Species [var. acutum]: Cell body slightly curved, tapered at rear, L/W= 20-30; both termini broad circle; cell wall smooth, transparent; chloroplasts with 3-4 pyrenoids in each semi-cells; 90-(92-176) μm long, 4-(4.8-8.4) μm wide (Illustrations of The Japanese Fresh-water Algae, 1977).

C. acutum 1 clip 110 x 4.3 μm L/W=23.4 Hiroshima, 1998