The transfer of a few Gyrodactylidae to Pleuronectiformes 

 iindoubtedly took place relatively recently and also undoubtedly from 

 littoral Perciformes. 



Finally, Diclidophoridae are represented on Pleuronecti- 

 formes by a genus encountered only on them and Tetrodontiformes 

 (Heterobothrium). Again there is no doubt that this genus descends 

 from forms which transferred to these orders of fishes from Perci- 

 formes. 



Finally the fauna of Monogenoidea of Pleuronectiformes is 

 basically relatively young and with the exception of Bothitrematidae 

 descends from the corresponding one of Perciformes. Inasmuch as 

 the links between Pleuronectiformes and Perciformes are commonly 

 recognized this is quite understandable. The separation of Pleuronecti- 

 formes took place approximately in the lower Eocene and even in the 

 beginning of the Paleocene, i.e., considerably after the separation 

 of Perciformes. Hence, it is possible to think that Bothitrematidae 

 and perhaps Entobdellinae separated on Pleuronectiformes also 

 approximately in the Eocene period. 



Finally the last order- -Tetrodontifornaes --has a fauna of 

 Monogenoidea consisting of three genera of Dactylogyridae, two of 

 Capsalidae,and one of Diclidophoridae. 



One genus of Dactylogyridae is encountered only on 

 Tetrodontiformes ( Ancyrocephaloides ), the second- -on these fishes 

 and on Perciformes (Diplectanotrema); whereas the third is widely 

 distributed on a number of orders, but basically on Perciformes 

 ( Ancyrocephalus ). Thus, there is every reason to believe that repre- 

 sentatives of this family became adapted to Tetrodontiformes rather 

 recently and transferred to them from Perciformes. The samie applies 

 also to Capsalidae which did not form any independent genera nor in- P- 317 



dependent species on Tetrodontiformes. Finally, Diclidophoridae are 

 represented by one independent species of Heterobothrium, also des- 

 cending from forms from Perciformes as has already been indicated. 



Hence we can make certain conclusions about a weak individuality of the 

 fauna of Monogenoidea of Tetrodontiformes which separated apparently 

 relatively recently from the one of Perciformes. It is curious that 

 Tetrodontiformes are known from the lower Eocene and perhaps from 

 the upper Cretaceous (Berg, 1947) but nevertheless the fauna of their 

 parasites is much less distinctive than that of Pleuronectiformes. 



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