Family: Unicells or cells loosely attached to form hyphae; cell body varied in shape, a constriction at the center in most species; cell walls consisting of two or more parts, with small pores and various ornaments (Illustrations of The Japanese Fresh-water Algae, 1977).
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).

C. acutum 2 clips 110 x 4.3 μm L/W=23.4 Hiroshima, 1998	C. toxon 2 clips 225 μm L/W=19 Hiroshima, 1998	C. setaceum 4 clips 295 μm L/W=37 Japan, 1998
C. acerosum 6 clips Asaka Saitama, 1998	C. acerosum or C. turgidum ? 6 clips 550 x 48 μm Uruguay, 1999	C. lunula 7 clips 680 μm Vermont-Maine USA, 1999
C. ehrenbergii 6 clips 425 μm L/W=5.4 Uruguay, 1999	C. cornu 11 clips conjugation 175-188 x 13-14 μm Otawara Tochigi, 2000	C. moniliferum stock Sak-1, axenic 2 clips Kurome river Asaka Saitama, 2000