52 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chlorophyta 

 Class Chlorophyceae 

 Order Chlorococcales 

 Family Scenedesmaceae 

 GENUS TETRASTRUM Chodat, 1895 (fig. 20) 



MORPHOLOGY 



Cells, 4-10 pcm. in diameter, are elliptical, triangular, trapezoidal, or 

 semicircular. Each cell has one or more spines on the free face. One to 4 

 cup-shaped chromatophores are parietal. Cells are joined quadrately to 

 form a 4-celled coenobia. 



REPRODUCTION 



A cell divides into 4 autospores that remain quadrately attached. 

 Cellular spines develop following release by rupture of the parent-cell 

 wall. 



OCCURRENCE 



Tetrastrum has a widespread distribution, but it is found generally 

 only in very few numbers. It is common in the euplankton. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 



pH 4.9 • 



Dissolved oxygen milligrams per liter 1.7 ■ 



Specific conductance micromho 10 



Total alkalinity milligrams per liter 2 



Total hardness do 5 



Total nitrogen do .01- 



Total phosphorus do .0 - 



SPECIES INFORMATION 



Refer to Ahlstrom and Tiffany (1934) and Prescott (1962). 



