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Centropyxis orbicularis
Centropyxis orbicularis, in side view (left) and ventral view, 84 µm in diameter (Netherlands)

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.

Centropyxis orbicularis
After Deflandre (1929)
Centropyxis orbicularis
Centropyxis orbicularis, after Lueftenegger et al., 1988
Centropyxis orbicularis
Centropyxis orbicularis
Test in side view, 100 µm in diameter and same shell in dorsal view
Centropyxis orbicularis
Centropyxis orbicularis
Test c. 160 µm, moss, Germany

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

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