CHAPTER IV 



OCCURRENCE OF FAMILIES OF MONOGENETIC TREMATODES 

 ON THE ORDERS OF THEIR HOSTS- -FISHES 



Before terminating the examination of the materials on the ] 



occurrence of monogenetic trennatodes of fishes it is necessary to become 

 acquainted with the correlations between the families of worms and the 

 orders of fishes. The data on this subject are reproduced in Table 16. 

 From it, we see that the inajority of families of worms is encountered on 

 one to two orders of hosts and, when in large numbers, on one of them in 

 the vast majority of species. These data, however, require clarifications. 

 Thus a number of families is encountered only on one order of their hosts 

 and until the present time have not been discovered on other orders. 



_ 



One must take into consideration that the doubtful cases and materials 

 which were discussed in the preceding chapters are excluded from Table 16 

 a priori and consequently will not be discussed here. However, all the known 

 genera are included in it. 



Amphibdellatidae, Bothitrematidae, Chimaericolidae, Dicly- 

 bothriidae, Hexabothriidae, Hexostomatidae, Loimoidae, Microbothriidae, 

 Plectanocotylidae, Protogyxodactylidae, Protomicrocotylidae, Tetraonchidae 

 and Tetraonchoididae, i.e., 13 of the 27 families, pertain here. And one 

 must bear in mind that these families are not equal in volume. Six of them 

 contain only one genus, and with a widely varying number of species (from 

 1 to 8). So far only one family with the species is known- -Bothitrematidae; 

 as should be expected, it is encountered on one family of fishes. One family 

 is known with two species of one genus, Tetraonchoididae --also encountered 

 only on one family of hosts. The family Amphibdellatidae which contains 

 three species of one genus , is also encountered on one family of fishes. 

 Finally, Tetraonchidae and Hexostomatidae, containing eight species each, 

 are encountered each on three families of fishes. Four families of 

 monogenetic trematodes of the group under examination include two genera 

 each, and have similar complexity, with three species each. These are 

 Protogyrodactylidae and Loimoidae, which are encountered on one family 

 of fishes; and Diclybotliriidae and Chimaericolidae which were discovered 

 on two families. Protomicrocotylidae and Plectanocotylidae, each con- 

 taining three genera and five species, are enumerated: the first on two 

 and the second on four families. Finally, Microbothriidae are discovered 

 on four and Hexabothriidae on eight families of hosts. 



In order to evaluate the data which have been presented, it is 

 interesting to note not only that the indicated families of Monogenoidea are 

 encountered on fishes of one order, i.e., undoubtedly related to each other 



308 



