The fauna of monogenetic trematodes of Clupeiformes in- 

 disputably consists of representatives of four families. There are no 

 families of Monogenoidea common for all Clupeiformes and their fauna 

 falls into three groups: parasitizing Clupeoidei (Clupeidae), Salmonoidei 

 (Salnnonidae, Thymallidae and Osmeridae), and encountered on Sal- 

 monoidei and Esocoidei (Esocidae) at the same time. '■ 



1 



The data about Bilaterocotyle (Protomicrocotylidae) from Chiro- 



centridae are not taken into consideration (see page 228 ). 



The first group consists of representatives of three genera 

 of Mazocraeidae, which are undoubtedly connected with each other in 

 their evolution (see page 419). However, besides these genera, three 

 more (two? --see page 417) genera parasitizing Scombridae pertain to 

 the same family. The close relation of the genera of Mazocraeidae 

 parasitizing Clupeidae and Scombridae does not arouse any doubts and 

 the genera Mazocraes and Octostoma (Fig. 263) are especially close 



Clupeidae 



MazKraeoides 



Ueomazocraes 



t 

 Mazocraes — 



^ ^ ScombncLae 



Pseudoanthocottjle 

 -^-Octostoma 



Fig. 263. Diagram of interrelations between the genera of Mazocraeidae 

 and their hosts. 



to each other. The last genus most probably descends from the first 

 or fronn ancestors very close to it. Thus, this gives us the right to 

 suppose that Mazocraeidae are primarily phylogenetic parasites of the 

 Clupeidae and secondarily for Perciformes. The transfer to the latter 

 is conditioned not by consanguinous relations of the host although they 

 have them but basically by the commonness of ecology of herrings and 

 scombrids and the relatively frequent and constant contact. As is known, 

 during a considerable period of their lives the scombrids feed on young 

 herrings (Nikolski, 1954) and in addition to that they are pelagically 

 gregarious fishes which at younger ages often migrate jointly which 

 was often also observed by us. 



356 



