Arcella intermedia (Deflandre, 1928) Tsyganov & Mazei 2006
Diagnosis: shell colorless, light yellow or brown, circular in apertural view, domed or hemispherical with an implicit basal border in lateral view. Apertural surface and basal border are smooth, but the dorsal surface has a number of regular depressions. Aperture circular with or without a distinct collar.
Dimensions: shell diameter 65-75 μm, shell height 35-50 μm, aperture diameter 16-23 μm. Aperture diameter/shell diameter 0.35-0.55; shell height/diameter ratio 0.5-0.7. My measurements: shell diameter 52-71 μm.
Ecology: fresh water, between algae and on the debris of shallow waters.
Remarks: This species belongs to the species complex of A. hemisphaerica, A. rotundata and A. gibbosa with all their described varieties.
See Tsyganov and Mazei, 2007.