40 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chlorophyta 

 Class Chlorophyceae 

 Order Chlorococcales 

 Family Hydrodictyaceae 

 GENUS PEDIASTRUM Meyen, 1829 (fig. 14) 



MORPHOLOGY 



Cells are coenocytic with smooth or rough walls. Peripheral cells are 

 shaped differently from interior cells and have 1 or 2 processes. 

 Chromatophores are discoid to diffuse. Coenobia are plate shaped and 

 consist of 4, 8, 16, 32, 64, 128, or 256 cells and may be as much as 450 

 ^m in diameter. 



REPRODUCTION 



Biflagellate zoospores formed by several cells in the colony are con- 

 tained in a vesicule of the parent-cell wall. The vesicule remains until 

 the new colony is formed and released. Isogamous sexual reproduction 

 is by a fusion of spindle-shaped biflagellate gametes formed like the 

 zoospores. 



OCCURRENCE 



The genus is widely distributed in the euplankton and tychoplankton 

 of all types of waters. Some species are indicative of particular en- 

 vironmental conditions; for example, Pediastrum simplex is indicative 

 of oligotrophic waters, whereas Pediastrum duplex or Pediastrum 

 Boryanum are indicative of eutrophic waters. The genus can occur in 

 great numbers. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 



pH 4.9 - 



Dissolved oxygen milligrams per liter 1.1 - 



Specific conductance micromho__ 30 



Total alkalinity milligrams per liter 4 



Total hardness do 5 



Total nitrogen do .00- 



Total phosphorus do .0 - 



SPECIES INFORMATION 



Refer to Brunnthaler (1915), Bigeard (1933), Harper (1916, 1918), 

 and Prescott (1962). 



