3 88 



FRESH-WATER BIOLOGY 



6 1 (50) Oral sucker, subterminal; acetabulum divided by transverse ridge 

 into two pockets. . . . Subfamily ZYGOCOTYLINAE Ward. 



Differs from all other subfamilies in position of oral sucker and 

 peculiar character of acetabulum. Testis lobed; ^cirrus sac lack- 

 ing. 



Representative American genus. 



Zygocotyle Stunkard 1916. 



Acetabulum consists of anterior part extending dorsad and 

 anteriad into body, and posterior overhanging lip bearing on each 

 side conical projection. Posterior end of esophagus surrounded 

 by muscular bulb in which fibers are not arranged in concentric 

 lamellae as in other amphistomes. Vitellaria well developed, with 

 large follicles, in extracecal region from oral sucker to acetabulum. 

 Uterus and germ glands intracecal. Eggs numerous, 0.14 by 

 0.083 mm. 



Type species. . . Zygocotyle ceratosa Stunkard 1916. 

 From intestine of Anas platyrhynchos ; Nebraska. 



FIG. 674. Zygocotyle ceratosa. Ventral view. X 5- (After Stunkard.) 



62 (49) Acetabulum conspicuously ventral and usually anterior to center of 



body. Reproductive organs completely or largely posterior 

 to acetabulum 63 



63 (160) No holdfast organs present except oral and ventral suckers. No 



sharp separation between anterior region with holdfast 

 organs and posterior region with genital organs. 



Suborder Distomata . . 64 



64 (159) Hermaphroditic distomes 65 



65(148) Ovary anterior to testes ... . ....... . 66 



66 (107) Coils of uterus do not extend posterior beyond testes, or at most not 



beyond the posterior testis 67 



Bunodera (see 103 in this key) forms the single exception. 



67 (106) Acetabulum a single typical sucker which may be stalked or united 



with special genital sucker but is not divided 68 



68 (105) Not more than two testes present 69 



69 (74) Both ovary and testes dendritic; uterus limited to a restricted 



area 70 



