Single Discocotylidae with two-branched intestines. There is 

 a copulatory organ. The testes are numerous or in the shape of a single, 

 large, follicular mass. The vaginal ducts exist or are absent. 



Parasites of Salmonidae, Thymallidae, Catostomidae and 

 Cyprinidae. 



Type genus, Discocotyle Diesing 1850. 



In addition to the type genus another genus, Octomacrum Mueller, 

 1934, also belongs here. 



Both genera differ from each other by the presence ( Discocotyle ) 

 or absence (Octomacrum) of vaginal ducts and by the arnnature of the 

 copulatory organ. 



It is most probable that the changes in the structure of Octo- 

 macrum are secondary in relation to Discocotyle which is more ancient in 

 origin. This is indirectly confirmed by the fact that the latter genus is 

 encountered both on transitory (migratory, nobis) and freshwater fishes, 

 whereas the first is only on fresh water fishes. 



2. Subfamily Diplozooninae Palombi, 1949 p. 426 



(Figs. 32, F, 113, F, 122, 231-234) 



Discocotylidae, grown together in pairs in the adult state. The 

 intestine in all stages of development is in the shape of a pipe which has 

 lateral outgrowths. The testis is single and rounded. The male sex ducts 

 of one individual grow together with the corresponding female ducts of the 

 other. 



Parasites of Cyprinidae and Cobitidae. 



Type and only genus, Diplozoon Nordmann, 1832. 



Widely distributed in Palearctica. A genus which does not have 

 many species. Its isolation by Palombi (Palombi, 1949) into an independent 

 superfamily seems fully correct to ua. The specialization of Diplozoon 



has gone very far. This is expressed not only by the singular growing to- 

 gether of the young individuals, without which single samples cannot continue 

 further development, but also in the fact that the larva of these worms is 

 deprived of the edge hooks and its attaching disc has only one pair of middle 

 hooks and a pair of attaching clamps. In connection with the question con- 

 cerning the formation of subsequent pairs of clamps, the absence of edge 

 hooks is very interesting, which has already been mentioned (see page 101 ). 



510 



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