84 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chrysophyta 

 Class Bacillariophyceae 

 Order Centrales 

 Family Coscinodiscaceae 

 GENUS MELOSIRA Agardh, 1824 (fig. 36) 



MORPHOLOGY 



Cells are cylindrical and united into long filaments. Cell length is 

 greater than width. Valve view is circular. Valves may be flat or con- 

 vex. If convex, they generally have a marginal ring of denticulations 

 that unite cells into filaments. Girdles may or may not have a sulcus. If 

 a sulcus is present, part of the girdle below the sulcus is smooth; if a 

 sulcus is absent, the entire girdle is ornamented. Crowded 

 chromatophores are numerous, small, and disc shaped. 



REPRODUCTION 



A single auxospore is formed within a cell. Microspores were observ- 

 ed by Schmidt (1923) in Melosira varians. 



OCCURRENCE 



Melosira, a filamentous centric alga, is one of the most ubiquitous of 

 the algal genera. It is widely distributed in all types of waters; 

 however, some species are indicative of particular environmental con- 

 ditions. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 



pH 3.4 ■ 



Dissolved oxygen milligrams per liter .1 - 



Specific conductance micromho 10 



Total alkalinity milligrams per liter 



Total hardness do 4 



Total nitrogen do .00- 



Total phosphorus do .0 - 



SPECIES INFORMATION 



Refer to Boyer (1927a). 



