2 20 



FRESH-WATER BIOLOGY 



[3 (12) Pseudopodia ray-like. 



Amoeba radiosa Ehrenberg 1830. 



r^:<^«* 



Body spherical with pseudopodia more or less rigid, not withdrawn 

 and retormed rapidly. Nucleus spherical. Habitat, very common 

 among algae; widely distributed. Size, usually less than icxjm with 

 pseudopodia extended. 



IiG. 278. Amoela radtusa. a, contractile vacuole X loc (After Leidy.) 



14(11) Pseudopodia not sharply distinguished from the body 15 



15 (20) Contractile vacuole spherical 16 



16(17) Posterior extremity villous Afnoeha Umax 'Du]3.rdm 1S41. 



Slug -like, usually moving with the broad end forward. Endo- 

 plasm filled with brilliant granules. Contractile vacuole usually 

 single. Nucleus changeable in form. Habitat ooze ol ponds. 

 Size, large individuals usually less than ioom- 



Fig. 279. Amoeba limax. x 225. (Alter Penard.) 



17 (16) Posterior extremity not villous 19 



18 (19) Surface wrinkled, large size. . . Amoeba verrucosa Ehrenberg 1838. 



A sluggish species, moving by a slow rolling motion. Pseudo- 

 podia short, broad lobes. Body proper enclosed by a delicate 

 membrane. Surface marked by lines crossing each other re- 

 sulting in a wrinkled appearance. Habitat sphagnous swamps. 

 Large individuals may reach 3cmd ^ in length when extended. 



Fig. 280. Amoeba verrucosa . X 100 (Alter Leidy.) 



19(18) Surface not wrinkled, small size. . . ylwoefta gM/Zw/a Dujardin 1841. 



Body usually oval in outline, moving with the broad end forward. 

 Pseudopodia short, broad lobes produced by sudden expansions of the 

 protoplasm. Nucleus single and one large contractile vacuole. Habitat 

 stagnant water. Size 30 m- 



Fig. 281. Amoeba guttula. X 400. (Alter Penard.) 



20 (15) Contractile vacuole not spherical. . . . Amoeba striata Penard 1890. 



Moving rapidly by broad extensions of ectoplasm but not changing 

 form rapidly. Usually from two to four longitudinal lines on the surface. 

 Two contractile vacuoles often present, the anterior one changeable in 

 shape. Habitat among algae; not abundant. Size, from 30 to 60 n. 



Fig. 282. Amoeba striata. X 250. (After Penard.) 



With shells Order Testacea . . 22 



Pseudopodia thick, finger-like, rarely filiform. 



Family Arcellidae . . 23 



Pseudopodia thick, sometimes pointed 24 



Shell membranous, more or less flexible 25 



Membrane covered with organic or foreign particles 26 



Shell membrane double Diplochlamys Greefif. . 27 



Hemispherical to cup-shaped, loosely coated with organic and siliceous 

 particles Diplochlamys fragilis Venard igog. 



Color gray, spotted with black. Inner membrane very fragile 

 but capable of distention. Nuclei usually from 30 to .40. Vacuoles 

 numerous. Pseudopodia short and thick. Diameter 70 to 125 fx. 

 Habitat mosses. Not common. Reported from Ontario by Dr. 

 Penard. 



Fig. 283. Diplochlamys jragilis. X 150. (After Penard.) 



