448 
Marine Cercariae 
■ Genus Stephanochasmus Looss. 
Head with two complete rows of spines. Intermediate host—fish, 
final host—fish. 
Stephanochasmus haccatus Nicoll (i. 1907, p. 80, Lebour, 1908 A, p. 14). 
(PI. XXIX, figs. 6, 7.) 
The encysted form is very common under the skin of Pleuronectid 
fishes, the dab Pleuronectes limanda L., witch P. cynoglossus L., lemon 
dab P. microcephalus Donov., and long rough dab Hippoglossus 
limandoides Bloch, all being infected on the Northumberland Coast. 
Johnstone (1904, p. .98) has recorded and described it from the West 
Coast of England and Nicoll and Small (1909, p. 244) from Millport. 
The cercaria occurs beneath the skin on the under side and sometimes 
on the gills, the fish serving as the intermediate host. The cyst 
is composed of two layers, the first thick and tough, the second 
transparent. 
The cercaria when pressed out of the cyst measures 2'9-3 mm. in 
length. It is pear-shaped with a very long neck, the body covered with 
spines which gradually disappear posteriorly. They are large near the 
head and surrounding the head are two rows of very long pointed 
spines, those in the upper row shorter than those in the lower (upper 
spines 0’022 mm. long, lower 0’026 mm. long). The number is 
variable, from 48 to 58 spines in two uninterrupted rows of 24 to 29 
spines each. Nicoll thinks it probable and it seems to be very likely 
that we have to do with several different species. Oral sucker 0'26 mm. 
across, prepharynx 0’50 mm. long, pharynx 0'18 mm. long, very muscular 
leading to broad oesophagus branching into two coeca which reach 
nearly to the posterior end of the body. Genital aperture immediately 
in front of ventral sucker. Ventral sucker 0’23-0'26 mm. across. Two 
round testes and an ovary occur at the hind end of the body. Vasa 
deferentia joining a thin club-shaped vesicula seminalis in front of 
which the cirrus sac encloses a small cirrus. Oviduct short, other 
female organs not yet developed. Excretory vesicle very large, circular 
and ojDaque occupying the posterior region. 
This cercaria is probably Stephanochasmus haccatus Nicoll, which he 
found in the halibut Hipg)oglossus vulgaris Flem. This worm has 
56 spines round its head. As Nicoll suggests however there may^ be 
S. caducus and S. triglae as well as S. haccatus encysted in these fish 
and we may have examples of them all. 
