Section [ Actinotaenium ]: Cell body cylindrical, slightly constricted at the center, cell surface smooth or dotted or punctated (Illustrations of The Japanese Fresh-water Algae, 1977).
Species [var. pseudarctoum]: Cell body small, 16-(17-26.5) μm long, (10.5-14)-18 μm wide, isthmus 10-(10.5-14)-17 μm, L/W=1.25-1.5; semicells nearly spherical or inverted broad ovoidal; both ends broader than the center; apex slightly flat; cell wall smooth;
[var. trigonum]: 16.5-21.5 μm long, 11.5-17 μm wide, isthmus 9-10.8 μm, apical view triangular in shape
[var. perminutum]: 9-13.5 μm long, 5.6-8.5 μm wide, isthmus 6-7 μm, L/W=2; semicells inverted ovoidal; apex rounded (Illustrations of The Japanese Fresh-water Algae, 1977).

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var. pseudarctoum: Cell body more than 16 μm long
C. pseudarctoum ? 18 x 11 μm Karakemi marsh Omachi Nagano, 2006
var. perminutum: Cell body less than 16 μm long
C. pseudarctoum v. perminutum 16 x 8.5 μm Kaga Ishikawa, 2000	C. pseudarctoum v. perminutum stock Ikk-1, axenic Cell division 16 x 8.5 μm Kaga Ishikawa, 2000	C. pseudarctoum v. perminutum 16 x 8.5 μm Sendabori Chiba, 2002

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