fresh water forms and at the same time, in considerable part, phylo- 

 genetically primary parasites of Cypriniformes. However, the fauna 

 of Dactylogyridae of Cypriniformes can be divided into five groups by 

 its structure and links with the hosts. To the first group pertain genera 

 peculiar exclusively to Cyprini- - Dogielius, Falciunguis , Pseudacol - 

 penteron, Paradactylogyrus, Pseudomurraytrema , and Hamatopedun - 

 cularia. The second group contains genera peculiar basically to 

 Cyprini and discovered on other orders of fishes, but not on Siluri to 

 which pertain Dactylogyrus, and Acolpenteron. The third group con- 

 sists of genera basically encountered on other orders of fishes but dis- 

 covered also on Cyprini and on Siluri- -that is Cleidodiscus , Urocleidus , 

 and Ancyrocephalus (see however, page 265 ). The fourth group is 



Apparently Metahaliotrema also belongs here. 



represented by two genera peculiar only to Siluri - -Ancylodiscoides and 

 Bychowskyella. Finally the fifth group consists of one genus - -Ancylodiscus , 

 encountered on marine Siluri and Perciformes. It is interesting that 

 the third group consists of those three genera about which we have often 

 said that they are artificial (see pages 258-261 ). With this, if one takes 

 into consideration our analysis of the genus Urocleidus (see page 350 ) 

 one can consider its attribution to the third group as erroneous and its 

 transfer to the second group as more correct, although this also is not 

 quite accurate because it is basically peculiar not to Cyprini, on which 

 it is rather an exception, but to Perciformes. In conclusion, speaking 

 about the fauna of Dactylogyridae of Cypriniformes, we must conclude 

 that actually Cyprini and Siluri each have their dactylogyrid-fauna 

 sharply differing from both groups. 



The fauna of Gyrodactylidae of Cypriniformes consists of 

 representatives of two genera of which one is known only from Cobitidae 

 (Paragyrodactylus) and a second ( Gyrodactylus) - -be sides Cypriniformes 

 from eight more orders and perhaps will also be found on a number of 

 others. There is reason to believe that the genus Gyrodactylus is 

 secondarily fresh water although it is very ancient in its origin. It is 

 also probable that the genus Gyrodactylus is phylogenetically secondary 

 for Cypriniformes. However, taking into consideration its wide dis- 

 tribution and at the same time the large species specialization one can 

 suppose that its adaptation to Cypriniformes took place almost at the 

 same time as the differentiation of the order itself. As indirect sub- 

 stantiation of this is the noteworthy fact that among the almost 30 

 species of Gyrodactylus known from Cypriniformes, only one was dis- 

 covered on Siluri and all the rest on Cyprini. 



360 



