Chap. 21 



THE PROTOZOANS 



441 



Other Sarcodina — Shelled Amebas 



A few common species of Sarcodina are presented according to their habits 

 of life, free living in fresh water; free living in salt water; and parasitic (Figs. 

 21.13,21.14). 



Fresh Water. Arcellas glide over submerged pond weeds with pseudopodia 



NEAR RELATIVES OF THE AMEBA 



Radiolorian 



Sun animalcule 



Shell is secreted 



Shell of microscopic 

 sand grains 



Fig. 21.13. Ornate relatives of the amebas. /, Acanthometron, whose radiating 

 needles are attached by musclelike bands, the myofrisks by which needles and body 

 are moved. 2, the sun animalcule, Actinophrys sol, a splendid relative of the better 

 known amebas. This one is common on the submerged vegetation of ponds. 3, 

 Arcella vulgaris, an amebalike animal with a tam-o'-shanter-shaped cover. A, sec- 

 tion showing the two nuclei and the pseudopodia extending from under the shell. 

 B, view through the top of a translucent shell. 4, Difflugia makes its covering of 

 microscopic sand grains firmly held together by a secretion. (Courtesy, Jahn and 

 Jahn: The Protozoa. Dubuque, Iowa, Wm. C. Brown and Co., 1949.) 



