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

A. gibbosa	A. gibbosa	Arcella sp. gibbosa ?	Arcella sp. gibbosa ?
Arcella sp.	Arcella sp.
A. discoides x 640	A. discoides x 640	A. discoides x 640	Arcella sp. x 640 three nuclei
A. vulgaris	A. vulgaris	Arcella sp.	Arcella sp.