Plagiopyxis vuattouxi Bonnet, 1974

Diagnosis: Shell very small, cryptostome simple, colorless or yellowish, with strong antero-posterior elongation. In dorsal view, elliptical or oblong shape, sometimes widening slightly in the posterior region. In lateral view, perfectly flat ventral sole with non-sloping ventral lip and very little prominent dorsal lip. In ventral view, hardly visible pseudostome, presenting the appearance of a very narrow curved fissure located in a very anterior position. Dorsal lip covering only very slightly the ventral lip. Colorless coating, consisting of irregular siliceous particles, reworked, united by a colorless or yellow-brownish cement. Wall often thickened in the dorso-posterior region of the test.

Dimensions: Length 48-52 µm; width 29-34 µm; dorso-ventral (height) 25-32 µm.

Ecology: Soil. Very common in savannah soils, mainly in hydromorphic formations on plateaus or at the bottom of slopes, rare in gallery forest soils.

Remarks: In Plagiopyxis vuattouxi, the very anterior position of the pseudostome may suggest an acrostome structure. During a superficial examination, in dorsal and ventral views, it is possible to confuse this species with Heleopera rectangularis Bonnet. However, the larger size of the latter and especially the dorso-ventral symmetry of P. vuattouxi, clearly visible in lateral view, make it possible to distinguish the two species with certainty.