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 (Illustrations of The Japanese Fresh-water Algae, 1977).
| Eucosmarium (細胞は扁平で中央のくびれが深い。) | |||
| Globuliferae: Cell surface smooth; 半細胞は円形, 楕円形, 腎臓形 | |||
C. contractum μm |
Cosmarium sp.7 μm = contractum ? |
Cosmarium sp.6 μm |
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| Margaritiferae: Cell surface granulated or spiny; 半細胞は截頭ピラミッド形, 梯形 | |||
C. botrytis μm |
Cosmarium sp.4 μm |
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| Cristatae: Cell surface granulated or spiny; 半細胞は半円形, 半楕円形 | |||
Cosmarium sp.1 μm |
C. tetraophthalmum μm |
C. echinodermum μm |
Cosmarium sp.3 μm |
Cosmarium sp.5 μm |
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| Tetridium: Cell surface granulated or spiny; 半細胞は方形 | |||
C. ornatum μm |
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