4Q2 



FRESH-WATER BIOLOGY 



36 (23) Esophagus plain Cryptonchus Cobb. 



PP 



Differs from Cylindrolaimus de Man in the form of the amphids, 

 and the strongly developed esophagus with its various regions, in 

 the presence of a dorsal tooth at the base of the pharynx and in 

 the absence of setae. 



Single species. 



Cryptonchus nudus Cobb 1913. 



'5314 91. . 



2.2 f:r -> 



x/az 



9 mm. At a point about two 

 body widths in front of 

 the cardia the nature of the esophagus suddenly changes, the 

 lining becoming notably less massive, and the radial structure 

 becoming relatively more massive, and at the same time changing 

 its character, so that there is a rather striking contrast between 

 this short posterior section and the main portion of the esophagus. 

 Wing space one-third as wide as the body. The anterior part of 

 the intestine for a distance equal to the body radius consists of 

 small cells packed with granules and possessing larger and differ- 

 ently formed nuclei. Eggs four times as long as the body is wide, 

 one-fourth as wide as long, and comparatively thick shelled; 

 uterus contains one at a time. 



Habitat: Found about the roots of aquatic plants, Potomac 

 River, Arlington, and in Douglas Lake, Mich. 



FIG. 792. Cryptonchus nudus. Ib, lip region; pp, labial papillae; am, 

 amphid; ph, pharynx; on, onchus or tooth; oe, esophagus; sp, spinneret. 

 (After Cobb.) 



37 (14) Pharynx without teeth 38 



38(49) Esophagus with bulbs 39 



39 (42) Amphids circular or nearly so ; pharynx compound, much elongated. 40 



40 (41) Cuticular external marking of amphid circular. . . Plectus Bastian. 

 Genus of about thirty species mostly about plants. Some aquatic, none marine. Some 



species, perhaps most, parthenogenetic or hermaphroditic. Obscure labial papillae usually present. 



Representative species Plectus tubifer Cobb 1914. 



i_ z. ii. _ 19. '49-35 92.6 . First lateral pore of the 



f* all ' '^r~ Xi ' 3.2 ' 2.3' cuticula immediately behind 



the lateral organs, whence 



^, i ; 9 . .10.. ;= 19.2. _ ^MM . 9i.5 > 79mnL similar, somewhat smaller 

 - 2 - pores, totalling about two 



hundred, form four subme- 



dian rows. Six rounded, rather massive lips sur- 

 round the short, napiform vestibule leading to the 

 pharynx. Amphids transversely elongated or 

 roundish, open behind. There is an obscure, pos- 

 terior, more or less closed, elon- 

 gated, triquetrous pharyngeal 

 chamber not indicated in the 

 f m formula. 



FIG. 793. Plectus tubifer. Male. 



a, mouth; b, papilla-like cephalic setae; c, lateral organ; d, pharynx; e, posterior chamber of pharynx; 

 /, esophagus; g, nerve-ring; h, excretory pore; i, renette cefl; j, glandular (?) cell; k, cardiac bulb; 

 /, cardia; m, intestine; n, blind end of anterior testicle; o, spermatocyte; p, flexure in posterior testicle; 

 q, blind end of posterior testicle; r, junction of testicles; s, vas deferens; /, glandular (?) organ; u, 

 muscle to one of the three supplementary organs; v, anterior supplementary organ; w, spiculum; x, anus; 

 y, one of the caudal papillae; z, spinneret. (After Cobb.) 



