Genus: Test variable, chitinoid; binucleate (Illustrated Guide, 1985). Group [Vulgaroides]: Test hemispherical; height 1/2 ~ 4/5 diam.; lacks external shelf or rim. Species: Test 30-100 μm in diameter; height of test about 1/2 the diameter; dome of hemispherical test evenly convex; pseudostome cicular, central; colorless, yellow, or brown; two vesicular nuclei; several contractile vacuoles (Kudo, 1966). Test 100-150 μm in diameter, 50-80 high (Illustrated Guide, 1985).

31 μm 63 μm 94 μm; x 640

Arcella vulgaris Ehrenberg ?, test 64 μm in diam., μm high, pseudostome 18 μm wide, P/W=0.3, x 640, Kenashitai (marsh), Hakkoda mountain, Aomori city, Aomori Pref., Japan, July 17, 2005 by Y. Tsukii
31 μm 63 μm 94 μm; x 640