4. Subfamily Merizocotylinae Johnston and Tiegs, 1922 



(Figs. 15, 30, 32, L, 47, 101, D, 274, D-F) 



Monocotylidae having an attaching disc with a centra*! depression 

 with 7-5 depressions adjoining it and a varying number of supplementary 

 ones lying between the edge of the disc and the preceding ones. As an 

 exception the middle hooks of the disc can be absent (Empruthotrema). The 

 anterior end has acephalic glands but lacks a distinct adoral sucker. The 

 eyes exist or are absent {?). Vaginal ducts are paired. The testis is single 

 or divided into two parts. 



Parasites of skates (Rajidae, Trigonidae) and sharks (Lamnidae, 

 Carcharhinidae and Sphyrnidae). 



Type genus, Merizocotyle Cerfontaine, 1894. 



Besides the type genus it also includes Thaumatocotyle Scott, 

 1904, Empruthotrema Johnston and Tiegs, 1922, and Cathariotrema 

 Johnston and Tiegs, 1922. 



The scheme of interrelations between the genera was indicated 

 by us in the remarks on the family. In connection with the indicated 

 tendencies of development of the attaching disc of Monocotylidae and their 

 undoubted evolutionary significance, one cannot agree with the consideration 

 of Brinkmann (Brinkmann, 1940) that the genus Thaumatocotyle is synony- 

 mous with Merizocotyle because the nature of the reductions and the new 

 formations of the discs of both genera, even though it seems close, is 

 nevertheless completely different. Unfortunately we did not have our own 

 material of a single one of the genera pertaining to the present subfamily 

 and are consequently deprived of the possibility of verifying a number of 

 data which seems dubious to us. Thus, the absence of eyes among a 

 majority of species demands substantiation, and it is possible that this fact 

 is not correct (sic). Thus, even though Thaumatocotyle is close to the 

 remaining genera, the structure of its disc and its being found in the sharks 

 in contrast to all the others, places it somewhat apart and it is possible 

 that after re -examination it will have to be isolated into a special subfanaily. 

 Finally, strange as it may seem at first sight, it seems to us that the 

 absence of middle hooks in Empruthotrema demands further substantiation. 

 It is possible that here takes place the preservation of middle hooks which 

 did not develop in the postembryonic period, i.e., of such sizes that 

 escape the attention of these researchers. Should this be substantiated 

 then the only unexplainable exception among the entire fannily will be only 

 illusory. 



441 



