PROTOZOA IN GENERAL 



271 



is a typical example. The disintegrating calcareous shells of this or- 

 ganism constitute a great mass of material on the bottom of the ocean 

 which is known as globigerina ooze and from which chalk is formed, 

 (c) Mycetozoa are characterized as being able to produce enormous 

 Plasmodia containing hundreds of nuclei and contractile vacuoles, as 

 well as having ability to reproduce by spore formation. They live 

 quite commonly in masses of decaying vegetable material upon which 



Fig. 88. — Shells of different Foraminifera. A, Rhabdamina abyssorum (X4.5) ; 

 B, Nodosaria hispida (Xl8); C, Globigerina buUoides (X55). (From Borradaille 

 and Potts, The Invertebrata, The Macmillan Company.) 



they feed, (d) Heliozoa is a group with thin, radially arranged, 

 threadlike, unbranched pseudopodia. Actinophrys sol is a common 

 one found in fresh-water streams and ponds, (e) Radiolaria is a 

 marine group with fine, raylike pseudopodia and a shell composed 

 largely of silica. The pseudopodia extend through the relatively large 

 apertures in the shell. 



