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).

Similar species -->> C. lundellii;

31 μm 63 μm 94 μm; x 640

Cosmarium pachydermum P. Lundell var. pachydermum: Cell body 78-117 μm long, 60-87 μm wide, constriction (isthmus) 25-34 μm wide; semicells broad half-ellipsoidal, each corner rounded; side view nearly circular, apical view ellipsoidal; cell wall densely puncatated (Illustrations of the Japanese Fresh-water Algae, 1977)

Cosmarium lundellii P. Lundell var. circular: Cell body 53-73 μm long, 48-56 μm wide, constriction (isthmus) 17-25 μm wide; semicells broad semicircular, each corner rounded; apex narrowly straight; side view nearly circular, apical view elongated ellipsoidal; cell wall puncatated (Photomicrographs of the Fresh-water Algae, vol. 5, 1986).