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).