holocephalan (Mendival-Herrera, 1946). As regards the third species it p. 301 

 was found only once and hasn't been described by anyone (since, nobis ) 

 (see page 410 ); one can state with certainty that it pertains to the family 

 Hexabothriidae (order Diclybothriidea). Again it is nnost probable that 

 this is a secondary parasite of Holocephali. In conclusion, one can con- 

 sider that the fauna of Monogenoidea of the Holocephali is composed of 

 species characteristic only for this class of fishes and for the fishes 

 belonging to Elasmobranchii, but peculiar basically to the latter genus 

 Calicotyle is encountered only on Elasmobranchii just as the species of 

 the fan-xily of Hexabothriidae are known only from the representatives of 

 this class). Undoubtedly this underscores the phylogenetic links between 

 Holocephali and Elasmobranchii, although as we have already indicated 

 the transfer of two species of worms fronn the latter onto the former took 

 place considerably later historically than the appearance of Chimaericolidae 



on Holocephali. As a confirmation of this, in addition to what has been 

 indicated before, is the fact of the absence of any special adaptations toward 

 parasitizing Holocephali among the three "new" species; whereas, in 

 Chimaericolidae all their organization is very specialized. As a contra- 

 diction to the phylogenetic significance of the finding of the species in- 

 dicated can be proposed the consideration about the commonness of the 

 conditions of existence and biology of Chimaera and Callorhynchus with 

 sharks and skates; however, this is hardly justified because then we 

 could expect the finding of Calicotyle and Hexabothriidae on fundic (bottom, 

 nobis) bony fishes with equal success which actually is not observed (see 

 however, page 227). 



As has been indicated before, Elasmobranchii have a fauna of 

 monogenetic trematodes composed of representatives of three orders. At 

 the same time, among Polyonchoinea the monogenetic trematodes of the 

 families Amphibdellatidae, Monocotylidae (the exception was indicated 

 above), Microbothriidae, and Loimoidae parasitize Selachii exclusively; 

 whereas Capsalidae and Acanthocotylidae occur on thenn and on Teleostei. 

 Let us note beforehand that of all Polyonchoinea, only one family from 

 Selachii (Amphibdellatidae) pertains to the order Tetraonchidea, whereas 

 all the rest- -to Dactylogyridea--Monopisthocotylinea. Thus, taking into 

 consideration that there are no Dactylogyrinea on Selachii, we can consider 

 that basically representatives of the more highly organized families of the 

 last order are encountered on them. From, the point of view of inter- 

 relations of the groups of fishes and at the sanne time of the phylogeny of 

 the parasites, the greatest interest in represented by both families 

 encountered on Elasmobranchii and on Teleostomi. As regards Capsalidae, 

 among them representatives of the genus Sprostonia , Microphyllida, 

 Benedenia, Entobdella , and Tristoma parasitize the group of hosts which 

 is under consideration. Of these five genera the first two are encountered 



1 



We do not take the indication of Capsala from, the shark, Squalus sp. 

 into consideration (see page 261 )• 



348 



