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.
Species: Cell body small, slightly longer than width, (20-28)-30 μm long, 17-(20-25) μm wide, isthmus 4-(4.8-5.6)-6 μm wide; semicells nearly half-circular, elliptical in apical view; cell wall smooth or covered with small dots (Illustrations of The Japanese Fresh-water Algae, 1977).