Section [ Actinotaenium ]: Cell body cylindrical, slightly constricted at the center, cell surface smooth or dotted or punctated (Illustrations of The Japanese Fresh-water Algae, 1977). Species [var. attenuatum G.S. West ]: Cell body cylindrical, 29-51 μm long, 15-24 μm wide, L/W=2-2.5; slightly constricted at the center; lateral margins slighlty convex, attenuated toward apex; cellwall dotted. [var. latius (W. et G.S. West) Gerloff ]: Cell body cylindrical, 39-42 μm long, 21-27 μm wide, L/W less than 2.0 (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No.6, a marsh pond at Sensho-ga-hara, near Akita-komagadake (mountain), Shizukuishi town, Iwate Pref., Japan, August 6, 2007 by Y. Tsukii