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, test μm long, μm wide, L/W=, x 640, rice field near Lake Nakatsuna, Omachi city, Nagano Pref., Japan, June 1, 2008 by Y. Tsukii
31 μm 63 μm 94 μm; x 640

Arcella vulgaris, test μm long, μm wide, L/W=, x 640, rice field near Lake Nakatsuna, Omachi city, Nagano Pref., Japan, June 1, 2008 by Y. Tsukii

Test 93 μm in diam., pseudostome 30 μm wide, P/T=0.32, x 640

Images of collecting locality: Rice field near Lake Nakatsuna, Omachi city, Nagano Pref., Japan, June 1, 2008 by Y. Tsukii