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). QuickTime Movies http://protist.i.hosei.ac.jp/

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

Arcella, A dividing cell, x 400, x 640, Yamagata Pref. 1999, by Y. Tsukii