Centropyxis orbicularis  Deflandre, 1929

Diagnosis: Shell in lateral view hemispherical, in dorsal view nearly circular;  aperture elongated‑elliptical, more arched along the margin that follows the outer contour of the shell. Shell usually build of numerous small quartz particles, sometimes mixed or replaced with small diatoms, embedded in a layer of organic cement; shell light gray or brown yellow, depending upon the density of the embedded xenosomes, which are sometimes absent aperture often with some larger quartz particles along the border.

Dimensions: Deflandre (1929) and Bonnet & Thomas (1960): Diameter 100-140 µm, height 70 and 50-95 µm respectively. Siemensma (2025, www.arcella.nl): Width 98-145 µm, height 62-96 µm.

Remarks: Very dark specimens are easily overlooked among debris. The species described by Lüftenegger et al. (1988) is probably a different one, as its circular aperture differs markedly from that described by Deflandre (1929).

References:
Deflandre, G. (1929): Le genre Centropyxis STEIN. – Arch. Protistenkd. 67: 322-375