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 large, L/W=5-8; inner-side nearly straight, outer-side curved; tapered at both termini (broad circle, slightly inversed); cell wall smooth, transparent, without bands; chloroplasts with many pyrenoids; [var. lunula] 250-(430-552)-1000 μm long, 47-(73-89)-120 μm wide (Illustrations of The Japanese Fresh-water Algae, 1977).

C. lunula 5 clips 680 μm Vermont-Maine USA, 1999