Genus: Cell body elongate, cylindrical or spindle-shaped, apex dorso-ventrally compressed with a deep incision; centrally constricted to form 2 semicells; cell wall dotted or covered with small pores; chloroplasts consisting of axis and lateral laminae, pyrenoids arranging linearly along the axis; zygotes spherical, smooth or rectangular with rounded corners (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Cell body 80-(160-184)-260 μm long, 20-(28-30)-50 μm wide; (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Chigo-ike (marsh pond) at the top of Yakebitai mountain, Shiga highland (Oku-shiga highland), Yamanouchi town, Nagano Pref., Japan, July 20, 2008 by Y. Tsukii