256 



FRESH-WATER BIOLOGY 



io6 (107) Without sand grains attached Urccolus Mereschkowsky. 



Representative species Urccolus cyclostomum Stein 1878. 



Anterior extremity oblicjuely truncate with an expanded rim about the 

 mouth. Pharynx nearly reaching the posterior extremity with its distal end 

 dilated. Surface usually spirally marked. Flagellum about as long as the 

 body. Length 50 m- Fresh water. Identical with Phialonema cyclostomum 

 Mereschkowsky. 



Fig. 410. Urceolus cyclostomum. X 500. (After Conn.) 



107 (106) With sand grains attached Urceolopsis Stokes. 



Representative species Urceolopsis sabulosa Stokes 1886. 



Body flexible and elastic, with a short, anterior, neck-like prolongation. 

 Usually densely covered with sand grains. Movements are rapid, the body 

 being held at an angle with the anterior end downward. The long flagellum 

 \ibrates strongly at its tip. Food particles are drawn into the oral aperture 

 with considerable force. Length 20 ^u. Among algae. 



Fig. 



Urceolopsis sabulosa. X 625. (After Stokes.) 



108 (103) Two flagella, one trailing; mouth depression obHque. 



Heteronema Dujardin. 

 Representative species. . Heteronema acus Ehrenberg 1840. 



Body very plastic, fusiform when extended. Primar>' flagellum as 

 long as the body and twice as long as the secondar>% trailing one. 

 Nucleus central; contractile vacuole in the anterior extremity. Length, 

 extended, 50 m- Fresh water. 



Fig. 412. Heteronema acus. X 500. (After Conn.) 



Numerous other forms reported by Conn should, without doubt, be 

 assigned to this genus. The species are undetermined. 



109 (102) Body rigid no 



no (hi) One flagellum; body flattened, usually furrowed and keeled. 



Pctalomonas Stein. 

 Representative species. . . PetaJomonas pkurosigma Stokes 1887. 



Body ovate, the posterior end pointed; lateral borders sigmoid. Dorsal 

 and ventral surfaces each traversed by a narrow, longitudinal furrow. Length 

 IS to 20 M- Standing pond water. 



Fig. 413. Pctalomonas pleurosigma. X 625 (After Stokes.) 



