Volume VIII 
JANUARY, 1916 
No. 3 
THE TREMATODE GENUS STEPHANOCHASMUS 
LOOSS IN THE GULF OF MEXICO. 
By HENRY S. PRATT, 
Haverford College, Haverford, Pa. 
(With Plate XIII.) 
Two species of the genus Stephanochasmus have been found in the 
fishes examined for parasites at the station of the Carnegie Institution 
of Washington, situated on the island of Tortugas in the Gulf of Mexico. 
These are S. casus Linton and S. sentus Linton. The anatomy of 
these worms contains several novel and interesting features, and that 
of the first named will be described here in detail. 
S. casus lives in the rectum of two common fishes, the gray snapper 
(Lutianus griseus) and the yellow tail ( Ocyurus chrysurus), where it 
was found by both Linton (1910) and myself. The length of the 
eleven specimens in my collection ranges between 2 mm. and 6 mm. 
(Fig. 1). The body is soft and contractile and is consequently much 
broader at some times than at others. The breadth of the specimen 
figured, which is somewhat contracted, is 1 mm. The breadth of a 
fully extended animal of the same length is about 0-7 mm. 
The living worm is usually deep red in colour, in consequence of 
the blood contained in the capacious intestine. In the various stages 
of contraction of the different individuals the organs may show a 
somewhat different arrangement. The testes and ovary, for instance, 
are pressed closely against one another when the body is much con¬ 
tracted (Fig. 2); but when it is extended these organs may be separated 
from one another by a considerable distance. The body is oval in 
cross section (Fig. 3). It is covered with the large spines characteristic 
of the genus, the number encircling the mouth being 36, arranged in 
two rows (Fig. 1). These rows are not interrupted ventrally, as is 
the case in certain species of the genus. All the spines are very easily 
lost by maceration. 
Parasitology vm 
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