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Chlorophyta: Gamophyceae: Zygnematales: Desmidiaceae

Cosmarium binum
Nordsted var. binum

Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation
Subgenus [Eucosmarium]: Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped.
Section [Cristatae]: Cell surface granulated, gnarled or spiny; semicells half circle, half ellipsoid (Illustrations of The Japanese Fresh-water Algae, 1977).

Species: Cell body 46-62 μm long, 36-45 μm wide, L/W= 1.25-1.33; semicells pyramidate-trapeziform, apex trucated and 4-6 crenate, lateral margins convex, 6-8 crenate, all the crenations consist of bigranules or emarginations, bicrenate granules arranged radially from the center, which locates just above the isthmus; the 6-7 vertical series of granulte ridges present at the center; side view of the semicells ovate-oblong, convexing at the center for both side; vertical view elliptic-oblong (Photomicrographs of the Freshwater Algae, vol. 3, 1985).


Cosmarium binum Nordsted var. binum, tape No. 0067, time code 0227, Torinome kasen park, Kuroiso city, Tochigi Pref., Japan, September, 1998 by Y. Tsukii


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