14 PROTOZOA 



Key to the classes of Protozoa: 

 ffi Cilia or flagella absent. 



\ Pseudopodia present, sometimes with rigid, axial filaments...!. Sarcodina 

 63 Pseudopodia absent, as well as all other loeomotory organs, in the adult 



animal 3. Sporozoa 



a^ Cilia or sucking tentacles, or flagella present. 



&i Flagella present 2. Mastigophora (Flagellata) 



&2 Cilia or sucking tentacles present 4. Infusoria 



Class 1. SARCODINA.* 



The most primitive Protozoa, in which the body is usually with- 

 out definite form, but in most cases possesses rigid skeletal structures. 

 Locomotion is effected by means of pseudopodia, which are more or less 

 temporaiy projections of the body. In the Heliozoa and Radiolaria these 

 are much less changeable in form than in the Rhizopoda and are usually 

 supported by a central skeletal filament. Contractile vacuoles are present 

 except in the marine forms. Encystment and conjugation characterize all. 

 The majority of the Sarcodina are marine animals and they are often 

 present in such large numbers in the sea that the empty shells form 

 important deposits at the bottom {Foraminifera). The affinities of the 

 Sarcodina are with the flagellates : the young of certain forms are flagellate 

 and in 31 astir/ amoeba and others the adult form has both pseudopodia and 

 flagella. The class was first called the Rhizopoda, but in 1880 Biitschli 

 substituted the term Sarcodina for Rhizopoda, giving the latter name to one 

 of the orders. The class contains 6,000 species, most of which are 

 Radiolaria and Foraminifera, grouped in 3 orders. 



Key to the orders of Sarcodina: 



Ci No central capsule present ; animals in both salt and fresh water. 

 6i Body naked or with shell, with very changeable pseudopodia which contain 



no central axial filament .1. Rhizopoda' 



62 Body naked or with shell, usually of spherical and relatively permanent form 

 with delicate ray-like pseudopodia, each of which contains a central 



filament 2. Heliozoa 



«2 Central capsule present ; marine animals of relatively permanent form with 

 ray-like pseudopodia 3. Radiolaria 



Order 1. RHIZOPODA. 



Body usually covered externally by a shell (but sometimes without) 

 which is a secretion of the ectosarc, and in many cases is covered with 

 sand or other foreign objects; pseudopodia variable in form: 2 suborders 

 and about 1,500 species, of which 200 live in fresh and 1,300 in salt water. 



Key to the suborders of Rhizopoda: 



Oi Rhizopoda with simple pseudopodia and with or without a shell. .1. Amcebida 



a2 Rhizopoda with branching and anastomosing pseudopodia and with or without 



a shell 2. Reticulariida 



* See "Freshwater Rhizopoda of North America," by J. Leidy, Rep. U. S. Geol. 

 Sur., etc., Vol. 12, 1879. 



