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. cuspidatum ]: Cell body (19.6-25.8)-31 μm long, (15.4-22.4)-28 μm wide, L/W=1.3, isthmus 4.2-7 μm wide; semicells inverted triangle in shape, apical and lateral margins slightly convexed, with a single elongated spine at each corner extended inward; apical view triangular, each side concaved, corners rounded (Illustrations of The Japanese Fresh-water Algae, 1977)

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S. cuspidatum 20 x 20 μm spines 10 μm Tanohara marsh Shiga highland Nagano, 2004	S. cuspidatum 18 x 18 μm spines 8 μm Tanohara marsh Shiga highland Nagano, 2005	S. cuspidatum x 18 μm spines 10 μm Tanohara marsh 3 Shiga highland Nagano, 2007	S. cuspidatum 22 x 20 μm spines 7 μm Hikage marsh Shiga highland Nagano, 2006
S. cuspidatum ? 22 x 20 μm 4 spines Shimo-no-koike Shiga highland Nagano, 2007	S. cuspidatum 25 x 21 μm spines 9 μm Tane-ike Togakushi highland Nagano, 2005	S. cuspidatum 23 x 21 μm spines 8 μm Karakemi marsh Omachi Nagano, 2006

Similar species -- >>triangularis S. subavicula; Arthrodesmus triangularis;

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