24 PROTOZOA 



ORDER 3. RADIOLABJA. 



Marine Sarcodina often of large size, with ray-like pseudopodia; 

 silicious skeleton present in most cases, which is often of great com- 

 plexity and beauty; pseudopodia usually with axial 

 filaments; body divided into two regions, the central 

 capsule and the extra-capsular portion; capsule sur- 

 rounded by a perforated chitinous membrane and oc- 

 cupying the center of the body containing also one or 

 more nuclei and often oil globules ; extra-capsular proto- 

 plasm often vacuolated and pigmented and containing 

 often yellow unicellular algae (zooxanthellae) which live 

 symbiotically in it; no contractile vacuole present; re- 

 production by division, the central capsule dividing first ; 

 in some forms the central capsule alone divides, and a 

 colony is the result; spore formation has also been ob- 

 served, in which flagellate spores are formed in the 

 central capsule : about 85 families and over 4,300 species, 

 which are found mostly in the deep sea. 



FAMILY THALASSICOLLIDAE. 



Skeleton wanting; central capsule simple, with a single nucleus. 

 THALASSICOLLA Huxley. Extra-capsular portion filled with alveoli 

 among which are numerous yellow algae. 



T. pelagica Haeckel. Diameter 2 mm.: in the Mediterranean. 



CLASS 2. MASTIGOPHORA. (FLAGELLATA.) 



Protozoa whose motile organs consist of one or more long whip-like 

 projections called flagella. The body is provided with an external mem- 

 brane which, in many cases, is very delicate, the body being more or 

 less amoeboid. A membranous shell of silica, chitin, or cellulose is also 

 often present. In one group, the Choanoflagellida, the base of the single 

 flagellum is surrounded by a high ridge called the collar (Fig. 28). A 

 single nucleus is present, and usually a contractile vacuole. 



The protoplasm usually shows no division into ectosarc and entosarc. 

 It often contains chromatophores which may be formed of chlorophyll 

 and green, or of diatomin and yellow or brown in color. Other bodies 

 allied to starch or oil are often present imbedded in the protoplasm. 

 Reproduction is by division and by spore formation; colony formation, 

 the result of incomplete division, is very common, the members of the 

 colony being sometimes enclosed in a common cellulose jelly, sometimes 

 connected by protoplasmic strands, and sometimes joined by both jelly 



