24 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chlorophyta. 

 Class Chlorophyceae 

 Order Zygnematales 

 Family Desmidiaceae 

 GENUS COSMARIUM Corda, 1834 (fig. 6) 



MORPHOLOGY 



Cells are variable in size, ranging from 9 to 100 ^m in diameter and 

 generally are longer than wide. Semicells are elliptical, semicircular, 

 subquadrate, or pyramidal. The apex is rounded, truncate, or subtrun- 

 cate, without an apical incision. A single, axial chromatophore is 

 located in each semicell. The genus is solitary. 



REPRODUCTION 



During sexual reproduction, the protoplasts of 2 conjugating cells 

 emerge at each isthmus, unite, and form a zygote. Each zygote 

 develops into 2 daughter cells, each of which develops a cell wall before 

 being released by rupture of the zygotic wall. 



OCCURRENCE 



There are many species in the genus, which has widespread distribu- 

 tion. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 



pH 5.2 - 



Dissolved oxygen milligrams per liter .7 - 



Specific conductance mieromho 10 



Total alkalinity milligrams per liter 2 



Total hardness do 6 



Total nitrogen do .09- 



Total phosphorus do .0 - 



SPECIES INFORMATION 



Refer to West and West (1905, 1908, 1912). 



