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Gamophyceae: Zygnematales: Desmidiaceae

 Cosmarium quadratum
f. willei W. et G.S. West

Cosmarium quadratum Species [Ralfs f. quadratum]: Cell body 48-(53-73) μm long, 25-(28-40) μm, isthmus 12-(20-26) μm wide, L/W=2; bay opening closed; semicells rectangular, rounded at base with frontal slight depression; apical corners broadly rounded; side view elliptical or oval; apical view elliptical; cellwall smooth.
[f. willei W. et G.S. West] Cell body 50-(55-82) μm long, (30-36.5)-40 μm, isthmus 17-27 μm wide, bay slightly opened; side margins of semicells nearly straight lacking slight depression at base (Illustrations of The Japanese Fresh-water Algae, 1977).

Cosmarium quadratum f. willei W. et G.S. West, cell body 75 μm long, 37 μm wide, isthmus 21 μm wide, L/W=2.0, x 640, a small wetland near Numa-no-hara marsh (Genseikaen), Madarao highland (Niigata & Nagano Pref.), Myoko village, Niigata Pref., Japan, May 15, 2005 by Y. Tsukii
scale 31 μm scale 63 μm scale 94 μm; x 640
Cosmarium quadratum
Cell body 74 μm long, 38 μm wide, isthmus 21 μm wide, L/W=1.9, x 640
Cosmarium quadratum

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