Centropyxis orbicularis Deflandre, 1929
Diagnosis: Shell in lateral view hemispherical, in dorsal view nearly circular; shell usually build of numerous small quartz particles, sometimes mixed or replaced with small diatoms, embedded in a layer of organic cement; shell light grey or brown yellow, depending upon the density of the embedded xenosomes; xenosomes sometimes absent; aperture nearly semicircular, often with some larger quartz particles along the border.
Dimensions: Deflandre (1929) and Bonnet and Thomas (1960): diameter 100-140 µm and height 70 and 50-95 µm respectively. Lueftenegger et al. (1988): diameter 95-119 µm and height 61-80 µm. My measurements: diam. 59-160 µm.
Remarks: Very dark specimens are easily overlooked between debris.
Deflandre, G. (1929): Le genre Centropyxis STEIN. – Arch. Protistenkd. 67: 322-375