Species: Cell body medium in size, body length about 4/3 longer than its width, (67-76)-90-105 μm long, (50-62)-75-90 μm wide, constriction (49-56)-79 μm wide; semicell half-circle in shape, apex slightly fattened; cell body covered with minute granules but smooth at the constriction zone; apical view of the cell body broad ellipsoidal (Illustrations of the Japanese fresh-water algae, 1977).

Similar species -->> C. connatum;

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

Cosmarium connatum (or C. alpestre ?), x 400, x 640, Uruguay, November 1999, photo by Yuuji Tsukii

Cosmarium alpestre Roy et Bisset: Cell body medium in size, body length about 4/3 longer than its width, (67-76)-90-105 μm long, (50-62)-75-90 μm wide, constriction (49-56)-79 μm wide; semicell half-circle in shape, apex slightly fattened; cell body covered with minute granules but smooth at the constriction zone; apical view of the cell body broad ellipsoidal (Illustrations of the Japanese fresh-water algae, 1977).

Cosmarium connatum Brébisson: Cell body large in size, body length about 4/3 longer than its width, (62-87)-100 μm long, (45-70)-74 κm wide, constriction 37-53 μm wide; semicell ellipsoidal at front view, nearly circular at side view and cicular or broad ellipsoidal at apical view; cell wall covered with many small pores and dots (Illustrations of the Japanese fresh-water algae, 1977).