No. 5 meserve: monogenetic trematodes 47 



Family: HEXOSTOMATIDAE Price, 1936 



Hexostoma euthynni, new species 

 (Plate 6, figs. 22-24) 



Host: Euthynnus alletteratus (Rafinesque) 

 Location: Gills 



Locality: James Island, Galapagos Islands 

 Number: 1 



Body elongated, tapering anteriorly from ovary, anterior end 

 pointed, constricted at middle of body proper posterior to ovary, 

 5.853 mm. in length by 0.953 mm. in width. Posterior haptor large, 

 0.953 mm. in length by 1.30 mm. in width, slightly wider than the 

 widest part of body. Eight large posterior suckers, elliptical, broader 

 than long, 0.203 mm. in length by 0.339 mm. in width, arranged 

 somewhat in form of a horseshoe. Each sucker has three heavy X- 

 shaped, chitinous, skeletal pieces imbedded longitudinally in its walls, 

 middle skeletal piece longer, imbedded in septum which divides 

 sucker into two parts; one X-shaped skeletal piece imbedded in 

 wall in each side of sucker. Two pairs of hooks at posterior end of 

 animal; anterior pair larger with a base which is imbedded and 

 parallel to the rest of the hook which is straight and points posteri- 

 orly, 0.068 mm. in length. Smaller pair of hooks approximately one 

 half the size of larger hooks, situated between and posterior to 

 larger anterior pair. Mouth subterminal, ventral. Two anterior mouth 

 suckers elliptical, longer than broad, 0.056 mm. in length by 0.04 

 mm. in width. Small pharynx just posterior to anterior suckers. 

 Esophagus short, bifurcating anterior to genital pore. Intestinal limbs 

 with lateral branches, not united behind. Cirrus consists of cup- 

 shaped body with two bean-shaped bodies attached to it posteriorly. 

 Diameter of cirrus cup 0.068 mm. Bean-shaped bodies 0.072 mm. 

 in length. Spines of bean-shaped body straight, sharp, pointed 

 toward mid-line and obliquely downward, 0.012 mm. in length. 

 Testes small, slightly lobed, in mid-line in anterior part of posterior 

 half of animal, twenty-six in number, length of testicular region 

 0.848 mm., width 0.271 mm. Vas deferens leaves base of penis cup 

 passing posteriorly dorsal and to right of uterus. From genital pore 

 to halfway to ovary it is slender without coils. It then broadens to 

 over twice its anterior width and passes posteriorly by tortuous 

 windings. Genital pore in mid-line, ventral, near posterior end just 



