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: Cell body cylindrical or dumbbell-shaped, dorso-ventrally not compressed, transverse section circular (Illustrations of The Japanese Fresh-water Algae, 1977).
Section Actinotaenium: Cell body cylindrical, slightly constricted at the center, cell surface smooth or dotted or punctated Species moved to genus Actinotaenium
C. clevei
a large variety ?
or C. turgidum ?
200 x 77 μm
Takamatsu
Kagawa, 2002
Cosmarium sp. ?
C. clevei ?
or Tetmemorus ?
51 x 20 μm
Imou bog
Toyohashi
Aichi, 2004
C. curtum ?
5 samples
40-46 x 19-22 μm
2002-2006
C. diplosporum
6 samples
31-43 μm
2003-2007
C. australe
10 samples
69-92 μm
1999-2008
C. capax
4 samples
46-126 μm
1998-2006
C. cucurbitinum
7 samples
45-70 x 21-29 μm
L/W=2.1-2.4
2003-2007
C. cucurbita
13 samples
30-59 x 17-24 μm
1999-2008
C. globosum
14 samples
30-36 x μm
2004-2007
Cosmarium sp.
30 x 21 μm
single pyrenoid
Saitama, 2001???
C. alpestre
9 samples
51-77 x 39-57 μm
1999-2008
C. westii ?
5 samples
62-71 x 36-40 μm
2003-2008
C. oblongum
24 samples
40-63 x 20-22 μm
2004-2008
C. pseudarctoum
4 samples
16-18 x μm
2000-2006Species remained in Cosmarium
C. thwaitesii
27 samples
29-44 x 16-24 μm
2004-2008
C. parvulum
6 samples
28-48 x 12-19 μm
single pyrenoid
2004-2007