in shape to the temporary resting cysts produced by many of the 

 motile Peridiniales. 



The Pyrrhophyta are both euplanktonic and tychoplanktonic. It 

 is presumed that they are important in the food chain of fresh-water 

 animals, as they are in the sea, although in fresh water they seldom 

 occur in such tremendous 'blooms' as they do in salt water at 

 certain seasons. The ubiquitous Ceratium hirundinella (O. F. M.) 

 Duj., however, frequently appears in such numbers as to give an 

 entire lake a definite coffee-color. 



Of the 7 recognized orders in the class Dinophyceae, 3 are repre- 

 sented in our collections. 



Key to the Orders 

 1. Motile - 2 



1. Non-motile 3 



2. Cells without walls; naked protoplasts with an 



envelope not divided into plates gymnodiniales 



2. Cells with walls; membrane with plates (obscure 



in Glenodinium and Hemidinium) peridiniales 



3. Cells arranged to form a filament *dinotrichales 



3. Cells solitary, attached or free-floating dinococcales 



ORDER GYMNODINIALES 



These are forms which, as their name imphes, have no definite 

 cell wall but occur as naked protoplasts. Some observers, however, 

 have described a fine periplast in which platelets have been dis- 

 cerned. Fresh-water species are ovoid or subrhomboidal and usually 

 are flattened when seen in side view. There is a longitudinal furrow 

 which may or may not extend into the epicone from the transverse 

 furrow. The latter is wound to the left (descends on the right side 

 of the organism when seen in ventral view) and joins the longitudi- 

 nal sulcus where the flagella are attached. There is 1 fresh-water 

 family. 



FAMILY GYMNODINIACEAE 



Characteristics as described for the order. 



GYMNODINIUM (Stein) Kofoid & Swezy 1921, p. 158 



Cells ovoid, ellipsoid, or pyriform, the transverse furrow complete, 

 spirally turning to the left and dividing the cell into 2 equal (or 

 slightly unequal), differently shaped portions; longitudinal furrow 

 extending to the poles or only part way into the epicone and 

 hypocone, but always farther into the latter than the former; pig- 

 mented species with numerous, golden-brown, elongate or ovoid 



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