94 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chrysophyta 

 Class Bacillariophyceae 

 Order Centrales 

 Family Coscinodiscaceae 

 GENUS STEPHANODISCUS Ehrenberg, 1845 (fig. 41) 



MORPHOLOGY 



Solitary, free-floating cells are discoid. Valves are circular, radially 

 punctate, and have short marginal spines. Outer areas of punctae are in 

 multiseriate rows; each row becomes uniseriate toward the center. 

 Small central area is irregularly punctate. Girdles are slightly undulate 

 and smooth and lack intercalary bands. There are 1 or 2 irregular or 

 numerous discoid chromatophores. 



REPRODUCTION 



A single auxospore is formed within a cell. 



OCCURRENCE 



This is a widely distributed diatom. It is an insignificant component 

 of algal communities indicating eutrophic conditions. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 33.0 



pH 4.6 - 9.4 



Dissolved oxygen milligrams per liter .1 - 16.6 



Specific conductance micromho 10 -10,800 



Total alkalinity milligrams per liter 3 - 470 



Total hardness do 9 - 1,800 



Total nitrogen do .00- 24.0 



Total phosphorus do .0 - 3.1 



SPECIES INFORMATION 



Refer to Boyer (1927a) and Skvortzow (1937). 



