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 [var. ehrenbergii]: Cell body large, swelled at the center, inner-side straight or slightly convex, 230-(384-416)-880 μm long, 44-(64-84)-170 μm wide, L/W=4-6; chloroplasts with 4-7 laminae, with many pyrenoids scattered (Illustrations of The Japanese Fresh-water Algae, 1977).