92 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chrysophyta 

 Class Bacillariophyceae 

 Order Pennales 

 Family Achnanthaceae 

 GENUS RHOICOSPHENIA Grunow, 1860 (fig. 40) 



MORPHOLOGY 



Wedge-shaped cells are sessile and attached at the narrower end to a 

 more or less branching system of gelatinous stalks affixed to 

 macrophytes. Cells are 4-8 /tm in diameter and 12-75 /*m long. The 

 hypotheca is concave and contains a median raphe and nodules. The 

 epitheca is convex and contains a median pseudoraphe. In girdle view, 

 cells are cuneate and curved in the longitudinal axis. Intercalary bands 

 are unornamented between striated girdles. Other striations are 

 transverse. There are 2 longitudinal septa. A single chromatophore is 

 laminate. 



REPRODUCTION 



Conjugating sister cells form a single auxospore. 



OCCURRENCE 



The alga has a widespread distribution. The single species, 

 Rhoicosphenia curvata, is found commonly in flowing alkaline waters. 

 It is generally intolerant of saline conditions. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 32.5 



pH 5.2 - 9.3 



Dissolved oxygen milligrams per liter 3.4 - 16.6 



Specific conductance micromho 10 -10,000 



Total alkalinity milligrams per liter 1 - 480 



Total hardness do 4 - 1,600 



Total nitroeen__ do .00- 32.0 



;pti' 



Total phosphorus do .0 - 3.1 



SPECIES INFORMATION 



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



