WISCONSIN PHYTOPLANKTON 79 



Class HETEROKONTEAE. 



Cells microscopic or macroscopic ; free-floating, sessile, or epiphytic. 

 Cell shape spherical, ovoid, pyriform, cylindrical or irregular. Cells 

 solitary, in colonies of regular to irregular shape, or united to form 

 simple filaments. Colonies or individual cells with or without a gelat- 

 inous envelope. Chromatophores one to many, parietal, generally disci- 

 form, rarely laminate, yellowish-green in color and without a pyrenoid. 

 Assimilation product oil, never starch. Cells uninucleate or multinu- 

 cleate. 



Asexual reproduction by vegetative cell division and a formation of 

 zoospores. Zoospores ovoid to pyriform, with two cilia of unequal 

 length and generally more than one yellowish-green chromatophore. 



Sexual reproduction, insofar as known, isogamous, by zoogametes that 

 are similar in structure to the zoospores. 



The various genera of the Heterokontae were formerly scattered 

 throughout the different families of the Chlorophyceae. The distinguish- 

 ing characteristics of this class are the yellowish-green chromatophores 

 without pyrenoids, with oil not starch the assimilation product; and 

 zoospores with two cilia of unequal length. There are three orders in 

 the class and representatives of all three are found in Wisconsin lakes. 



KEY TO THE ORDERS. 



Vegetative cells motile HETEBOCHLORIDALES 



Vegetative cells immobile. 



Cells solitary or in colonies, never in filaments HETEROCOCCAXES 



Cells united to form simple filaments HETEBOTBICHALES 



Order HETEROCHLORIDALES. 



Cells solitary, free-swimming, ovoid to pyriform in shape. Motile 

 phase dominant, rarely metamorphosing over into an amoeboid or pal- 

 mella phase. Cells with two cilia of unequal length, one or more chro- 

 matophores of a yellowish-green color and without an eyespot. Assimi- 

 lation product leucosin or fat, never starch. 



Asexual reproduction by vegetative division of cells. 



Sexual reproduction unknown. 



The order has but one family, the Chloramoebaceae, whose characters 

 are those of the order. 



