2. Family Hexostomatidae Price, 1936 



(Figs. 37, 299) 



Plagiopeltinae Monticelli, 1903. 



Mazocraeinea, having large sizes in the adult state. The 

 attaching apparatus consists of a widened disc, weakly delimited from the 

 body on which are located 2 pairs of middle hooks and 8 clamps, secondarily 

 changed into suckers. The clamps lie in two symmetrical groups but form 

 almost one straight (group, nobis) so that the first pair (according by the 

 time of inception), which usually has smaller dimensions, is located near 

 the medial line of the disc and the subsequent ones toward its periphery to 

 the right and to the left. The clamps are equipped with 3 chitinous parts p. 421 



representing the remnants of the reduced capsule, apparently of the 

 mazocraeid-type. The anterior part of the body bears a buccal opening 

 lying terminally. The eyes are absent. The buccal cavity has 2 suckers. 

 The intestine is powerfully developed and forms a net-like interlacing of 

 the branches which begins immediately behind the esophagus and terminates 

 in the attaching disc. The basic trunks of the intestines are noticeable only 

 at the very beginning of their extensions. The male copulatory organ is not 

 armed but opens outside together with the opening of the sac-shaped uterus. 

 The testes are numerous. The ovary is of the flask-shaped type but has a 

 large number of curvatures and outgrowths and forms a compact mass, 

 mainly U-shaped with the apex turned toward the anterior end of the body. 

 The vaginal ducts are double and marge anteriorly into one which opens 

 outside dorsally. The end of the unpaired vaginal duct is armed with 2 

 large chitinous plates with an indented iiite-^ior edge. 



Parasites of tunas and of the fainilies close to them (Cybiidae 

 and Carangidae). 



Type and only geaus, Hex ostoma Rafinesque, 1815. 



Price correctly elevates che subfamily Plagiopeltinae earlier 

 ( Plagiopeltis Diesing =Hexostoma Rafinesque) abstracted by Moniicelli 

 (Monticelli, 1903) into the rank of a family because there is no doubt that 

 it is a very individualized group which cannot be included into any of the 

 known families of Oligonchoinea. 



The general plan of the structure of Hexostomatidae principally 

 does not differ from the one of other Oligonchoinea, but it has a number of 

 very interesting peculiarities in the structure of the attaching apparatus 



504 



