Genus: Colonies of 4 (or 2, 8, 16) cells attached side by side, arranged linearly or zigzag; cell body elliptical or spindle or crescent in shape; terminal cells with spiny projections in many species; cell wall usually smooth, but in some species granulated or dented or ridged (Illustrations of The Japanese Fresh-water Algae, 1977).
Species [ var. quadricauda ]: Colonies of 2, 4 or 8 cells arranging linearly; cell body elongated ellipsoidal, 11-18 μm long, 3.5-7 μm wide; terminal cells with long spiny projections (10-17 μm long); cell wall smooth (Illustrations of The Japanese Fresh-water Algae, 1977).
S= length of Spines; L=Body length; W=Body width (terminal cells)

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L/W = about 3, terminal cells spindle-shaped
var. biornatus cell μm L/W= S/L= Koga museum Koga Ibaraki, 2003	var. biornatus cell 32 x 12 μm L/W=2.7 Tachikawa Tokyo, 2001	var. biornatus cell 21-23 x 8 μm L/W= Murakuni ike Iwatsuki-bunka p. Saitama, 2006	var. biornatus cell 14 x 4.5 μm L/W=3.1 Iruma river Kawagoe Saitama, 2004
var. biornatus cell 8 x 3 μm L/W=2.7 S/L=0.5 Shikinawa-ike Fukuoka, 2001
L/W = about 4; cell body elongated
var. biornatus cell 24 x 5.5 μm L/W=4.4 S/L=1.1 Saitama, 1999	var. biornatus cell 26 x 8 μm L/W=3.9 S/L=1.0 Saitama, 2000	var. biornatus cell 22 x 6 μm L/W=3.7 S/L=0.8-0.9 Saitama, 2001	var. biornatus cell 18 x 7 μm L/W=2.6 S/L=0.7 Japan, 1999
var. biornatus ? S. protuberans ? cell 11.5 x 3.5 μm L/W=3.3 S/L=1.0 Uruguay, 1999

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