Arcella salobris   Useros et al., 2023

Diagnosis: Round test with hemispherical shape and round borders. Thin lip surrounding the aperture. The preapertural area is not clearly marked, its margins are generally smooth. Because of this, the preapertural area is often difficult to differentiate in the apertural view. The test is formed by building units surrounded by relatively thick cement. Pores can be observed in the cement.

Dimensions: According to Useros et al. (2023): Shell diameter 70—78 μm; aperture diameter 18—27 μm; aperture diameter with rim 22—27 μm, although the rim was only visible on a few individuals; height 37—52 μm.

Habitat: Aquatic, variable salinity (observed as active between 5—13 g/L, but the tolerance range may be wider). In the sediment of an athalassohaline little stream.

Geographical distribution: Salobral de Ocaña, Toledo Province, Castilla la Mancha, Spain (39º59′N,3º37′W).

Remarks: Arcella salobris is morphologically very similar to A. euryhalina, but the preapertural area has smooth borders and is not so clearly visible in A. salobris. Arcella salobris also tends to have a more hemispherical shape in the lateral view. It is very similar to both A. hemisphaerica and A. rotundata, but those species do not have thick cement between their building units, according to the images in Lahr and Lopes (2009), and have not been recorded in athalassohaline environments.