58 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chrysophyta 

 Class Bacillariophyceae 

 Order Pennales 

 Family Achnanthaceae 

 GENUS ACHNANTHES Bory, 1822 (fig. 23) 



MORPHOLOGY 



Cells are rectangular and longitudinally bent or curved in girdle 

 view. They generally are attached by gelatinous stalks or are sessile 

 and united into bundles at the valves, rarely into filaments. Values are 

 generally linear-lanceolate to elliptical. The epitheca is convex and has 

 a pseudoraphe; the hypotheca is commonly concave and has a raphe, in- 

 conspicuous polar nodules, a distinct center nodule, and sometimes a 

 stauros. Striae are transverse or radiate. Costae are prominant in some 

 species. There are 1, 2, or numerous discoid chromatophores. 



REPRODUCTION 



Auxospore formation is by conjugation of paired gametes, 2 of which 

 are formed from each of 2 protoplasts. 



OCCURRENCE 



The genus is widely distributed. Freshwater species are generally 

 epiphytic upon filamentous chlorophytes and submerged phanerogams. 

 They are found frequently in the tychoplankton. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 33.5 



pH 3.4 - 9.7 



Dissolved oxygen milligrams per liter .8 - 20.6 



Specific conductance micromho 10 -37,400 



Total alkalinity milligrams per liter - 480 



Total hardness do 5 - 2,000 



Total nitrogen do .00- 32.0 



Total phospnorus do .0 - 3.5 



SPECIES INFORMATION 



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



