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Gamophyceae: Zygnematales: Desmidiaceae

Cosmarium pseudarctoum
Nordstedt var. var. perminutum (G.S. West) Ström
= Actinotaenium pseudarctoum Nordstedt var. var. perminutum (G.S. West) Ström

Cosmarium pseudarctoum 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 (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Cell body small, 16-(17-26.5) μm long, (10.5-14)-18 μm wide, isthmus 10-(10.5-14)-17 μm, L/W=1.25-1.5; semicells nearly spherical or inverted broad ovoidal; both ends broader than the center; apex slightly flat; cell wall smooth;
var. perminutum: 9-13.5 μm long, 5.6-8.5 μm wide, isthmus 6-7 μm, L/W=2; semicells inverted ovoidal; apex rounded (Illustrations of The Japanese Fresh-water Algae, 1977).


Cosmarium pseudarctoum Nordstedt var. perminutum (G.S. West) Ström, cell body 16 μm long, 8.5 μm wide, isthmus 7 μm wide, x 400, x 640, Kaga city, Ishikawa Pref., Japan, 2000, by Y. Tsukii
scale 50 μm scale 100 μm scale 150 μm; x 400 : scale 31 μm scale 63 μm scale 94 μm; x 640

Cosmarium (pseudarctoum ?), x 640, Kaga city, Ishikawa Pref., 2000 by Y. Tsukii
scale 31 μm scale 63 μm scale 94 μm; x 640


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