hosts (common existence or frequent contact, sometimes alimentary) 

 and certain biological peculiarities of the worms themselves (the ability 

 to move in the adult state and other peculiarities of development), 



Dactylopteriformes were obviously studied insufficiently. 

 Only one species- - Far ancyrocephaloides daicoci Yamaguti, is known 

 from them. Taking into consideration the indubitable links between 

 the Dactylopteriformes and Perciformes,one can consider with certain- 

 ty that P. diacoci descends fronn Dactylogyridae (Ancyrocephalinae) p. 316 

 of the latter. 



Enough has been said before about the fauna of Echenei- 

 formes consisting of representatives of the genus Dionchus (Dionchidae). 

 Without any doubt the forms parasitizing the fishes of this order trans- 

 ferred to them from Carangidae secondarily, and one species did not 

 even separate and was preserved as common to Echeneidae and 

 Carangidae [the host records for this species--Dionchus remorae 

 (MacCallum) are doubtful, nobis]. 



The fauna of Monogenoidea of Pleuronectiformes is formed 

 of representatives of five families of monogenetic trematodes. Dactylo- 

 gyridae and Bothitrematidae are represented each by one species only; 

 however, each is quite different in its origin. Thu3, Protancyrocephalu3 

 strelkowi Bychowsky, even though it is specific for flatfishes and even 

 separated on them into an independent genus, is nevertheless undoubted- 

 ly a comparatively young parasite of flatfishes and descends from forms 

 which undoubtedly came from Perciformes. 



The situation is quite different with Bothitrema bothi 

 (MacCallum) which undoubtedly is a very ancient parasite of Pleuro- 

 nectiformes (see pages 394-397 ). We are not in a position to say 

 anything definite now about the origin of Bothitrema. It is quite 

 possible that it is a very ancient group which separated from the common 

 trunk of Tetraonchidea before the separation of the remaining families 

 except Tetraonchidae. 



Apparently Capsalidae parasitizing the Pleuronectiformes 

 are also a very ancient separation. This is substantiated by the fact 

 that Entobdellinae, which are characteristic basically for these species, 

 have a disc apparently deprived of septa (see page 380 ). 



Nevertheless, It Is not possible to doubt that the primary forms of 

 Capsalidae of Pleuronecriformes transferred to them from Peiciformes and thus 

 are secondary from the first. 



368 



