Cosmarium sp. Corda, 1834
Generally unicellular, the cells are compressed with the length slightly greater than the breadth and a distinct median constriction, some have their cells joined into long filaments. The cell wall is smooth or variously ornamented. The front view of the semicells may be semicircular, elliptic, reniform, trapezoidal or subquadrate. The vertical view is usually elliptical in outline and often with lateral elevations midway between the poles. Each semicell has a single axial chlorpolast with four radiating plates and the pyrenoids are found in the axial portion.
A common unicellular green algas in freshwater, Cosmarium are attractive in their symmetry and shapes as well as diversity in ornamentation. They are free-floating and intermingled with other algae.
Conjugation takes place when two cells come together, each surrounded by a common gelatinous sheath. The cells breaks at the isthmus and the cell contents fuse to form a zygote midway between the conjugating cells. The zygote divides into two cells.
Bold, H. C., C. J. Alexopoulos & T. Delevoryas, 1987. Morphology of plants and fungi. Harper & Row, New York. (5th ed.). 912pp.