Section [Margaritiferae]: Cell surface granulated, gnarled or spiny; semicells pyramidal with flattened apex or trapezoid (Illustrations of The Japanese Fresh-water Algae, 1977).
Species [var. subcostatum]: Cell body 26-38 μm long, 23-32 μm wide, isthmus 6.5-12 μm.
[f. minor W. et G.S. West]: Cell body 19-26 μm long, 18-23 μm wide, isthmus 4.5-9 μm.
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Similar species -->> C. furcatospermum (18- μm); C. formosulum;
C. subcostatum
var. subcostatum
33 x 26 μm
Ishinazaka
Furukawa
Miyagi, 2004
C. subcostatum
f. minor
26 x 21 μm
Ohnuma
Nasu-shiobara
Tochigi, 2006
C. subcostatum
f. minor
21 x 16 μm
Imou bog
Toyohashi
Aichi, 2004
C. subcostatum
f. minor
17 x 16 μm
Tane-ike
Togakushi highland
Nagano, 2005