composition enter the representatives of two orders of Polyonchoinea 

 and one of Oligonchoinea. 



From Dactylogyridae only one monotypic g enus-- Lingua - 

 dactyla is known from Molva (Gadidae), This genus is very singular 

 (see page 352 ), in connection with which it is separated by us into a 

 special subfamily of Dactylogyridae. In contrast to all the remaining 

 representatives of this family it has a number of both primitive and 

 conversely very specialized traits in connection with which its rela- 

 tively ancient separation from other Dactylogyridae, and apparently 

 very prolonged common existence with the contemporary hosts, does 

 not occasion any doubts. 



As regards Gyrodactylidea, a number of species of Gyro- 

 dactylus is known on Gadiformes both in marine as in fresh waters 

 [on Lota lota (L. )] . All the species of this genus are strictly specific 

 to their hosts. As was shown by B. E, Bychowsky and J. I. Poljanski 

 (1953), one can maintain for a number of them that they have been 

 connected with their hosts at least from the preglacial period and 

 possibly even from the Paleocene. 



Among Oligonchoinea, representatives of Anthocotylidae 

 and Diclidophoridae are known on Gadiformes. In addition, the worms 

 of the first family are known from Perciformes. At the same time 

 there is no doubt that its initial (primary, nobis)species are encountered 

 on Perciformes, whereas the secondarily changed ones are encountered 

 on Gadiformes (see page427 ). Besides being on the Gadiformes, the 

 Diclidophoridae are distributed very widely. However, only the genus 

 Diclidophora, which is encountered also only on Macruriformes which 

 are undoubtedly close to them, is characteristic for Gadiformes. As 

 we show later the genus Diclidophora represents a very changed or 

 altered genus (see page 435 ), and beyond any doubt it descends from 

 forms parasitizing other orders of fishes. The correlations between 

 Diclidophoridae and their hosts will be indicated later in detail (see 

 page 315 ). On the whole the fauna of Monogenoidea of Gadiformes 

 shows that it is heterogeneous in its origin and is linked by its roots 

 with the corresponding fauna of Percifornnes. 



As is known, many authors consider that Gadiformes are 

 descendents of common ancestors with Cyprinidae. However, L. C. 

 Berg supposes that such were the forms consanguinous to Pachycor- 

 midae and that the Gadiformes arose at the end of the Cretaceous 

 period (Berg, 1940). Also, A. N. Svetovidov is not inclined to con- 

 sider Gadiformes as being to close to Perciformes, although he points 



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