a corona of chitinous hooks. The anterior end of the body has 2 

 groups of cephalic glands. The buccal opening often has a ternninal 



sucker. The species which do not have suckers on the disc are viviparous, 

 the rest egg -laying. 



This order unites highly specialized species which are exempli- 

 fied by live-bearing in part of thenn (Gyrodactylidae) and the parasitizing of 

 Amphibia and Reptilia by the rest (Polystomatidae and Sphyranuridae). 

 With this one must note as a very indicative phenomenon that the representa- 

 tives of Gyrodactylidae and in particular, different Gyrodactylus- -being 

 typical parasites of fishes, are capable of parasitizing Amphibia; to be 

 more specific, their larval stages--tadpoles (Stunkard and Dunihue, 1933; 

 Pastukhova, 1950 and others). This can hardly be evaluated simply as a 

 fortuitous occurrence of hosts of the first and the second groups ! 



The morphology of the larvae of Polystomatidae is unusually 

 similar to that of young forms of Gyrodactylidae, but in the adult state they 

 sharply differ in a number of relations. This is fully natural because the 

 live-bearing habit, peculiar to Gyrodactylidae, places a distinct imprint 

 on the entire organization of these worms. Within the limits of Poly- p. 398 



stomatidae and Spyranuridae, the common principle of structure appears 

 very constant and one clearly observes the tendency toward the complication 

 of the ducts of the sex system and the multiplication of the number of testes 

 (see page 55). At the same time, the canalis genito-intestinalis , a formation 

 connected with high productivity and higher tempo in the deposition of eggs, 

 appears first among these families (see page 55 ), 



The order consists of two suborders --Gyrodactylinea Bychowsky, 

 and Polyopisthocotylinea (Odhner) Bychowsky. 



1. Suborder Gyrodactylinea Bychowsky, 1937 



Gyrodactylidea, predominantly of small sizes; viviparous. The 

 young worms are born with a completely formed sex system. The attaching 

 armature consists of 16 hooks, 2 middle hooks (the latter can be absent as 

 an exception) and of a connecting apparatus. In connection with the latter 

 sometimes there are supplementary chitinous formations which serve to 

 support the disc in its open state. The anterior end has two cephalic out- 

 growths into which open the ducts of the glands. The eyes are absent. The 

 digestive system with 2 intestinal trunks terminating blindly and not form- 

 ing lateral outgrowths. The ovary is V-shaped; the testis is round. 



Parasites of marine and freshwater Teleostei and cephalopods. 



The suborder includes one family- -Gyrodactylidae (Beneden and 

 Hesse) Cobbold. 



476 



