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. cornu]: Cell body slightly curved, tapered at both ends, but inner side at center straight, 95-160 μm long, 5-(7.8-13) μm wide, L/W = 16-17; 3-4 pyrenoids in each semicell
[ var. upsaliense ]: Cell body 40-85 μm long, 5-7(-9) μm wide, L/W = 9; cell wall smooth; chloroplasts with 3-4 pyrenoids (Illustrations of The Japanese Fresh-water Algae, 1977).
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Similar species -->> C. littorale; C. sinense;
C. cornu
225 x 15 μm
180 x 14 μm
L/W=12.9-15.0
Ishinazaka
Furukawa
Miyagi, 2003
C. cornu
conjugation
175-188 x 13-14 μm
L/W=13-14.4
Otawara
Tochigi, 2000
Movies 
C. cornu
180 x 11 μm
L/W=16.3
Kaga
Ishikawa, 2000
C. cornu
155 x 8 μm
L/W=19
Ishinazaka
Furukawa
Miyagi, 2003
C. cornu
140 x 12 μm
L/W=11.7
Kuroiso Park
Kuroiso
Tochigi, 2003
C. cornu
135 x 11 μm
L/W=12.3
Numappara marsh
Kuroiso
Tochigi, 2003
C. cornu
128 x 12 μm
L/W=10.7
Koigakubo marsh
Tessei-cho
Okayama, 2004
C. cornu ?
μm
L/W=
Watarase Wetland
Fujioka
Tochigi, 2005
C. cornu ?
153,190 μm
L/W=16,17
Aizu Recreation p.
Aizuwakamatsu
Fukushima, 2005
C. cornu ?
170,205 μm
L/W=15,18
near Akai wetland
Aizuwakamatsu
Fukushima, 2005
C. cornu
232 x 14 μm
L/W=
Izumo Shrine
Izumo
Shimane, 2006
