CHAPTER V 



ABOUT CERTAIN COMMON PECULIARITIES OF 



PHYLOGENETIC DEVELOPMENT OF 



MONOGENETIC TREMATODES 



If, after accepting the proposed phylogenetic scheme and the p. 460 



nature of the distribution of corresponding groups of Monogenoidea on their 

 hosts as a basis, one tries to evaluate the correlations between the antiquity 

 of the group of the hosts and the level of organization of their initial parasites 

 he shall obtain very interesting data. Thus, of the 6 orders of Monogenoidea 

 accepted by us, Chimaericolidea from Oligonchoinea and Gyrodactylidea 

 from Polyonchoinea undoubtedly appear the most specialized while at the same 

 time having very primitive and very complex traits of organization. If the 

 first are linked with the most ancient hosts, the second on the other hand 

 have a wide distribution, although they are encountered primarily also on the 

 more ancient of the contemporary Teleostomi (excluding Acipenseriformes), 

 but with this it is possible to think that they appeared on them a very long 

 time ago because as has already been said, the genus Gyrodactyloides is 

 undoubtedly derived from Gyrodactvlus -like ancestors and at the same time 

 it is primarily connected with the relatively ancient group of Salmonoidei 

 and it did not transfer on them from the highest Teleostei. The finding of 

 Polystomatidae and Sphyranuridae on Amphibia and Reptilia, and the unusual 

 adaptability of their life cycles to their hosts (see page 119) also speaks for 

 the antiquity of this group, for contemporary Amphibia and Reptilia separated 

 a very long time ago and are historically considerably older than contemporary 

 Teleostei, with the exception perhaps of the Clupeiformes. Taking into con- 

 sideration that the group Polystomatidae represents a progressively develop- 

 ing and very highly organized group, whereas Gyrodactylidae separated a very 

 long time ago, because it is only they that have worked out the viviparousness 

 which is peculiar to them, and also that it parasitizes hosts which are very 

 ancient in their origin, one can consider that this line is the most specialized 

 in the phylogenetic branch of the lowest Monogenoidea. 



Continuing to examine both subclasses of Monogenoidea from this 

 point of view we see quite clearly that basically the more ancient the host 

 the more specialized the parasite. This can be attributed to the fact that the 

 time during which the present parasite is found on the corresponding host 

 was very prolonged. Hence, it is clear that the degree of morphological and 

 biological specialization which determines the occurrence of a specific group 

 of parasites on a particular group of hosts allows us to speak about a longer 

 or shorter period of existence of both groups. At the same time, we must remember 

 that for monogenetic trematodes specific occurrence is characteristic in the 

 vast number of known species and consequently it would not be sufficient and p. 461 

 perhaps would even be erroneous to base the determination of the historical links on it. 

 The specific occurrence and the degree of morphological specialization of the 

 group is another matter. These data can be utilized relatively for correction 



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