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 [Eucosmarium]: Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped.
Section [Pyramidatae]: Cell surface smooth; semicells pyramidal with flattened apex or trapezoid (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: cell body (22.5-39)-47 μm long, (15.4-24)-30 μm wide, constriction (5.6-8.6)-9 μm wide, (Illustrations of The Japanese Fresh-water Algae, 1977).