Species:
[ var. parvulum ]: Cell body curved, not swelled at the center (inner side straight or slightly concaved),
tapered toward both thorn-like or slightly rounded ends (cf. C. calosporum),
a small pore present on its outer side,
60-160 μm long, (8.5-15)-17 μm wide, L/W=7-10;
cell wall smooth, transparent; chloroplasts with fewer laminae (only two visible);
3-5 pyrenoids in each chloroplast.
[ var. angustum ]: Elongate and thinner than var. parvulum,
75-(98-141) μm long, 5-(8.5-11) μm wide, L/W=11-15;
curvature variable (Illustrations of The Japanese Fresh-water Algae, 1977).