Species [ var. venus ]: Cell body small, strongly curved, inner side not convex, both ends pointed, 48-(54-60)-85 μm long, 6-(9)-11 μm wide, L/W=8-9; cell wall smooth, transparent or brownish in color; 1-2 pyrenoids in each chloroplast, one lamina visible. [ var. incurvum (Brébisson) Krieger ]: Smaller than var. venus, 30-(50-73)-80 μm long, 6-(8.4-11)-14 μm wide, L/W=5-7 (Illustrations of The Japanese Fresh-water Algae, 1977).

Similar species --->> C. cynthia;

31 μm 63 μm 94 μm; x 640