Sphyranuridae (the only genus Sphyranura, see page 401 ) is 

 characterized by a disc which is transversely elongated and sharply de- 

 lineated from the body on which there are two powerful suckers, two 

 nniddle hooks and 16 edge hooks of which two are located in the suckers 

 and the remaining along the edge of the disc. 



Hexabothrildae (Fig. 2) are characterized by the presence of a well-isolated 

 disc, carrying on the posterior end a more or less well-developed appendage of signifi- 

 cantly smaller diameter than the disc itself. Six powerfully developed suckers are located 



on the disc. Along the middle line a strongly 

 curved long hook is located in such a way that 

 its sharp edge is located near the inner surface 

 of the sucker while its remaining portion is 

 located in its interior (or within the tissue of 

 the sucker, nobis ). Undoubtedly, in spite of 

 this powerful development these hooks are 

 homologous to the corresponding edge or mar- 

 ginal hooks of the Polystomatidae and other 

 families. The posterior appendage carries 

 two well -developed suckers which are apparently 

 devoid of hooks on its free lower edge. Between 

 these appendage suckers there exists usually 

 one pair of small middle hooks. In a number 

 of species the middle liooks are absent alto- 

 gether. One must indicate, nevertheless, 

 that the question relative to the chitinous 

 armature of Hexabothriidae demands reinves- 

 tigation (see page 406). 



aiMM 



Fig. 48. Heterocotyle sp. , attaching 

 disc of an adult individual from the 

 gills of Dasybatus zugei M. H. from 

 the region of Nagasaki (East China 

 Sea). 



The family Diclybothriidae close to the preceeding one has an 

 analogous disc, nevertheless six of its suckers, also equipped with power- 

 fully developed chitinous hooks, stand much closer in their structure and 

 function to the valves of the successive families than to the actual suckers. 

 The absence of the chitinous parts characteristic of clamps draws them 

 closer to the latter, but during the research on live subjects it is clearly 

 seen that their common configuration and their method of attachment is of 

 typically valve -type character. The posterior appendage is well developed 

 in the genus Diclybothrium (Fig. 51) and is almost completely reduced in 

 the second genus Paradiclybothrium (Fig. 52). When the posterior append- 

 age is developed, it carries two rudimentary suckers and four pairs of 

 hooks. Two pairs of hooks have the same shape or form as those in the 

 suckers. One pair represents the unchanged small edge hooks and the 

 latter represents small central or middle hooks. (For details see the 

 chapter on embryology, page 101 . ) Among Paradiclybothriunri the chitinous 



p. 38 



31 



