Centropyxis rioplatensis  Boltovskoy and Lena, 1974

Diagnosis: Shell elongated, with the oral and aboral extremities rounded and both sides convex. Ventral opening, located in a depression. The edges of this depression are different: the anterior one is abrupt and the posterior one gently indented. Chitinoid walls, with agglutinated material Consisting of very fine grains of sand. The surface of the shell is slightly rough. Yellow color.

Dimensions: Length 115-191 μm, width 83-103 μm.

Habitat: Freshwater, sediment.

Remarks: The closest species is Centropyxis constricta (Ehrenberg), a typical form from which it differs by presenting: a) a more elongated contour, b) an always rounded aboral end, c) a smoother texture and a more yellowish color and c) a smaller size (Boltovskoy and Lena, 1974).