Arcella dentata Ehrenberg, 1830
Diagnosis: Test circular and dentate in front view, crown-like in profile; diameter more than twice the height; aperture circular, large; colorless to brown; fifteen to seventeen spines; with teeth or dentate border. The ventral side, turned to the substratum, resembles an inverted funnel, with a circular aperture in the centre. The opposite, dorsal side is dish-shaped with flattened vertex, and bears 7-20 spines or ridges; the spines are bent dorsally and more or less evenly spaced around the circumference in a single row.
Dimensions: in literature about 95 µm in diameter, aperture 30 µm in diameter. Diameter with the spines 123-184 µm. The shell of A. dentata is about 120 µm in diameter (107-133 µm, n = 25) and about 50 µm in height (41-58 µm, n = 25).
Ecology: Habitat bogs and swamps, Sphagnum.