PROTOZOA 



161 



Class I. Rhizpoda (root-footed). Type: Amoeba. The Rhizopoda are amoeboid 

 in form with pseudopodia, which may be either blunt (Fig. 67) or slender (Fig. 74). 

 The protoplasm may be naked (Amceba) or may secrete a shell either calcareous 

 (Foraminifera) or siliceous (Radioloria). In the shelled forms the pseudopodia 

 pass out through openings in the skeleton (Fig. 75). Reproduction is usually by 

 division, or by the formation of many spores. Encystment frequently occurs. 



Class II. Mastigophora (whip bearers). Types: Euglena, Chilomonas, Volvox, 

 Trypanosoma. Active protozoa which may be simple or colonial. They bear one 

 or more large lashes or flagella. The trypanosomes are blood-parasites. 



Class III. Infusoria (in infusions). Types: Paramecium, Stentor, Vorticella. 

 Predominantly active protozoa, usually without shell, but with distinct cortical 

 portion from which project permanent vibratile threads of protoplasm (cilia, 

 flagella, or tentacles), from the possession of which the sub-classes are named. 



FIG. 75. 



PIG. 75. Actinomma, a radiolarian with a shell and no mouth. A, whole animal with a portion 

 of two spheres of shell removed. B, section, showing relation of protoplasm to the skeleton, c., 

 central capsule; n, nucleus; p, protoplasm; o, openings through which the pseudopodia extend. 

 (From Parker and Haswell.) 



There is usually a permanent mouth. The nucleuses always present and assumes 

 a great variety of shapes. The infusoria are typically free-swimming, but many 

 are capable of attachment by a contractile stalk, to foreign objects (Vorticella). 

 Reproduction is normally by equal division, but budding and spore formation 

 occur. Conjugation is common, and may be either temporary or permanent. 



Class IV. Sporozoa (spore- animals). Types: Plasmodium vivax, Gregarina. 

 Protozoa predominantly passive in habit, parasitic, with no pseudopodia, and no 

 cilia in the adult. Remarkable for encysted resting stages and spore formation. 

 Conjugation often precedes the formation of the cyst. 



202. Place in Nature. Protozoa are an important element 

 in the food of many aquatic animals. Despite their minute 

 size, their immense numbers and universal distribution make 



