Species: [var. calosporum] Cell body well curved, inner side straight or concave, tapered toward both ends, truncated with slanted edges (cf. C. parvulum); small pores present at outside of the ends; 70-(95-110)-116 μm long, 8-(12-13) μm wide, L/W=7-10 (cf. C. dianae); 3-5 pyrenoids in each chloroplast; cell wall smooth or brownish in color.
[var. brasiliense] Slender than var. calosporum, 90-(126-150)-195 μm long, 5-(8)-11 μm wide, L/W=12-16
[var. maius] Larger than var. calosporum, curvature small, 120-(176)-192 μm long, 13-(17)-18 μm wide, L/W=11-12 (Illustrations of The Japanese Fresh-water Algae, 1977).
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Similar species -- >> C. parvulum; C. dianae ( > 150 μm, L/W > 10 );
v. calosporum
108 x 12 μm
L/W=9.0
Furuike marsh
Togakushi highland
Nagano, 2005
v. maius ?
156 x 13 μm
L/W=12
Numappara marsh
Kuroiso
Tochigi, 2003
v. calosporum
or v. maius ?
125-130 μm
L/W=7.9
Kuroiso Park
Kuroiso
Tochigi, 2003
v. calosporum
or v. maius ?
135 x 14 μm
L/W=9.6
Hakama marsh
Madarao highland
Niigata, 2005
