Genus: Variable in shape; strong constriction at center; semicell ellipsoidal, polygonal, etc.; cell wall with simple or branching spines, most of them laterally aligned; 4 plate-like chloroplasts in each semicell; one or more pyrenoids in each chloroplast (Illustrations of The Japanese Fresh-water Algae, 1977). Species:

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Oze-shokubutu-kenkyu-mihonen, Oze-ga-hara (Oze marsh), Katashina village, Gunma Pref., Japan, June 29, 2006 by Y. Tsukii