254 



FRESH-WATER BIOLOGY 



89 (94) Body flexible; one or two flagella 9" 



90 (93) Flagella two. . . 9^ 



91 (92) Secondary flagellum very small, directed backward. Astasia Stein. 



Representative species. 



Fig. 403. 



Astasia trichophora. 

 (After Conn.) 



X 410. 



Astasia trichophora Ehrenberg 1830. 



Body elongate, usually wider posteriorly. 

 Primary flagellum very thick at the base and 

 long. Nucleus central; contractile vacuole an- 

 teriorly located. Length, when extended, 30 to 

 60 (1. Common among diatoms and algae. 



92 (91) 



Secondary flagellum about half as long as the primary; both flagella 



directed forward. . . . Distigma Ehrenberg. 



Representative species. . . Distigma proieus Ehrenberg 1830. 



Body very plastic; when contracted, distended in one 

 or two regions. Endoplasm with dark-colored corpuscles. 

 Nucleus central ; contractile vacuole in the anterior region. 

 Length, when extended, Q5 m- Pond water. , 



Fig. 404. Distigma proteus. cv, contractile vacuole; n, nucleus; 

 ph, pharynx. X 330. (After Stein.) 



93(90) Flagellum single; body elongate, tapering posteriorly. A long tubu- 

 lar pharynx. Atractonema Stein. 



Representative species. . Atractonema tortuosa Stokes 1885. 



Body flexible but persistent in shape, colorless, 

 enclosing oblong dark-bordered corpuscles. Fla- 

 gellum about half as long as the body. Movements 

 rotary on the long axis. Length 50 to 80 p.. In 

 vegetable infusions. 



Fig. 405. Atractonema tortuosa. X 625. (After Stokes.) 



94 (89) Body not flexible 95 



95 (98) With longitudinal or spiral ridges. . 96 



96 (97) Elongate or crescentic, with four longitudinal ridges; flagella, two, 



unequal. ... . Sphenomonas Stein. 



Representative species. . . Sphenomonas quadrangularis Stein 1878. 



Body subfusiform, with the ridges forming a quadrate outline in cross sec- 

 tion. Long flagellum stout, four times the length of the shorter one. A 

 large amylaceous corpuscle usually enclosed in the endoplasm. Length 40 ji. 

 Fresh water. 



Fig. 406. Sphenomonas quadrangularis. X 400. (After BUtschli.) 



97 (96) Nearly ellipsoidal, with many spiral ridges. . Tropidoscyphus Stein. 



98 (9s) Without ridges 99 



