310 
A New Trematode 
The preparations in toto show clearly numerous cysts, each containing a 
Trematode larva belonging to the group of metastatic Distomatids (Monogena), 
which differ from the group of Digenea by possessing a simple cycle of develop¬ 
ment. Our larva should be referred to the provisional genus Tetracotyle, which 
must stand until the complete life-history of the Trematodes included in it is 
known. The cyst which harbours the Tetracotyle larva is ellipsoidal in shape, 
0-658-0-686 mm. long and 0-434-0-490 mm. wide. Close to the anterior end the 
parasite shows an oval oral sucker measuring 0-034 mm. by 0-077 mm. (Figs. 2, 
4, 5 , a.). From this sucker originates the oesophagus which branches into two 
intestinal trunks that are clearly shown only in the middle portion of the larva. 
Laterally to the oral sucker are found two cyst-glands composed of 
numerous unicellular glands (Fig. 6,cd.) which by means of a common biramous 
duct open exteriorly into two obliquely directed slits. The clusters of both 
glands are near each other behind the oral sucker (Fig. 2, cd.) and posteriorly 
they extend almost to the ventral sucker. The secretion of these glands forms 
the larval portion of the cysts. 
The ventral sucker is circular in shape, 0-098 mm. in diameter, and is 
situated near the middle of the larva. Behind the ventral sucker the dermal 
cuticle invaginates inside the body forming, in longitudinal section, a T-shaped 
depression (Fig. 3). On the dorsal side the skin forms two longitudinal invagina¬ 
tions which border a protruded portion of the dorsal wall. 
The portion of the body lying between the ventral and dorsal invaginations 
contains the rudiments of the ovary, testes, and genital ducts, which open 
into the ventral invagination. 
Although we were unable to examine the larva in the extended condition 
outside the cyst, we believe that the above description is sufficient to enable 
us to compare the Tetracotyle larva described above with Tetracotyle species 
previously found in fish, namely: T. ovata, T. echinatum and T. percae. The 
characteristic features of these four species are shown in the following table: 
Tetracotyle ovata 
v. Linstow 
T. echinatum 
Diesing 
T. percae fluviatilis 
v. Linstow 
T. sogdiana 
Pavl. & Anitch. 
Form of cyst 
Elliptic 
Oviform 
— 
Elliptic 
Dimensions 
in mm. 
0-84 x 0-57 
0-5 x 0-6 
0-4 x 0-075 
0-68 x 0-32 
0-658—0-686 x 
0-434-0-490 
Oral sucker 
0-098 x 0-13 
— 
0-065 
0-084 x 0-077 
Ventral sucker 
Behind the middle 
of the body 
0-16-0-21 
— 
Behind the middle 
of the bodv 
0-095 
Anteriorly to the 
middle of the b< 
0-98 
Cyst-glands and 
glandular pits 
Glandular pits 
elongated oval, 
not larger than 
the oral sucker 
Glandular pits 
slightly larger 
than oral 
sucker 
Width of glandular 
pits three times 
less than their 
length 
Dermal covering 
Smooth 
With rare spinelets 
Smooth 
Smooth 
Localisation in 
Under the 
Under the 
Under the 
Under the peri¬ 
host 
peritoneum 
Abramis brama 
„ bjorkia 
Osmerus eperlanus 
peritoneum 
Acerina cernua 
Leuciscus idus 
peritoneum 
Perea fluviatilis 
toneum, in the 
pancreas 
Schizothorax 
intermedium 
Acerina cernua 
