486 



FRESH-WATER BIOLOGY 



15 (16) Number of teeth three, equal, small, mobile, well forward near the 



mouth. . Ironus Bastian. 

 Genus with about six known 

 species, confined to fresh water, 

 though there is a very similar 

 genus, Thallasironus de Man, for 

 the reception of similar marine 

 forms. Some species hermaphro- 

 ditic. Salivary glands in esophagus. 



Representative species. 



Ironus americanus 

 Cobb 1914. 



16 23 27 29 1.3 



From the size of the apparently 

 matured ova it is assumed that the 

 eggs are considerably elongated. 

 It is unlikely that more than one is 

 contained in the uterus at a time. 



Habitat: Deer Bottom, Pikes 

 Peak region, Colorado. 



Fig. 781. Ironus americanus. 



I, head and anterior portion of neck; 

 II, head, lateral view "teeth" ex- 

 truded; III, head, " teeth " withdrawn 

 with second set formed in preparation 

 for the next moult; IV, tail end of 

 female. 



a, one of the three pharyngeal 

 teeth, shown extruded; h, papilla; c, 

 cephalic seta; d, amphid; e, pharynx; 

 /, toothlet; g, toothlet; h, esophagus; 



f, lining of esophagus; j, nerve-rmg; 

 k, intestine; /, anus; in, caudal gland; 

 n, terminus. (After Cobb.) 



16 (15) Number of teeth one; or more than one, and unequal 17 



17 (22) Teeth, at least one of them, usually massive; thick, more or less 

 papillate lips closing over the capacious pharynx. • • • 18 



Main tooth dorsal (sometimes all nearly obsolete) ; Hps thick, armed 



with papillae; no setae Mononchus Bastian. 



Genus of a score or more species, some in fresh water, others 

 in soil, where they hunt and devour nematodes and other small 

 organisms. The movements, especially those of the head, are often 

 very active. The males are very rare. The name Mononchus 

 indicates the presence of a single pharyngeal tooth, but sometimes 

 there are one or two additional teeth; sometimes all are absent. 

 The relatively powerful lips can be everted, and are utilized to 

 grasp the prey and force it against the pharjmgeal teeth. In some 

 species the wall of the pharynx bears series of minute rasp-like 

 denticulations. Some species are hermaphroditic. 



Representative species. Mononchus major Cobb 1893. 





> 3 4nua., ^y^ elegant species is 

 a soil inhabitating form 



> 3 4 mim sometimes found in wet 

 places. No American species are figured as yet. The adjacent il- 

 lustrations are derived from Australian specimens. 



Fig. 782. Mononchus major. 

 I side view of male; 11, side view of head of same; III, front view of 

 head; IV, side view of tail; V, details of male papillae. 

 a mouth; h, lip-papiUa; c, lip; d, esophagus; e, nerve-ring; /, phar- 

 yngeal tooth; g, inner^'ated papilla of skin; U, esophagus; t, base of 

 phSnx;i, cardiac collum; k, intestine; /, flexure in testicle ;. m blind 

 end of testicle; «, vas deferens; o, lip; p, mouth opening ; 9, ejaculatory 

 duct- T spicula; s, ejaculatory duct; t, accessory piece; w post-anal 

 papillae! %, spicula; w, ejaculatory duct; x, ventral row male papillae, 

 y, anus; 2, three anal glands. (After Cobb.) 



