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).

Large, small, smaller_1, smaller_2 varieties

31 μm 63 μm 94 μm; x 640

Arcella vulgaris ?, test μm long, 49 μm wide, pseudostome 15 μm wide, x 640, Numa-no-hara marsh (Genseikaen), Madarao highland (Niigata & Nagano Pref.), Myoko village, Niigata Pref., Japan, May 15, 2005 by Y. Tsukii
31 μm 63 μm 94 μm; x 640