Species [ var. orbiculare ]: 33.6-44.8 μm long, 28-39 μm wide, isthmus 7-11 μm wide; semicells nearly semicircular in side view; cell wall dotted. [ var. ralfsii W. et G.S. West ]: 31-41 μm long, 22-36 μm wide, isthmus 7-11 μm wide; semicells close to triangular in side view. [ var. messikommeri Hirano ]: 21 μm long, 22 μm wide, isthmus 6.5 μm wide; semicells longitudinally depressed, semicircular or spindle-shaped in side view; bay opened. [ f. subangulata Messikommer ]: 39 μm long, 29.4 μm wide, isthmus 12.6 μm wide; semicells conical in side view; bay opened [ var. depressum Roy et Bisset ]: 19.6-29.4 μm long, 19.6-28 μm wide, isthmus 7-8.4 μm wide; semicells longitudinally depressed semicircular in side view. [ var. hibernicum W. et G.S. West ]: Larger than var. orbiculare, 42-65 μm long, 36-56 μm wide, isthmus 9.5-20 μm wide; apex of semicells flattened (Illustrations of The Japanese Fresh-water Algae, 1977).

Similar species -->> Spondylosium javanicum;

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Karakemi marsh, Yasaka, Omachi city (formerly Yasaka village), Nagano Pref., Japan, May 8, 2006 by Y. Tsukii