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. acuminatus ]: Colonies of 4 or 8 cells; cells arranging linearly (4 cells) or zigzag (8 cells); cell body elongated spindle-shaped, outer cells curved outward, 12-30 μm long, 2.5-6 μm wide; cell wall smooth (Illustrations of The Japanese Fresh-water Algae, 1977).

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Cells aligned side by side
Terminal cells slightly curved
f. maximus cell 62 x 6 μm L/W=10.3 Japan, 1998	var. acuminatus 4-cells type cell μm Kodama town Saitama, 2003	v. acuminatus ? 8-cells type cell 50 x 6 μm L/W=8.3 Japan, 1998	v. acuminatus 8-cells type cell 27 x 4.5 μm L/W=6.0 Japan, 1997
v. acuminatus cell μm Omine-numa Tsukiyono Gunma, 2003	v. acuminatus cell 23-25 x 3.5 μm near Yamaguchi Univ. Yamaguchi, 2004	v. acuminatus cell 30-39 x 5-8 μm Sannoh-bori Sannoh Park Saitama, 2005	v. acuminatus cell 26 x 6 μm Futayo-no-ike Haguro mountain Yamagata, 2005
v. acuminatus cell 20 x 3 μm Hasu-ike Shiga highland Nagano, 2005	v. acuminatus cell 40 x 5.5 μm Shirahata-Numa Urawa Saitama, 2005
Terminal cells strongly curved
v. tortuosus ? 8- or 4-cells type cell 35 x 4 μm L/W=8.8 Japan, 1998	v. tortuosus ? cell 41 x 5 μm L/W=8.2 Nanbata castle p. Fujimi Saitama, 2005
Cells aligned zigzag
Terminal cells slightly curved
v. acuminatus cell 25 x 3 μm L/W=8.3 Mizumoto Park Tokyo, 2001	v. acuminatus cell μm Omine-numa Tsukiyono Gunma, 2003	v. acuminatus cell μm Omine-numa Minakami Gunma, 2007	v. acuminatus cell μm castle ruin p. Sakura Chiba, 2008
v. acuminatus inner 21 x 4.5 μm outer 31 x 4.5 μm Nishi-Urawa Saitama, 2001	v. acuminatus cell 17 x 3.5 μm L/W=4.9 Tatebayashi Gunma, 2001
v. acuminatus cell 14 x 5 μm L/W=2.8 Lake Biwa Maihara Shiga, 2003	v. acuminatus 8-cells type cell 23 x 3 μm L/W=7.7 Japan, 1998	v. acuminatus cell μm L/W= Higusa-numa Hikari Chiba, 2003	v. acuminatus cell 21 x 5 μm L/W= near Yamaguchi Univ. Yamaguchi, 2004
v. acuminatus cell 22 x 4.5 μm L/W=4.9 riverside park Abukuma river Fukushima, 2005	v. acuminatus cell 13-16 x 5 μm L/W=2.6-3.2 Chaya-numa p. Fukushima city Fukushima, 2005	v. acuminatus cell 16 x 4-5 μm L/W= kenko-fukushi m.p. Koshigaya Saitama, 2005	v. acuminatus cell 14 x 3 μm L/W= Motoyurugi Fujioka Gunma, 2004
Terminal cells strongly curved
S. acuminatus cell μm Showa-machi G.P. Showa Saitama, 2003	S. acuminatus cell 17 x 3 μm L/W=5.7 Uruguay, 1999	S. acuminatus cell 37 x 4 μm L/W=9.3 Saitama, 1999	S. acuminatus or S. javanensis ? cell 37 x 4 μm L/W=9.3 Iwajuku Gunma, 2001
S. acuminatus cell μm L/W= Nishi-Urawa Saitama, 2003
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S. acuminatus or S. acutus ? 4-cells type cell 15 x 3 μm L/W=5.0 Japan, 1998	S. acuminatus or S. acutus ? stock Skg-21 cell 16 x 4 μm L/W=4.0 Kawagoe Saitama, 2001	S. acuminatus or S. acutus f. tetradesmiformis ? 4-cells type cell 19 x 4 μm L/W=4.8 Koriyama Fukushima, 2001	S. acuminatus or S. acutus f. costulatus ? cell μm L/W= Nishi-Urawa Saitama, 2003
S. acuminatus or S. acutus ? cell μm L/W= Matsubushi Saitama, 2003	S. acuminatus ? cell 40 x 5 μm L/W=8.0 Nishi-nasuno Tochigi, 2001	S. acuminatus ? or S. javanensis ? cell 30 x 5 μm L/W=6.0 Mizumoto Park Tokyo, 2001	S. acuminatus or S. acutus ? 9-15 x 3-4.5μm Uruguay, 1999
S. acuminatus cell 22 x 5 μm Hasu-ike Shiga highland Nagano, 2005	S. acuminatus cell 16 x 4 μm riverside park Abukuma river Fukushima, 2005	S. acuminatus cell 15 x 4 μm near Yoshino p. Mitsukaido Ibaraki, 2006

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