Cyclopyxis arenata (Cushman, 1930) Boltovskoy, 1956
Basionym: Pseudarcella arenata Cushman, 1930
Diagnosis: Cushman (1930): Test about twice as broad as high, plano-convex in side view, dorsal side strongly convex, ventral side flattened and slightly concave in the middle, cicrcular in outline; wall very thin, composed of distinct sand grains firmly cemented, somewhat chitinous; aperture circulare with a simple flattened tooth.
Boltovskoy and Lena (1966): Hemispherical shell. Convex dorsal side, ventral somewhat concave in its middle part. Rounded aperture, located in the center of the ventral side. Agglutinated walls, covered with medium-sized sand grains. Color from white to ocher.
Dimensions: Cushman (1930): Diameter 250-300 µm; height 150-180 µm.
Ecology: Freshwater. Rio Grande, Ushuaia, Patagonia (Boltovskoy and Lena (1966):.