Discocotylidae from Cypriniformes are again peculiar only 

 to Cyprini and are not known from Siluri, To this family pertain two 

 genera parasitizing Cypriniformes and one of them besides is encountered 

 on Cyprinidae (Diplozoon) and a second, both on Cyprinidae and Cato- 

 stomidae (Octomactrum). The third genus Discocotyle, which was 

 already mentioned (see page 308 ) is encountered on Salmonidae and p_ 3^]^ 



apparently is primary or initial or more precisely is closer to the 

 ancestral forms than both genera to the Cypriniformes. Again there 

 is no doubt that the genus Diplozoon is phylogenetically younger than 

 Octomacrum. and especially Discocotyle. However, the great special- 

 ization of this genus points to the considerable antiquity of its separation. 

 If one takes into consideration what has been said above, one can con- 

 clude that this took place not later than the Cretaceous period. If this 

 is so then both genera on Cypriniformes are their initial phylogenetic 

 parasites. At first glance this conclusion stands in distinct contra- 

 diction with what has been said about Discocotylidae earlier (see page 

 308); however, it is not so. Actually we consider that Discocotylidae 

 became adjusted secondarily to existence in fresh water and that they 

 descend from marine Mazocraeidae but at the same time phylogenetically 

 they are primary parasites of Cypriniformes, i.e. , their evolution 

 as independent genera began at the same time or simultaneously with 

 the formation of Cyprinidae and Catostomidae. 



Finally jCalceostomatidae on Cypriniformes are represented 

 by two genera- -Anonchohaptor from Catostomidae and Fredericianella 

 from Ariidae (?, see page 363 ). Both genera are insufficiently studied 

 and we cannot say anything definite about their links with their hosts, 

 especially since their position in the system is far from being clear to 

 us (see page 362 ). The only thing that can be said with certainty is that 

 the genera mentioned became adapted to parasitizing fresh water Cyprini- 

 formes independently from the remaining Dactylogyridae. 



In addition to what has been said before, the analysis of the 

 fauna of Monogenoidea of Cypriniformes leads to the general conclusions 

 about its relative antiquity and a fresh water origin of its greatest part. 

 At the same time> there is reason to believe that the division of Cyprini- 

 formes into two separate orders is natural because the data on the dis- 

 tribution on them of monogenetic trematodes confirm the considerable 

 separation of Cyprini from Siluri. 



The fauna of Monogenoidea of Anguilliformes is not very 

 large and consists of representatives of two genera of Dactylogyridae 

 and one of Acanthocotylidae. 



361 



