Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation. Subgenus [ Dysphinctium ]: Cell body cylindrical or dumbbell-shaped, dorso-ventrally not compressed, transverse section circular . 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: Cell body cylindrical ellipsoid, slightly constricted at the center, 60-(68-76)-79 μm long, 40-(43-54) μ wide, isthmus 38-(41-52) μm wide; semicells semi-elliptical, slightly flattened at the apex, with 2 pyrenoids (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: standing water on a bank under Kurome-gawa-bashi (bridge), Kurome River, Asaka city, Saitama Pref., December 10, 2006, by Y. Tsukii