Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation (Illustrations of The Japanese Fresh-water Algae, 1977). Species:

31 μm 63 μm 94 μm; x 640

Cosmarium repandum Nordstedt f. minor W. et G.S. West, cell body 18 μm long, 15 μm wide, isthmus 5 μm wide, x 640, Imou bog, Toyohashi city, Aichi Pref., Japan, September 11, 2004 by Y. Tsukii