1. Family Diclybothriidae Bychowsky and Gussew, 1950 



(Figs. 51, 52, 90, 220, 221) 



Diplobothriinae Monticelli, 1903; Diclybothriinae Price, 1936. 



"Anterior end with two lateral sucker-shaped depressions not 

 connected with the buccal opening (bothridia). There are two pairs of eye 

 spots. The intestinal tract is 2-branched with lateral, exterior and in- 

 terior outgrowths, the intestinal trunks merge at the posterior end of the 

 body into the unpaired trunk extending into the middle or posterior end of 

 the attaching disc. The unpaired trunk of the intestine can have lateral 

 outgrowths, but it never extends into the posterior narrowed part of the 

 attaching disc. The attaching disc has 3 pairs of clamps or sucker?, inside 

 of each of which lies one large chitinous hook. There is a more or less 

 well-developed appendix (the narrowed part of the disc) which bears 3 pairs 

 of relatively large and one pair of very small hooks and in a number of 

 cases a rudimentary pair of suckers on the posterior part of the disc. The 

 small hooks and the rudimentary suckers can often be seen only in live 

 subjects or in serial sections. " 



"Parasites of sturgeon-types, Acipenseriformes, and Polyo- 

 dontidae" (Bychowsky and Gussew, 1950). 



Type genus, Diclybothrium Leuckhart, 1835. 



In addition to the type genus there is also another--Paradicly- p. 405 

 bothrium Bychowsky and Gussew, 1950. 



This family is characterized by very notable characteristics. 

 The analysis which was conducted by us with Gussew (Bychowsky and 

 Gussew, 1950) shows that in comparison with Hexabothriidae the repre- 

 sentatives of both genera of Diclybothriidae are more specialized and the 

 process of specialization is along the lines of the gradual disappearance of 

 the attaching muscular formations, primarily during the time of its 

 inception, with the preservation of all chitinous elements. Thus, in 

 Diclybothrium the remnants of the first pair of suckers (suckers of the 

 narrowed part of the disc) are also retained, whereas, Paradiclybothrium 

 does not have them. At the same time further simplification in the 

 structure of the attaching clamps of the widened part of the disc, which 

 structually resemble the usual suckers more closely although this 

 similarity is clearly of a convergent nature, also takes place in the last 

 genus. Proofs of the fact that historically this process proceeded 



precisely in this fashion are on the one hand the peculiarities of the develop- 

 ment of the chitinous elements of the disc and on the other, the details of 

 the structure of the male sex system, particularly the presence of the 

 bifurcation of the seminal duct and the penis of Paradiclybothrium which 



485 



