Genus: Cell body short, radiate in shape; apical view of the cell, triangular, polygonal, ellipsoidal or spindle-shaped; zygospores formed outside of mother cells (Illustrations of The Japanese Fresh-water Algae, 1977)
Subgenus: lacks arm-like projections (Illustrations of The Japanese Fresh-water Algae, 1977)
Species (var. bidentatum): cell body excluding spines 31-62 μm long, 37-64.5 μm wide (excluding spines), constriction 11-26.5 μm wide, (Illustrations of The Japanese Fresh-water Algae, 1977)
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S. longispinum
v. bidentatum ?
60-78 x 60-65 μm
Ushidome-ike
Norikura highland
Nagano, 2005
S. longispinum
v. bidentatum ?
69 x 60 μm
Ushidome-ike
Norikura highland
Nagano, 2006
S. longispinum
v. bidentatum ?
μm
Ushidome-ike
Norikura highland
Nagano, 2007
