Centropyxis constricta

C. constricta, length 127-139 µm (Croatia, Bhutan, Mongolia)

Centropyxis constricta (Ehrenberg, 1841) Penard, 1902
Basionym: Arcella constricta Ehrenberg, 1841

Diagnosis: Shell elongated ovoid, with rounded fundus and tapering gradually towards the aperture. Main body spherical in lateral view, flattened slightly towards the aperture, without forming a clear distinction between body and apertural rim. Shell relatively smooth, composed of small to medium mineral particles, usually with a few large quartz particles on the fundus. Aperture large, oval, invaginated and sub-terminal. Apertural area smooth and covered mainly of flattish particles embedded in a thick layer of organic cement.

Dimensions: Literature 90-150 µm, my measurements 80-139 µm.

Ecology: Freshwater, mosses, soil and forest litter.

C. constricta, after Deflandre, 1929

C. constricta, a,b after Ehrenberg, 1841, c 1843

Remarks: Ehrenberg (1841) gives following description: “A constricta, ovata, apertura maxima marginali ibique leviter constricta. Multas vidi. Icon!”
(translated: oval, the largest marginal opening! and there slightly constricted. I have seen many. Icon!).
Both Penard (1902) and Deflandre (1929) complained about the difficulty of distinguishing this species from other species. Deflandre has made an attempt to re-describe this species. Penard already described this species as highly variable.