Arcella crenata  Playfair, 1917

Diagnosis: Shell in side-view with a high, arched dome, sometimes very much inflated, and as broad as the base, the margin showing sometimes smooth, but generally crenate. The surface dented in, all over the dome, with small, equal-sized pits. Base sometimes with a rolled edge in side view. Many forms of this type are found, but the pitted shell and high, arched dome are characteristic.

Dimensions: According to Playfair (1917): Shell diameter 50—84 µm; height 31—53 µm; aperture 15—20 µm; height of the apertural invagination 8—11 µm.

Ecology: Freshwater. On submerged plants.