78 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chrysophyta 

 Class Bacillariophyceae 

 Order Pennales 

 Family Fragilariaceae 

 GENUS FRAGILARIA Lyngbye, 1819; emend., Rabenhorst, 

 1864 (fig. 33) 



MORPHOLOGY 



Cells are linear to fusiform, bilaterally symmetrical, commonly at- 

 tenuated at the poles, sometimes capitate, and often medially inflated. 

 Cells are rectangular in girdle view and have 0, 1, or 2 intercalary 

 bands. They are united into free-floating or sessile colonies, which are 

 generally zigzag chains but sometimes are flat, stellate colonies. The 

 pseudoraphe is narrow and indistinct or broad and prominent. 

 Transverse striae or punctae are present. Chromatophores are 

 numerous small discoid bodies or 1 to 4 laminate plates. 



REPRODUCTION 



A single auxospore is formed within a cell. 



OCCURRENCE 



Fragilaria is widely distributed. It generally is indicative of alkaline 

 waters of moderate conductivity. The genus is found in the littoral 

 zone, as well as in the euplankton (Patrick and Reimer, 1966). 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 33.5 



pH 3.4 - 10.0 



Dissolved oxygen milligrams per liter 2.0 - 18.7 



Specific conductance micromho 22 -41,000 



Total alkalinity milligrams per liter - 480 



Total hardness do 5 - 1,800 



Total nitrogen,. do .00- 28.0 



Total phospnorus do .0 - 4.0 



SPECIES INFORMATION 



Refer to Boyer (1927a) and Patrick and Reimer (1966). 



