Arcella euryhalina   Useros et al., 2023

Diagnosis: Shell round, circular in oral and aboral view, hemispherical in lateral view, with round borders and no ridges or depressions. The aperture is circular and invaginated, surrounded by a thin collar. The borders of the pre-apertural area are generally clear and well-marked. There is a very large amount of cement between the building units of the cell, which covers the majority of the test surface.

Dimensions: According to Useros et al. (2023): Shell diameter 58—77 μm; aperture diameter 16—26 μm; aperture diameter with rim 19—30 μm; height 30—45 μm.

Ecology.. Aquatic, variable salinity (4 to 36 g/L). In the sediment of an athalassohaline lake. In culture, these organisms grew optimally in pure freshwater, and survived at 50 g/L.

Distribution Discovered in Lake Pétrola, Albacete Province, Castilla La Mancha, Spain (38º50′N,1º33′W).

Remarks: Arcella euryhalina is morphologically very similar to A. salobris, but the pre-apertural area is generally wider and with a more marked margin in A. euryhalina. It also has a thicker cement layer between the building units.