Family: Test rigid, chitinoid, often areolar, smooth; pseudostome ventral, round (Illustrated Guide, 1985).
Genus: Test variable, chitinoid; binucleate (Illustrated Guide, 1985).

A. vulgaris 9 clips test μm φ Higashi-hiroshima Hiroshima, 1998	A. vulgaris 5 clips test μm φ Japan, 1998	A. vulgaris 6 clips test μm φ Japan, 1998
A. vulgaris ? 5 clips test μm φ Tokyo, 1998	A. gibbosa 7 clips test μm φ Kuroiso Tochigi, 1998	Arcella sp. 2 clips test μm φ Japan, 1998
Arcella sp. 3 clips test μm φ Japan, 1998