Centropyxis plagiostoma  Bonnet & Thomas, 1955

Diagnosis: In frontal view, generally transparent or slightly yellowish, with a circular shape; in lateral view, fairly flat with a thickness about one-third of the ventral diameter, and resembling the shape of a bean seed. The aperture is slightly invaginated, without internal bridges. In frontal view, the aperture is bordered by a collar of irregular mineral fragments, delimiting a small aperture approximately one-third of the overall diameter. It is poorly defined, with jagged edges due to the presence of the mineral grains. This aperture is generally located in the upper third of the shell and is never central. The shell surface consists of irregular, exogenous plates set on the chitinous membranes forming the shell.

Dimensions: According to Bonnet and Thomas (1955): Shell diameter 64—95 µm; height 38—43 µm; aperture diameter 12—18 × 18—30 µm.

Habitat: Mosses and Sphagnum.

Remarks: This species can be confused with C. cavitastoma. Important differences are observed in the structural peculiarities of the ventral zone. The aperture of C. plagiostoma is located on the anterior half of the ventral surface. It is elliptical to almost circular, with an uneven edge often completely or partially covered with large quartz particles (“dents”); distinctly invaginated, pre-oral portion abruptly curved, thus the ventral surface itself is flat and gradually inclined. In C. cavitastoma the ventral surface forms a vast funnel with a maximum depth in the apertural area.

References: Bonnet, L. , Thomas, R. (1955). Étude sur les Thécamoebiens du sol (I). Soc. D’Hist. Nat. Toulosuse, 90: 411-428.