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).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640