Genus: Cell body small, length = width, strong constriction at its center; semicells inverted triangular, ellipsoidal, rectangular, etc. in shape; straight or slightly curved spiny projections at each corner; one pyrenoid in each semicell; cell wall smooth (Illustrations of The Japanese Fresh-water Algae, 1977). Species:

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Shimo-no-koike (pond), Shiga highland, Yamanouchi town, Nagano Pref., Japan, June 1, 2006 by Y. Tsukii