PHYLUM PROTOZOA IN GENERAL 



67 



A larg-e number of Mastigophora live in quiet streams, ponds, lakes, 

 and in the ocean, Euglena is a very common!}^ studied fresh-water 

 form. Noctiluca is an interesting marine form which is pelagic (lives 

 at the surface) in its habits and appears as a thick, creamy scum. 

 This soupy mass of organisms may cover an area of hundreds of 

 square rods. When stimulated, these animals are luminescent and at 

 night frequently give up an attractive greenish or bluish white light ; 

 Uroglena is a fresh-water form which is often found in water supply 

 basins and causes a pungent, oily odor and unpleasant taste in the 

 water. Giardia (Fig. 386), Trichomonas, Chilomastix, Retortamonas 

 and Enteronomas are all genera with representatives occurring in the 

 digestive tract of man. 



Arcella 



Actinophrya 



Fig. 24. — Group of typical Sarcodina. (From Curtis and Guthrie, Textbook of 

 General Zoology, published by John Wiley and Sons, Inc.) 



2. Class Sarcodina (sarkodi'na, fleshy) or Rhizopoda (rizop'Oda, 

 root foot). — ^A distinctive feature of nearly all species of this class is 

 the capacity to form protoplasmic processes called pseudopodia (false 

 feet) which are temporary structures and can be withdrawn. The ani- 

 mal is able to accomplish locomotion by extending the protoplasm into 

 these pseudopodia. The representatives of this class include many free- 

 living forms as well as numerous parasitic ones. A number of the rep- 

 resentatives of class Sarcodina secrete an external shell of lime, silicon, 

 chitin, cellulose, or some bind in sand or other solid substances with one 

 of the secretions. The class is commonly divided into five orders, (a) 

 Amoebina are irregularly-shaped forms with lobelike pseudopodia. 

 Some of the species are naked, and others are covered by a shell. 

 Amoeba proteus is the free-living naked form which is commonly 

 studied. Endamoeba histolytica is the most common parasitic form, 

 Arcella, which secretes its shell, and Difflugia, which constructs its 



