Species [var. pachydermum]:
Cell body 78-117 μm long, 60-87 μm wide, isthmus 25-34 μm wide,
semicells semielliptical in shape, corners rounded.
[var. aethiopicum W. et G.S. West ]: Semicells nearly half-circle; cellwall thin;
cell body 64-107 μm long, 56-80 μm wide, isthmus 28-34 μm wide.
[var. ellipticum Hinode ]: Semicells rectangular at base; curvature of lateral margins weak compared to var. pachydermum;
cell body 94-100 μm long, 67-74 μm wide, isthmus 28-34 μm wide.
[var. heptagonum Grönblad ]: Semicells irregular pentagon in shape;
posterior half of lateral margins nearly straight;
cell body 94-100 μm long, 67-74 μm wide, isthmus 28-34 μm wide
(Illustrations of The Japanese Fresh-water Algae, 1977).
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