110 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
cells), with which they live in intimate mutual partnership (symbiosis). 
Most Radiolarians float on the surface of the sea; others live below 
the surface at varying depths; and some are abyssal. They are 
abundant as fossils, and of much importance in the formation of the 
ooze of great depths. 
Examples.—Thalassicola, Eucyrttdium, and the colonial Collozoum 
and Spherozoum, 
Fic. 51.—A pelagic Foraminifer— Hastigerina (Globigerina) 
murrayt.—After Brady. 
Note central shell, projecting calcareous spines with a protoplasmic 
axis ; also fine curved pseudopodia and vacuolated protoplasm. 
C. Predominantly active forms (ciliate and flagellate), 
generally called Infusorians.—Protozoa, with a definite rind and 
with 1-3 undulating flagella, are included as (8) Flagellata, a very 
large group, among which are such familiar forms as the common 
Euglena of ponds ; the Monads; Volvox, a colonial form ; Codosdga, a 
colony in which the individual cells are furnished with a collar (Choano- 
flagellata), The Hzemoflagellata are important blood parasites, generally 
called Trypanosomes (see p. 121), 
