TEEMATODES 



173 



Fig. 278 Diagram of a monogenetic 

 trematode (Benham). 1, mouth; 2, 

 anterior sucker ; 3, brain ; 4, vagina ; 

 5, excretory pore ; 6, intestine ; 7, pos- 

 terior sucking disc ; 8, hook ; 9, genital 

 pore ; 10, excretory canal ; 11, penis ; 

 12, vagina ; 13, uterus ; 14, ovary ; 15, 

 sperm duct ; 16, yolk glands ; 17, testes ; 

 18, genito-intestinal canal. 



The order contains 4 



ORDER 1. MONOGENEA * 



Monogenetic trematodes (Fig. 278). Usually external parasites on 

 fish and other aquatic animals. Most forms live on but a single host and 

 are found most often on the gills, 

 being that part of a fish's body where 

 the blood is nearest the surface and 

 where a parasite is also protected; 

 some, however, live in the mouth and 

 some in the cloaca. The genus 

 Polystoma is entoparasitic. The or- 

 gans of attachment are at the extremi- 

 ties of the body. At the hinder end 

 is a large disc more or less sharply 

 set off with either suckers or hooks, 

 or both these organs. At the for- 

 ward end is usually a pair of suckers 

 with the mouth between them. These 

 may, however, be absent or their place 

 may be taken by a single oral sucker, 

 by paired glands, or by tentacle-like structures, 

 families and about 500 species. 



Key to the families of Monogenea*: 



Oj Large posterior sucking disc without suckers or marginal hooks. 



6 X A pair of anterior suckers or sucker-like projections with mouth between. 



1. TRISTOMIDAE 



6, A single anterior sucker, or none 2. MONOCOTYLIDAE 



o a Disc-like posterior region with either paired suckers or marginal hooks. 



&! Posterior region with suckers 3. POLYSTOMIDAE 



6 2 Posterior region without suckers * .... 4. GYBODACTYLIDAE 



FAMILY 1. TEISTOMIDAE. 



Mostly broad, flat worms, with a pair of anterior suckers or sucker- 

 like membranes, one on either side of the mouth, and a large posterior 

 sucking disc in which hooks are often located, the anterior suckers 

 being without hooks; a pair of eye spots often present; intestine bifur- 

 cate and often much branched; genital pores near the forward end, the 

 male and female openings being in some cases separated from each 

 other: on the skin or gills of marine fishes or in the mouth or cloaca; 

 about 11 genera. 



* "Notes on Trematode Parasites of Fishes," by E. Linton, Proc. U. S. Nat. 

 Mus., Vol. 20, p. 507, 1898. "Notes on Some Exotic Species of Ectoparasitic 

 Trematodes," by S. Goto, Jour. Sci. Coll., Imp. Univ., Vol. 12, p. 263, 1899. 

 "Synopsis of the Trematodes, Part I. The Heterocotylea," by H. S. Pratt, Am. 

 Nat., Vol. 34, p. 645, 1900. "Fish Parasites of the Woods Hole Region," by E. 

 Linton, Bull. Fish. Com., Vol. 19, p. 405, 1901. 



