534 FRESH-WATER BIOLOGY 



74 (71) Without papillae on tail of male and with single intestinal cecum. 



Hysterothylacium Ward and Magath. 



Anterior end with narrow lateral wings. Lips three, not prominent. Esophagus long, 

 slender, with terminal bulb. Intestine with short simple cecum at anterior end, extending 

 posteriad. Males with two equal spicules. Females unknown. 



Type species. . . Hysterothylacium brachyurum Ward and Magath. 



Male 32 mm. long; maximum width 0.66 mm. Lateral ala one-quarter width of body. 

 Esophagus 3.1 mm. long, o.i to 0.13 mm. broad; bulb with three teeth; cecum 0.94 by 0.08 

 mm. Spicules 0.72 mm. long, 0.045 mm. wide. Pyriform sperm vesicle prominent. 



In stomach of black bass; Lake St. Clair. 



75 (7) Esophagus slender, non-muscular; lumen a capillary chitinous tube 



traversing a row of granular cells. 



Suborder Trichosyringata . . 76 



76 (77) Anus lacking; alimentary canal non-functional in adult. Adults 



free living Family MERMITHIDAE Braun 1883. 



These forms are only distantly related to aquatic biology as the adults occur free in soil, or 

 less often on plants as the famous "cabbage-snake." The early life is spent as a parasite in 

 the body cavity of some insect or crustacean from which they occasionally escape into an 

 apple or other peculiar environment. 



They are very slender, greatly elongated, threadworms in which the alimentary canal is 

 transformed in the adult into a fat body. .The eggs are spherical, with two peculiar stalked, 

 tasselated appendages at the poles. The adults are fully considered in the chapter on Free- 

 living Nematodes (consult page 503). 



The Mermithidae are often confused with Gordiacea to which they bear a certain superficial 

 resemblance. The differences are discussed later (page 535). 



77 (76) Alimentary canal complete and functional. Adults always para- 



sitic. . . Family TRICHINELLIDAE Stiles and Crane 1910.. 



Esophagus formed by capillary tube traversing chain of cells. Anterior region of body 

 slender, posterior region swollen. Anus terminal. Male with single spicule (or none?). 

 Female with one ovary. Vulva near junction of anterior and posterior body regions. 



The well known human parasite, Trichinella spiralis, commonly called trichina, is included 

 in this group though in another subfamily from the following. 



Subfamily TRICHURINAE Ransom 1911 . . 78 



78 (79) Anterior region of body very slender and much longer than posterior 



region ...... . . Trichuris Roederer and Wagler 1761. 



In North American aquatic host. 



Trichuris opaca Barker and Noyes 1915. 



Male 22 to 28 mm. long; anterior region 13 to 19 mm. 

 long, 0.06 to 0.08 mm. thick; posterior region 7 to 9 mm. 

 long, 0.14 to 0.16 mm. thick. Spicule 2 mm. long; sheath 

 o.i 8 mm. long, 0.07 mm. in diameter. 



Female 22 to 30 mm. long; anterior region 18 to 19 

 mm. by 0.06 to 0.07 mm.; posterior region 10 to n mm. 

 by 0.23 to 0.25 mm. Vulva between first and second an- 

 terior eleventh of posterior region. 



Duodenum of muskrat. Nebraska. 



FIG. 831. Trichuris opaca. Posterior end of male. X 20. 

 (Alter Barker.) 



