AMOEBOID PROTOZOA (SARCODINA) 2 19 



KEY TO NORTH AMERICAN FRESH-WATER SARCODINA 



1 (161) Pseudo podia without axial filaments. . . Class Rhizopoda . . 2 



2 (144) Pseudopodia lobose, sometimes pointed but never anastomosing. 



Subclass Amoebea . . 3 



3 (21) Without shells Order Gymnamoebida . . 4 



4 One family recognized. Characteristics of the order. 



Family Amoebidae . . 5 



5 (6) Body and pseudopodia bristling with minute spicules. 



Dinamoeba Leidy. 

 Representative species Dinamoeba mirabilis Leidy 1874. 



Very changeable in shape with many tapering pseudo- 

 podia. Papillae-like projections often appearing al the pos- 

 terior extremity. Entire body sometimes surrounded by a 

 jelly-like envelop. A contractile vacuole and two nuclei 

 present. Habitat standing water. Size may reach 200 M, 

 including pseudopodia. 



FIG. 274. Dinamoeba mirabilis. X 100. (After Leidy.) 



6(5) Body smooth, without spicules 7 



7 (8) Body usually enclosing symbiotic bacteria. Large size. Nuclei many. 



Pelomyxa Greeff. 

 Representative species. ........ Pelomyxa palustris Greeff 1870. 



A very large form moving slowly by broad extensions 

 of the ectoplasm. Endoplasm enclosing sand, brilliant 

 corpuscles and bacteria; with numerous vacuoles in the ecto- 

 plasm. Nuclei may number 1000 or more. Habitat ooze 

 of ponds and sphagnous swamps. Maximum length 2000 fi. 

 P. carolinensis Wilson, described in American Naturalist, 

 Vol. 34, p. 535, is apparently without symbiotic bacteria. 



FIG. 275. Pelomyxa paluslris. X 25. (After Penard.) 



8(7) Body not enclosing symbiotic bacteria. . . . ; .. 9 



9 (10) Ectoplasmic membranes produced between the pseudopodia. 



Hyalodiscus Hertwig and Lesser. 

 Representative species. . . . Hyalodiscus rubicundus H. and L. 1874. 



Body discoidal, moving by extending thin sheets of ecto- 

 plasm which are penetrated by ray-like pseudopodia. En- 

 doplasm reddish-yellow in color enclosing numerous vacuoles 

 and one or more nuclei. Habitat ooze of ponds, not common. 

 Size 40 to 60 n. 



FIG. 276. Hyalodiscus rubicundus. X 315. (After Penard.) 



10 (9) Ectoplasmic membranes not produced between the pseudopodia. 



Amoeba Ehrenberg . . n 



11(14) Pseudopodia sharply distinguished from the body 12 



12 (13) Pseudopodia lobe-like Amoeba proteus Leidy 1878. 



Very changeable in form, usually with numerous pseudo- 

 podia. The nucleus is always single, oval and of large size. 

 Contractile vacuoles one or more. Habitat both stagnant 

 and clear water. Size, one of the largest species of the genus; 

 may reach 300 n or more when extended. 



FIG. 277. Amoeba Proteus. X 100. (Original from a preparation.) 



