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 46 μm long, 32 μm wide, isthmus 10 μm wide, L/W=1.3; semicells semicircular with a flattened apex, both sides slightly wavy (5-7 waves); cell wall dotted (Illustrations of The Japanese Fresh-water Algae, 1977).
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