but did not describe them. He kindly lent me
a specimen 3-2 mm. long and 0-8 mm. in greatest breadth, having 41
clamps, and I have tried to illustrate this. The sclerites could not be
made out perfectly and their arrangement defies ordinary powers of
description, but they are not arranged as he showed them and differ
in the two valves (Fig. 23 B).

Family DISCOCOTYLID.E Price, 1936.

Opisthaptor comprising 3 or 4 pairs of clamps, each typically having
2 pairs of separate marginal sclerites and a well-developed middle
segment bearing rows of lacunae extending on either side of a central
rib and sometimes segmented ; otherwise variously modified, some-
times having an additional pair of basal segments, in the extreme
forming by fusion two lateral segments and one median segment, all
of them U-shaped. Cotylophore sometimes terminating in a languet.
Lateral vagince present or absent.

The sub-families can be distinguished by the nature of the opis-
thaptor and the presence or absence of vaginae. In the Plectano-

DlSCOCOTYLIDiE 125

cotylinae there are 3 pairs of clamps and vaginae are absent ; in the
remaining three groups there are 4 pairs of clamps and vaginae are present.
In the Anthocotylinae the clamps of the most anterior pair are very
large, the others very small. In the Chimaericolinae and Discocotylinae
respectively the opisthaptor is either attached to the body by a narrow
stalk or not, and the posterior region of the body is narrow and trans-
versely striated in the former group, but neither narrow nor striated in
the latter. I have also given (Dawes, 1946, p. 74) some diagnostic
characters based on the nature of the sclerites.

Sub-family Discocotylinae Price, 1936.

Four European genera can be separated by the use of rather
unusual characters. In Diplozoon only the adults are united in pairs
in permanent copula ; in Vallisia the body is curiously asymmetrical,
having a lateral flexure. Other genera are more or less bilaterally
symmetrical and the components of the opisthaptor are strictly
symmetrical in Discocotyle, but show asymmetry in Grubea, which has
4 equal haptors on one side, but only 1 small haptor on the other.

Genus DISCOCOTYLE Diesing, 1850.
(Placoplectanum Diesing, 1858.)

Body elongate and truncated posteriorly. Prohaptor a pair of
buccal suckers. Opisthaptor comprising 4 pairs of clamps, which are
generally sessile and disposed along the lateral margins of a somewhat
rectangular cotylophore. Sclerites of the clamps uniformly developed,
consisting in each case of 2 pairs of lateral pieces which are dorsal
and ventral in position and which articulate with or approach the
extremities of a well-developed U-shaped median piece, the dorsal
lateral sclerites each having a spur. Genital pore equipped with
hooklets with one point. Lateral vaginae opening to the exterior in
the antero-lateral regions, and uniting in the anterior one-third of the
body to form a long median vaginal canal.

Discocotyle sagittata (Leuckart, 1842) Dies., 1850. (Fig. 24 A-F.)

Cyclocotyla lanceolata Zaringer, 1829 (p. 21) (name only) ; Octobothrium sagit-
tatum Leuckart, 1842 (pp. 49-57, PL 2, fig. 5a-k) ; Placoplectanum sagit-
tatum (Leuckart) Diesing, 1858 (p. 384) ; Mazocraes sagittatum (Leuckart)
Southwell & Kirshner, 1937 (pp. 431-3, fig. 3) ; Discocotyle salmonis
Shaffer, 1916 (p. 257).

Hosts : sea trout, salmon.
Location : gills.

Baylis (1928) recorded the occurrence of this trematode in the sea
trout at Jersey and (1939) in Yorkshire, Friend (1939) on the same host
in Scotland, finding it invariably on trout in Talla reservoir (Peebles-
shire) and elsewhere. I have specimens from the sea trout in Cam-
bridgeshire. Southwell & Kirshner (1937) found more than one

126

THE TREMATODA OF BRITISH FISHES

DISCOCOTYLID^E 127

hundred specimens on the pallid mucus -covered gills of a brown trout
which was found dead in a reservoir in North Wales, death of the host
being attributed to the parasites. The species also occurs on the
Continent and in U.S.A. Luhe (1909, p. 7, fig. 3) dealt with specimens
6-9 mm. long, Southwell & Kirshner with immature specimens
2 mm. long and 0-35 mm. broad, but also large and broad mature
specimens measuring 6 by 1 mm. Their description contains several
errors. The prepharynx was described as the oesophagus, the lateral
vaginae as the main excretory canals, and the median vagina as the
" common longitudinal trunk " of the excretory system. But these
specimens had about 40 testes and very large ovoid eggs measuring
0-250 x 0-130 mm.

My specimens differ in the degree of maturity attained and the
state of contraction of the body, older specimens seeming to have the
more characteristic shape, others being somewhat attenuated. Size :
6-5-7-0 mm. long and 1-3-2-2 mm. broad. Shape elongate and a fairly
uniform girth in the posterior region, or broadest in the middle and
tapering towards the extremities, the posterior end truncated, the
anterior constricted to a breadth of 0-3-0-5 mm. about 0-65 mm. behind
the extremity. Colour off-white. Prohaptor a pair of buccal suckers
0-13-0-16 mm. long and 0-10-0-12 mm. broad, diagonally arranged just
behind the anterior margin of the body (which is accidentally over-
turned in Fig. 24 B). Opisihaptor : cotylophore clearly differentiated,
sometimes having a shallow posterior notch, 0-8-0-9 mm. long and
1-1-1-3 mm. broad, but sometimes as broad as the body, or only half
as broad in the contracted state, generally two-fifths to three-fifths
as broad. Clamps diminishing slightly in size in a posterior
direction, those of the anterior pair measuring 0-33-0-38 x 0-23
mm., those of the most posterior 0-28-0-32 x 0-23 mm. Sclerites
as described for the genus and shown in Fig. 24 C ; hooklets as
described by Price (19436, p. 11) for " D. salmonis " absent. Gut :
prepharynx very short pharynx ; ovoid or spherical, measuring
about 0-76 x 0-62 mm. or 0-71 mm. diameter ; oesophagus fairly
long, extending back to the level of the genital pore. Intestinal
crura very long and wide, dividing the body approximately into
longitudinal one -thirds, particularly in young specimens, having
branched median and lateral diverticula which are more evident,
longer and more branched in older specimens, uniting to form a median
intestine at the base of the cotylophore and sending long diverticula
into its tissue. Reproductive systems : genital pore median, and about
0-5 mm. from the anterior extremity and 0-26 mm. behind the posterior
end of the pharynx. Testes numerous, numbering about 90, and
occupying the available space between the intestinal crura in the
posterior half of the body proper. Vas deferens and seminal vesicle
slightly convoluted. Ovary elongate and curved, or bunched into a
mass immediately in front of the testes and slightly lateral, but confined
within the bounds of the intestine. Vitellaria extensive, the follicles
mainly arranged lateral to the intestinal crura, but in older specimens
many median to them, extending throughout the body from the

128 THE TREMATODA OF BRITISH FISHES

anterior constriction to the base of the cotylophore. Uterus slightly
convoluted, and containing about 12 eggs of variable shape and
sizes measuring 0-310-0-335 x 0-131-0*135 mm., sometimes having
a nodular process at one pole, occasionally having incompletely-formed
shells. Vaginse opening to the exterior laterally at the level of the
anterior constriction and forming a median vagina just behind the
bifurcation of the gut. Note : one abortive egg was observed to be
0-122 mm. long and 0-080 mm. broad and to have a shell three times
the normal thickness, and also a small nodule of shell-forming substance
near one pole. Normal eggs contained in the uterus are undeveloped.
Price (loc. cit., p. 12) thought the validity of " D. salmonis " very
doubtful, but allowed the species to stand in the absence of a modern
description of D. sagittata. This American form comes within the
range of variability of the European species and, in spite of differences
like the size of the eggs and the presence of hooks, must be regarded
as a synonym of the type-species. Another form which is probably
identical with this species is D. sybillce (T. Scott, 1909), which was found
on the gills of the sea trout at Aberdeen, and the same may be true of
species which have been recorded in Australia and Japan.

Genus VALLISIA Perugia & Parona, 1890.

Body asymmetrical, flexed laterally. Cotylophore indistinctly
marked off from the rest of the body by a constriction and having
near its margins 4 pairs of sessile clamps with sclerites of Discocotylid
type, also 1 pair of hooks on a terminal process.

The only species, Vallisia striata Perugia & Perona, 1890 (p. 21,
PI. 1, figs. 8, 9 ; Pis. 2, figs. 10, 11) (Octocotyle arcuata Sonsino, 1890) is
a parasite on the gills of the horse mackerel in the Adriatic. According
to the original description it is 10-5 mm. long, the anterior part 6 mm.
and the posterior 4-5 mm., and 1-9 mm. broad, the anterior region
tapering to a blunt point bearing a circular mouth bordered by
pleated cuticular lips. The clamps are uniform in size, the major
axis 0-112 mm. long. Each egg has two polar filaments about as long
as the capsule, which measures 0-238 X 0-070 mm.

Genus GRUBEA Diesing, 1858.

Body symmetrical, but equipped with an asymmetrical cotylophore
having an ear-like lobe bearing 4 similar clamps on the right side
and 1 small clamp on the left, as well as 2 pairs of hooks in a
terminal position. Lips of the genital pore equipped with 2 rows
of 8 hooks, one row on the anterior margin and the other on the
posterior, and an additional bipartite hook of larger size in each of the
lateral angles.

The only species of this genus, G. cochlear Diesing, 1858 (6, p. 385)
(Octobothrium scombri Nordmann of Grube, 1855 ; Pleurocotyle scombri
of Pratt, 1900) was found on the gills of the mackerel and horse
mackerel at Naples.

DISCOCOTYLIM] 129

Genus DIPLOZOON Nordmann, 1832.

{Diporpa Dujardin, 1845 ; Diplozoum of Burmeister, 1835.)

Adults united in pairs in permanent copula. Opisthaptor : 4 pairs
of clamp-like suckers set close together along the postero-lateral
margins of a rectangular cotylophore. The larvae equipped with 1,
2, 3 and 4 pairs of clamps at progressively later stages of development.
Terminal part of the cotylophore equipped with 2 pairs of hooks,
those of one pair needle-like, those of the other recurved. Intestine
not bifurcate, but long and having numerous branched diverticula.
Genital pore situated in the posterior region of each member of the
copulating pair, encircled by a gonotyl (genital sucker), which fuses at
maturity with a dorsal papilla bearing the vaginal pore of the other
individual, corresponding change occurring in the inverse sense, so
that the male duct of each individual is contiguous with the female
duct of the other. Testis single, compact, situated close in front of
the opisthaptor. Ovary elongate and formed into a loop immediately
in front of the testis. Vitellaria comprising numerous follicles, and
tending to fill the anterior region of the body in front of the point of
union of the individuals. Uterus slightly folded, its pore situated
near the point of fusion of the genital pores. Eggs ovoid, operculate
and equipped with a long and much- coiled filament at the anopercular
pole. Parasites of freshwater fishes.

Diplozoon paradoxum Nordmann, 1832.

Diporpa dujardinii Diesing, 1850 (p. 420).

Hosts : various Cyprinidae and other fresh-water fishes, e.g. 3-spined
stickleback.

Location : gills.

This species is well known in widely separated parts of Europe
(Finland, Russia, Germany, France, Switzerland and Italy) and
occurs in British fresh-water, although nobody seems to have taken
the trouble to record its occurrence in Britain. The trematode is
familiar enough from accounts given in various text-books of zoology
(Gamble, 1896, pp. 59-61, figs. 27, 28 ; Benham, 1901, pp. 55, 57,
fig. 4, 1-8) and is figured elsewhere (Braun, 1889-93, PI. 13, figs. 1-5) .
According to the original description the length is 3-5 " lines,"
according to Luhe (1909, p. 7, fig. 4) 4-11 mm. Both Benham and
Gamble reproduced figures of the egg, larva, young individuals and
adults after Zeller, whose works (1872 ; 1888) are still authoritative.
Beneden (1858, pp. 39-44, PI. 4, figs. 1-12) gave a fairly comprehensive
account of the anatomy of specimens found on the bream, which
was the first-known host, and references to the earlier literature. I
have a single specimen comprising two individuals in copula and have
provided figures in another place (Dawes, 1946, fig. 21 A, B, a, b).
Size : anterior region (in front of the point of fusion) 2-64 mm. long,
region of fusion about 0-6 mm. long, posterior region 2-22 mm. long

9

130 THE TREMATODA OF BRITISH FISHES

and about half as broad. Prohaptor a pair of buccal suckers situated
very close to the pointed anterior extremity, their anterior borders
about 003 mm. behind it, mean dimensions 0-132 x 0-116 mm.
Opisthaptor : cotylophore about 0-4 mm. long and 0-7 mm. broad,
separated from the rest of the body by a slight constriction, the
breadth of the body here being about 0-5 mm. Clamps transversely
elongate, diminishing in size in a posterior direction, the most anterior
measuring 0-19 X 0-10 mm., the most posterior 0-13 X 008 mm.
Sclerites of Discocotylid pattern, arranged as shown in fig. 21 b (Dawes,
loc. cit.). Gut : pharynx longitudinally ovoid, smaller than and
very close to the buccal suckers, measuring 0-09 x 0-07 mm. Repro-
ductive systems : anterior region of the body filled with coarse vitelline
follicles almost to the level of the pharynx. Eggs few (3 in utero),
very large, but of variable sizes (0-37 x 0-12 mm., 0-33 x 0-10 mm.
and 0-29 x 0-12 mm.), each having a very long filament formed into
a compact spiral at one pole.

The Japanese species D. nipponicum Goto, 1891 (pp. 151-92,
Pis. 21, 22, figs. 1-25 ; PI. 23, figs. 1-20) is said to be common on the
gills of the crucian carp and to differ from D. paradoxum in the small-
ness of the clamps, the greater length of the posterior region of the
body, the shortness of a connecting canal between the intestine and
the oviduct, the presence of a pair of " sticky glands " near the mouth
and the absence of diverticula of the intestine in the posterior region
of the body, but it is probably identical with the type species.

Sub-family Anthocotylike Price, 1936.

Genus ANTH0C0TYLE Beneden & Hesse, 1863.

Body elongate, tapering from the middle towards the extremities,
broadening immediately in front of the opisthaptor. Prohaptor a
pair of small buccal suckers. Opisthaptor comprising 4 pairs of
clamp-like suckers, the most anterior pair sessile and enormously
developed, the remaining 3 pairs minute and pedunculate, and a
minute terminal languette armed with 2 pairs of hooks, those of the
external pair the larger. Sclerites of large and small clamps alike
constructed on the characteristic Discocotylid plan. Cirrus equipped
with 40 hooklets having simple points. Lateral vaginae opening to
the exterior ventrally near the lateral margins of the body, slightly
behind the level of the genital pore and continuous with the main
lateral vitelloducts. Eggs having a short filament about as long as
the capsule at each pole.

Anthocotyle merluccii Beneden & Hesse, 1863. (Fig. 25 A-F.)

Anthocotyle merlucii americanus MacCallum, 1916 (pp. 25-7, figs. 10, 10 A) ;
A. americanus Price, 1943.

Hosts : hake, coal -fish.
Location : gills.

DISCOCOTYLIDiE

131

T. Scott (1901, p. 148, PL 8, fig. 24) obtained a few specimens of
this widely distributed species on hake landed at the fish market,
Aberdeen, and in the brief description gave the length as about
16 mm., but probably less in the living state. The trematode was
found on the same host from the Irish Atlantic Slope by Rees &
Llewellyn, and it probably occurs right round our coast, as well as
near Brest, in the Mediterranean, and in Canada and U.S.A. The

oo

Fig. 25. — Anthocotyle merluccii. A, entire trematode (reproductive systems
omitted) ; B, posterior end, showing the mode of attachment to a gill-
lamella of the host ; C, one of the small clamps and its peduncle, show-
ing the sclerites, which are fundamentally similar to those of the large
clamps ; D, the terminal languette, showing the two pairs of dissimilar
hooks ; E, the egg ; F, diagram of the organs in the anterior region.
(After Cerfontaine, 1895.)

original description (1864, p. 105, figs. 8-12) is very general, but a
detailed account of structure was given by Cerfontaine (1895a, p. 511,
figs. 1-9), who found specimens attached to the inner lamellae of the
gills. Size : 10-15 mm. long. Shape : body tapering to an obtuse
point anteriorly, broadening progressively towards the middle,
narrowing in the posterior half, but broadening again to maximum
breadth in front of the opisthaptor. Opisthaptor : large clamps
having dorsal and ventral valves, hinged anteriorly and opening

132 THE TREMATODA OF BRITISH FISHES

posteriorly by a wide slit bordered by a somewhat pleated membrane.
Sclerites arranged as a pair of lateral pieces in the dorsal and another
pair of similar pieces in the ventral valve, as well as a large median
piece of U- shape which is flexed at the hinge of the clamp and extends
into both valves. Lateral sclerites of the ventral valve also extending
over the hinged region and for a short distance into the dorsal valve.
Numerous delicate rod-like sclerites also line the cavity of the clamp.
Small clamps each borne on a short peduncle containing bundles
of muscle fibrils, the sclerites fundamentally similar to those of the
large clamps. The 2 pairs of hooks borne on the terminal languette,
which is itself about as large as a small clamp, together with its
peduncle, dissimilar and unequal in size, those of the outer pair the
larger and more strongly curved and having median and lateral
roots, of which the former is the larger (according to Price a third
pair of hooks was possibly overlooked by Cerfontaine) . Gut : mouth
terminal, transversely oval, pharynx small (little larger than one of
the buccal suckers), oesophagus short, intestine bifurcate, the crura
uniting between the large clamps of the opisthaptor and sending
several simple diverticula into the cotylophore. Intestinal crura
having a few short median and more as well as larger lateral diverticula
which branch only slightly. Excretory system : pores dorsal near the
lateral margins of the body at the level of the genital pore. Nervous
system : brain situated at the level of the posterior end of the pharynx,
giving off 2 pairs of anterior and 2 pairs of posterior nerves, the more
median posterior nerves being prominent, following the course of the
intestine, and uniting at the base of the languette, which receives 2
small nerves. Paired nerves serve the smaller clamps, and a trans-
verse commissure connects the main nerve trunks between the larger.
Reproductive systems : genital pore median immediately behind the
bifurcation of the intestine. Testes numerous, situated in the
posterior half of the body proper and confined between the intestinal
crura. Vas deferens median, but sinuous cirrus equipped with 40
hooklets having simple points. Ovary fl -shaped and having folded
limbs, situated in front of the testes in the second quarter of the
body, its blind end in the median plane near the origin of the vas
deferens and the oviduct. Uterus comparatively straight. Vitellaria
well developed, extending laterally along the course of the intestine
between the levels of the vaginal pores and the posterior end of the
testes. Vaginal pores ventro- lateral, vaginae continuous with the
main lateral vitelloducts, provided with 2 anastomoses immediately
in front of the ovary. Eggs clear yellow in colour, each having a
polar filament about as long as the capsule at each pole.

In making the sub-species of MacCallum a species, A. americanus,
Price (19436, p. 14, fig. 1, i-m) admitted that it might be identical
with A. merluccii, but drew attention to the disparity in size between
the large clamps on the two sides of the body. This difference
between American and European specimens is seen to be an un-
reliable criterion of distinction, when it is considered that in the
specimens found at Woods Hole and described by Linton (1940,

DISCO COTYLIDiE 133

p. 14, PI. 16, figs. 200, 201) the asymmetry is the opposite of that
noted by Price, the left anterior clamp being larger than the right, as
in European specimens. Assuming that Cerfontaine overlooked the
small intermediate hooks (which are 02 mm. long according to
Price), there is no significant difference between American and
European forms.

Sub -family Plectanocotylin^e Monticelli, 1903.
Genus PLECTAN0C0TYLE Diesing, 1850.

(Plectanophorus Diesing, 1858 ; Phyllocotyle Beneden & Hesse, 1863 ;
Plectanocotyle Monticelli, 1888 (in the Octocotylidse)).

Body elongate, very extensile, tapering towards the extremities,
but broadening near the opisthaptor. Prohaptor a pair of buccal
suckers. Opisthaptor a rather narrow cotylophore bearing 3 pairs
of suckers and an extensile terminal languette, which may assume
a discoidal shape terminally and on which there are 3 pairs of dis-
similar hooks. Copulatory organ equipped with a number of delicate
cuticular rods, as many as 5 on each side. Testes numerous, occupying
the posterior half of the body. Ovary very elongate and flexed in
front of the testes. Vaginae absent. Type-species P. elliptica
Diesing, 1850, recorded in Europe, but found by Kollar, a friend of
Diesing, on the gills of " Labrax mucronatus " in America and very
ill- defined.

Plectanocotyle gurnardi (Beneden & Hesse, 1863) Pees & Llewellyn,
1941.

Phyllocotyle gurnardi Beneden & Hesse, 1863 (1864, pp. 103-4, PI. 10, figs.
1-7) ; Plectanocotyle lorenzii Monticelli, 1899 (6, pp. 1045-53, figs. 1-12) ;
Plectanocotyle caudata Lebour, 1908 (a, pp. 42-3, PI. 5, figs. 4-7).

Hosts : yellow gurnard, red gurnard, grey gurnard, streaked
gurnard.

Location : gills.

There are several records of the occurrence of this species round
our coasts. T. Scott (1901, pp. 147-8, PI. 8, fig. 23) briefly described
specimens about 2 mm. long and 0-6 mm. broad found on the grey
gurnard taken off the Scottish coast (locality not specified) and (1905,
p. 116) referred them to the " species " P. lorenzii, also (1905, pp.
115-16, PL 6, figs. 19, 20) recording the occurrence of P. gurnardi on
the grey gurnard in the Moray Firth. A. Scott (1904) found specimens
on the yellow gurnard caught in the Irish Sea; Lebour (1908a, pp.
42-3, PI. 5, figs. 4-7) described (as P. caudata) specimens found on
the grey gurnard at Cullercoats ; Nicoll (1915) reported specimens on
the red gurnard at Plymouth ; Little (1929a) specimens on the grey
gurnard and the yellow gurnard at Galway ; and Rees & Llewellyn
(1941) on the grey gurnard and red gurnard on the Irish Atlantic
Slope. The trematode also occurs near Brest, off the coast of Belgium
and in the Mediterranean. The original description concerned

134 THE TREMATODA OF BRITISH FISHES

specimens 10 mm. long and of elongate form, tapering towards the
anterior extremity and decidedly flattened. The main haptors were
described as 3 pairs of sessile suckers of medium size disposed in 2
parallel lines and a " languet " equipped with a sucker-like cupule
bearing 2 pairs of hooks, those of the lateral pair much the larger.
The eggs of the specimens concerned were oval and had a fairly long
filament at one pole, and the margin of the genital pore was equipped
with 5 pairs of hooklets, 2 short ones terminating in a minute globule.
Lebour's specimens were referred to a new species, although closely
resembling the forms described by Beneden & Hesse and Monticelli,
being thought to differ in the short peduncles on which the " suckers "
were borne. But Lebour showed shrewd powers of judgment in
suggesting that all three forms represent the same species in various
stages of contraction. Llewellyn (19416, pp. 431-2, fig. 1) concurred,
actually finding specimens contracted to intermediate degree as
compared with the specimens of Monticelli and of Lebour, and also
showed that the erection of the genus Phyllocotyle was quite un-
necessary. He rightly relegated P. lorenzii and P. caudata to
synonymy with P. gurnardi, and made a contribution to our know-
ledge of the terminal process and its 3 pairs of hooklets. Size :
4-1 mm. long and about 0-8 mm. in greatest breadth at the middle
of the body. Shape elongate, tapering towards the extremities, but
broadening slightly near the base of the opisthaptor. Prohaptor a
pair of small buccal suckers. Opisthaptor : cotylophore shield-
shaped and about 1 mm. broad and long, terminating in a small
process (languet) about 0-7 mm. long which is sometimes enlarged at
its tip to form a cupule 0-2 mm. diameter which bears 3 pairs of
hooklets, otherwise borne on a short appendage of uniform girth.
Hooklets of the outermost pair much the largest and having 2 roots,
hooklets of the most median pair about half as long and having 2 roots
or not, hooklets of the pair intermediate in position between the
lateral and median hooklets minute (and overlooked by Beneden &
Hesse, and by Monticelli). Clamps forming 3 pairs and set on short
peduncles which may be inconspicuous. Sclerites not described, but
probably of typical Discocotylid type. Gut : mouth circular and
terminal, prepharynx short, pharynx small, oesophagus very short
intestine bifurcate, its crura largely hidden by vitelline follicles, but
probably uniting posteriorly. Reproductive systems : genital pore
(pores ?) just behind the termination of the oesophagus, genital hook-
lets numbering 5 on either side, the 2 central ones much shorter
than the others and terminating each in a small knob (as Beneden
& Hesse indicated, but, as Lebour stressed, not conforming to
their figures), cirrus cuticular. Testes numerous and situated in the
posterior region, extending from the middle of the body to a level
about 0-6 mm. from the anterior end of the opisthaptor. Ovary
elongate and folded so that one limb crosses the other, situated just
in front of the middle of the body. Vitellaria well developed in the
lateral regions along the entire length of the body behind the genital
pore, the follicles not entering the tissue of the opisthaptor. Uterus

discocotyud^ 135

narrow, its terminal part sometimes dilated and filled with eggs of
pale yellow colour 0-065 mm. long, each having a single polar filament
about as long as or slightly longer than the capsule.

Sub -family Chim^ricolinje Dawes, 1946.

(Chimcericolidce Brinkmann, 1942.)

Opisthaptor comprising 3 pairs of clamps, each clamp having
1 pair of lateral sclerites and 1 middle sclerite, all three being horse-
shoe-shaped. Vaginae absent.

Genus CHI1VLERIC0LA Brinkmann, 1942.

(Octobothrium Leuckart, 1827, in part ; Discocotyle Diesing, 1850, in
part ; Placoplectanum Diesing, 1858, in part ; Octocotyle Diesing, 1850,

in part.)

Chimaericola leptogaster (Leuckart, 1830) Brinkmann, 1942.

(Fig. 26 A-G.)

Octobothrium leptogaster Leuckart, 1830 (p. 612) ; Discocotyle leptogaster
(Leuckart) Diesing, 1850 (p. 424) ; Placoplectanum leptogaster (Leuckart)
Diesing, 1858 (p. 384) ; Octocotyle (Octobothrium) leptogaster (Leuckart)
Parona & Perugia, 1890 (p. 6) ; Neoheterobothrium leptogaster (Leuckart)
Price, 1943 (a, p. 51).

Host : rabbit-fish.
Location : gills.

T. Scott (1910, p. 69, PI. 7, figs. 2-5 ; 1912, p. 350, PL 27, fig. 5)
described a specimen of this species taken from a rabbit-fish from
the North Sea, remarking that the species is " apparently not rare,"
but the only other British record is that of Rees & Llewellyn (1941),
who found the trematode on hosts taken off the Irish Atlantic Slope.
Scott's description is very brief and concerns a specimen 39 mm. long,
in which the body seems to have been little more than one -third, the
opisthaptor less than one -tenth, and its transversely- striated peduncle
nearly three -fifths of the total length. Brinkmann (1942, p. 3, figs.
1-11) described in great detail even larger specimens found on the
same host in Norwegian and Swedish waters, and reviewed the
dimensions of this trematode specified by several of the earlier writers.
Size : up to 50 mm. long, about 10-12-5 mm. in greatest breadth and
about 4-5 mm. in greatest thickness. Shape : main part of the body
proper elliptical and tapering to a uniformly narrow posterior " stalk,"
which is very extensile and contractile, being sometimes twice as
long as the body proper, but more often only two-thirds as long, and
sometimes deformed. Cuticle : wrinkled or folded so as to simulate
segmentation in the " stalk." Prohaptor absent. Opisthaptor :
cotylophore distinctly marked off and bearing 4 pairs of bowl-like
muscular clamps having short peduncles, each clamp having 3 sclerites
of horse -shoe -shape, two of them forming a lateral pair, the third a
middle piece. Lateral sclerites each having a row of minute cavities

136

THE TREMATODA OF BRITISH FISHES

-0-3

Fig. 26. — Chimcericola leptogaster. A, the entire trematode showing the
reproductive systems ; B, the anterior region, showing the zone of the
vitellaria (line shading) and the extensions anteriorly and underlying
the testes posteriorly ; C, diagram of the digestive system ; D, the
opisthaptor, showing the extrinsic muscles of the clamps and the
peduncles of the latter ; E, a clamp of the right side as seen in anterior
view, showing the sclerites ; F, a clamp of the left side as seen in ventral
view, showing the sclerites from a different aspect ; G, diagram of the
reproductive systems, represented as viewed from the ventral side, and
spread out transversely and longitudinally the better to show compo-
nent organs. Note the ascending and descending limbs of the uterus
(ut), the coiled oviduct (ov) and the anterior transverse vitelloduct (avk).
(After Brinkmann, 19426.)

DISCOCOTYLID^ 137

simulating denticles. Hooklets forming 2 pairs, those of one pair
minute (about 0-06 mm. long), those of the other somewhat larger
(see Ruskowsky, 1934, p. 486 ; not evident in Brinkmann's specimens
or figured in Scott's). Gut : mouth longitudinally oval. Prepharynx
having a dorsal and 2 lateral pouches with folded walls. Pharynx
globular and 0-16 mm. diameter, its wall muscular in the anterior and
glandular in the posterior half. (Esophagus short. Intestine forming
a large median sac extending back to a level just behind the vaginal
pores, and here bifurcating to form long caeca which become narrower
in the " stalk " and extend far into the cotylophore, where they
terminate in 2 irregular pouches. Median intestine and caeca in
front of the " stalk " having lateral diverticula which may branch
once or twice ; intestinal epithelium in the region of the " stalk ' :
folded to an extent which depends on the degree of contraction of the
whole worm. Glands : numerous unicellular glands situated around
the excretory vesicles and the most anterior intestinal diverticula
opening into the oesophagus. Excretory system : vesicles situated
one on either side of the body near the foremost diverticula, the
terminal canals short, the pores lateral at the level of the pharynx,
the main canals ventro- lateral to the caeca. Reproductive systems :
common genital pore median and near the oesophagus in the anterior
one-third of the body proper. Cirrus equipped with numerous
hooklets 0-018 mm. long, consisting of a slender straight or slightly
curved shaft and a base about twice as stout. Prostate glands well
developed, vas deferens extending along a straight course between
the uterus and the median intestine, widening anteriorly, to form a
seminal vesicle. Testes numerous and situated in the posterior half
of the broad anterior region. Ovary lobed and situated in front of
the testes in the middle one-third of the body proper. Oviduct
slightly convoluted and curving round the main vitelloducts and the
genito-intestinal canal, which opens into the left caecum. Ootype
globular and median, uterus very long and formed into several
descending and ascending limbs (seven all told) between the ootype
and the genital pore, metraterm dilated. Vitellaria extending
throughout the lateral regions as far back as the base of the " stalk,"
from which follicles are excluded. Main lateral masses of follicles
connected by a bridge formed by others above the anterior half of the
uterine region and having medio -lateral extensions underlying the
testes (Fig. 26 B). Vaginal pores situated in the anterior one-third
of the body proper, terminal parts of the vaginal canals having much-
folded walls and forming a hemispherical complex including uni-
cellular glands ; lower parts of the vaginal canals continuous with
the main lateral vitelloducts, each having a dilatation. Eggs lemon-
shaped and measuring 0-185 x 0-103 mm. (0-2 x 009 mm. according
to Parona & Perugia, 1892), operculate at the blunter end, some-
times having one polar filament which may be much longer than
the capsule (see T. Scott, 1910, PI. 7, fig. 5). Notes : Brinkmann
figured what seems to be a subsidiary transverse vitelloduct situated
just behind the level of the vaginal pores and opening into the vaginal

138 THE TREMATODA OF BRITISH FISHES

canals near its extremities. There is a description of this trematode
by Ruskowski (1934, p. 486, fig. 2).

Family MAZOCRAEIME Price, 1936.

(Octobothriidae Taschenberg, 1879 ; Octocotylidse Beneden & Hesse,
1863 ; Mazocriidae Southwell & Kirshner, 1937 — in part, in each case.)

Opisthaptor generally comprising 4 pairs of clamp-like suckers
equally spaced out along the lateral regions of an indistinct cotylophore
or of the postero-ventral regions of the body. Cuticular supports of
the clamps relatively simple, each clamp having single dorsal and
ventral hoops with forked tips which articulate with a straight basal
piece, sometimes having a rudimentary piece attached to it. Tip
of the cotylophore invariably provided with 2-3 pairs of dissimilar
hooklets. Testes generally numerous, but sometimes only a single
elongate and lobed testis is present, occupying the space between the
caeca in the posterior region of the body. Ovary elongate and folded,
situated near the anterior end of the testis or testes. Vitellaria
lateral and follicular. Vagina, when present, opening by a median
dorsal pore. Of 3 genera which must be considered, Ophicotyle has
a cotylophore bearing 2 pairs of small sucker-like organs in addition
to the usual complement of clamps, which are the only components
of the haptor in other genera ; Mazocraes has genital hooklets arranged
in two transverse rows and dorsal vaginae are present ; Kuhnia has
genital hooklets arranged in 2 longitudinal rows and dorsal vaginae are
absent.

Genus MAZOCRAES Hermann, 1782.

{Octobothrium Leuckart, 1827, in part ; Octostoma Kuhn, 1829 ; Octo-
cotyle Diesing, 1850 ; Octoplectanum Diesing, 1858 ; Octobothrium
{Octocotyle) of St. Remy, 1891 ; Glossocotyle Beneden & Hesse, 1863.)

Opisthaptor comprising an almost triangular cotylophore bearing
4 pairs of clamps and 2 pairs of dissimilar hooklets, those of the outer
pair the larger. Genital pore transversely elongate and equipped
with 12 bipartite hooklets, 5 along each Up and 1 in each of the lateral
angles (Fig. 27 F-H). Vaginal pore median and dorsal. Eggs
generally having 2 polar filaments.

Mazocraes alosae Hermann, 1782 (p. 182, PL 4, figs. 13, 14.)

Octobothrium lanceolatum Leuckart, 1828, of authors ; Octostoma alosce (Her-
mann) Kuhn, 1829 (pp. 358-61, PI. 17, figs. 1-3) ; Octocotyle lanceolata
(Leuckart) Diesing, 1850 (p. 422) ; Octoplectanum lanceolatum (Leuckart)
Diesing, 1858 (p. 383) ; Glossocotyle alosce Beneden & Hesse, 1863 (1864,
pp. 102-3, PI. 9, figs. 11-18) ; Octobothrium alosce (Hermann) Cerfontaine,
1896 (p. 516).

Hosts : allis shad, twaite shad.
Location : gills.

T. Scott (1901, p. 145, PL 8, fig. 21) gave a very meagre account
of specimens of this species found on both hosts in Scotland (locality

MAZOCR A^IDJE 139

unspecified), barely mentioning the shape, the buccal suckers and
clamps and the hooks, one pair larger than the other, not even
mentioning the genital hooklets. To judge by the figure and the
stated magnification, the specimen must have been rather more than
6 mm. long. No eggs were seen. A. Scott (1906, p. 193, PL 9, fig. 1)
found numerous specimens on the gills of a shad sent from Carnarvon
to Liverpool, but neither gave the diagnostic characters nor stated
the size, although the specimen figures must have been about 7 mm.
long and 1*3 mm. in greatest breadth, the ill-defined cotylophore
taking up about 015 of the total length. Bay lis & Idris Jones
(1933) recorded the occurrence of the trematode in the twaite shad
at Plymouth, and it has been found near Brest, off the coast of
Belgium and in the Rhine. Dujardin (1845, p. 313, PL 8, fig. F (12))
gave the diagnostic characters, and Beneden (1858, pp. 45-9, PL 5,
figs. 1-18) described specimens of corresponding size and gave fairly
good figures. Size : 10-12 mm. long and 1-4-1-5 mm. broad. Shape
elongate, very slender anteriorly. Colour reddish-grey. Prohaptor a
pair of minute buccal suckers. Opisthaptor : cotylophore ill-defined
and rhomboidal, the 4 pairs of clamps arranged in 2 oblique rows
laterally on extensile and retractile peduncles ; hooklets more or less
terminal, those of the lateral pair larger than those of the median.
Reproductive systems : genital hooklets arranged in 2 transverse rows
of 5 plus 2 somewhat larger ones forming a pair laterally in an inter-
mediate position. Eggs yellow, very large and almost fusiform
measuring about 0-26 x 085 mm., according to Beneden having
two polar filaments about as long as the capsule. According to
Beneden & Hesse (1864, but see my note under Ophicotyle fintce
on pp. 140-1) the hooks of the opisthaptor are strongly recurved, and
the presence of moderately long polar filaments on the eggs was
confirmed.

Mazocraes harengi (Beneden & Hesse, 1863) Baylis & Idris Jones, 1933.

Octocotyle harengi Beneden & Hesse, 1863 (1864, pp. 98-9, PL 9, figs. 1-10) ;
Octobothrium harengi (Beneden & Hesse) Taschenberg, 1879 (a, p. 244) ;
Octoplectanum harengi (Beneden & Hesse) of Linstow, 1889 (p. 95) and of
Nicoll, 1915 (p. 369).

Hosts : herring, allis shad.
Location : gills.

T. Scott (1901, pp. 145-6) mentioned two damaged specimens
of this species which were found on a herring sent from Annan
in the Solway Firth. Baylis & Idris Jones (1933) recorded the
occurrence of the trematode on the allis shad at Plymouth, and
it occurs also near Brest. Size : about 10 mm. long. Shape
slender and lanceolate, tapering gradually anteriorly and more
sharply posteriorly. Prohaptor a pair of buccal suckers of
moderate size. Opisthaptor : cotylophore bearing 4 pairs of clamps
and an ovoid posterior prolongation carrying 2 pairs of hooks, those
of the outer pair much the larger and having a broad base which

140 THE TREMATODA OF BRITISH FISHES

narrows abruptly below and a slender point. Gut : mouth having a
wrinkled (" denticulate ") border ; intestine bifurcate, but without
apparent lateral diverticula, extending back as far as the clamps of
the most posterior pair, which project slightly from the margins of
the cotylophore. Eggs rather narrow, and having 2 delicate polar
filaments slightly longer than the capsule.

Mazocraes pilchardi (Beneden & Hesse, 1863).

Octocotyle pilchardi Beneden & Hesse, 1863 (1864, p. 99, PI. 9, figs. 29-35);
Octobothrium pilchardi (Beneden & Hesse) Taschenberg, 1879 (a, p. 244) ;
Octoplectanwm pilchardi (Beneden & Hesse) of Linstow, 1889 (p. 95) and
of Nicoll, 1915 (p. 369).

Host : pilchard.
Location : gills.

This species was discovered near Brest, but has not been found
in Britain. According to the original description it is similar to
M . harengi, but smaller, and has clamps which become progressively
smaller posteriorly and are set on short peduncles. The eggs were
said to be rust- coloured, ovoid and equipped with a long filament
terminating in a small plate-like swelling at one pole and a stump-like
process at the other.

Mazocraes heterocotyle (Beneden, 1870) sp. inq.

Octostoma heterocotyle Beneden, 1870 (p. 67) ; Octoplectanum heterocotyle
(Beneden) of Linstow, 1885 (pp. 252-3, PL 15, fig. 30), and of Nicoll, 1915
(p. 369) ; Octobothrium heterocotyle (Beneden) Taschenberg, 1879 (a, p. 245).

Host : sprat.
Location : gills.

This species was found on the coast of Belgium, but unrecorded
in Britain.

Genus inq. OPHICOTYLE Beneden & Hesse, 1863.

{Octobothrium of Taschenberg, 1879, and Saint-Remy, 1891.)

Body lanceolate and broadest in the posterior half, tapering
gradually anteriorly and more abruptly posteriorly. Cotylophore
oval and having 4 pairs of clamps, and a posterior prolongation
bearing 2 pairs of minute accessory suckers and 2 pairs of hooks,
those of the lateral pair larger than the others.

Ophicotyle fintae Beneden & Hesse, 1863.

Octobothrium fintas (Beneden & Hesse) Taschenberg, 1879 (a, p. 244).

Host : twaite shad.
Location : gills.

Under the name of this trematode, which was found near Brest,
Beneden & Hesse (1864, p. 101) described a form which answers to

MAZOCRAEID^ 141

the generic description, not of Ophicotyle, but of Glossocotyle. The
reason seems to be the inadvertent interchange in the text of the
descriptions for Ophicotyle fintce and Glossocotyle alosce. The descrip-
tive terms used are of a general character, but there is no possibility
of confounding the two types of opisthaptor. If we assume, however,
that the specific headings and the references to the figures of PI. 9
(in the text, but not on p. 134) are correctly set out, there remains a
difficulty even when the descriptions are interchanged, because the
absolute sizes indicated in the plate do not conform with the re-
arranged diagnoses. We must therefore accept the sizes of the two
worms as originally specified. 0. fintce is about 3 mm. long and,
apart from the opisthaptor, very similar to Mazocraes alosce, particu-
larly in the arrangement of the genital hooklets.

Genus KUHNIA Sproston, 1945.

(Octostoma Kuhn, 1829, in part, nee Otto, 1823 ; Octobothrium of

Leuckart, 1842, in part ; Octocotyle Diesing, 1850, nee Goto, 1894, in

part ; Oetoplectanum Diesing, 1858, in part.)

Cotylophore of the opisthaptor bearing 4 pairs of almost sessile
clamps arranged in 2 lateral rows and at least 2 pairs of hooks, the
inner small and the outer larger and with a ridged shaft and 2 roots.
Genital hooklets arranged along the lips of a longitudinal slit-like
genital pore, those of one pair occupying the anterior and posterior
angles. Vagina absent. Other characters as in Mazocraes. Para-
sites on the gills of Scombridse.

Kuhnia scombri (Kuhn, 1829) Sproston, 1945. (Fig. 27 A-E.)

Octostoma scombri Kuhn, 1829 (pp. 361-2, PI. 17, figs. 4-5) ; Octobothrium
scombri (Kuhn) of Nordmann, 1832 (pp. 77-8) and authors ; Octocotyle
scombri of Dujardin, 1845 ; O. truncata Diesing, 1850 (p. 422) ; Oetoplec-
tanum truncatum of Diesing, 1858 (p. 383) ; Pleurocotyle sco?nbri of
Taschenberg, 1878 (pp. 575-7) ; Octocotyle major Goto, 1894 (pp. 203-5,
PL 9, figs. 1-6) ; Octocotyle scombri of Nicoll, 1915 (p. 351) ; Pleurocotyle
scombri of Nicoll, 1915 (p. 352).

Hosts : mackerel.
Location : gills.

T. Scott (1901, p. 146, PL 8, fig. 20) gave a brief account of
specimens about 5-5 mm. long which were found on the mackerel
near Aberdeen. A. Scott found the trematode several times
(1900; 1904, p. 116; 1906, p. 193, PL 9, fig. 2) on the same
host in the Irish Sea, merely repeating that it is "a very
slender species and easily overlooked." His figure indicates that one
specimen was about 6 mm. long and 0-9 mm. in greatest breadth,
with an armed genital pore about 0-4 mm. from the anterior
extremity. Other zoologists have found the trematode in various
parts of Britain on the same host, Nicoll (1914) at Plymouth,
Baylis (1928) at Guernsey, Baylis & Idris Jones (1933) at Plymouth,
and Rees & Llewellyn (1941) on the Irish Atlantic Slope, and it

142

THE TREMATODA OF BRITISH FTSHES

Fig. 27. — A-E, Kuhnia scombri : A, the entire trematode ; B, the opis-
thaptor ; C, the posterior end of B, showing the hooks ; D, the genital
hooklets in situ, the anterior region above ; E, one of the clamps. F,
Mazocraes sp. ? the genital hooklets. (Note. — One hooklet of both the
anterior and posterior rows apparently missing.) G, showing the full
complement of genital hooklets in the anterior row ; H, the posterior
end of the opisthaptor, showing the hooklets. (Original.)

HEXOSTOMATIDJE 143

occurs in this host and sometimes in the Spanish mackerel and other
hosts in the Mediterranean, Russia, Canada and Japan. Size ;
1-6-5 mm. long and one-tenth to one-sixth as broad. Shape :
lanceolate and broadest near the middle, tapering towards the narrow
anterior one- quarter and towards the opisthaptor. Prohaptor : a
pair of elongate oval buccal suckers. Opisthaptor : cotylophore
heart-shaped and clearly marked off from the rest of the body, about
0-2-0-6 mm. long, the clamps arranged in two diverging rows. Large
hooks of the lateral pair having a stout blade and a ridged shaft
with a projecting process ; small hooks of the median pair S- shaped
with a twisted shaft and a sickle-like point (Fig. 27 C). Gut : caeca
extending into the cotylophore and generally unequal in length, also
devoid of diverticula. Reproductive systems : genital hooklets of the
longitudinal series about 0-02 mm. long and with semicircular blades
which are sometimes sharply bent on the shaft ; hooks of the lateral
pair about the same size or a little larger and having a broad base
and blades of lesser curvature. Gonads situated in the posterior
half of the body proper, the testes behind the ovary. Vitellaria well
developed laterally and extending from the genital pore almost to the
base of the cotylophore. Eggs fusiform and operculate, bearing 2
polar filaments about as long as the capsule, or one slightly shorter,
but very variable in shape and size, measuring 0-194-0-312 x 0-049-
0-126 mm., its internal lining sculptured.

Family HEXOSTOMATID.E Price, 1936.

Prohaptor a pair of minute buccal suckers. Opisthaptor com-
prising 4 pairs of sessile, transversely- oval suckers and 2 pairs of
hooklets. Suckers of the most posterior pair much smaller than the
others, their reduced sclerites exhibiting some fusion. Sclerites of the
large suckers numbering 3 in each, their shapes indeterminate, but
the middle piece somewhat X- shaped. Vaginal pore median and
dorsal near the level of the genital pore. Vagina bilobed, its distal
part lined with tuberculate cuticle.

Genus HEXOSTOMA Rafinesque, 1815, nee Hexastoma Rudolphi,

1809, nee Hexastoma Kuhn, 1828.

(Hexacotyle Blainville, 1828.)

With the characters of the family. Parasites of the tunny. The
type-species, H. thynni (Delaroche, 1811), occurs at Naples, the
Balearic Isles and on the Atlantic coast of North America. H.
thunnince (Parona & Perugia, 1889) at Genoa. A third species, H.
extensicaudum (Dawes, 1940) was found by F. S. Russell on the gills of
the tunny in the North Sea. Three other species occur in Japan, and
one of them, H. acutum (Goto, 1894), was recorded by Baylis (1939) as
occurring in the North Sea, but this may be a doubtful record in
view of the new species since described.

144 THE TREMATODA OF BRITISH FISHES

Hexostoma extensicaudum (Dawes, 1940a) Dawes, 1946.

(Fig. 28 A, B 1-4.)

Hexacotyle extensicauda Dawes, 1940 (a, pp. 271-86, figs. 1-6).

Host : tunny.
Location : gills.

Size : about 11 mm. long. Shape elongate, divisible into anterior,
middle and posterior regions measuring 1-5 x 1-3, 5-5x3-3 and
4-0 X 2-6 mm. Anterior region terminating in a median papilla
0-25 mm. long and 0-3 mm. broad and passing abruptly into the
middle region, which is separated from the posterior by a narrow
waist 1-7 mm. broad. Prohaptor a pair of minute buccal suckers no
more than 01 mm. diameter. Opisthaptor : cotylophore ill denned
and bearing 4 pairs of suckers, those of the most posterior pair being
very small, and 2 pairs of hooklets. Suckers of the first 3 pairs oval
in outline, cup-like, having their long axes in the transverse plane
and occupying about 0067 of the length of the body. Suckers of
the most posterior pair more deeply concave than those in front,
their breadth approximately 0-03 of the length of the body. Ratio
of the breadths of the small and large suckers 0-45. Hooklets each
having a strongly recurved point and a " guard " which approaches
the tip in spanner fashion. Hooklets of the lateral pair 075 mm.
long, those of the median pair only 001 5 mm. Sclerites of the large
suckers taking the form of 3 dissimilar pieces, respectively lateral,
middle and median topographically, the middle sclerite large and
approximately X-shaped, but differing in shape in the different
suckers, and sunk deeply in the musculature of the suckers. Sclerites
of the small posterior suckers rudimentary (or vestigial ?), showing
some signs of the fundamental tripartite nature. Musculature : outer
circular muscles of the integument absent or vestigial; oblique and
longitudinal muscles present, the latter being thicker dorsally than
ventrally, and posteriorly than anteriorly, divided ventrally into
superficial and deep components, which function respectively in
bringing about release and adhesion of the suckers by virtue of their
insertion in the rim and centre respectively. Gut : pharynx small
and non-muscular. (Esophagus short and narrow. Caeca long and
equipped with profusely- branched median and lateral diverticula,
extending into the cotylophore. Reproductive systems : common
genital pore near the bifurcation of the intestine at the junction of
the anterior and middle regions of the body. Genital atrium capacious,
0-6 mm. long, 0-3 mm. broad and 0-4 mm. deep. Vaginal pore median
dorsal, close behind the level of the genital pore. Distal part of the
vagina bilobed, capacious, quite as large as the genital atrium, and
lined with cuticle bearing numerous tubercles. Copulatory organ
conical, fibrillar, 0-35 mm. long and 0-2 mm. broad. Vas deferens
long and convoluted. Prostate glands well developed. Testes
numerous, but confined to the region between the caeca in the waist
connecting the middle and posterior divisions of the body. Ovary

HEXOSTOMATIDiE

145

U-shaped and having limbs folded about a dozen times in the trans-
verse plane in front of the testes. Vitellaria well developed, extending
throughout the dorsal part of the middle division of the body, their
follicles equally abundant in the dorsal and ventral regions laterally,
and consisting of groups of vitelline cells in various stages of secretory
activity, one cell of each group being large and distended with droplets

Fig. 28. — Hexostoma extensicaudum. A, entire trematode ; B, the sclerites
of the opisthaptor, 1-4 those of suckers of the lst-4th pairs. Note. —
In 1-3 the three sclerites of each sucker are represented from left to right
as median, middle and lateral pieces ; in 4 the sclerites are shown in situ.
(After Dawes, 1940a.)

of shell-forming material. Uterus little folded, the terminal part
(metraterm) straight. Ootype elongate in the transverse plane and
situated between the testes and the ovary. Oviduct equipped with
an ovicapt having 2 sphincters. Eggs not numerous, ovoid and
very large (0-250 x 0-150 mm.), each having 2 polar filaments about
0-25 mm. long and hollow in their basal parts. Note: this trematode
causes much erosion of the tissues of the host, more especially in the
upper part of the gills, but also near the free edge, where the opist-
haptor adheres.

10

146 THE TREMATODA OF BRITISH FISHES

VII. TREMATODES OF THE ORDER DIGENEA.

In the present state of knowledge the complete classification of
the Digenea cannot be achieved. There is no difficulty in separating
families, but their arrangement in higher taxonomic units cannot be
agreed upon. Some writers (Fuhrmann, 1928 ; Sprehn, 1933) have
simply enumerated families ; others (Poche, 1926 ; Craig & Faust,
1940) have set out groups such as sub-orders, tribes, sub-tribes and
super-families, but not with any outstanding success. Many families
of Digenea stand to-day more or less isolated, and some which have
been arranged together are not known to be phylogenetically related
beyond doubt. Classification was at one time based entirely on the
characters of adults, and both difficulties and doubts arose when it
became clear that larval characters must also be taken into account.
Some larval and adult characters proved to be of high taxonomic
value, notably the excretory system. Cort (1917) first showed and
others subsequently proved the importance of this system, particularly
the arrangement of flame- cells and excretory canals which is indicated
in the flame -cell formula established by Faust. The formula is a
mathematical expression which indicates the manner in which the
canals branch, and it is just as applicable to cercariae and rediae, even
miracidia, as to adults. But several zoologists have issued a note
of caution against too implicit a reliance on this system in taxonomy,
noting striking differences in the details in trematodes placed by
universal agreement in the same family. The number of excretory
canals and flame- cells often increases during the development of a
cercaria into a metacercaria or an adult, probably in response to
particular physiological needs, and similar definitive arrangements do
not necessarily denote phylogenetic relationship, but may be due to
convergence in evolution. Force was added to this contention of
Brown (1933) by Hopkins (1941a), who found that the flame-cell
formula of the Monorchiidae, which is 2[(2 + 2) + (2 -f 2)], is no less
characteristic in a number of other families (Microphallidae, Hetero-
phyidae, Allocreadiidae), as well as in members of others (Fello-
distomatidae, Zoogonidae), trematodes which differ so markedly in
structure and life -history that they cannot be closely related. It is
logical to doubt the taxonomic value of the excretory system in
instances where a primitive condition seems to persist in unrelated
forms. We must admit, however, that there is good reason to doubt
the apparent closeness of the relationship between two trematodes,
on whatever grounds this is judged, when notable differences exist
between the characters of the excretory system, especially if they
occur in both larvae and adults. The types to which cercariae belong
sometimes indicate relationship, but some character s of certain
cercariae are of no more than specific value, the cx^jtory vesicle
ranging from a sac-like form to a Y-shape through various inter-
mediate shapes. Obviously, taxonomy demands the use of both
larval and adult characters and difficulties prevail because our know-
ledge of larvae is scanty. But larvae show more conspicuous adaptive

DIGENEA 147

characters than adults and may lead us into error. Of other criteria
which are available to the taxonomist host-parasite relationships
were stressed by Szidat (1939a), who claimed degrees of specificity
which have not been generally acknowledged, perhaps because of
erroneous diagnosis. Certainly, most of the trematode parasites of
fishes occur only in this class of vertebrate, and belong to well-defined
families. To attempt the arrangement of these families into higher
units is hardly advantageous at present, and will not be attempted.
The characters given for the families are largely those by which the
adults may be recognized.

Key to the Families of Digenea Parasitic in European Fishes.

(1) Mouth situated near the middle of the bodv

GASTEROSTOMATA (Bucephalus).

(2) Mouth situated near the anterior extremity . . (PROSOSTOMATA).

I. Adults inhabiting the blood vascular system, or cyst-like spaces
in the tissues.

a. Parasites of the blood vascular system . . Aporocotylid^.

b. Cyst-dwellers ...... Dldymozoidje.

II. Adults not inhabiting the blood vascular system or cyst-like

spaces.

a. Ventral sucker absent in the adult . . . Mesometrid^j.

b. Ventral sucker present in the adult.

a'. Ovary situated behind the testes ; uterus having
descending and ascending limbs.

(a) Vitellaria rarely follicular ; caeca long or short,

but devoid of anterior extensions (i.e. intestine
never H -shaped),
(i) Vitellaria paired and compact ; caeca long ;

excretory vesicle Y-shaped . Hemiurid^e.

(ii) Vitellaria rarely paired, generally compact ;
caeca short, rarely fairly long ; excretory
vesicle sac-like . . . Zoogonid^e.

(b) Vitellaria follicular ; caeca long and having a pair

of anterior extensions (i.e. intestine H -shaped)

AcCACXEUIDiE.

b'. Ovary situated in front of the testis or testes.

(a") Only one testis (two in Monorcheides) ; uterus
having descending and ascending limbs.

(a) Vitellaria compact, or only slightly lobed

HAPLOPORIDiE.

(b) Vitellaria follicular, but not extensive

MONORCHnDJE.

(b") Two testes present ; uterus sometimes having
only an ascending limb.
(a) Uterus having only an ascending limb,
(a') Intestine a single simple caecum

HaPLOSPLANCHNTD^.

(&') Intestine bifurcate (i.e. two caeca
present).

(a") Cuticle smooth ; excretory vesicle
Y-, T- or funnel-shaped.

148 THE TREMATODA OF BRITISH FISHES

Key to the Families of Digenea Parasitic in European Fishes — cont.

(i) Excretory vesicle Y-shaped ;
vitellaria not extending to
the posterior extremity ;
receptaculum seminis absent

AZYGHDiE.

(ii) Excretory vesicle not Y-
shaped ; vitellaria extend-
ing to the posterior ex-
tremity ; receptaculum
seminis present Allocreadiid^.
(&") Cuticle spinous ; excretory vesicle
Y-shaped.

(i) Cirrus-pouch present ; cirrus
and metraterm equipped
with spine-like structures

ACANTHOCOLPID JE .

(ii) Cirrus-pouch absent ; cirrus
and metraterm not equipped
with spine-like structures

ACANTHOSTOMATIDiE .

(6) Uterus having descending and ascending
limbs.
(a') Cirrus-pouch absent.

(i) Receptaculum seminis absent ;
pharynx long ; excretory vesicle
-shaped . Ptychogonimid^;.

(ii) Receptaculum seminis present ;
pharynx short or absent ; ex-
cretory vesicle tubular

GORGODERIDiE.

(&') Cirrus-pouch present.

(i) Oral sucker having six anterior

processes . . Bunoderid^e.

(ii) Oral sucker devoid of anterior

processes . Fellodistomatid^:.

Sub-order GASTEROSTOMATA Odhner, 1905.

Mouth ventral, near the middle of the body. Haptor a muscular
sucker with or without tentacles, or a rhynchus, at the anterior
extremity. Intestine sac-like. Genital pore ventral, near the posterior
extremity. Gonads globular, generally near the mid-body or posterior.
Vitellaria located in the anterior region. Uterus having 2 or 3 folded
limbs. Cercaria furcocercous.

Family BUCEPHALID.E Poche, 1907.
( Gasterostomidse Braun, 1893.)
With the characters of the sub-order.

BUCEPHALIDiE 149

Sub-family Bucephalus Nicoll, 1914.

Haptor a muscular sucker, simple and globular in Bucephalopsis ,
provided with a number of retractile tentacles or fimbriae in Bucephalus,
shallow and surmounted by a fan-shaped hood in Rhipidocotyle.

Genus BUCEPHALUS Baer, 1827.
(Gasterostomum Siebold, 1848 ; Eubucephalus Diesing, 1855.)

This genus was erected for a new furcocercous cercaria, Bucephalus
polymorphus, the name denoting a whimsical likeness to the head of
an ox, the long furcal rami representing the horns. Gasterostomum
was the generic name chosen for an adult trematode, G. fimbriatum,
inhabiting the intestine of freshwater fishes, particularly the perch,
and shown by Wagener (1858) to be the adult corresponding to
Bucephalus polymorphus, the name of which by priority rights now
stands for both the adult and its larva. Manter (1940a) remarked
on the curious coincidence which makes the name Bucephalus appro-
priate for the adult, but in this case it is the extended tentacles which
are comparable with horns. According to Liihe (1909) there is a
circlet of 6 tentacles, but Nagaty (1937) asserted that the full number
is 7. They show specific differences in shape and number, and they
are invariably inconspicuous in the retracted condition, then appear-
ing as small papillae.

Bucephalus polymorphus Baer, 1827 (pp. 570-89, PI. 30, figs. 1-27).

(Fig. 29 D-G.)

Distoma campanula Dujardin, 1845 (p. 435) ; Gasterostomum fimbriatum
Siebold, 1848 (v. 1, p. 129) ; G. laciniatum Molin, 1859 (p. 821) ; Bucephalus
elegans Woodhead, 1930 (pp. 1-10, figs. 1-19) ; B. varicus Manter, 1940
(a, pp. 335-7, figs. 3-9).

Hosts : adults in the pike (outside Britain adults in the pike,
perch, burbot, gudgeon ; metacercarise in the houting, dace, silver
bream, bleak) ; cercaria? in freshwater mussels (Anodonta, Unio).

Location : adults in the intestine, metacercariae encysted beneath
the skin.

Baylis (1939, p. 474) recorded the occurrence of this species in the
pike in Wiltshire and Berkshire, and it has been found in France,
East Prussia, Italy, the Red Sea and America.

Size and shape : rarely more than 2 mm. long, often about 1 mm.,
but mature when 0-6 mm. long ; elongate and broadest in the middle,
rounded posteriorly and truncated anteriorly. Cuticle covered with
minute spines, which are most abundant anteriorly. Haptor oval,
008-019 mm. long and 007-0-17 mm. broad in specimens 0-6-2-3 mm.
long. Tentacles 7 in number, 3 dorsal, 2 lateral and 2 ventro-lateral,
when extended tapering gradually from base to tip and then showing
2 ventral processes, when retracted having the region behind the tip
telescoped into the base, sometimes apparently absent. Gut directed

150

THE TREMATODA OF BRITISH FISHES

Fig. 29. — A, Aspidogaster conchicola ; diagram of the genital organs. B,
Aspidogaster limacoides ; entire trematode in dorsal view ; C, schematic
diagram showing the connexions between ducts shown in B. D-G,
Bucephalus polymorphus : D, an individual having extended tentacles ;
E, the anterior end of the same in end view ; F, an individual having
partially retracted tentacles ; G, the anterior end of the same. (A,
after Stafford, 1895; B, C, after Bychowsky and Bychowsky, 1934;
D-G, after Nagaty, 1937.)

BUCEPHALID.E 151

forward or backward, mouth almost central ; pharynx nearly spherical
(0-03-0-10 mm. diameter) ; intestine a simple sac connected with the
pharynx by a narrow neck (" oesophagus "). Excretory system
having a terminal pore and a sac-like vesicle extending almost to
the haptor. Reproductive systems : genital pore close to the excretory
pore on the ventral surface, cirrus pouch 0-17-0-57 mm. long and
005-0-10 mm. broad; seminal vesicle oval, cirrus stout and spinous.
Gonads globular and arranged one behind another ; ovary foremost,
on the right side of the body and slightly dorsal to the gut and the
anterior half of the cirrus pouch, the ovary 0-05-0-13 mm. diameter,
the testes 0-06-0-19 mm. Vitellaria coarsely follicular, comprising
9-24 follicles 02-0 06 mm. diameter on either side of the median
plane just in front of the mouth, not extending more than half-way
between the mouth and the haptor. Uterus having ascending and
descending limbs and numerous folds, rarely extending anterior to the
vitellaria. Eggs small (0-021-0-027 x 0-013-0-023 mm.) and
numerous, operculate and devoid of filaments or thickenings.

Early descriptions of this species are incomplete. Wagener did
not at first (1852a) mention tentacles in " Gasterostomum fimbriatum"
but later (1858) described tentacles with a single ventral process
The form " Bucephalus elegans " was credited with tentacles of this
kind, but Nagaty (1937) recorded remarkable variations in B. poly-
morphus, some specimens of which have tentacles with a single
process, although 2 processes are typically present, for this reason
regarding Woodhead's specimens as belonging also to this species.
Manter (1940a) disagreed with this conclusion and chose to regard
Nagaty's specimens as forming a distinct species, B. varicus. But a
comparison of various slight differences which Manter made in support
of his claim is not very convincing, although the hosts provide a
problem. Nagaty's specimens were obtained from several fishes,
especially species of " Trachynotus " and " Caranax," in the Red Sea,
Manter 's from species of Caranx at Tortugas and a " small yellow
jack " in the Pacific, while the normal hosts of Bucephalus polymorphous
are freshwater fishes. But the cercarise are pelagic and a second
intermediate host is required in the life cycle, both this and the final
host being fishes. One intermediate host is the houting, which occurs
in the sea as well as in fresh water, so that the possibility of marine
fishes being infected is not entirely remote. Nagaty thus seems to
have been justified in attributing his specimens to the species Buce-
phalus polymorphus, from which they could not be separated on
morphological grounds. Six other species of the genus occur in
widely separated parts, 2 in India, 2 in America, 1 in southern Russia
and 1 in Japan.

Genus BUCEPHALOPSIS Diesing, 1855.

(Prosorhynchoides Dollfus, 1929.)

Diesing (1855c) erected a sub-genus, Bucephalopsis, for the larval
form Bucephalus haimeanus Lacaze-Duthiers, 1854, found in Ostrea

152 THE TREMATODA OF BRITISH FISHES

and Cardium in the Balearic Isles. Tennent (1906) fed encysted
American larvae belonging to this species to various fishes and referred
the corresponding excysted forms to the species then known as
" Gasterostomum gracilescens " (Distoma gracilescens Rudolphi, 1819).
When Nicoll elevated the sub-genus to generic rank he named B.
gracilescens (Rudolphi, 1819) as its type. Lebour (1908a, p. 9 ;
1911, p. 425) was not satisfied that American and British forms were
identical, but only because of differences in size and in the arrange-
ment of the vitellaria. American forms from the gar were about
1 mm. long, British forms from the angler about 6 times this length,
and the vitellaria were arranged in paired clusters or cords respectively.
Eckmarm (19326) consequently referred the American form to the
species Bucephalopsis haimeanus (Lacaze-Duthiers, 1854). Nagaty
accepted this as a valid species, although it seems to me to be a
synonym of B. gracilescens, whose larva was acknowledged by Lebour
to be " Bucephalus haimeanus" The identical nature of American
and British forms seems much more likely when small specimens
from the angler are used for purposes of comparison, the vitelline
follicles in many of my own somewhat contracted specimens being
arranged exactly as Tennent described.

Nagaty (1937) reviewed 19 species of Bucephalopsis, 4 of them
new and some of them apparently invalid. Apart from the type
species, only 4 of these forms have been found in Europe, none in
British waters, so that they are of interest only in so far as they
represent possible synonyms of Bucephalopsis gracilescens, which is
common in Britain.

Bucephalopsis gracilescens (Rudolphi, 1819) Nicoll, 1914 (pp. 472-91),

nee Tennent, 1906. (Fig. 30 A, B ; 31 A-K.)

Distoma gracilescens Rudolphi, 1819 (p. Ill, 409) ; Gasterostomum gracilescens
(Rud.) of authors.

Hosts : In Britain, adults occur in the angler and the conger,
encysted metacercariae in the cod, haddock, whiting, pollack, common
ling and greater forkbeard, and cercariae in the cockle.

Location : adults occur in the stomach, pyloric caeca and intestine,
metacercariae in the nerves, particularly the auditory nerve and the
spinal nerves near the tail.

Cobbold (1859, p. 161) first recorded this species in Britain and it
was not found here subsequently for nearly 50 years, but then became
known at Cullercoats, St. Andrews, Aberdeen, Liverpool and Ply-
mouth. It also occurs at Trieste, in the Balearic Isles, near Banyuls
and at Woods Hole, U.S.A. Lebour (1908a) found heavy infections
in every angler she inspected on the Northumberland coast, several
hundred mature specimens in a single host. She also found encysted
metacercariae in the cranial and spinal nerves of the haddock, cod
and whiting, these being commonest in the haddock and occurring
most abundantly on the auditory nerves and in the tail. Johnstone

BUCEPHALIDiE

153

Fig. 30. — A and B, Bucephalopsis gracilescens : C, "Prosorhynchus
grandis." D, "P. squamatus" E, anterior end of Rhipidocotyle viperce.
F, "Prosorhynchus aculeatus." G, P. crucibulum. (A— D, after Lebour,
1908 ; E, after NicoU, 1914 ; F and G, after Nicoll, 1910.)

154 THE TREMATODA OF BRITISH FISHES

(1905) also found cysts of this kind in the brain of the cod and haddock
at Liverpool. Nicoll (19096) found juvenile specimens in the stomach
of the cod at St. Andrews, and later (1915) recorded similar forms in
the stomach of the pollack at Aberdeen. These fishes are not the
normal hosts, and they must have acquired the metacercarise by
feeding on other gadoid fishes infected with them in the normal
way. Nicoll (1914) regarded the adults of this species as common
parasites of the angler at Plymouth, and Bay lis & Idris Jones (1933)
obtained mature specimens from the angler and conger there. I
have found large numbers of adults in the angler at Plymouth,
but not in every individual examined. Olsson (1868, p. 55) estimated
the numbers of worms inhabiting the gut of a single fish as varying
between one and two thousand, which must approach the maximum
number that can be accommodated.

Lebour's specimens were much larger than my own and showed
the following characters : Size averaging about 6 mm. in length.
Colour none, apart from the eggs. Shape continually changing
in life, but generally elongate, tapering towards the extremities,
broadest in the anterior region. Cuticle completely covered with
minute spines. Haptor a sucker 0-4 mm. diameter. Gut : mouth
situated at the end of the first quarter of the body. Pharynx globular
and smaller than the haptor (0-3 mm. diameter). Intestine sac-like
and (according to figs. 1 and 2, PI. 1) projecting anteriorly. Excretory
system : vesicle club-shaped, extending nearly to the level of the
mid-intestine, filled with refractive granules. Reproductive systems :
genital pore almost terminal. Cirrus pouch elongate. Pars prostatica
narrow. Seminal vesicle pyramidal. Cirrus long and spinous, occupy-
ing almost the entire length of the pouch. Prostate glands filling the
peripheral part of the same. Testes oval in outline, situated obliquely
one behind the other just in front of the cirrus pouch ; ovary globular
and somewhat smaller, situated on the right between the anterior
testis and the gut. Male duct and oviduct short ; Laurer's canal
directed posteriorly. Ootype located between the ovary and the
anterior testis. Uterus extending forward as far as the gut, then
posteriorly to the genital pore in juveniles, much convoluted in the
adult. Vitellaria comprising a chain of large follicles (15-18 shown)
on each side, extending from a point just behind the haptor to the
termination of the gut, vitelloducts uniting to form the vitelline
reservoir just behind and on the right of the ovary. Eggs very
numerous, small (0 026 mm. long), and golden brown.

My own specimens do not exceed 3 mm. in length, and most of
them are no more than 1 mm. long. Many conform to the shape
described by Lebour, but mass fixation leads to very great differences
in shape, with consequent alteration in the arrangement of the internal
organs (Fig. 31 A-K), although the living trematodes show just as
considerable changes during movement. Well-extended specimens
have the intestine directed partly forward (I), the vitelline follicles
in line between the uterus and the haptor and well behind the latter,
and the gonads far hi front of the cirrus pouch. Contracted specimens

BUCEPHALID^;

155

Fig. 31. — Bucephalopsis gracilescens. A-H, small specimens, all from the
same host, showing great variability in form and in the topography of
the internal organs ; I-K, larger individuals from another Angler, show-
ing similar variability. (A-H are referable to the upper, I-K to the
lower scale.) (Original.)

156

THE TREMATODA OF BRITISH FISHES

may be broader than long (H) and have vitelline follicles, uterus and
gut crowded in the anterior region, the gonads, excretory vesicle and
cirrus pouch filling the posterior. Intermediate states of contraction
do not produce graded differences in the positions of the internal
organs, because they are not regular (A-H) ; instead, there is a
variety of topographical arrangements which defy description.
Variability does not concern only changes of this kind. In small
and large individuals the proportions of the organs vary, presumably
as a result of growth, and relative differences in size occur in some
instances. Variation in shape tends to vitiate measurements, but
well extended small and large specimens provided these figures :

mm.

mm.

0-9-1-2

30

0-3-0-4

0-6

0-20-0-21

0-24

0-10-0-11 (dia.)

0-23 x 013

0-11-0-13 (dia.)

0-27-0-35 x 0-18

0-27-0-36

0-85

0021 x 0016

0-025 x 0018

Length of the body .
Breadth of the body
Diameter of the haptor
Dimensions of the ovary
Dimensions of the testes
Length of cirrus pouch
Mean size of the eggs

Comparison of small with larger specimens thus reveals the fact that
the body is relatively broader, the gonads relatively smaller, the
cirrus pouch of about the same relative size, but in the contracted
state of the body appearing proportionately larger, the haptor
relatively very much smaller, and the eggs absolutely slightly smaller,
but proportionately much larger. In short, the shape of the body, its
proportions and the sizes and dispositions of the internal organs are
all subject to considerable variability, even in specimens of one
species taken from the same host. For this reason such criteria
must be used with great circumspection when different species are
being compared, or when a new species is being set up. Linton
(1940, pp. 30-3, PI. 18, figs. 245-9) stressed this point regarding
variability in relation to American specimens from the garfish. This
is not the place to discuss in detail the species of Bucephalopsis which
have been reported outside Europe, but some of these will un-
doubtedly prove to be synonyms of B. gracilescens. Thus B. south-
welli Nagaty, 1937, cannot be separated from the type species on
morphological grounds, and other species from the Red Sea may well
be variants of it whose main differences will be resolved ultimately in
terms of growth and movements of the body. Another synonym of
B. gracilescens is B. elongatus Ozaki, 1928, and other Japanese species
differ from this mainly in the shape and size of the body and the sizes
of the eggs — all unreliable characters of distinction. Altogether about
twenty species have been recorded, and two which deserve mention
here are B. triglce (Beneden, 1870) nee Nicoll, 1909 (Gasterostomum
triglce Beneden, 1870, p. 30, PI. 3, fig. 15), which was found in the
yellow and grey gurnards in Belgium, and B. tergestinus (Stossich,
1883) {Gasterostomum tergestinum Stossich, 1883, pp. 119-20, PI. 2,
fig. 5), which was found in the black goby and Gobius jozo at Trieste.

BUCEPHALIDiE 157

Other species range from Russia to the Red Sea, India, Australia and
Japan, and one species occurs at Woods Hole. For further informa-
tion see Dawes (1946).

Genus RHIPIDOCOTYLE Diesing, 1858.

(Nannoenterum Ozaki, 1924.)

When Diesing erected the sub-genus Rhipidocotyle he allocated two
species to it, but did not name the type. Stiles and Hassall (1908)
chose " Gasterostomum gracilescens (Rudolphi, 1819)," but in elevating
the sub -genus to generic rank Nicoll showed that the alternative
species " G. minimum Wagener, 1852 " must stand as the type, being
the only one of the two species in which a sucker and a fan-shaped
hood are combined as implied by the name chosen by Diesing.
Eckmann (19326) re-examined the type specimens of this species and
concurred, but showed that " G. minimum " is identical with " G.
galeatum (Rudolphi, 1819)," which thus became the type. She
rightly relegated Nannoenterum to synonymy with Rhipidocotyle,
the only differences between the two being trifling matters of shape
and the relative positions of the uterus and vitellaria. The type
species is well known in Britain, but no other species occurs here, 4
occurring in U.S.A., 1 in Canada, 1 in Japan and 2 in the Red Sea.

Rhipidocotyle galeata (Rudolphi, 1819) Eckmann, 1932, emend.

(Fig. 30 E.)

Monostomum galeatum Rudolphi, 1819 (p. 86, pp. 349-50) ; Gasterostomum
galeatum (Rudolphi) of Stossich, 1898 (p. 62) ; G. minimum Wagener, 1852
(pp. 558-63, fig. 2) ; G. triglce (Beneden) of Nicoll, 1909 ; Rhipidocotyle
minima (Wagener) of Diesing, 1858 (pp. 361-2), and of Nicoll, 1914
(pp. 492-3) ; R. viperce Nicoll, 1914 (pp. 493-4, fig. 4), nee Beneden,
1870.

Hosts : greater weever, lesser weever, red gurnard, yellow gurnard,
grey gurnard.

Location : intestine.

Nicoll (19096) found many specimens of this species in the grey
gurnard at St. Andrews, naming them Gasterostomum triglce. Later
(1914) he got a few more specimens from the greater weever at
Plymouth, recording these as Rhipidocotyle viperce, and others from
the yellow, grey and red gurnards and the lesser weever, which were
called R. minima. Little (1929a) found " R. minima " in the grey
gurnard at Gal way, and Baylis & Idris Jones (1933) found it in
the yellow and grey gurnards at Plymouth. Size : mature when
0-7-1-2 mm. long and 0-4 mm. in greatest breadth. Shape: elongate
oval, truncated at the anterior end, pointed at the posterior. Cuticle
covered with minute spines. Haptor shallow and sucker-like, not
very muscular, up to 013 mm. diameter, the hood 5-rayed. Gut :
pharynx about 05 mm. diameter and 0-8 mm. from the anterior

158 THE TREMATODA OF BRITISH FISHES

extremity. Intestine simple, but often obscured by the folds of the
uterus. Reproductive systems : cirrus pouch very elongate, extending
forward to a level just in front of the mouth. Cirrus short, but pars
prostatica long. Gonads grouped together on the right in front of
the mouth ; the ovary globular, 0-1 mm. diameter and 0-6 mm. from
the anterior extremity ; the testes 0-12 mm. diameter, one behind the
other, slightly lateral to and contiguous with the ovary. Vitellaria
lateral, extending from the level of the ovary to a point 0-25 mm.
from the anterior extremity, the much-folded uterus filling up the
available space between them and extending back to a level between
the testes and the gut. Eggs 0036-0037 mm. long and 0018-
0021 mm. broad.

Nicoll (1914, p. 942) amended his description (19096, pp. 23-4)
of " Gasterostomum triglce" remarking on the great length of the
excretory vesicle and the relatively posterior position of the pharynx,
which, in some specimens, is at the level of the anterior testis, but
in others near the blind end of the cirrus pouch. Variability seems
to affect the relative sizes of the pharynx and the haptor also,
for these organs may be of fairly equal or unequal sizes. The
form " Rhipidocotyle viperce " resembled " E. minima " in general
appearance, but differed in the arrangement of the gonads and in
the length of the cirrus pouch. Eckmann seems to have been justified
in referring these forms to E. galeata, and Nagaty's opinion that
Nicoll's specimens are " identical with " the American species E.
septapapillata Krull, 1934, may be taken to indicate that the list of
synonyms of the type-species is incomplete.

Sub-family Prosorhynchinje Nicoll, 1914.

Haptor a rhynchus.

A number of genera have been referred to this sub -family, but
they seem to have been resolved into two, most of them representing
synonyms of Prosorhynchus, but one remaining apparently valid.
This is Alcicornis MacCallum, 1917, which was erected for A. carangis
(an intestinal parasite of Caranx ruber brought from Key West to the
New York Aquarium), but now contains also A. baylisi Nagaty,
1937, a parasite of Caranx sp. in the Red Sea. The type genus is
well known in various parts of the world, and I have already made a
short statement about the synonymy (Dawes, 1946, p. 194).

Genus Prosorhynchus Odhner, 1905.

(Gotonius Ozaki, 1924 ; Skrjabiniella Issaitschikow, 1928 ; Mordvilkovia
Pigulewsky, 1931 ; Dollfusina Eckmann, 1932 ; Dollfustrema Eckmann,
1934 ; Neidhartia Nagaty, 1937; Pseudoprosorhynchus Yamaguti, 1938.)

In erecting this genus Odhner (1905) placed in it P. crucibulum
(Rudolphi, 1819) and two new species, P. aculeatus and P. squamatus,
which Eckmann (19326) regarded as identical. Nagaty (1937) con-

BTTCEPHALID^ 159

curred, but Manter (1940a) had more faith in Odhner's discrimination
and made a new species, P. caudovatus, for Eckmann's " P. cruci-
bulum " on account of the polar processes on the eggs. Two forms
found in Britain, P. grandis Lebour, 1908 and P. triglce sp. inq.
Nicoll, 1914, were relegated, along with several others, to synonymy
with P. crucibulum by Nagaty, who recognized along with the type
and P. aculeatus three species from the Far East and a new species from
the Red Sea, Manter (1940a) adding three new species from America,
Srivistava (1937) two more from India. The only species with which
we are concerned are Prosorhynchus crucibulum in its various forms
and P. aculeatus. As the main differences by which the latter can be
distinguished from the former are the oval instead of conical shape
of the rhynchus and the triangular instead of linear arrangement of
the gonads, characters which may be regarded as coming within the
limits of variability of a single species, these two species are regarded as
identical, for reasons which will be given after structure has been
considered.

Prosorhynchus crucibulum (Rudolphi, 1819) Odhner, 1905.

(Fig. 30 C, D, F, G.)

Monostoma crucibulum Rudolphi, 1819 (p. 83, pp. 342-3) ; Gasterostomum
crucibulum (Rud.) of authors ; G. armatum Molin, 1859 (pp. 291, 820) ;
Bucephalus crux Levinsen, 1881 (pp. 80-1, PL 1, fig. 7a-j) ; Prosorhynchus
aculeatus Odhner, 1905 (pp. 297, 302, 305) ; P. squamatus Odhner, 1905 (pp.
297-304, PL 2, figs. 1-5) ; P. grandis Lebour, 1908 (a, p. 13, PL 1, fig. 5) ;
P. triglce Nicoll, 1910 (p. 495, fig. 5) ; P. costai Travassos, Artigas & Pereira,
1928 (p. 33, fig. 121) ; P. scalpellus McFarlane, 1936 (pp. 336-7, 7 figs.) ;
Mordvilkovia elongata Pigulewski, 1931 (pp. 437-8, fig. 2) ; Skrjabiniella
aculeatus (Odhner) Issaitschikow, 1928 (p. 23).

Hosts : In Britain, conger, short-spined cottus (father-lasher),
long-spined cottus, Montagu's sea snail, grey gurnard, cod, whiting.
Location : intestine and pyloric caeca (abnormally, in the stomach).

Nicoll (1907) recorded this species as P. squamatus in the long
spined cottus (listed as Cottus bubalis Euphr. — father-lasher) at St.
Andrews. Lebour (1908a) found it once in 13 specimens of the
" bull-head " (father-lasher implied) at Culler coats and described it
as P. squamatus, other specimens from the cod and whiting being
called P. grandis. Nicoll (1910) found both P. squamatus and P.
crucibulum in the conger at Millport and (1914) also at Plymouth,
where P. triglce was found in the grey gurnard. Little (1929a)
recorded the occurrence of P. triglce in the grey gurnard, P. aculeatus
in the conger and encysted stages of P. crucibulum on the gills of the
cod at Galway. Baylis & Idris Jones (1933) found P. aculeatus in
the conger and P. crucibulum in both the conger and the angler at
Plymouth, Jones (1943) in conger off our west coast. Outside Britain,
the trematode has been found in Italy (at Padua), off the coast of
Belgium, in the Baltic Sea, near Greenland, in the Red Sea and in

160 THE TREMATODA OF BRITISH FISHES

U.S.A. (at Woods Hole). The list of synonyms indicates that it is
difficult to describe, and it will be as well first of all to deal with forms
obtained by Nicoll (1910) from the conger in the Firth of Clyde and
definitely assigned to P. crucibulum. Size : 2-3-7 mm. long when
mature, greatest breadth about three-eighths of the length. Colour :
absent in small, yellowish-brown hi large specimens. Shape : elongate
and slightly flat, truncated anteriorly, pointed posteriorly ; average
specimens 3 15 mm. long, 1-1 mm. broad. Cuticle : covered with
scale-like spines, which are more numerous anteriorly. Haptor : a
very large wedge- or cornucopia-shaped rhynchus measuring 0-62 X
0-57 mm. in the average specimen, but frequently a button-like
process in small worms, generally having a projecting circular ridge.
Gut : mouth almost exactly central. Pharynx globular and 0-21 mm.
diameter. Intestine ovoid and connected with the pharynx by a
narrow oesophagus. Overall length about 0-3 mm. Excretory system :
vesicle comparatively short, extending through the final one-third of
the body. Reproductive systems : cirrus pouch short and stout,
situated on the left and co-extensive with the excretory vesicle.
Gonads variable in relative positions, generally ovary situated on
the right just behind the pharynx ; testes diagonally arranged a little
farther back ; diameters of ovary and testes respectively 0-25 mm.
and 0-28 mm. Uterus having ascending and descending limbs, mainly
situated on the left, but forming several loops between the gut and
the vitellaria and several more posteriorly on the right. Vitellaria
forming a continuous arc of irregular follicles behind the rhynchus
and in front of the uterus, unequally distributed on right and left.
Eggs numerous, pale yellow to dark brown in colour, measuring
0026-0030 x 0016-0021 mm. (mean 0029 X 0019 mm.).

Nicoll (1910) also redescribed " P. aculeatus," and the following
points must be noted carefully because they include the main features
of contrast in what he regarded as two distinct species. Size :
1-2-5 mm. long when mature, greatest breadth about half the length.
Shape : almost elliptical, but pointed towards either end, average
specimen measuring 2 x 0-95 mm. Colour : yellowish- brown.
Cuticle : covered with scale -like spines. Haptor : a rhynchus which
may be protruded like a small button, or retracted and then forming
a shallow, saucer-like depression of simple ovoid shape measuring
0-27 X 0-15 mm., its diameter nearly twice the depth. Gut : mouth
little more than one-quarter of the length of the body from the
posterior extremity ; pharynx 14 mm. diameter ; intestine a simple
sac extending forward, but not to the middle of the body. Excretory
system : vesicle extending forward to the level of the anterior testes,
or slightly in front of the pharynx. Reproductive systems : cirrus
pouch thick and of moderate length, co-extensive with the excretory
vesicle. Gonads arranged in the form of a triangle in the posterior
half of the body as in " P. crucibulum," but in the region of the gut ;
testes never symmetrical and measuring 0-26 x 0-20 mm. ; ovary
situated on the right and not much smaller than the testes. Uterus
having ascending and descending limbs and numerous regular folds,

BTTCEPHALID^ 161

mainly between the vitellaria and the gut. Vitelline follicles large ,
forming a regularly arranged arc crossing the body 0-4 mm. from its
anterior end. Eggs broad oval in shape, measuring 026-0 031 x
0-016-0-020 (mean dimensions 0-0285 x 0-0185 mm.).

Nicoll stated that " P. crucibulum " was met with half as frequently
as "P. aculeatus " in the conger, but is probably quite as common.
He amended this statement later (1914), stating that the two " species "
are found in association and are equally common. Apart from the
size ranges, which overlap slightly, they must have been difficult to
separate. From Nicoll's descriptions it is not difficult to see the
characters of P. crucibulum in " P. aculeatus" if we assume that the
body is more extended anteriorly, but has the rhynchus more con-
siderably introverted. This would bring the gut, the uterine folds
and the vitelline follicles into a relatively more anterior position, and
would destroy what is regarded as a characteristic arrangement of
the loops of the uterus in " P. aculeatus." Considering the way in
which the animal can alter its shape, this implies that the two forms
are identical. Size is not a criterion of distinction, because Nagaty
found very small specimens of P. crucibulum 0-8-1-8 mm. long, i.e.
smaller than Nicoll's specimens of "P. aculeatus," and even the
smallest of them contained eggs, although Nicoll regarded specimens
less than 2 mm. long as immature. The size range of P. crucibulum
may be taken as 0-8-6 mm. when mature if we accept the measure-
ments of Molin (4-6 mm.), Odhner (1-75-2-25 mm.), Ozaki (1-75-
3-4 mm.) and Eckmann (2-4 mm.) as well as those given. Differences
in the form and histological appearance of the rhynchus are incon-
clusive because they take no account of the state of the organ. It
is odd that Nagaty should regard " P. aculeatus " as a valid species,
but "P. squamatus " and "P. grandis " as synonyms of P. crucibulum,
because the last two differ more considerably from the type than the
first-named, and occur in different hosts (" squamatus " in the long-
spined and short-spined cottus and Montagu's sea snail, " grandis,"
in the cod and whiting). In "P. grandis," as described by Lebour,
the vitelline follicles form an arc and the eggs are relatively large
(about 0033 mm. long), but neither of these characters are significant.
Extension of the anterior end of the body breaks the arc of follicles,
and the eggs of small American specimens of "P. squamatus "
described by Linton (1940, p. 28, figs. 240-2) contained eggs of the
average dimensions 036 x 0-024 mm. The various forms of P.
crucibulum which have been described grade almost imperceptibly
one into another.

D. O. Jones (1943) redescribed "P. aculeatus" (as Skrjabiniella) ,
wrongly including the name Gasterostomum crucibulum in the synonymy.
Her specimen was small (1-3 x 0-66 mm.), and showed the general
characters indicated by Nicoll (1910), but not the regular folds of the
uterus which Nicoll regarded as characteristic of this form. Her
Fig. 1 gives a more detailed impression of structure than Nicoll's,
her Fig. 2 a better idea of the structure of the cirrus, which has a
lateral opening and a tongue-like terminal process. Structural

11

162 THE TREMATODA OF BRITISH FISHES

characters which Jones made clear include the accommodation of
the seminal vesicle inside the cirrus pouch, the existence of a recep-
taculum seminis uterinum and an ovicapt, and the binding together
of sperms by secretion in the ejaculatory duct. The eggs came
within the range specified by Nicoll, are slightly pointed at one pole
and undergo segmentation while still in the uterus. Jones repeated
the comparison made by Ozaki (1928) between the rhynchus in "P.
aculeatus " and P. uniporus Ozaki, 1924, which Manter (1940a)
regarded as its synonym, at the same time mentioning that P.
magniovatus Yamaguti differs only in the larger size of the eggs. It
seems likely that other synonyms of P. crucibulum will be found
among the species obtained in the Galapagos by Manter, who admitted
that additional material might show P. rotundus to be a synonym of
P. scalpellus, which Nagaty included in the synonyms of P. crucibulum.

Sub-order PROSOSTOMATA Odhner, 1905.
Family ALLOCREADIID^ Stossich, 1904.

Size and shape : small or medium size, long oval or elongate,
tapering anteriorly and rounded posteriorly, slightly flattened.
Cuticle : rarely spinous. Suckers : never very large and rarely far
apart. Out : prepharynx sometimes long, pharynx small, oesophagus
of medium length, caeca fairly or very long. Excretory system :
vesicle tubular or funnel-like with a long and broad median stem, flame-
cell formula 2[(4 + 4 -f 4) + (4 + 4 -f- 4)]. Reproductive systems :
genital pore median or slightly lateral near the end of the oesophagus.
Cirrus pouch large and elongate. Cirrus well developed. Vesicula
seminalis interna invariably present (sometimes externa also). Testes
large and globular, one behind the other in the posterior region.
Ovary spherical or lobed, situated in front of the testes, rarely median.
Receptaculum seminis large, Laurer's canal present. Vitellaria
follicular and lateral, mainly in the posterior half or two-thirds of
the body, sometimes extending anterior to the ventral sucker.
Uterus having only an ascending limb. Eggs variable in size and
shape, polar filaments sometimes present.

There have been a few proposals to split the Allocreadiidae into
several families, but conflicting opinions as to how this can best be
done show that the time is not yet ripe for such a change. Four
sub -famiHes are represented in Britain. Spinous forms belong to
the Lepocreadiinae and are parasites of marine fishes. Most non-
spinous forms belong to the Allocreadiinae and, with the exception of
the type-genus, are also parasites of marine fishes. Two non-spinous
forms parasitic in freshwater fishes, Crepidostomum and Sphaerostoma,
belong respectively to the Crepidostomatinae (see p. 192) and the
Sphaerostomatinae, and in the former the oral sucker has distinctive
anterior processes.

ALLOCREADIID^] 163

Sub-family Allocreadiin^] Looss, 1902.

Key to genera.

I. Genital pore median, oesophagus long or short, testes lobed or not.

1. Testes not lobed, eggs without polar filaments.

a. Cirrus pouch not projecting behind the ventral sucker.

(a) (Esophagus long, pars prostatica present, vitellaria

confined to the region behind the ventral sucker
(parasites of freshwater fishes) . . Allocreadium.

(b) (Esophagus short, pars prostatica absent, vitellaria

extending in front of the ventral sucker (parasites

of marine fishes) Cainocreadium.

b. Cirrus pouch projecting behind the ventral sucker Peracreadium.

2. Testes irregularly lobed, eggs having a filament at the anopercular

pole ......... Helicometra.

II. Genital pore slightly lateral, on the left, oesophagus short, testes
rounded.

1. Ovary globular, vitellaria extending anterior to the ventral

sucker, cirrus pouch not extending back behind it . Plagioporus.

2. Ovary 3-lobed, vitellaria not extending anterior to the ventral

sucker, cirrus pouch extending back behind it . . Podocotyle.

Genus ALLOCREADIUM Looss, 1900.
(Creadium Looss, 1899, nee Vieill., 1816.)

Allocreadium isoporum (Looss, 1894) Looss, 1900. (Fig. 34 A.)

Distoma isoporum Looss, 1894 (pp. 49-56, PI. 1, figs. 15-18 ; PI. 5, figs. 102-
112) ; Creadium isoporum of Looss, 1899 (pp. 570, 571, 595).

Hosts : Cyprinidse (carp, tench, bream, roach, chub, minnow,
barbel) and pike on the Continent (Rhine, Lake Constance) ; roach
in Cambridgeshire and chub in Berkshire (see Baylis, 1939).

Location : intestine (free in the lumen, not attached to the wall).

Size : 3-5 mm. long and 0-3-0-75 mm. broad. Shape : elongate
and spindle-like, broadest just behind the ventral sucker, tapering to
a point posteriorly, having slight " shoulders " and a cylindrical
" neck " anteriorly. Colour : white, or pale yellow or red, with
granules of dark pigment massed at the sides of the pharynx, these
being the vestiges of the eye-spots of the cercaria. Suckers : about
equal in size, the ventral larger than the oral at most in the ratio
14/13 and situated just in front of the middle of the body. Gut :
prepharynx short. Pharynx much smaller than the oral sucker.
(Esophagus long, terminating just in front of the ventral sucker,
caeca very long and of unequal lengths. Excretory system : median
stem of vesicle narrow, but dilated terminally, extending to the
posterior testis. Reproductive systems : genital pore situated beneath
the oesophagus and about 0-3 mm. in front of the ventral sucker.
Cirrus pouch large and pyriform, 0-45 mm. long and 0-2 mm. broad.
Testes almost spherical, about 0-5 mm. diameter, one behind the

164 THE TREMATODA OF BRITISH FISHES

other behind the middle of the body. Ovary much smaller than the
testes and near the middle of the body, diameter 0-25-0-3 mm.
Vitellaria dorsal and lateral to the caeca and confined to the posterior
half of the body ; follicles large, and tending to fill the available space
behind the posterior testis. Uterus having a few large loops in front
of the testes, extending lateral to the caeca above the ventral sucker.
Eggs few and large (0 09 X 06 mm.), and having thin, horn-yellow
shells, when laid containing an ovum and 10-15 vitelline cells.
Development : according to Luhe (1909) the snails Sphcerium corneum
and 8. rivicola serve as the first intermediate hosts, insect larvae
(Ephemera vulgata, Chcetopteryx villosa, Anabolia nervosa) as the
second, containing encysted metacercariae. The cercaria is said to
be the rhopalocercous Cercaria isopori Looss. Szidat (19396) has
reminded us that the life-history is by no means established, quoting
Looss (1894) as writing : ' Was die Jugendform unseres Wurmes
anlangt, so glaube ich, dieselbe zu kennen, wenngleich die Annahme
ihrer Zuge horigkeit zu den erwachsenen Thiere nur auf die Ahnlichkeit
in der Organisation, nich auf den direkten Nachweis durch den
Versuch gegrundet ist."

Three other species of Allocreadium occur in Europe, but not in
Britain, A. transversale (Rudolphi, 1802) Odhner, 1901 (pp. 505-6),
A. angusticolle (Hausman, 1896) Odhner, 1901 (p. 517) and A. poly-
morphum Layman, 1933. The first of these occurs in the spined
loach at Griefswald and Rossiten (East Prussia), where Szidat (1938a)
found the only specimen discovered for more than 130 years. The
second of these species occurs in the miller's thumb at Basel and in
Lake Constance. Looss (1899) referred it to the genus Creadium,
Nicoll (1909a) to Peracreadium and Hunninen & Cable (1943)
tentatively to Plagioporus. The life-history of this species was
studied by Mathias (1937). The third of these species was found in
Cottus kneri in Lake Bajkal (Russia), associating in the intestine with
a species of Crepidostomum.

Genus CAINOCREADIUM Nicoll, 1909.
Cainocreadium labracis (Dujardin, 1845) Nicoll, 1909. (Fig. 32 D.)

Distomum (Dicrocoelium) labracis Dujardin, 1845 (p. 398) ; Allocreadium
labracis (Dujardin) of Johnstone, 1908 ; Echinostoma labracis (Dujardin)
of Beneden, 1870 (p. 45).

Host : bass.
Location : intestine.

This species occurs in various parts of Europe (Rennes, Catania,
Isle of Elba) and was found by Johnstone in different parts of the
Irish Sea (Morecambe Bay, Cardigan Bay). Nicoll (1914) also found
it, at Plymouth. The bass seems to be a specific host ; the type-
specimens and specimens found by other zoologists (Stossich, Molin,
Beneden) invariably came from it. According to Johnstone (1908,
pp. 44-53, PI. 3 and figs. 1-4) bass taken from the Irish Sea are nearly

ALLOCREADIIDiE

165

Fig. 32. — A, Podocotyle atomon. B, P. atomon var. dispar. C, P. syn-
gnathi. D, Cainocreadium labracis. E, Helicometra fasciata ; F, an
egg of the same. G, Lepidauchen stenostoma. H, Crepidostomum
farionis. (A, after Lebour, 1908 ; B, after Nicoll, 1909 ; C and G,
after Nicoll, 1913 ; D, after Johnstone, 1908 ; E and F, after Nicoll,
1910 ; H, after Brown, 1927.)

166 THE TREMATODA OF BRITISH FISHES

always infected, although only the largest specimen obtained was
described. The specimens were said to be unsuitable for histological
study, and the topography of the internal organs might have been
altered by the manner of fixation, immersion in fresh water and
subsequent treatment with formalin, but a clear impression of
structure was given. Size : comparatively large for an Allocreadiid,
up to 9-7 mm. long and 2 mm. in greatest breadth. Shape : elongate
and spindle-like, slightly constricted near the middle. Suckers :
oral 0-76 mm. diameter, ventral 0-94 mm., but slightly longer than
broad and situated just in front of the middle of the body ; ratio of
the diameters in a smaller specimen 7/10. Gut : prepharynx short or
absent (shown in fig. 1, but not in PI. 3). Pharynx globular. (Eso-
phagus very short, terminating far in front of the ventral sucker. Caeca
very long and fairly wide. Excretory system : median stem of vesicle
long, extending forward at least to the testes, and narrow. Repro-
ductive systems : genital pore median and situated near the end of
the oesophagus. Cirrus pouch long and club-shaped, extending almost
to the hinder margin of the ventral sucker, but not behind it. Seminal
vesicle wide and straight, or only slightly convoluted. Cirrus narrow,
thick-walled and unarmed, often protruded. Testes almost spherical,
their outlines slightly irregular, one behind the other and contiguous
in the middle of the hindbody. Ovary having 3 equal and rounded
lobes and a swelling at the base, smaller than the testes and in front
of them on the right side. Vitellaria mainly lateral, but the follicles
tending to fill the median space behind the testes, encroaching on it
in the middle of the body, extending from the posterior extremity to
the level of the pharynx, the texture in front of the ventral sucker
very loose. Vitelline reservoir situated just in front of the testes,
median to the ovary. Uterus forming a number of folds between the
ventral sucker and the anterior testis ; metraterm commencing above
the seminal vesicle and decidedly muscular. Eggs measuring
0-079-0-095 x 0-048-0-064 mm., according to Odhner (1901) 007-
0-08 x 0-037 mm.

Genus PERACREADIUM Nicoll, 1909.

Members of this genus are typically parasites of Labridae. The
two species which are best known both occur in Britain, but are
probably identical. A third species, P. perezi Mathias, 1926, occurs
in the ballan wrasse and the gilt-head, but not in Britain.

Peracreadium genu (Rudolphi, 1819) Nicoll, 1909.

Distoma genu Rudolphi, 1819 (pp. 107-8, 397-8) ; Distomum fasciatum
Stossich, 1893 (p. 64) ; Allocreadium genu (Rudolphi) of Odhner, 1911.

Hosts : ballan wrasse, (?) shanny, five-bearded rockling.
Location : posterior end of intestine and rectum.

This species was described by Odhner (1901, pp. 497-9, PI. 33, fig.
3), and was found frequently by Nicoll (1910) in considerable numbers

ALLOCREADIID^E 167

at Millport, in association with the trematode he called " Helicometra
pulchella" but which seems to have been H. fasciata. Neither at
Millport nor at Plymouth, where Nicoll examined various Labridse
(thirty specimens), was the trematode found in any host but the ballan
wrasse, although an immature specimen 04 mm. long was found in
the shanny and was probably an adventitious parasite. Rees
(1945) found P. genu in the last-named host at Aberystwyth. Nicoll
remarked on the absence of the trematode on the East coast. His
specimens were 1-5-2-4 mm. long, but his description (1910, pp.
326-8) refers to the mean specimen 2 mm. long and 0-6 mm. in
greatest breadth. Colour : neutral grey. Shape : elongate, some-
what flat, but thick and broadest near the ventral sucker. Suckers :
ventral larger than the oral and 0-8 mm. from the anterior extremity,
dimensions 0-32 x 0-355 mm. and 0-2 mm. diameter. Gut : pre-
pharynx very short; pharynx globular and 13 mm. diameter,
oesophagus 0-11 mm. long, caeca long. Excretory system : vesicle
simple, extending to the anterior testis. Reproductive systems :
genital pore near the oesophagus. Cirrus-pouch long, extending back
to the level of the ovary, of uniform girth, containing a convoluted
seminal vesicle. Small pars prostatica ; long ejaculatory duct, the
cirrus frequently seen to be inserted in the metraterm of the same indi-
vidual (as noted by Olsson (1868) for P. commune). Testes irregular
oval outline, one behind the other and contiguous in the posterior
third of the body. Ovary globular, just in front and on the right
of the testes. Receptaculum seminis large, postero-dorsal to the
ovary. Vitellaria filling the lateral margins of the body behind the
ventral sucker, encroaching on the median plane behind the testes,
absent at the level of the ventral sucker, but forming a wedge-shaped
mass on each side slightly further forward, here extending to the
pharynx. Follicles of moderate size (004 mm. diameter). Uterus
short, containing no more than 30 eggs. Eggs yellow, slightly
thickened at the anopercular pole, measuring 0-080-0-088 x 0-044-
0056 mm. (mean, 00845 x 0051 mm.).

Peracreadium commune (Olsson, 1867) Nicoll, 1910.

Distoma commune Olsson, 1867 (pp. 31-2) ; Distoma labri Beneden, 1870 (p.
45), nee Stossich, 1886, nee Rudolphi, 1819 ; Allocreadium commune (Olsson)
of Odhner, 1902.

Hosts : ballan wrasse, gilt-head (Baillon's wrasse).
Location : rectum.

Nicoll (1910, pp. 328-9) found this species less frequently than
P. genu at Millport, only two specimens being obtained together.
It was described by Odhner (1902, pp. 499-503, PI. 33, fig. 6), who
commented on differences from P. genu, but Nicoll had difficulty in
separating the two species, regarding P. commune as very similar, but
broader and flatter, tinged with brown, and " not unreadily dis-
tinguishable " from P. genu by the arrangement of the vitellaria, the
follicles of which are continuously distributed between the pharynx

168 THE TREMATODA OF BRITISH FISHES

and the posterior extremity (i.e. uninterrupted at the level of the
ventral sucker). Odhner claimed this to be a constant difference
between the two species, but Nicoll was unable to confirm this and
could not deny that they might be identical. Odhner found the
eggs to be much narrower than in P. genu, but this was not true for
Nicoll's specimens. Other differences concern the pharynx, which
is almost fusiform in shape, 0-12 mm. long and 008 mm. broad in a
specimen 2 mm. long, and the ventral sucker, which is oval and
measures 0-31 X 0-22 mm. Both these characters were regarded by
Nicoll as distinctive. But it seems likely that they, and also the
smaller gonads and differently arranged vitellaria, will prove to come
well within the range of variability of a single species.

Genus HELIC0METRA Odhner, 1902 nee Travassos, 1928.
(Loborchis Luhe, in Stossich, 1902.)

Nicoll (1910, pp. 335-6) briefly reviewed this genus and mentioned
five species at that time allocated to it, namely Helicometra pulchella
(Rudolphi, 1819), H.fasciata (Rudolphi, 1819), H. sinuata (Rudolphi,
1819), H. mutabilis (Stossich, 1902) and H. flava (Stossich, 1903).
He examined specimens of H. mutabilis and Distomum gobii Stossich,
1883, which were lent to him from the collection of Stossich by
Monticelli, but not another related form, Distomum labri Stossich,
1886, although he relegated all three forms to synonymy with " H.
pulchella." It is unfortunately true that Nicoll did not take H.
fasciata and H. sinuata into consideration when naming his specimens,
and this had dire consequences. Palombi (1929a) studied the
morphology and life-history of the former species at Naples and reviewed
the genus, relegating H. pulchella of Nicoll, 1910 to synonymy
with H. fasciata, which occurs in twenty-one species of fishes in
Europe (Atlantic and Mediterranean), as well as others in America
(Florida and Mexico ; see Manter, 1934, p. 172, and 1940a, p. 387).
Of the three species which Palombi regarded as valid only one has lobed
testes ; this is Helicometra fasciata, which is the commonest British
species — possibly the only species occurring here. The other two,
H. pulchella and H. sinuata, can be distinguished by the diagonal or
tandem arrangement of the testes and the nature of the vitellaria,
which in the former are mainly lateral, but in the latter tend to fill
the posterior region of the body. H. pulchella has been named in
British waters, although there is some doubt about its occurrence
here, but H. sinuata is a Mediterranean species. Several other
species are known, but it will be sufficient to name them. H. torta
Linton, 1910 and H. execta Linton, 1910, both occur at Tortugas, H.
plovmornini Issaitschikow, 1928, in the Russian Arctic, and a doubtful
species called H. gurnardi Thapar & Dayal, 1934, was discovered in
a grey gurnard in the Aquarium of the Zoological Society, London.
Before dealing with H. fasciata it might be mentioned that a form
closely related to H. torta and H. execta has 9 testes arranged in two

ALLOCREADIIDiE 169

longitudinal rows and was therefore referred to a new species and
genus, Helicometrina nimia, by Linton (1910). This is interesting
because the testes show a tendency to degenerate in Helicometra,
even some members of the same species having 2, 1 or none, and any
phenomena of this kind are worth investigating. Apparently the
multiplication of the testes occurs in several species since referred to
Helicometrina, H. azumce Layman, 1930, having two rows of 5, H.parva
Manter, 1933, only 3, and H. elongata Noble & Park, 1937, 9, in
longitudinal rows of 5 and 4. All four species occur in marine fishes,
nimia and parva at Tortugas, elongata in California, and azumce in
Peter the Great Bay.

Helicometra fasciata (Rudolphi, 1819) Odhner, 1902 (pp. 160-1).

(Fig. 32 E.)

Distoma fasciatum Rudolphi, 1819 (p. 97, pp. 373-4) nee Stossich, 1885 (p. 160),
1886 (p. 32), 1892 (p. 64), 1898 (p. 46); D. gobii Stossich, 1883 (pp. 116-17,
PI. 2, figs. 6, 7) ; Loborchis mutabilis Stossich, 1902 (pp. 579-82, 1 fig.) ;
Allocreadium fasciatum (Stossich) Odhner, 1901 (pp. 499-503, PI. 33, fig. 1) ;
Distoma (Dicrocozlium) fasciatum (Rudolphi) of Barbagallo & Drago, 1903
(p. 410) ; Helicometra mutabilis (Stossich) Stossich, 1903 (pp. 375-6) and
1904 (p. 13) ; H. gobii (Stossich) of Wallin, 1910 (p. 61) ; H.flava Stossich,
1903 (pp. 373-6, 1 fig.) and of Wallin, 1910 (p. 61) ; H. pulchella (Rudolphi)
of Nicoll, 1910 ; H. epinepheli Yamaguti, 1934 ; H. hypodytes Yamaguti,
1934.

Hosts : in Britain, comber, red gurnard, rock goby, gattorugine,
shanny, ballan wrasse, cuckoo wrasse, gold-sinny, common topknot,
eel, conger, cornish sucker, gilt-head (Baillon's wrasse), long-spined
cottus.

Location : lower intestine.

Baylis & Idris Jones (1933) recorded this species in the gilt-head
(Baillon's wrasse) at Plymouth, differentiating it from H. pulchella . All
the other hosts mentioned stand on the assumption that H. pulchella of
Nicoll is really H. fasciata, except that Rees (1945) recorded the long-
spined cottus as a host at Aberystwyth. Nicoll (1910) found specimens
with lobed testes in the ballan wrasse and conger at Millport, and (1914)
similar specimens in all the hosts mentioned in the list above, except the
gilt-head, at Plymouth. Little's record for H. pulchella may refer to
this species, which occurs at Banyuls and elsewhere in the Mediterranean,
in Florida, Mexico and the Far East, generally in moderate numbers —
twenty specimens in a single host. Particularly large specimens have
been found in the conger. Nicoll (1910, pp. 336-40, PI. 29, figs. 3, 4)
described the trematode (as H. pulchella), but characters put forward
by Palombi (1929, a, pp. 244-54, figs. 7-26, PL 10, figs. 1-5) are
shown here in parentheses. Size : 1 -3-4-3 mm. long, average length
2-5 mm., and 0-83 mm. broad (1-5-3 x 0-4-0-75 x 0-33 mm.),
attaining maturity when 1-25 mm. long, sometimes containing
malformed eggs when only 1-1 mm. long. Colour : very evident at
maturity in the contents of the intestine because of a rich brown

170 THE TREMATODA OF BRITISH FISHES

colour ; juveniles colourless. Shape : long oval outline, much
flattened behind the ventral sucker, tapering gradually in front of it.
Suckers : almost globular, the ventral retaining its spherical form
even when compressed slightly, and larger than the oral, situated
slightly more than one-third of the body length (or about 0-9 mm.)
from the anterior extremity ; diameters 0-35 mm. and 0-23 mm.
(0-22-0-3 mm. and 0-15-0-2 mm.). Gut : prepharynx very short.
Pharynx almost globular and about 0-1 mm. diameter (0 09 mm.).
(Esophagus nearly half as long again (0-15-0-3 mm. long, and S-shaped).
Caeca long, but not quite reaching the posterior extremity. Bifurcation
of the gut midway between the pharynx and the ventral sucker.
Excretory system : median canal extending forward to the ovary,
flame cell formula 2[(2 + 2) + (2 + 2)] (see Hopkins, 19416, figs. 1, 2).
Reproductive systems : genital pore median near the middle of the
oesophagus. Cirrus pouch short and narrow (pyriform), straight or
slightly curved, extending back to or slightly beyond the anterior
border of the ventral sucker, containing a convoluted seminal vesicle
and the ejaculatory duct, a distinct pars prostatica being absent,
although gland-cells open into the duct, (cirrus 015 mm. long).
Testes irregularly lobed, the lobes 5 to 7 in number and frilled or
divided into lobules, all indentations being confined to the posterior
and lateral regions. Anterior testis less lobulated than the posterior.
Position of the testes one behind the other and contiguous (leaving
a post-testicular space occupying one-sixth to one-tenth of the body-
length). Breadth of the testes about 0-37 mm. Ovary smaller than
the anterior testis and situated in front of and contiguous with it,
median or slightly lateral, irregularly 3- or 4-lobed and broader than
long. Receptaculum seminis pyriform (0-11-0-20 mm. long and
007 mm. broad) and generally on the right of the ovary. Laurer's
canal present. Vitellaria mainly lateral, following the caeca and
extending into more lateral regions, continuing in a forward direction
to the level of the pharynx, here spreading towards the median dorsal
line, extending posteriorly between the caeca and the excretory vesicle
to the limits of the posterior testis (merging in the median plane
posteriorly). Uterus having an ascending limb confined between the
ovary and the ventral sucker, formed into a spiral of 3 to 5 super-
imposed loops each slightly in front of the one underneath. Eggs in
the uterus numbering about 50 at any time, dark brown and moderately
thick-shelled, convex on one side and concave on the other, having
a polar filament 6 to 8 times as long as the capsule at the anopercular
pole ; dimensions 0-063-0-084 mm. long, 0-032-0-037 mm. broad
and 0-027-0-033 (misprinted as 0-33) mm. in maximum thickness
from the convex to the concave surface, mean 0-073 X 0033 x
0-030 mm. (0-060-0-075 x 0-025-0-029 mm. ; filament 0-2 mm. long).
Eggs still in utero having their filaments directed forwards and
sometimes intertwined ; ovum unsegmented when the egg is laid.

Nicoll (1914, p. 476) regarded this as the commonest Allocreadiid
at Plymouth, remarking that as a parasite of littoral fishes it replaces
Podocotyle atomon, which predominates on the East coast of Britain.

ALLOCREADIID^ 171

It has never been recorded from the North Sea. The main hosts
seem to be gobies and blennies. Palombi (1929a) reported variability
in adults, particularly as regards the shape and size of the pharynx,
the length and position of the cirrus pouch and the shape of the
ovary. He found the metacercariae of H. fasciata encysted in Leander
serratus, L. squilla and L. xiphias. Adult specimens found by
Mathias (1934, pp. 569-71, fig. 2) in Trigla aspera and Scorpcena
porcus near Banyuls were 2-4-3-5 mm. long and 0-67-0-8 mm. in
maximum breadth, with suckers 0-20-0-25 mm. and 0-30-0-38 mm.
diameter and 0-39-0-54 mm. apart. In nearly all of them the testes
were lobed and the vitellaria scattered in the posterior region, and
the polar filaments of the eggs were six to eight times as long as
the capsule, the dimensions of which were given as 0-07-0-08 x
0011-003 mm.

Helicometra pulchella (Rudolphi, 1819) Odhner, 1902 (pp. 161-2, fig. 3).

Distoma pulchellum Rudolphi 1819 (pp. 94, 367) ; Distomum pulchellum
(Rudolphi) Diesing, 1850 (p. 338) ; D. labri Stossich, 1886 (p. 30), 1887
(p. 91), 1888 (p. 12) ; Allocreadium labri (Stossich) Odhner, 1901 (pp. 493-6,
PI. 33, fig. 2) ; Distoma (Dicrocoelium) pulchellum Barbagallo & Drago,
1903 (p. 410) ; Allocreadium alacre Stossich, nee Looss, of Palombi, 1929
(p. 13, fig. 5).

Hosts : Baylis & Idris Jones (1933), and Baylis (1939) recorded
these at Plymouth as the comber, streaked gurnard, yellow gurnard
and red gurnard, Little (1929) at Galway as the yellow gurnard and
streaked gurnard. According to Palombi the hosts at Naples, Trieste
and Catania are the cuckoo wrasse, greater weever, butterfly blenny
and Gobius jozo. Rees (1945) named the shanny as a host at Aberyst-
wyth.

Location : intestine and stomach (of red gurnard).

According to Palombi (1929a, pp. 277-81, figs. 27-9)— Size :
1-35-2 mm. long and 0-65-0-75 mm. in greatest breadth. Shape:
outline oval, tapering anteriorly. Suckers : oral 0-15-0-20 mm.
diameter (misprinted as 0-15-0-38 mm. on p. 280 ; see the table on
p. 281), ventral 0-22-0-25 mm., means 0-18 and 0-24 mm. Gut :
pharynx broader than long, dimensions 0-066-0-086 x 0-075-0-13 mm.
(but in the table on p. 281 diameter given as 0-075-0-100, mean
0087 mm.). Reproductive systems : genital pore ventral to the
middle of the oesophagus. Cirrus pouch extending along the anterior
margin of the ventral sucker to a level near its middle. Testes
globular, diagonally arranged in the posterior half of the body. Ovary
tri- or multilobulate, and situated in front of the testes and on the
same side as the more posterior of them. Receptaculum seminis
globular, as large as the ovary and situated near it. Vitellaria
extending laterally between the pharynx and the ends of the cseca,
confluent posteriorly. Eggs variable in size and number, 0-050-
0-058 mm. long (mean 0053 mm.), the filament not exceeding 0-2 mm.
in length.

For a description of Helicometra sinuata (Rudolphi, 1819) Odhner,

172 THE TREMATODA OF BRITISH FISHES

1902 see Palombi (1929a, pp. 281-5, figs. 30-33). This species has
been found in the greater weever and other hosts in various parts of
Italy (Naples, Trieste, Venice, Portoferraio), and occurs in America
(Costa Rica). Although larger than H. pulchella it has smaller eggs
(0042-0050 mm. long), and is distinguishable from this species by
characters already noted.

Genus PLAGI0P0RUS Stafford, 1904.
(Lebouria Nicholl, 1909 ; Caudotestis Yamaguti, 1934.)

This genus, the synonymy of which has been discussed by Miller
(1941), is represented in Britain by three species, Plagioporus alacer,
P. varius and P. idoneus. Another species, P. tumidulus (Rudolphi,
1819) occurs in European waters, but not British, in the ocean pipe-
fish and the greater pipe-fish ; another, P. acerince (Pigulewski,
1931) was found in the ruffe in the R. Sodsch (Ukraine), and a sixth
species, P. nicolli (Issaitschikow, 1928) occurs in Icelus bicomis in
the Arctic.

Plagioporus alacer (Looss, 1901). (Fig. 33 B.)

Distomum alacre Looss, 1901 (pp. 401-2, fig. 2) ; Lebouria alacris (Looss) of
Nicoll, 1910, 1914, 1915.

Hosts : in Britain, ballan wrasse, cuckoo wrasse, gilt-head
(Baillon's wrasse), gold-sinny, rock cook.
Location : intestine.

Johnstone (1907, pp. 186-8, fig. 17) recorded this species at
Liverpool as Distomum sp. (see Nicoll, 1915, p. 357), and it was found
by Nicoll (1910, 1914) at Millport and Plymouth. According to
Looss (1901a, p. 401) its characters are : Size : hardly more than
1-5 mm. long; greatest breadth near the ventral sucker 0-4 mm.
Shape : outline oval, pointed at the extremities. Suckers : ventral
larger than the oral and situated just in front of the middle of the
body ; diameters 0-3 mm. and 014 mm. Gut : pharynx small
(007 mm. diameter). (Esophagus fairly long. Caeca long, extending to
a level midway between the hinder testis and the posterior extremity.
Bifurcation of the intestine midway between the suckers. Repro-
ductive systems : genital pore slightly on the left near the termination
of the oesophagus. Cirrus pouch large and muscular, reaching back
to a point above the middle of the ventral sucker. Seminal vesicle
S-shaped. Pars prostatica narrow and of medium length. Ejaculatory
duct and cirrus scarcely distinguishable. Testes oval or rounded,
situated one behind the other in the posterior region. Ovary small
and spherical, situated in front of the testes. Receptaculum seminis
and Laurer's canal present, the latter rather long. Vitellaria com-
prising numerous large follicles, extending from the pharynx to the
posterior extremity; vitelline reservoir placed between the anterior
testis and the ventral sucker. Uterus short and having a few folds
between the testes and this sucker. Metraterm about half as long as

ALLOCRTCADITDJE 173

the cirrus pouch. Eggs relatively large (008 x 005 mm.), and few,
yellow and thin-shelled. Nicoll (1910, pp. 332-4, PI. 29, fig. 2)
described specimens from the ballan wrasse at Millport. They were
0-8-1-45 mm. long (mean 1 mm.) and 0-46 mm. broad and had larger
suckers, the oral 0155 mm. diameter, the transversely oval ventral
sucker situated 0-46 mm. from the anterior extremity and measuring
0-22 x 0-26 mm., the ratio of the diameters thus about 5/3. Other
points of structure noted were the large size of the pharynx (0077 x
0066 mm.) and the length of the oesophagus (009 mm.). The uterus
contained no more than 20 eggs measuring 0081-0088 x 0-041-
0054 mm. (mean 0083 x 0049 mm.).

Plagioporus varius (Nicoll, 1910). (Fig. 33 A.)

Lebouria varia Nicoll, 1910 ; {Lebouria) alacris Looss of Nicoll, 1909 (p. 8,
PI. 1, fig. 1) ; Lebouria idonea Nicoll of Johnstone, 1910 (pp. 16-18, fig. 1).

Hosts : dragonet, cuckoo wrasse, ballan wrasse, plaice, flounder,
John Dory.

Location : intestine.

This species was found by Johnstone (1910) in dragonets from
Morecambe Bay. Nicoll (1910) thought it almost exclusively con-
fined to this host, and (1915) recorded its occurrence in the dragonet at
St. Andrews, Millport, Plymouth and Liverpool, as well as in the
plaice at Millport. Little (1929a) found it in the flounder at Galway,
Bay lis & Idris Jones (1933) in the cuckoo wrasse, ballan wrasse
and dragonet at Plymouth, where I have found it in the John Dory,
but not in dragonets, wrasses or plaice. Nicoll (19096, p. 8, PI. 1,
fig. 1) described a specimen found in the dragonet at St. Andrews,
and (19096, p. 9) a small and immature form from the same host at
Luce Bay. In a later paper Nicoll (1910, p. 329) mentioned specimens
obtained in the Clyde, and gave a description based mainly on
specimens from the south coast, expressing the opinion that this
species is certainly distinct from Plagioporus alacer, adding that the
differences are " not by any means striking owing to the rather
considerable amount of variation which occurs." Comparison of his
Figs. 1 and 2 shows this qualification to be true ; the two species bear
a close resemblance, when allowance is made for differences in size.
Taking the descriptions of Nicoll to be compatible and with a few
observations of my own in parentheses, we arrive at the following
characters for P. varia. Size : up to 1-75 mm. long and about
one-third as broad, smallest specimen obtained 0-32 mm. long (show-
ing the cercaria to be small) ; specimens 1-1-1-2 mm. long (with or)
without eggs, length at maturity about 1-25 mm. (10-11 mm.).
Cuticle : smooth (slightly wrinkled) ; subcutaneous glands numerous,
particularly in the anterior region. Suckers : in specimens 1-4-
1-5 mm. long, oral 0-21-0-18 mm. diameter ; ventral transversely oval
and measuring 0-34-0-35 x 0-29-0-32 mm., the ventral about 0-55 mm.
from the anterior extremity ; in specimens 11 mm. long and 0-45 mm.
in greatest breadth, oral 013 mm. long and 0-14 mm. broad, ventral

174 THE TREMATODA OF BRITISH FISHES

measuring 0*31 X 0-21 mm., the anterior rim 0-33 mm. behind the
anterior extremity. Gut : prepharynx short ; pharynx more than
half as broad as the oral sucker, 014-0-11 mm. long and 0*11-0-10 mm.
broad (012 x 0-08 mm.). (Esophagus 006 mm. long. Caeca diverging
widely and terminating slightly behind the posterior testis (midway
between it and the hind end of the body) . Reproductive systems :
genital pore median or on the left of the oesophagus (immediately
beneath the pharynx). Cirrus pouch short and club-shaped, slightly
curved, not extending back beyond the middle of the ventral sucker.
Seminal vesicle convoluted. Ejaculatory duct short and nearly
straight, but sometimes slightly folded. Pars prostatica indistinct,
but gland- cells present. Testes irregularly ovoid and diagonally
contiguous, their faces of contact slightly flattened; diameters
0-2-0-28 mm. (0-09-0-11 x 0-17 mm., the post-testicular space
0-33 mm. long). Ovary globular and between the anterior testis and
the ventral sucker on the right, diameter 0-1 mm. Receptaculum
seminis pyriform, located between the ovary and the testes. Vitellaria
very well developed, especially in the posterior region, the follicles
mainly lateral, but spreading to the inner sides of the cseca, com-
pletely filling the post-testicular space, overlapping the gonads to a
variable extent, sparse or absent at the level of the ventral sucker,
abundant in front of it, but not as numerous as posteriorly, their
anterior distribution variable, sometimes to the pharynx, or only to
the oesophagus (confirmed). Follicles large, 0-055 mm. diameter
(004 X 0-025 mm. anteriorly and 0052 x 0-03 mm. posteriorly).
Uterus containing not more than 20 eggs of elliptical shape, but
with a somewhat flattened operculum and a slight knob at the
anopercular pole, not as pronounced as in P. idoneus, dimensions
0-085-0-092 x 0-038-0-051 mm. ? mean 0-088 X 0-045 mm. (about
18 eggs whose mean dimensions are 0-081 X 0-052 mm.). Notes :
Allocation to this species largely depends on the distribution of the
vitelline follicles, but it must be stressed that this is not invariably
precisely as determined by Nicoll, follicles sometimes being relatively
abundant near the ventral sucker. In the last analysis the distinc-
tions between P. varia and P. alacris will probably prove to be
insignificant, but it is preferable to maintain the latter as a valid
species, at least for the present.

Plagioporus idoneus (Nicoll, 1909). (Fig. 33 C.)

Lebouria idonea Nicoll, 1909 ; Allocreadium sp. ; under host-name in Nicoll
(1915, p. 356).

Hosts : wolf- fish and Anarrhichas latifrons.

Location : intestine (in large numbers) and stomach (fewer).

Nicoll (1915) recorded the occurrence of this species at St. Andrews
and Northumberland (Cullercoats) in the former host, and at Aberdeen
in the latter (see p. 356). He had described it in a previous paper
(1909a, p. 441, PI. 9, figs. 9-12). Size : 1-5-2-5 mm. long, 0-7-1-0 mm.
in greater breadth and 0-2-0-3 mm. thick ; smallest mature and

ALLOCREADIIDiE 175

largest immature specimens alike, 1-58 mm. long. Colour : yellow.
Shape : outline oval, somewhat attenuated anteriorly. Cutaneous
glands : large ovoid cells in the antero-lateral regions. Muscular
system : including numerous myoblasts arranged in groups. Suckers :
oral 0-17-0-28 mm. diameter, ventral near the middle of the body,
transversely oval, 0041 x 0-031-0-58 x 0-48 mm. (about twice as
large as the oral). Gut: prepharynx wide. Pharynx relatively large
(0-15-0-21 mm. diameter). (Esophagus 0-1-0-18 mm. long. Caeca wide
and long ; bifurcation of the gut midway between the suckers.
Pharynx and oesophagus lined with cuticle, that of the former deeply-
staining. Caeca with an epithelial lining and thread-like processes at
the free ends of the cells. Excretory system : vesicle extending
forward to the anterior testis. Reproductive systems : genital pore
midway between the suckers, generally median ; genital atrium small.
Cirrus-pouch 0-4 mm. long, extending only slightly behind the ventral
sucker. Seminal vesicle much convoluted ; ejaculatory duct looped ;
pars prostatica ill-defined. Testes transversely ovoid, their borders
irregular, obliquely one behind the other and almost contiguous, the
anterior slightly smaller than the posterior. Ovary globular, slightly
in front of the anterior testis, but on the right adjacent to the caecum.
Receptaculum seminis above or in front of the ovary. Vitellaria
extending from the pharynx to the posterior extremity, the follicles
filling the post-testicular region and encroaching on the median
dorsal space in the anterior region, comprising nests of 12-20 cells
each 0-023 mm. diameter. Uterus confined between the ventral
sucker and the ovary, containing about 60 eggs of pale yellow colour
with a knob-like projection at the anopercular pole (more pronounced
than in P. varia), their dimensions 0071-0075 x 0-039-0-044 mm.
(mean 0073 X 0041 mm.).

Genus P0D0C0TYLE (Dujardin ; 1845) Odhner, 1905.
(Sinistroporus Stafford, 1904 ; Podocotyloides Yamaguti, 1934.)

Taxonomic matters regarding this genus have been discussed by
Odhner (1905), Nicoll (1907) and Manter (1926). Park (1937) prepared a
key to nineteen species, eight of them set up by himself, and included
the British form Podocotyle atomon var. dispar Nicoll, 1909, but excluded
the Italian species P. furcata (Bremser, in Rudolphi, 1819) and the
British form P. atherince sp. inq. Nicoll, 1914. It might be mentioned
that Park found the distribution of vitelline follicles very variable,
but chose a number of less variable characters for the separation of
species, notably the flat or cylindrical form of the body, the straight
or coiled nature of the seminal vesicle, the relative length of the
cirrus pouch, the characters of the genital organs and the relative
positions of the testes. Apparently all European and some other
forms have a seminal vesicle which is coiled. The best-known and
type species, Podocotyle atomon, is common in Britain, less common
species here being P. reflexa, P. syngnathi and P. atherince, which is
probably a synonym of the type species. Two species occur only in

176 THE TREMATODA OF BRTTTSH FISHES

the Russian Arctic. P. odhneri and P. levinseni, both of which were
erected by Issaitschikow (1928), the first occurring in Gymnacanthus
tricuspis, the second in the sea-snail and the lumpsucker. The
species P. furcata occurs in Italy, but not in Britain, in the red mullet
and the dover sole, and the Swedish species P. olssoni Odhner, 1905,
has been recorded in " Lumprenus " maculatus and Gadus melano-
stomus. The forms with which we have to deal can be separated
by the key :

I. Testes very close together (cirrus pouch extending behind the ventral

sucker) ........ P. atherince sp. inq.

II. Testes considerably apart, or separated by vitelline follicles.

1. Cirrus pouch not extending behind the ventral sucker P. syngnathi.

2. Cirrus pouch extending behind the ventral sucker :

a. (Esophagus twice as long as the pharynx :

(a) Vitelline follicles not present in front of the ventral

sucker. . . . . . . .P. atomon.

(b) Vitelline follicles extending in front of the ventral

sucker . . . . ... P. atomon var. dispar.

b. (Esophagus about as long as the pharynx (body cylindrical)

P. reflexa.

Podocotyle atherinse sp. inq. Nicoll, 1914.

Host : sand smelt.

Location : anterior part of the intestine.

Nicoll (1914, p. 474, fig. 1) described under this name a solitary
specimen found at Plymouth, which he could not refer to any known
species of Podocotyle, and which was even only a doubtful member
of the genus, but was placed in it with due regard for the shape of
the ovary, the position of the genital pore and the length of the cirrus
pouch. Actually, the positions of the testes contradict this diagnosis,
the specimen in this character resembling a species of Plagioporus.
The main characters of this trematode are as follows. Size : IT mm.
long and 0-49 mm. in greatest breadth. Shape : nearly oval in out-
line, slightly attenuated anteriorly. Colour : dark grey. Suckers :
oral globular and 0T3 mm. diameter; ventral transversely oval,
0-21 mm. long, 0-28 mm. broad and situated 0-46 mm. from the
anterior extremity. Gut : prepharynx absent, pharynx 007 mm.
diameter. (Esophagus 0T1 mm. long. Caeca wide and long, extending
almost to the posterior extremity. Reproductive systems : genital
pore slightly on the left near the termination of the oesophagus.
Cirrus pouch long and slender, curving round the ventral sucker and
extending back to the level of the ovary, containing a simple ejacu-
latory duct and a long and convoluted seminal vesicle. Testes
irregularly globular and 0T7 mm. long, continuous and diagonally-
arranged, the posterior one on the right and 0T3 mm. from the
posterior extremity. Ovary having 3 backwardly-directed lobes and
situated on the right of the anterior testis, measuring 01 3 mm. along
the major axis and situated 014 mm. behind the ventral sucker.
Receptaculum seminis pyriform, just in front of the former testis.

ALLOCREADIIDJE 177

Vitellaria mainly confined to the lateral regions between the ventral
sucker and the hind end of the body, but encroaching on the post-
testicular space without merging. Uterus having very few folds, and
containing a small number of eggs measuring 0-069-0072 x 0036 mm.,
each having a knob-like process at the anopercular pole. Nicoll
suggested that the trematode is probably an abnormal specimen of
Podocotyle atomon with displaced testes, and this seems to be the
best solution of a problem which cannot be settled with such scanty
material.

Podocotyle syngnathi Nicoll, 1913. (Fig. 32 C.)

Hosts : greater pipe-fish, broad-nosed pipe-fish, ocean pipe-fish.
Location : intestine.

Nicoll (1913a, p. 238, PL 11, figs. 1, 2) found this species at Ply-
mouth in 4 out of 9 greater pipe-fish, 1 out of 6 broad-nosed pipe-fish
and 4 out of 8 ocean pipe-fish. Baylis & Idris Jones (1933) recorded
it in the ocean pipe-fish, also at Plymouth. It very closely resembles
other species of Podocotyle, differing from them in the noticeable
shortness of the cirrus pouch. The smallest specimens were found
in the ocean pipe-fish and were just about to produce eggs when
2-2 mm. long, contrasting with P. atomon from the same individual
host, which contained eggs when 1 mm. long. The five largest
specimens were 4-55-5-95 mm. long (mean 5-36 mm.) and 0-78 mm.
in greatest breadth posteriorly, but breadth varies from one-seventh
to one-ninth of the length of the body according to the degree of
extension. Suckers : oral smaller than the ventral, dimensions
0-38 mm. diameter and 0-43 X 0-55 mm., ventral 1-25 mm. from the
anterior extremity, and thus about one- quarter of the distance along
the body. Gut : prepharynx very short, pharynx about 019 mm.
diameter. (Esophagus 0-17 mm. long. Cseca long and somewhat dilated
posteriorly. Excretory system : vesicle long, extending to the anterior
end of the ovary. Reproductive system : genital pore on the left of
the oesophagus. Cirrus-pouch short and stout, not extending behind
the middle of the ventral sucker, containing a comparatively compact
seminal vesicle and a short ejaculatory duct. Testes diagonally
ovoid, situated one behind the other in the posterior region, but not
contiguous; dimensions 0-57 X 0-47 mm., the post-testicular space
slightly more than 1 mm. long (one-fourth to one-sixth body-length).
Ovary having 3 posterior lobes, about 0-1 mm. in front of the anterior
testis. Receptaculum seminis in front of the ovary, more anteriorly
situated than in P. atomon. Vitellaria of more limited extent, ending
some distance behind the ventral sucker, tending to fill the posterior
region, but often interrupted on one side or both sides opposite the
posterior testis. Transverse vitelloducts in front of the ovary.
Uterus confined within the boundaries of the caeca between the
receptaculum seminis and the ventral sucker, containing about 50
eggs measuring 0-082-0-102 x 0-045-0-050 mm. (mean 0-092 x
0-047 mm.).

12

178 THE TREMATODA OF BRITISH FISHES

Podocotyle atomon (Rudolphi, 1802) Odhner, 1905 (pp. 320-6, PL 2,
figs. 9, 10). (Fig. 32 A, B.)

Fasciola atomon Rudolphi, 1802 (p. 70) ; Distoma atomon Rudolphi, 1809 (pp.
362-3) ; D. simplex Rudolphi, 1809, and of Olsson (1868, p. 34), Lovinsen
(1881, pp. 67-9, PI. 3, fig. 1) and Linton (1899, pp. 525-6, PI. 47, figs. 3-7) ;
D. reflexum Creplin, 1825 (p. 54), nee Olsson, 1868, nee Zschokke, 1890;
D. angulatum Dujardin, 1845 (pp. 401-2) ; D. ceglefini of Beneden, 1870 (p.
57), Linstow, 1889, and Stossich, 1886 ; Allocreadium atomon (Rudolphi) of
Odhner, 1901 (pp. 506-13, PI. 33, figs. 9, 10) ; Sinistroporus simplex
Stafford, 1904 (pp. 484-5) in part ; Psilostomwn redactum Nicoll, 1906 (pp.
525-7, PL 13, figs. 9, 10) ; Podocotyle atomon var. dispar Nicoll, 1909
(— Distomum vitellosum Linton of Johnstone, 1907) ; ? Fasciola ceglefini
Miiller, 1776 (p. 224).

Hosts : in Britain, father- lasher, long-spined cottus, Montagu's
sea snail, 2-spotted goby, butter-fish, viviparous blenny, 3-spined
stickleback, 15-spined stickleback, bib, whiting, coal-fish, pollack,
5-bearded rockling, 3-bearded rockling, Norwegian topknot, common
topknot, sole, plaice, flounder, dab, ocean pipefish, eel, gilt-head.

Location : intestine and pyloric caeca.

This familiar species has been found in most places where marine
trematodes have been sought in this country — at Millport, St. Andrews,
Culler coats, Plymouth and Liverpool — and elsewhere at Gal way,
Greifswald, in Greenland, Sweden, Canada and U.S.A. As the list
of hosts indicates, it is the commonest trematode of fishes of rock-
pools on the sea-shore and it has been described by several continental
and British zoologists. The father lasher seems to be the commonest
host not only in Britain, but also in Sweden and Greenland. The
taxonomy of the species has been discussed by Odhner (1905, p. 320)
and by Nicoll (1907, p. 73), so that detailed consideration of the
synonymy is unnecessary here. Abundant information exists about
the characters of specimens found in the British Isles, so that it is
unnecessary also to consider the detailed descriptions of continental
zoologists, but it will be necessary to examine several statements
which establish the fact that the species shows great variability.
Johnstone's brief description (1907, p. 182, fig. 15) of specimens
found in flounders in the tanks at Piel, Barrow-in-Furness, can be
considered first of all. These specimens were 2-2-5 mm. long and
0-25-0-5 mm. broad, elongate, somewhat pointed at the extremities,
but little flattened. The ventral sucker was nearly twice as large as
the oral, and borne on an eminence at the end of the first quarter of
the body, respective diameters being 0-42 and 0-23 mm. A pre-
pharynx was neither mentioned nor shown, but the gut comprised a
large pharynx, a short oesophagus and long and straight caeca. The
genital pore was near the hind end of the pharynx, and the cirrus
pouch extended behind the ventral sucker. The testes were situated
in the hindmost one-third of the body, one behind the other, the
globular ovary occupying a position in front of them. The vitellaria
comprised 4 longitudinal rows of follicles extending (according to
the figure) from just behind the ventral sucker to the hinder end of
the body, with conspicuous vitelloducts, the transverse ones crossing

ALLOCREADIIDiE

179

Fig. 33. — A, Plagioporus varius. B, P. alacer. C, P. idoneus. D, Lepida-
pedon rachion. E, L. elongatum. F, Opechona bacillaris. G, O.
retractilis. (A, B. F, after Nicoll, 1910 ; C, after Nicoll, 1909 ; rest after
Lebour, 1908a.)

180 THE TREMATODA OF BRITISH FISHES

the ovary. The uterus, a compact mass of few folds anterior to the
gonads, containing a small number of eggs about 008 mm. long and
004 mm. broad.

Several other British accounts of the structure of this trematode
are available (Nicoll, 1907, p. 74, PL 1, figs. 1, 2 ; 19096, pp. 6-7 ;
Lebour, 1908a, p. 16, PL 4, fig. 8), but they can be correlated. Size :
rarely exceeding 3-5 mm. long, mature when 1 mm., but generally
1 -5-2-5 mm. long (but according to Levinsen 3-5 mm., and to Olsson
3-9 mm.). Shape : outline elongate oval, rounded posteriorly and
attenuated in the very extensile anterior region. Colour : trans-
lucent greenish-yellow. Cuticle : non-spinous, but striated trans-
versely and longitudinally, sometimes thrown into irregular wrinkles.
Suckers : ventral larger than the oral and generally elliptical in
outline, the oral globular, diameters 0-22-0-42 mm. and 0- 12-0-29 mm.
in specimens 1-3 mm. long. Both suckers thus diminishing in relative
size during growth, like the space between them, which may be
one-third of the body-length in small specimens, but only one-fifth
in large ones. Gut : prepharynx small, but distinct and about half as
long as the pharynx, which is 01 mm. diameter. (Esophagus some-
times twice as long as the pharynx and straight, but otherwise shorter
and S-shaped, terminating just in front of the ventral sucker. Caeca
very long. Excretory system : pore terminal, vesicle a long and
simple sac extending to the level of the ovary, widening near its
junctions with the lateral canals. Reproductive systems : genital
pore situated midway between the suckers and on the left of the
oesophagus. Cirrus pouch long, narrow and somewhat club-shaped,
extending some distance behind the ventral sucker, containing a large
bipartite or looped seminal vesicle, a folded ejaculatory duct and a
tapering cirrus ; a definite pars prostatica absent, but gland- cells
present. Testes globular and one behind the other and slightly
separated in the middle of the posterior region, leaving a post-
testicular space about one-fifth as long as the body. Ovary lobed,
sometimes trilobed, and situated in front of the anterior testis on the
right. Receptaculum seminis pyriform and near the ovary, Laurer's
canal situated on the left. Vitellaria extending from the ventral
sucker to the posterior extremity, the follicles never distributed in
front of the sucker and mainly lateral in front, but filling the post-
testicular space. Uterus generally containing 20 to 60 yellowish-
brown eggs (according to Odhner, 1905, 20-30, but more than 80
shown in his fig. 9, PL 33), measuring 0060-0084 x 0040-0045 mm.
(but specimens from the 15-spined stickleback at St. Andrews con-
tained unusually large eggs, measuring 0085-0093 x 0051-0-062 mm. ;
see Nicoll, 19096, p. 6).

Nicoll (1907) examined sticklebacks from rock-pools, brackish
ditches communicating with the sea, and streams near their entrance
to the sea, noting that the fishes taken from streams were never
parasitized, those from the other habitats being infected to equal
degrees. In another place (19096, p. 7), where he commented on the
great variability seen in Podocotyle atomon, he noted that differences

ALLOCREADIIDiE 181

affect the characters on which Odhner (1905) depended for determining
P. reflexa, which was said to differ from the type -species in its more
elongate and less flattened shape and more closely approximated
suckers, and that certain other characters used by Odhner are of
little specific value, citing the relative length of the oesophagus, the
greater breadth of the testes and greater length of the cirrus pouch,
the median position of the ovary and the discontinuity of the vitelline
follicles. He stressed also the fact that freshwater treatment such as
was used by Johnstone and investigated by himself (1909a, p. 452)
alters the characters of specimens so that they answer to Odhner's
description of P. reflexa more closely than to existing descriptions of
P. atomon, causing elongation of the body, thickening as well, but the
shortening of the " neck " region, also raising the ventral sucker into
greater prominence. Only under better conditions of fixation is it
safe to differentiate between species such as P. reflexa and P. olssoni
as Odhner did, the characters of greatest reliability then including
the breadth of the body, the length of the " neck " and the length of
the cirrus pouch. In none of Nicoll's specimens was the breadth of
the body less than one-seventh of the body-length, the length of the
" neck " less than one-sixth of total length, and for this reason Nicoll
concluded that specimens from the 15-spined stickleback were not
identical with specimens from the same host which Odhner referred
to P. reflexa, the specific identity of which he admitted on account of
the more flattened shape and greater breadth and the much longer
" neck," and certain characters of the reproductive systems. Nicoll
regarded these specimens (which were 1-7-2-3 mm. long and had
suckers 0-14-0-16 mm. and 0-20-0-25 mm. long) as " absolutely
typical examples of P. atomon, apart from the large size of the ova."
Commenting further on P. atomon Nicoll was struck with the
remarkable diversity of form which it presents. It displays variation
in the extent of the yolk-glands (vitellaria), the length of the cirrus
pouch, the shape and situation of the testes and, in particular, the
size of the ova. Yet he proposed (1909a, p. 452) for Johnstone's
specimens the provisional name Podocotyle atomon var. dispar,
although his experimental distortion by freshwater treatment of
typical specimens of usual form militated against this proposal.
This form must be relegated to synonymity with Podocotyle atomon.

Podocotyle reflexa (Creplin, 1825) Odhner, 1905 (p. 326) must be
regarded as a somewhat doubtful species, though it is notable for its
elongate form. Odhner found it frequently in the 15-spined stickle-
back and in the grey gurnard on the west coast of Sweden, and Nicoll
(1915) recorded its occurrence outside British waters in the lump-
sucker, and at Plymouth in the 5-bearded rockling and the 15-spined
stickleback. Baylis & Idris Jones (1933) also found it at Plymouth
in the same species of stickleback and in the 3 -bearded rockling.
Rees (1945) found it in the 5-bearded rockling at Aberystwyth.
According to Odhner it has the following characters : — Size : 3-4-5 mm.
long. Shape : elongate, only one-twelfth to one-seventh as broad
as long ; forebody one-fifth to one-seventh of total length ; flattening

182 THE TREMATODA OF BRITISH FISHES

insignificant or absent. Suckers : approximately as in P. atomon,
the ventral prominent. Gut : oesophagus generally longer than the
pharynx. Reproductive systems : cirrus pouch straight, over-reaching
the ventral sucker by half its length. Cirrus feebly developed. Ovary
median. Vitellaria discontinuous near the testes, but filling the post-
testicular region. Eggs 0077-0091 mm. long.

Some of Nicoll's comments on the points of difference by which
Odhner recognized this species have already been mentioned. In
considering variability in P. atomon, this zoologist stressed that the
cirrus pouch may extend barely beyond the ventral sucker, or nearly
half-way to the ovary. The vitellaria are extremely variable, and may
be absent between the testes, or fill most of the available space in this
situation. Yet some credence was placed on the characters given by
Odhner, although the manner of fixation can produce in P. atomon
alterations of structure which will render it more like P. reflexa than
the species to which it belongs.

Sub-family Lepocreadiin^e Odhner, 1905.

Key to Genera.

I. Pharynx of medium size ; prepharynx and oesophagus present ; ventral
sucker not significantly smaller than the oral.

a. Body elongate, or ribbon-like, never flask-shaped.

(a) Prepharynx long, oesophagus short . . . Lepidapedon.

(b) Prepharynx short ; oesophagus or pseudo-oesophagus long

Opechona.

b. Body flask-shaped, not elongate ..... Neophasis.
II. Pharynx large (one-tenth as long as the body) ; prepharynx short ;

oesophagus absent ; ventral sucker smaller than the oral Lepidauchen.

Genus LEPIDAPED0N Stafford, 1904.

(Lepodora Odhner, 1905.)

This genus was erected for Distoma rachion Cobbold, 1858, and
although Stafford gave no description, his name for the genus has
priority rights over the name Odhner proposed. It contains two
species, both of which are well known on both sides of the Atlantic,
but no key is necessary, shape alone serving to separate them.

Lepidapedon rachion (Cobbold, 1858) Stafford, 1904 (p. 485).

(Fig. 33 D.)

Distomum rachion Cobbold, 1858 (p. 158, PI. 31, figs. 9, 10) ; Distoma incre-
scent Olsson, 1868, in part ; Lepodora rachicea (Cobbold) of Odhner, 1905
(pp. 332-8, fig. 3, PI. 2, figs. 12-15) ; Lebour, 1908 (pp. 19, 20, PI. 2, figs.
2-4) and authors.

Hosts : haddock, cod, coal-fish, pollack, wrasse.
Location : intestine.

Nicoll (1907) found this species in more than half the haddock he
examined at St. Andrews and (1910) in 55 per cent, of the pollack

ALLOCBEADIIDiE 183

and 45 per cent, of the coal-fish examined at Millport. He also
found it (1914) frequently in the pollack at Plymouth, but not in
40 gadoids of other species. Lebour (1908a) found it in three-
quarters of the haddock she examined at Cullercoats, and Little
(1929a) found it in the cod at Galway. I found 16 specimens of it
at Plymouth in an unidentified wrasse, and it has been recorded in
U.S.A. (on the coast of Maine, see Manter, 1926 ; at Woods Hole,
see Linton, 1940 ; and at Tortugas, see Manter, 1934) and also in
Canada (see Stafford, 1904, and Miller, 1941). It was described by
Odhner (1905, p. 332), Nicoll (1907, p. 77, PL 1, figs. 3, 4) and Lebour
(1908a, p. 19, PI. 2, figs. 2-4). The trematode is sluggish in its
movements and does not long survive removal from the host. Colour :
pale yellow, somewhat opaque. Shape : elongate oval, rounded at
the extremities. Size : 1-88-4-47 mm. long and 0-61-0-90 mm.
broad, mean size 2-65 x 0-69 mm. (Nicoll) ; 2-4 mm. long and one-
quarter or one-fifth as broad (Lebour). Cuticle : spinous, spines
0012 mm. long, having broad bases and arranged in alternating
transverse rows, becoming sparser near the middle of the body and
absent in the posterior region except for a few lateral spines. Suckers :
ventral much smaller than the oral and almost exactly occupying
the middle of the body, diameters 0-14-0-23 mm. and 0-24-0-38 mm.
(Nicoll) ; 0-20 mm. and 0-36 mm. in a specimen 3-5 mm. long (Lebour).
Gut : prepharynx long (0-3 mm.). Pharynx large (0-2 mm. diameter)
(0-21 x 0-16 mm. ; Nicoll). (Esophagus very short. Caeca wide and
long, bifurcation of the gut well in front of the ventral sucker.
Excretory system : pore terminal, vesicle sac-like and short. Repro-
ductive systems : genital pore located between the oesophagus and the
ventral sucker slightly on the left. Cirrus-pouch large, partially
divided by a constriction into anterior and posterior parts, the latter
behind the ventral sucker and containing a folded seminal vesicle,
the former mainly in front of it and containing a small cirrus and
pars prostatica (Note : Lebour referred to a vesicula seminalis
externa, but mentions an enclosing membrane, this and her figure
conforming to Nicoll's description of a constricted cirrus-pouch and
a true vesicula seminalis interna). Testes globular, one behind the
other in the posterior third of the body. Ovary spherical or ovoid,
immediately in front of the anterior testis. Receptaculum seminis
pyriform, situated between the ovary and the anterior testis at the
level of the transverse vitelloducts and Laurer's canal. Vitellaria
filling the lateral regions between the ventral sucker and the posterior
extremity (according to Lebour, extending to the level of the genital
pore), encroaching on the median plane near the testes. Uterus
confined to the region in front of the gonads, containing 30 to more
than 100 eggs of pale yellow colour and more pointed at one pole
than the other, dimensions 0059-0068 x 0-033-0-040 (Nicoll).

My specimens of this species, from the intestine of an
unidentified wrasse, are clearly recognizable from the above
diagnosis, although the prepharynx is relatively short, the
vitellaria relatively better developed (though of similar extent),

184 THE TREMATODA OF BRITISH FISHES

and the gonads transversely oval instead of spherical. Size :
1 -55-2-80 mm. long and 0-50-0-65 mm. in greatest breadth in the
posterior region. Shape and cuticle exactly as described above.
Slickers : having centres 0-50-0-85 mm. apart, oral 0-22-0-27 mm.
diameter, ventral 0-14-0-19 mm. diameter and situated 0-6-1-0 mm.
from the anterior extremity. Gut : prephar}Tix 0-10-0- 15 mm. long.
PharjTix 0-15-0-19 mm. diameter. (Esophagus very short. Caeca wide
and long, arising as stated above. Reproductive systems : genital
pore as stated, cirrus-pouch as described by Nicoll, the anterior part
cask-shaped and somewhat smaller than the ventral sucker, the
posterior part containing the seminal vesicle considerably larger than
this sucker. Testes transversely oval and contiguous almost exactly
in the middle of the posterior half of the body, dimensions 0-12-0-24 x
0-32-0-34 mm. (anterior) and 0-21-0-27 x 0-30-0-35 mm. (posterior).
Post-testicular space 0-21-0-47 mm. long. Ovary of similar shape to
the testes and immediately in front of the more anterior, 08 mm.
long and 0-11-0-23 mm. broad. Vitellaria well developed, com-
prising numerous coarse follicles filling the lateral regions behind the
level of the genital pore (never extending in front of it), encroaching
on the median plane in the post-testicular space and approaching as
near as possible to it in the region of the gonads. Uterus having few
folds confined to the region in front of the gonads and between the
cseca. Eggs measuring 0-064-0-071 X 0-033-0040 mm. (i.e. some-
what longer, but not broader than those examined by Nicoll).

Note : Lebour (1908a, p. 20) mentioned a larva which she found
in Cardium edide (described by Lebour, 1907), and which may belong
to this species. Cercarise were developed in sausage-shaped sporo-
cysts which riddled the soft parts of the host and contained both
free and encysted cercarise. Free forms mostly had tails, but the tail
seems to be cast off prior to encystment and may be seen moving
independently inside the sporocysts. Cercaria : 0-2 mm. long, oval,
spinous, having an oral sucker 004 mm. diameter and a much smaller
ventral sucker, a long prepharynx, a conspicuous pharynx, a very
short oesophagus and long caeca. The excretory vesicle does not
conform strictly with that of the adult, being bilobed (i.e. having a
very short median stem), but as Lebour points out, this character is
not a serious point of difference, being subject to much modification
with growth.

Lepidapedon elongatum (Lebour, 1908) NicoU, 1915. (Fig. 33 E.)

Lepodora elongata Lebour, 1908.

Host : cod.

Location : duodenum and intestine.

Lebour found this trematode at Cullercoats, twice obtaining a
few specimens from a single host, but it has not been found since
anywhere in Britain, although it occurs in widely separated parts of
U.S.A. (Tortugas, Woods Hole). It may be the species mentioned
by Odhner (1905, p. 337), but not described. Nicoll (1910, p. 341)

ALLOCREADIID^E 1 85

stated that it takes the place of L. raehion in the cod, but whether or
not this remains true depends on Little's diagnosis (1929a). In some
respects it seems to be of doubtful validity, but it has been accepted
by American zoologists. Size : 3-5 mm. long and 0-54 mm. broad.
Shape : much longer than L. raehion in proportion to the breadth,
tapering gradually from the middle of the body in an anterior direction.
Colour translucent and colourless. Cuticle entirely spinous. Suckers :
ventral slightly larger than the oral and well in front of the middle of
the body, diameters 12 mm. and 0-10 mm. Gut : prepharynx
0-3 mm. long, but relatively short. Pharynx 008 mm. long. (Esophagus
long (0-3 mm.). Caeca wide and long, extending to the posterior
extremity. Excretory system : vesicle a narrow sac in the dorsal
region, extending forward almost to the anterior testis. Reproductive
systems : genital pore much nearer the ventral sucker than the
oesophagus and on the left. Cirrus-pouch long, its posterior part
longer than in L. raehion and S-shaped instead of globular (Note :
this presupposes that the cirrus-pouch encloses the entire seminal
vesicle, as Nicoll supposed for L. raehion), the seminal vesicle following
this shape. Pars prostatica, cirrus and genital atrium as in L. raehion,
the gonads similarly arranged also, but more widely-spaced in the
posterior region. Testes one behind the other with a small space
between them, diagonally ovoid (0-36 x 0-30 mm.). Ovary spherical,
0-24 mm. diameter. Receptaculum seminis pyriform. Laurer's canal
on the left, its proximal part much swollen. Transverse vitelloducts at
this level, i.e., slightly behind the ovary. Uterus having few folds,
containing more than 100 eggs which are more pointed at one pole
than the other and measure 0066 x 0036 mm. Vitellaria extending
from slightly behind the ventral sucker to the posterior extremity,
apparently (according to Lebour's fig. 5, PL 2) not filling the post-
testicular space, here preserving their bilaterality. Notes : Manter
(1934, p. 296) found this species in several fishes at fair depths at
Tortugas (in 1 out of 35 Coelorhynchus carminatus at 200 fathoms ;
in 1 out of 13 Lcemone?na barbatulum at 140-197 fathoms ; in 1 out of
6 Urophycis chesteri at 367 fathoms ; and in 1 out of 7 Epigonus
occidentalis at 250 fathoms), recognizing the species by the longer
oesophagus, smaller pharynx, failure of the vitellaria to reach the
ventral sucker and the closeness of the genital pore to this sucker.
He was unable to separate the species by the sizes of the eggs, which
in both measured 0059-0068 mm. in length. Linton (1940) recorded
both species at Woods Hole, and his determinations show the sizes of
the eggs to be very variable characters, 006-0-07 X 003-004 mm.
(L. elongatum) and 0-054-0-07 x 0-03-0-04 mm. (L. raehion).

Genus 0PECH0NA Looss, 1907.

(Pharyngora Lebour, 1908.)

Ward & Fillingham (1934) pointed out that in discussing what
he regarded as an improper method of designating a genus, Looss
(1907, p. 616) used the name Opechona for a supposititious genus of

186 THE TREMATODA OF BRITISH FISHES

which the type would be Distomum bacillare. Quoting opinion IB
of the International Rules of Zoological Nomenclature to the effect
that the designation of a type constitutes an indication which estab-
lishes the validity of the name of the genus, these writers insisted
that Pharyngora must be relegated to synonymy with Opechona.
Two species occur in Britain.

Opechona bacillaris (Molin, 1859) Looss, 1907 (p. 616). (Fig. 33 F.)

Distoma bacillare Molin, 1859 (pp. 834-5) ; D. (Dicroccelium) bacillare (Molin)
Stossich, 1886 (p. 58) ; Pharyngora bacillaris (Molin) of Nicoll, 1915.

Hosts : mackerel, lumpsucker.
Location : intestine.

Nicoll (1915) recorded the occurrence of this species in the mackerel
at Millport, Aberdeen, Plymouth and Cullercoats, and in the lump-
sucker at St. Andrews and Plymouth. Lebour (1908a, p. 17, PI. 2,
fig. 1) described two specimens, one of them immature, which she
found in the mackerel at Cullercoats, and Markowski (1933, pp. 12-13,
fig. 4) made observations on 90 specimens found in the same host in
the Baltic Sea, his findings being shown below in parentheses.
The trematode has also been found in Italy (at Padua) and Sicily
(at Catania). Size- : 1-9-3-2 mm. long (2-4-5 mm.) and one-quarter
to one -fifth as broad when contracted, much less when extended.
Cuticle : contrary to previous findings, spinous (confirmed). (Colour :
mature individuals brownish, juveniles colourless.) Suckers : oral
larger than the ventral and having thick walls so as to appear pharynx-
like ; ventral situated at the end of the first quarter of the body,
diameters 002 mm. and 0015 mm. (0-27-0-285 mm. and 012-
0195 mm.). (Note : Lebour's figures, to judge by the illustration,
are misprints for 0-2 mm. and 0-15 mm.) Gut : prepharynx of
variable length, sometimes much longer than the conspicuous pharynx,
generally scarcely visible. (Esophagus a little longer than the pharynx
when not extended. Caeca extending nearly to the posterior extremity ;
bifurcation of the gut slightly in front of the ventral sucker (pre-
pharynx present; pharynx 0-15 mm. long and 0-105 mm. broad;
oesophagus 006-015 mm. long; pseudo- oesophagus 0-3-0-6 mm. long;
caeca long). Excretory system : vesicle sac-like, extending to the
posterior testis. Reproductive systems : genital pore near the anterior
margin of the ventral sucker and slightly on the left. Cirrus-pouch
broad club-shaped and 0-04 mm. long, containing a straight ejacu-
latory duct and a bipartite seminal vesicle which is ovoid in its
posterior part, somewhat triangular in its anterior part (vesiculae
seminales interna and externa present). Testes globular and one
behind the other, but not confluent, in the posterior region (con-
firmed ; dimensions 0-15-0-345 mm. long and 0-165-0-27 mm. broad).
Ovary of irregular shape, in front of the anterior testis and separated
from it by a slight space (3-lobed, 0-075-0-18 mm. long). Recep-
taculum seminis and Laurer's canal present, the exact positions
undetermined (dimensions of the former 01 2 x 0-09 mm., situated

ALLOCREADITDiE 1 87

between the ovary and the anterior testis). Vitellaria lateral, not
extending in front of (only slightly in front of) the seminal vesicle,
underlying the caeca and filling the space behind the testes. Uterus
having a few folds confined to the region in front of the gonads
(confirmed). Eggs not numerous, pale vellow, measuring 008 x
004 mm. (008 x 0-035-0-041 mm.).

Opechona retractilis (Lebour, 1908). (Fig. 33 G.)
Pharyngora retractilis Lebour, 1908.

Host : whiting.

Location : upper intestine and stomach.

Lebour (1908a, p. 22, PL 2, fig. 7) found several specimens at
Cullercoats, and Nicoll (1915) recorded them under the name " bacil-
laris," his further record of this species at Plymouth being invalidated
by his supposition (1910, p. 34) that the two species are identical, as
Markowski (1933a, p. 12) chose to regard them. Ward & Fillingham
(1934) expressed the alternative view that Lebour 's species may be
distinct, and the opinion that if the differences between these two
species are regarded as intraspecific several other species automatically
become less well established. Lebour suggested that retractilis differs
from bacillaris in several characters, but she stressed the vesicula
seminalis externa as a really distinctive character. I found 3 large
and 4 somewhat smaller specimens in the stomach of the whiting at
Plymouth, and 27 small specimens from the intestine of 3 hosts of the
same species there. They differ mainly from Lebour 's specimens in
the shorter pharynx and smaller testes and eggs, but they cannot be
allocated to O. bacillaris and must represent O. retractilis, a vesicula
seminalis externa being clearly evident in some of them. I shall give
a short diagnosis of Lebour's specimens, and supplement this with a
brief account of my own specimens of different sizes.

According to Lebour — Size : 4-6 mm. long and 0-5 mm. broad,
but very contractile when alive. Shape elongate, gradually tapering
anteriorly, of uniform breadth between the ventral sucker and the
anterior testis, tapering and slightly rounded posteriorly. Colour
translucent and colourless. Suckers : oral of characteristic shape
and larger than the ventral, which is situated slightly in front of the
midbody ; diameters 0-20 mm. and 0-12 mm. Cuticle entirely spinous.
Gut : prepharynx long, but very variable, three times as long as the
pharynx in extended individuals, hardly apparent in the contracted
condition. Pharynx 0-12 mm . long and half as broad. (Esophagus long
(0-4-0-8 mm.). Caeca wide and long ; bifurcation of the gut about one-
quarter of the distance along the body. Excretory system : vesicle
very small (about 0-2 mm. long), extending forward only one-third of
the distance between the pore and the posterior testis. Reproductive
systems : genital pore slightly in front of the ventral sucker, median
or slightly lateral. Genital atrium roomy. Cirrus-pouch cylindrical
(length unspecified), containing besides the anterior part of the
seminal vesicle (i.e. vesicula seminalis interna) a pars prostatica and

188 THE TREMATODA OF BRITISH FISHES

cirrus. Vesicula seminalis externa present. Testes ovoid, but some-
what irregular, measuring 0-56 x 0-30 mm., one behind the other
with a small space between them, the hindmost 0-6 mm. from the
posterior extremity. Ovary heart-shaped, in front of and separated
from the anterior testis by a small space. Receptaculum seminis
pyriform, Laurer's canal present. Shell-glands large and conspicuous.
Vitellaria extending laterally from the ventral sucker to near the
posterior extremity, filling the space between and behind the testes
and underlying the caeca. Vitelline reservoir near the shell-glands.
Uterus having a few folds between the ovary and the cirrus-pouch,
containing only 20-40 eggs 010 mm. long. Metraterm somewhat
inflated.

My own observations include measurements of specimens which
fall into three size groups, and the figures in the first and second
parentheses refer to the specimens of the smaller and smallest sizes.
The smallest specimens had just commenced to form eggs, the uterus
containing 2 or 3 only, and the three largest specimens were uniform,
measurements being made on only one of them. Size : 5-8 mm. long
(2-3-3-4 mm.) (1-9-2-05 mm.) and 0-6 mm. in greatest breadth
(0-20-0-25) (0-18-0-20 mm.). Cuticle spinous, the spines very small
and fine. Suckers : oral campanulate or pyriform and broader
anteriorly, 0-3 mm. long and 0-35 mm. in greatest breadth (0-16-
0-22 x 0-13-0-21 mm.) (0-16-0-20 x 012-017 mm.). Ventral sucker
smaller than the oral, 0-2 mm. diameter (0-08-0-14 mm.) (0-09-
0-11 mm.), its anterior margin 1-75 mm. (0-8-1-3 mm.) (0-7 mm.)
from the anterior extremity. Gut : prepharynx shorter than the
pharynx (0-10-0-12 mm. long) (0-08-0-10 mm.), pharynx more or less
elongate, 011 x 010 mm. (0-11-0-12 x 0075-009 mm.) (010-
0-12 x 005-0-07 mm.), oesophagus very long (0-3-0-8 mm.) (0-28-
0-30 mm.), caeca long and narrow, arising immediately in front of the
genital pore and ventral sucker. Reproductive systems : genital pore
median, slightly in front of the ventral sucker, cirrus-pouch about
0-65-0-7 mm. long, and extending approximately to the midbody,
vesicula seminalis externa well behind it. Testes longitudinally oval,
and situated one behind the other in the posterior quarter (third in
small specimens) of the body, dimensions of the anterior and posterior
respectively 0-55 x 0-35 mm. and 0-45 x 0-40 mm. (0-16-0-27 x
012-017 mm.) (016-0-19 x 010-011 mm.), 0-5 mm. apart (con-
tiguous in small specimens). Post-testicular space 0-85 mm. long
(0-32-0-35 mm.) (0-21-0-25 mm.). Ovary much smaller than the
testes and situated slightly in front of the more anterior, slightly
lobed in small specimens. Receptaculum seminis globular, some-
times larger than the ovary, and overlapping its posterior border and
the anterior border of the foremost testis. Vitellaria well developed,
mainly confined to the posterior half of the body, extending from the
extremity to the anterior end of the cirrus-pouch, but not quite to the
ventral sucker. Follicles rather coarse and mainly lateral, but filling
the spaces between the gonads and the post-testicular space. Vitelline
reservoir smaller than the ovary and between it and the anterior

ALLOCREADIID^E 189

testis. Uterus having only a few small folds, mainly between the
ovary and the posterior end of the seminal vesicle. Eggs large and
variable, measuring 0080-0093 X 0043-0-054 mm. (0071-0086 x
0-038-0047 mm. in the small and smallest specimens).

Genus NE0PHASIS Stafford, 1904.
(Acanthopsolus Odhner, 1905.)

The type- species of this genus, JV. pusilla Stafford, 1904, occurs in
the urinary bladder of the wolf -fish in Canada. It bears a very close
resemblance to JV. lageniformis, as the re-description by Miller (1941,
p. 33, fig. 5) shows, but is smaller and has suckers of greater absolute
size, differing in other characters also. Another species, Neophasis
oculata (Levinsen, 1881) {Acanthopsolus oculatus (Levinsen) of
Odhner, 1905 (pp. 328-31, PI. 2, fig. 11) ; Distoma oculatum Levinsen,
1881 (pp. 64, 67, PL 2, figs. 7, 8)) occurs off the coast of Greenland and
at Egedesminde, the hosts being the father-lasher and the short-
spined cottus. I have re-drawn it in Fig. 36 F, and need only mention
that it is supposed to differ from N. lageniformis and JV. pusilla mainly
in the shape, the diagonal arrangement of the testes, the absence of a
receptaculum seminis and the relatively small size of the eggs. Stiles
& Hassall give a British record of this species, Johnstone (1907,
pp. 186-8, fig. 17) having mentioned characters in which his Distomum
sp. from the cuckoo wrasse agreed with D. osculatum Levinsen. In
the same place, however, Johnstone gave reasons for the unlikelihood
of identity with this species, and Nicoll (1915, p. 35) allocated his
specimens to Lebouria, now Plagioporus alacer. The differences
between the three species mentioned seem to me hardly to warrant
specific distinctions, and it is my belief that further study will resolve
them into a single species, Neophasis pusilla.

Neophasis lageniformis (Lebour, 1910) Miller, 1941. (Fig. 35 G.)

Acanthopsolus lageniformis Lebour, 1910 (pp. 29-35, PI. 1, figs. 1-8) ; Disto-
mum sp. Lebour, 1908 (a, pp. 31-3, PI. 3, figs. 6-8).

Host : wolf -fish.

Location : upper part of intestine ; juveniles in the stomach,
pharynx and buccal cavity.

Lebour (1910, p. 29) described adults of this species found at
Cullercoats, remarking that when abundant they occurred in hundreds,
and that they are rarer in spring than in summer and disappear in
winter. Nicoll (1915) recorded the species as occurring also at St.
Andrews. Lebour's first record largely concerned small immature
specimens found in the stomach of the host. They agreed in every
way with a cercaria which she previously found in sporocysts in great
abundance in a whelk (Buccinum undatum) taken on the Northumber-
land coast, except that they had lost the tail. The largest adults were
found in the upper intestine of three out of twelve wolf-fish whose
stomachs contained the remains of whelks. They had the following

190 THE TREMATODA OF BRITISH FISHES

characters (Lebour, 1910) : — Size: very small, 0-54-1-3 mm. long and
about half this in greatest breadth posteriorly. Shape : flask-
shaped, narrowing considerably anteriorly, broad and rounded
posteriorly, almost circular in transverse section, but slightly flattened
in front of the ventral sucker. Cuticle spinous, the spines arranged
in rows, flat and scale-like near the mouth, very sharp further back
in the anterior third of the body, progressively smaller beyond this to
the posterior extremity. Eye-spots : two dark brown masses of
pigment with radiating flecks situated one on either side of the
pharynx at variable distances from the mouth, according to the state
of the highly mobile neck. Suckers : of nearly equal sizes, the oral
slightly the larger in adults. Dimensions : oral 0-06 mm. diameter, or

007 x 005 mm. in a preserved specimen 0-35 mm. long, 009 x

008 mm. in one 0-54 mm. long ; ventral 006 mm. diameter in all
specimens examined (apparently failing to increase in size from the
full-grown cercaria to the adult), situated just in the anterior half of
the body. Gut : prepharynx 0-08 mm. long, narrow and thin-walled,
or so contracted as to appear absent, its wall telescoped by the
pharynx ; pharynx 0-07 mm. long and two-thirds as broad, oesophagus
short and broad, caeca long, extending to the posterior extremity
(correction to Lebour, 1908, p. 32) ; bifurcation of the gut very close
to the ventral sucker. Excretory system : vesicle pyriform, reaching
nearly to the level of the testes ; pore slightly dorsal. Reproductive
systems : genital pore slit-like, median and near the anterior margin
of the ventral sucker, in life constantly opening and closing. Genital
atrium small, receiving the male and female ducts on the right and
left respectively. Cirrus-pouch club-shaped, dorsal to the ventral
sucker and projecting behind it (in whole mounts curving round it),
containing a large seminal vesicle constricted into almost equal
anterior and posterior parts. An ill-developed pars prostatica and a
long ejaculatory duct and cirrus. The part of the ejaculatory duct
adjacent to the pars prostatica is provided with sharp " spines " with
rounded bases ; the cirrus is devoid of them. Vasa deferentia extending
separately to the seminal vesicle. Testes longitudinally ovoid,
symmetrical and widely separated in the last quarter of the body,
008 mm. long and 005 mm. broad. Ovary spherical, lateral and
slightly in front of the right testis and somewhat smaller than it.
Oviduct long and convoluted. Receptaculum seminis globular, con-
spicuous, but small; Laurer's canal present. Vitellaria very well
developed, the follicles forming groups scattered throughout the
available space between the pharynx and the posterior extremity,
mainly dorsal, but partially covering the caeca ventrally. Transverse
vitelloduct short and wide and situated behind the ovary (shown
between the testes). Uterus having an ascending limb only, formed
into few folds distended locally by the relatively enormous single
eggs. Metraterm having spines similar to but thinner and sparser than
those of the ejaculatory duct. Eggs very few, seldom more than 4
and rarely as many as 8, about 0-08-0- 10 mm. long and two-thirds
as broad, in small flukes as large as the testes.

ALLOCREADIID^E 191

The smallest preserved specimens containing eggs were 0-54 mm.
long, but younger specimens from the pharynx and buccal cavity
and 0-34-0-50 mm. long showed all stages in the development of the
vitellaria. Other small individuals described by Lebour (1908a,
p. 32) and 0-3-0-4 mm. long had suckers of equal sizes (007 mm.
diameter). The cercarise described by Lebour (1910, p. 32) develop
in rediae (previously described as sporocysts by Lebour, 1906). The
liver of the whelk becomes packed with these stages and develops an
unhealthy brown colour. Smaller redise (0-3 mm. long) are colourless,
but larger ones (0-5-3-2 mm. long) are yellow, and either short and
housing 2 or more cercarise, or elongate and containing 16-32.
Tailed and tail-less cercariae occur in the same redia and the latter
are commoner, the tail being very easily detached. The body of
the cercaria is about 0-5 mm. long when alive, contracting to about
0-35 mm. when preserved, and the shape is indeterminate on account
of changing movements, but never flask-shaped like that of the
adult. Other characters are like those of the adults, conspicuous
rudiments of the gonads occurring in the positions they will continue
to occupy, in some specimens traces of the genital ducts as well.

Genus LEPIDAUCHEN Nicoll, 1913.

Lepidauchen stenostoma Nicoll, 1913. (Fig. 32 G.)

Host : ballan wrasse (at Plymouth).
Location : intestine.

The only two specimens of this species ever found were described
by Nicoll (1913a, p. 240, PI. 11, fig. 3). Size: 2-9-3-25 mm. long
and 1-3 mm. in greatest breadth. Shape : long oval outline, broadest
near the middle of the body, tapering towards the broadly rounded
extremities and flattened. Cuticle spinous, the spines confined to
the anterior half of the body. Suckers : oral expanded at its anterior
end and having a slit-like aperture, 0-55 mm. diameter, ventral of the
usual form, 0-27 mm. diameter and 1-12 mm. from the anterior
extremity. Gut : prepharynx small, pharynx very large (0-31 x
0-34 mm.). (Esophagus absent. Caeca long and widely divergent.
Reproductive systems : genital pore median and situated beneath the
pharynx. Cirrus-pouch entirely in front of the ventral sucker, con-
taining a globular seminal vesicle (other details unobserved). Testes
fairly large and globular, one behind the other and contiguous with it
in the posterior region. Post-testicular space 0-45 mm. long. Ovary
transversely ovoid, in front of and almost touching the anterior
testis, and slightly on its left, dimensions 0-37 x 0-26 mm. Laurer's
canal not observed. Sperms observed in the receptaculum seminis
uterinum. Vitellaria voluminous, filling most of the posterior region
and extending forward laterally to the level of the pharynx, the
follicles mainly ventro-lateral, but merging dorsally in front of the
ventral sucker and ventrally in the posterior region, where they
approach and partially cover the lateral margins of the gonads.

192 THE TREMATODA OF BRITISH FISHES

Uterus having an ascending limb folded between the gonads and the
ventral sucker, here tending to fill the space between the caeca, the
first two or three folds containing spermatozoa. Eggs not numerous
(less than 100), brownish-yellow, measuring 0-078-0-084 x 0-046-
0-050 mm. Note: Nicoll (1913a) experienced difficulty in defining
the systematic position of Lepidauchen, regarding it as intermediate
anatomically between Lepocreadium and Stephanostomum. Later
(1915, p. 344) he placed it in the Lepocreadiinae.

Sub-family Crepidostomatin^: nom. nov.

(Stephanophialinse Nicoll, 1909).

Genus CREPID0ST0MUM Braun, 1900.

(Stephanophiala Nicoll, 1909 ; Acrodactyla Stafford, 1904 ;
Acrolichanus Ward, 1917.)

Crepidostomum farionis (Muller, 1784) Liihe, 1909. (Fig. 32 H.)

Fasciola farionis Muller, 1784 (p. 91, PI. 72, figs. 1-3) ; Distoma farionis of
R. Blanchard, 1891 (pp. 481-3, fig. 38) ; D. laureatum Zeder, 1800 of
authors ; Crepidostomum laureatum (Zeder) of Braun, 1900 (p. 232) and
authors ; Stephanophiala laureata (Zeder) of Nicoll, 1909 (a, pp. 398-419,
PI. 9, figs. 1-5) ; S. transmarina Nicoll, 1909 (a, p. 397) ; S. vitelloba Faust,
1918 ; Crepidostomum ussuriense Layman, 1930 ; C. vitellobum (Faust) of
Hopkins, 1931.

Hosts : sea trout, char, houting, grayling.
Location : intestine, pyloric caeca, gall-bladder.

This is a very widely distributed trematode which is common in
some Scottish and Yorkshire rivers and occurs elsewhere in Britain,
as well as in France, Austria, Germany, Sweden, Denmark, Finland,
Russia, Canada, Alaska and U.S.A. Olsson (1876, p. 21, PL 4,
figs. 1-5) gave a fairly accurate description which was augmented by
R. Blanchard (1891), particularly in regard to the female reproductive
organs. Looss (1902, p. 452) first indicated the structure of the
distinctive anterior papillae. Nicoll (1909a) completely re-described
the worm after studying four or five mature specimens from each of two
trout taken from the River Spey, as well as several immature specimens
from two others taken from a tributary of this river. Brown (1927,
p. 86, Pis. 6, 7, figs. 1-12) studied adults obtained from the trout and
grayling of Yorkshire rivers, finding the trematode for the first time
in the gall-bladder, also investigating the life-history. Baylis (1928 ;
1939) recorded the occurrence of the trematode in brown trout in
Hampshire.

Most writers have dealt with small specimens 2-4 mm. long, but
Olsson discovered some which were 6 mm. long, and Liihe (1909,
p. 63, fig. 54) took this into consideration in formulating his brief
diagnosis. The description given here is largely based on the observa-
tions of Nicoll, with the findings of Brown shown in parentheses.
Size : 3-4 mm. long (3-5 mm.) and one-quarter as broad near the
ventral sucker. Shape : long oval outline, tapering towards the

ALLOCREADIIDJE 193

extremities, rounded during contraction of the body, flat. Forebody
much more mobile than the rest of the body. Colour pale, but distinct
red (white, neglecting the eggs, as Olsson found ; antero-dorsal region
covered with scattered pigment granules). Cuticle of uniform thick-
ness, -0025-0 003 mm. Suckers : oral not quite terminal, almost
globular and about 0-31 mm. diameter, the anterior border thicker
(0093 mm. thick) than the remainder (0-05-0065 mm.) (see Nicoll).
Ventral sucker transversely elongate and about one-third of the
distance along the body, 0-50 x 0-43 mm. and 0-16 mm. deep. (Ratio
of the diameters of the suckers 1/1-5, the ventral sucker well within
the anterior half of the body.) Anterior papillce : 6 tongue-like
outgrowths of the muscle substance of the oral sucker about 0-3-
0-4 mm. long (2 ventral, 4 dorsal), their bases all in the same trans-
verse plane and equidistant from one another ; the ventral near the
mouth and having bases which bulge into the buccal cavity. Musculo,-
ture : circular, longitudinal and diagonal fibrils and underlying these
myoblasts. Subcutaneous glands : pyriform cells (0-036 x 0-019 mm.)
mainly restricted to the anterior region, many of them opening at
the rim of the oral sucker. Gut : prepharynx very small. Pharynx
0-15-0- 19 mm. diameter, but dorso-ventrally flattened. (Esophagus
about the same length as the pharynx. Caeca long. Prepharynx and
pharynx lined with cuticle, oesophagus and the anterior parts of the
caeca having a thick membrane, the posterior parts of the caeca an
epithelium of vacuolated cells with long fibrillar free processes
(? artifact). Excretory system : median canal extending to the level
of the anterior testis, lateral canals to the oral sucker, both having a
membranous, not an epithelial lining; pore slightly dorsal. Repro-
ductive systems : genital atrium absent, or represented by a shallow
depression into which the male and female ducts open side by side
[ Olsson 's representation of widely- separated apertures erroneous],
situated beneath the end of the pharynx. Cirrus-pouch club-shaped,
0-45-0-55 mm. long and 0-12 mm. in greatest breadth, extending to a
point above the middle of the ventral sucker, its walls containing
inner circular and outer longitudinal muscles. Seminal vesicle
elongate oval, measuring 0-2 x 0-04 mm. Pars prostatica globose.
Gland- cells numerous and confined to the posterior part of the cirrus-
pouch. Cirrus sometimes formed into a single loop, but variable.
Testes globular or ovoid, situated one behind the other in the middle
of the hind- body and close together or separated by a small space ;
dimensions 0-27 x 0-34 mm. (anterior) and 0-34 x 0-33 mm.
(posterior). Ovary almost globular, close behind the ventral sucker
and far in front of the testes, median or slightly lateral, dimensions
0-23 x 0-19 X 0-16 mm. Receptaculum seminis very small, ovoid
and situated behind the ovary, giving off a moderately long and
straight Laurer's canal. Vitellaria very well developed, comprising
two continuous antero-lateral arrays of follicles between the pharynx
and the posterior extremity, tending to fill the spaces between and
behind the testes, mainly lateral to the caeca in front of the ovary.
Transverse vitelloducts at the level of the receptaculum seminis

13

194 THE TREMATODA OF BRITISH FISHES

Uterus much folded between the testes and the ventral sucker, metra-
term straight, extending alongside the entire cirrus-pouch, lined with
cuticle and having muscular walls. Eggs comparatively few (generally
fewer than 100), more widely rounded at the anopercular pole, bright
yellow and darkening only slightly in transit through the uterus,
containing unsegmented ova when laid, measuring 0075-0-080 x
0040-0044 mm. (0-075 x 0042 mm.) [Hopkins (1934, p. 14) gave
the dimensions of the eggs as 0-065-0-085 x 0-040-0-050 mm.].
(Linton (1940, p. 101) as averaging 0-08 x 004 mm.) Notes : Brown
found all trout from the River Warfe infected, and also 84 per cent, of
grayling. The first intermediate hosts are Pisidium amnicum and,
rarely, Sphcerium corneum, the second include the larvae of mayflies
(Ephemera danica in England (Brown, 1927) ; Hexagenia sp. in Canada
(Cooper, 1915)) and the freshwater shrimp, Gammarus pulex (see Baylis,
1931). Two generations of rediae occur, and these are characterized
by the absence of procruscula and a functional intestine. The
cercaria is a Xiphidiocercaria with body and tail of about equal
length (0-45-0-52 mm. and 0-45 mm.) and 2 conspicuous eye-spots.
It penetrates the second intermediate host by means of the stylet and
the secretion of two groups of 3 penetration-glands. The metacercaria
encysts in the mayfly larva, generally in the fat bodies, sometimes
in the muscles. The cysts are pyriform (0-26-0-40 x 0-31-0-48 mm.)
and easily visible through the translucent exoskeleton of the host on
account of their dark brown colour. The most usual site is the
ventral surface near the 2nd-5th pairs of gills, and a single host may
harbour 1-26 cysts, which do not interfere with its development and
are carried over into the adult stage. Encysted larvae retain the
eye-spots and develop the anterior papillae, but lose the stylet.
Encysted forms show clear relationship to the adult Crepidostomum
farionis, but are only 0-40-0-65 mm. long and 0-13-0-24 mm. broad.
The suckers at this time are of equal sizes and the eye-spots are
beginning to disintegrate. The earliest larvae found in the trout
occurred in the pyloric caeca and showed great advance on the
encj^sted forms. They were 0-79 mm. long and 0-31 mm. broad, the
suckers measuring 0-14 mm. (oral) and 0-19 mm. (ventral). Such
forms still contain obvious vestiges of the penetration-glands.

Hopkins (1934) examined many specimens of C . farionis from various
parts of U.S.A. and Alaska, as well as some specimens from Britain and
descriptions of others, concluding that European and American forms
differ only in very minor characters, which fall well within the range
of individual variation. The name Stephanophiala transmarina Nicoll,
1909 (proposed for what Nicoll regarded as an American species), was
relegated to synonymy with Crepidostomum farionis, after Hopkins
had also examined specimens described and named Crepidostomum
transmarinum by Hunninen and Hunter (1933) and regarded as distinct
from the European species. Hopkins (loc. cit., p. 12) also gave reasons
for regarding Crepidostomum ussuriense Layman, 1930, emend, and C .
vitellobum (Faust) of Hopkins, 1931, as other synonyms of this species.
The former was found in Salvelinus sp. in Peter the Great Bay.

ALLOCREADIIDiE 1 95

Other European species of the genus include Crepidostomum
auriculatum (Wedl, 1857) Luhe, 1909 (p. 63) {Distoma auriculatum
Wedl, 1857 ; Acrodactyla auriculata (Wedl) Odhner, 1910 ; Acro-
lichanus auriculatus (Wedl) Skwortzoff, 1927 ; Acrolichanus similis
Wisniewski, 1933), which occurs in Acipenser ruthenus L. in the
Danube, Volga and Oka. Hopkins (1934, pp. 37-8) gave a brief
diagnosis of this species, and also of C. latum (Pigulewski, 1931)
(Stephanophiala lata Pigulewski, 1931 (pp. 17-18, fig. 5)), a parasite
of the rudd in the Ukraine. Crepidostomum suecicum Nybelin, 1932,
a parasite of various freshwater fishes (grayling, sea trout, turbot,
miller's thumb and char) in Sweden was regarded as identical with
C. metcecus (Braun, 1900), a parasite of bats. Hopkins regarded
fishes as the natural hosts, bats as " accidental " hosts. A Russian
species of the genus not included in Hopkins' fist is C. baicalense
Layman, 1933, discovered in Thymallus arcticus and Cottus kneri in
Lake Bajkal. For accounts of several American species of the genus
(the best-known of which is C. cornutum (Osborne, 1903), originally
described as Bunodera) the reader is referred to the monograph by
Hopkins, which contains much valuable information concerning the
life-histories of the papillose Allocreadiidse.

Sub-family Sph^rostomatin^: Poche, 1926.
(Sphcerostomatidce Thapar & Dayal, 1934.)
Genus SPHJER0ST0MA Rudolphi, 1809.
Sphaerostoma bramae (Miiller, 1776) Luhe, 1909. (Fig. 34 B).

Fasciola bramae, Miiller, 1776 (p. 224, v. 1, PL 30, fig. 6) ; Distoma globiporum
Rudolphi, 1802 (1809, pp. 364-7) in part ; Sphcerostoma globiporum (Rudolphi)
Looss, 1899 (pp. 595, 649).

Host : roach. (Elsewhere in Europe, hosts mainly Cyprinids
(carp, bream, white bream, bleak, roach, minnow, chub, rudd, barbel,
loach, etc.), but also perch, grayling, pike, eel.)

Location : intestine.

Nicoll (1924) regarded this as one of the nine characteristic
trematodes of British freshwater fishes and the commonest of them
all. But like other parasites of its kind, it has been neglected in this
country, although Baylis (1939) recorded its occurrence in the roach
in Cambridgeshire. On the Continent it occurs in the Rhine, Lake
Constance, Lake of Lucerne, the Baltic Sea, Denmark and Norway.
It was described by Looss (1885, p. 22, PI. 24, fig. 18), and short
diagnoses of both the species and the genus were given by Liihe (1909,
p. 142, fig. 110). Markowski (1933, pp. 11-13, fig. 3) described
specimens taken from the common eel in the Baltic (Chlapowo).
Size : 1- more than 4-2 mm. long and about three-eighths as broad.
Shape : outline oval, slightly attenuated at the extremities, the
anterior region more mobile than the posterior. Suckers : ventral

196

THE TREMATODA OF BRITISH FISHES

Fig. 34. — A, Allocreadium isoporutn. B, Sphcerostoma bramce. C, Azygia
lucii. D, Bunodera luciopercce. E, Phyllodistomum folium. F, " P.
angulatum," a synonym of P. macrocotyle. G, Probilotrema richiardii.
(A-E, after Looss, 1894-5 ; F, after Linstow, 1907 ; G, after Dollfus,
1937.)

ACANTHOCOLPID^E 197

almost twice as large as the oral, about 0-45 mm. diameter in the
largest specimens and situated near the middle of the body, in smaller
specimens 1-1-5 mm. long, dimensions 0-25 x 0-31 mm. and 015-
0-28 mm. Gut : pharynx small, 075 mm. diameter in small
specimens. (Esophagus long, terminating nearer the ventral than the
oral sucker. Caeca very long. Reproductive systems : genital pore
median near the termination of the oesophagus and far in front of
the ventral sucker. Cirrus-pouch large, but almost confined to the
forebody, and hardly tapering anteriorly, containing a short and
thick cirrus, an inconspicuous pars prostatica and a large and folded
seminal vesicle. Testes rarely having smooth borders, generally
somewhat lobed or irregularly ovoid and widely separated, the
anterior close behind the ventral sucker and lateral, the posterior
near the ends of the caeca and median, diameter in small specimens
0-13-0-15 mm. Ovary smaller than the testes, 0-10 mm. diameter
in small specimens, situated nearer the posterior testis and on the
side opposite the anterior, the receptaculum seminis near it on the
other side of the body. Vitellaria very well developed, comprising
numerous large follicles which extend along the dorsal surfaces of the
caeca, spreading slightly, and along the sides of the oesophagus to the
level of the pharynx, sometimes restricted to the region behind
the seminal vesicle or the ventral sucker. Uterus having a few large
folds which almost encircle the ventral sucker, but sometimes a few
small transverse folds. Eggs yellowish -brown, measuring 0-057-0-076
X 0-049-0-06 mm., arranged in the uterus in a single row. According
to Liihe, the microcercous Xiphidiocercaria, Cercaria micrura Filippi,
which has a distinctive array of bristles, is the larva of this species ;
it develops in tubular sporocysts in Bythinia tentaculata, later on
leaving the snail and penetrating a species of Herpobdella and encysting
underneath the skin as a metacercaria measuring about 0-42 x
0-15 mm., contained in an ovoid cyst 0-2 mm. long and 0-1 mm. broad.

Family ACANTHOCOLPIME Liihe, 1909.

Liihe (1906) erected a sub-family Acanthocolpinae for a new
genus and species of trematode, Acanthocolpus liodorus, found in the
intestine of Chirocentrus dorab in Ceylon, and later elevated it to
family rank. With this genus he associated the genera Steph