Genus: Cell body crescent in shape (long, curved, tapered at both ends); cross section rounded; cell wall smooth or with longitudinal lines, bands on the cell wall in some species; chloroplast laminae ridged and radially arranged, which makes cross section star-shaped; pyrenoids aligned or scattered (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Cell body elongated, slightly curved, inner side concave, both ends broadly rounded, 150-410 μm long, 10-20 μm wide, L/W=10-18 (cf. C. idiosporum, 220-312 μ, L/W=20-26); 3-11 pyrenoids in each semicell (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No. 1, 2, Numa-no-hara marsh (Genseikaen), Madarao highland (Niigata & Nagano Pref.), Myoko village, Niigata Pref., Japan, June 17, 2006 by Y. Tsukii