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: Colonies enclosed by a gelatinous envelope, always curved; cell body reniform, sometimes elliptical, with broadly rounded ends, young cells 6.5-7 μm long, 3 μm wide, mature cells up to 16.5 μm long, 9 μm wide; cells arranged in cruciate series (when 2 cells), or in double series, sometimes irregular (when 8 cells) ; cell wall smooth, without teeth, spines or granulations (Photomicrographs of the Freshwater Algae, vol. 3, 1985).

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Cell body ovoid
var. arcuatus cell 14 x 7 μm L/W=2.0 Saitama, 1999	var. arcuatus cell μm L/W= Chiba-Minato Park Chiba, 2003	var. arcuatus cell 13 x 5 μm Tashirodaira m. Hakkoda mountain Aomori, 2005
Cell body reniform or ellipsoid
var. platidisca cell 11 x 4.5 μm Ochiai-numa 2 Noshiro Akita, 2007	var. platidisca cell μm Kataki-numa Yuri-Honjo Akita, 2008	var. platidisca cell 15 x 8 μm L/W=1.9 near Yamaguchi Univ. Yamaguchi, 2004	var. platidisca cell division cell 11 x 6 μm L/W=1.8 Koshigaya Saitama, 2001
var. platidisca cell 12 x 8 μm L/W=1.5 Tega-numa Abiko Chiba, 2000	var. platidisca ? or S. ecornis ? cell 12 x 5.5 μm L/W=2.2 Sanda Hyogo, 2001	var. platidisca ? or S. ecornis ? cell 10 x 5 μm L/W=2.0 Umi-no-nakamichi Fukuoka, 2001	var. platidisca ? or S. ecornis ? cell 10 x 4.5 μm L/W=2.2 Kabuto-yama Nishi-no-miya Hyogo, 2004
var. platidisca ? or S. ecornis ? cell 10 x 5 μm L/W=2.0 water reservoir near Yamaguchi Univ. Yamaguchi, 2004

Similar species -- > > S. ecornis

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