Genus: Variable in shape and in size; mostly longer than wide; strong constriction at center; semicell pyramid-shaped, apically flattened with indentation (or notch, some species lack this notch); laterally straight or wavy or indented; one chloroplast in each semicell; one pyrenoid for each chloroplast (Illustrations of The Japanese Fresh-water Algae, 1977). Subgenus: Entomum (Apical area deeply indented or notched) Section: Excisa (Cell surface granulated or dented; apical area with spiny projections) Species:

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Ohnuma (a pond at Ohnuma enchi), Nasu-shiobara city (formerly Shiobara town), Tochigi Pref., Japan, April 1, 2007, by Y. Tsukii