Phylum Protozoa 357 



among the microscopic forms floating on the ocean's surface. These 

 floating masses are very important as the food source of all the larger 

 forms and are sometimes known as the "oceanic meadows." Some 

 dinoflagellates produce a poisonous substance which does not harm the 

 molluscs that feed upon them; however, during periods when these 

 dinoflagellates form the chief food of the molluscs, the latter may become 

 poisonous to human beings. Some dinoflagellates are red in color and 

 may become so abundant as to give the water a reddish color. When 

 this occurs, causing the so-called "red tides," many fish may be killed. 

 Another interesting dinoflagellate is that known as Noctiluca. 

 As the name indicates, these are the forms which make the oceanic 

 waters luminescent at night. The Noctiluca (Fig. 113,F) are 

 large animals, about 1 mm. in diameter, each consisting of a gelatinous 

 sphere. 



The Zoomastigina. — As the members of this subclass contain 

 no chlorophyll they are either holozoic or saprozoic in their nutrition. 

 Many of them are free-living and may be found in pond water. They 

 are colorless forms, and except for the absence of the chloroplast, 

 structurally resemble the Euglena. Many of the Zoomastigina are 

 parasitic, and in their habits show some very amazing biotic relation- 

 ships. 



Those protozoans which live symbiotically in the intestine of the 

 termites are members of this subclass. As mentioned previously, they 

 apparently are able partially to digest the cellulose ingested by their 

 hosts, thus making food available to the termites. The termite if de- 

 prived of its protozoan fauna literally and actually starves to death (Fig. 

 113,C). 



There are many Zoomastigina flagellates which parasitize many 

 animals including human beings. Among the various genera, one of 

 the commonest is Trichomonas (Fig. 113,^). In man there are three 

 species: T. hominis which is found in the colon, T. buccalis in the 

 mouth, and T. vaginalis in the vagina. Another species, T. foetus, in 

 cattle is responsible for abortions. Representatives of the genera 

 Chilomastix and Giardia (Fig. 113,5) are also found parasitic in the 

 intestine of human beings. 



Some of the parasitic flagellates live in the blood of vertebrates. 

 The members of one genus, Trypanosoma (Fig. l\3,D), are able to 

 live in the blood of most species of vertebrates. All of these very small 

 forms are characterized by the possession of a long undulating membrane 



