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 [ Cyclidium ]: Cell surface smooth; semicells half circle, half ellipsoid (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: (Illustrations of The Japanese Fresh-water Algae, 1977).
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Similar species -->> C. obsoletum; C. taxichondrum;
C. ralfsii
var. montanum ?
74 x 67 μm
Kabuto-yama
Nishi-no-miya
Hyogo, 2004
C. ralfsii
stock Hnka-4
60 x 61 μm
Kabuto-yama
Nishi-no-miya
Hyogo, 2004
