DIVISION PYRRHOPHYTA 



By far the majority of the Pyrrhophyta are swimming unicells, 

 but there are a few sedentary forms, and in one of the orders, the 

 Dinotrichales, there is a filamentous expression. Some genera in the 

 plankton of the sea form simple colonies. The division in its present 

 definition includes three classes (Pascher, 1931; Smith, 1938), and 

 in one of these, the Dinophyceae, there is an approach to the same 

 evolutionary series which characterize some of the other algal 

 divisions. There are, for example (besides the filamentous tendency 

 mentioned above), palmelloid forms comparable to the Tetrasporales 

 of the Chlorophyta, and a Chlorococcales parallel is seen in the 

 Dinococcales. 



Morphologically the division is extremely heterogeneous, but the 

 diverse forms are bound together by fundamental similarities. The 

 more significant of these are their brown pigment, food reserve in 

 the form of starch, and the presence of cellulose in the cell wall. 

 Oil may be present in addition to starch, however, and some forms 

 do not possess a definite cell wall. 



Of the three classes in the Pyrrhophyta, the class Dinophyceae is 

 much the largest, including most of the known fresh-water species 

 of the division, although the majority of the Dinophyceae are marine. 

 In the sea, this class exhibits a great diversity and there are many 

 bizarre forms, most of which are holozoic or saprophytic, and are 

 red or yellow in color. 



The Desmokontae, mostly marine, have no representatives reported 

 from our region. 



Although but few members of the third class, Cryptophyceae, have 

 been recorded in our region, many species of this almost altogether 

 fresh-water class are to be expected there. Most forms are biflagel- 

 lated protozoa-like organisms, but 2 non-motile genera, colonial 

 in expression, are known. Filamentous forms are lacking in this class. 



Key to the Classes 



Chromatophores numerous brown discs dinophyceae 



Chromatophores 1 or 2 brown, elongate, parietal plates cryptophyceae 



CLASS DINOPHYCEAE 



( Dinoflagellates ) 



The cells in this class contain numerous disc-like or spindle- 

 shaped chromatophores ( at least in the fresh-water forms ) in which 

 several pigments have been identified. The predominating one is 



[423] 



