to the fact that the closest relatives of Gadiformes--Macuriformes-- p. 313 



are connected with certain Acanthopterygii (Svetovidov, 1948). 



The fauna of parasites of the closest order--Macruriformes-- 

 is very small. It consists only of two genera of Diclidophoridae-- 

 Diclidophora and Diclidophoropsis. Only one species of the first genus 

 is known on Macruriformes, whereas all the rest, as has just been in- 

 dicated, are encountered on Gadiformes. In contrast to this, two species 

 of Diclidophoropsis are known from Macruriformes and Perciformes. 

 On the whole an impression is created that this family of fishes has a 

 fauna of Monogenoidea which links, so to speak, the one of Gadiformes 

 and Perciformes. 



It is understandable that the transfer of ancestors of both 

 genera from some fannilies of fishes onto others is very mysterious 

 but it is most probable that Diclidophoropsis transferred to Macruri- 

 formes from Perciformes and Diclidophora--from Gadiformes, and 

 thus, in spite of the fact that the species of both genera fronn Macruri- 

 formes are independent, the fauna as a whole is secondary. Taking 

 into consideration however, the independence of the species, which has 

 just been pointed out, one must suppose that nevertheless they became 

 adapted to their corresponding fishes a relatively long time ago. 



The fauna of monogenetic trematodes of Gasterosteiformes 

 is obviously secondary and consists of one species of Dactylogyrus and 

 three species of Gyrodactylus . At the same time , if Dactylogyrus were 

 obviously acquired in fresh water and beyond doubt represent the 

 descendents of some sort of forms from carp fishes, then on the other 

 hand, the question about Gyrodactylus is more complex. Thus, one of 

 the species (G. arcuatus Bychowsky) is encountered on purely marine 

 fishes [ Eleginus navaga (Pallas), Boreogadus saida (Lepechin)] it is 

 true in the form of a special subspecies, and is encountered in purely 

 marine regions on sticklebacks. Even though they are discovered 

 basically in fresh waters, two other species were nevertheless often 

 encountered in the sea. Hence, it becomes difficult to speak about the 

 origin of Gyrodactylus of Gasterosteiformes. 



Four species of Dactylogyridae and two species of Gyro- 

 dactylidae are discovered on the Cyprinodontiformes. In both cases 

 they are clearly secondary parasites of Cyprinodontiformes which 

 transferred to parasitizing these fishes from fresiiwater Perciformes. 



Beyond any doubt this transfer did not have any phylogenetic 

 character^ and was the result of a constant contact between the repre- 

 sentatives of both orders with each other. 



364 



