As regards Dactylogyridae, two species of Dactylogyrus 

 are known from Anguillidae and one--of Ancyrocephalus, from 

 Muraenidae. Both species of Dactylogyrus are known only from eels 

 and it is quite possible that it is the same species (see page 277 ). In 

 addition, the only species of Ancyrocephalus (A. alatus, Chauhan) is 

 encountered also on Percifornnes and on Cypriniformes. Beyond any 

 doubt the representatives of both genera are recent parasites of 

 Anguilliformes which transferred to them from Cypriniformes (Dactylo- 

 gyrus^) and possibly from Perciformes ( Ancyrocephalus) . 



The situation is quite different with the only species of 

 Acanthocotylidae - - Enoplocotyle minima Tagliani. Undoubtedly it is a 

 very primitive species; however, it has certain peculiarities indicating 

 secondary simplifications (see page 385). Inasmuch as all the remaining 

 Acanthocotylidae are encountered exclusively on skates (see, however, 

 page275 ) and are, as we have already said, the primary parasites of 

 Selachii it is clear that Enoplocotyle transferred to Anguilliformes 

 secondarily; however, as was already indicated (see page 302) in a very 

 remote period. Thus, one can consider Enoplocotyle as a characteristic 

 genus only for Anguilliformes and connected for a long time with them 

 in the process of evolution. 



Beloniformes have the repreeentatives of four genera-- 

 Ancyrocephalus , Axine, Neoaxine , and Axinoides in their fauna of 

 Monogenoidea. The first of these genera is represented by two species 

 encountered only on Beloniformes. Undoubtedly these are parasites p. 312 



which became adapted secondarily to inhabiting the present fishes and 

 transferred to them in relatively recent times from Perciformes, being 

 in this fashion the phylogenetically secondary parasites of Beloniformes. 

 The genus Axine, basically encountered on Beloniformes (on tw^o families 

 Belonidae and Exocoetidae) is known also from Perciformes (see page 

 256 ). The genera Neoaxine and Axinoides are known only from Belonidae. 

 Taking into consideration the secondary nature of the structure of the 

 attaching apparatus of these Microcotylidae, it is most probable that they 

 transferred to parasitizing the family under discussion from Perci- 

 formes and this in the relatively recent past. It is noteworthy that in 

 the Perciformes they are encountered only on Carangidae, The latter 

 separated in the Eocene (Belonidae are known from the lower Oligocene; 

 Berg, 1940) just as did the Beloniformes. There are no consanguinous 

 links between both hosts of Axine and Axinoides . Hence, it is most 

 probable that the transfer of parasitizing from one group of hosts to 

 another was linked by the presence of ecological contacts of both. 



The fauna of monogenetic trematodes of Gadiformes is 

 somewhat more diversified than among the preceding orders. Into its 



362 



