Parasites of Elasmobranchii and, as an exception, Holocephali, 



Type genus, Hexabothrium Nordmann, 1840. 



In addition to the type genus, Squalonchocotyle Cerfontaine, 1899; 

 Rajonchocotyle, Cerfontaine, 1899; Rajonchocotyloides Price, 1940; 

 Heteronchotyle Brooks, 1934; Pseudohexabothrium Brinkmann, 1952; and, 

 Rhinobatonchocotyle Doran, 1953, enter into the composition of the family. 



As was mentioned before, 

 the development of the worms of this 

 family is completely unstudied and 

 consequently we do not have any data 

 about the larvae. In spite of that, one 

 can attempt to visualize their structure 

 on the basis of analysis of the peculi- 

 arities of adult worms. The question 

 of the chitinous armature seems to be 

 most interesting. As is known from 

 what has > een said before, the adult 

 forms h^-ve 3 pairs of edge and one 

 pair of middle hooks, with this the 

 pair of suckers lying in the narrowed 

 part cf tn.; disc lacks armature which 

 Fig. 289. Neopolystoma exhamatum represents an exception to all that is 

 Ozaki. A--Cuticular "button holes or known to us of ''he correlations be- 

 loops" between the anterior suckers tween the chitinous parts and th<_ 



suckern. In his -voik, Cerfontaine 

 draws att;ntic.:. to Lhii^ and indicates 

 that the anBtoinical structure of (:be 

 large suckers Wi.ich c J-ntai'.i these 

 hooks and of the srnali ones lying in 

 the offshoot aie very eiiri.ilar and 

 even shows on a drawing )f s. section 

 through the last place where the edge booklet should have been "if it a ere 

 there" (Cerfontaine 1900, Table XX, Fig. 6). For verification of che 

 correctness of the observations on the structure of the attaching ar-paratus 

 of Hexabothriidae, supposing that errors and the oversight of the very 

 small chitinous hooks similar to the ones which were indicated in a number 

 of preceding groups are possible, we especially studied live worms during 

 our work at southern Sakhalin and the southern Kurile Islands (1946 and 

 1949). As a result, it appeared that besides the ones which are located in 

 the 3 pairs of large suckers the edge hooks are actually absent, at any late 

 in those species of Rajonchocotyle and Squalonchotyle v/hich we examined. 

 However, in a number of individuals of different species of both genera we 

 discovered, it is true with great difficulty, very interesting "remnants" of p. 407 

 2 pairs of edge hooks which appeared in the larvae. In a number of forms 



of the disc (edge hooks are absent!); 

 B--Edge hooks and their "loops" 

 between the posterior suckers of 

 the disc (edge hooks lie separately 

 from the "button holes or Loops!". 

 (According to Ozaki, 1935), 



487 



