Plagiopyxis pusilla (Bonnet, 1961) Bonnet, 1980
= Plagiopyxis callida var. pusilla Bonnet, 1961

Diagnosis: Shell small, peaked cryptostoma type, dark yellow to brownish, subcircular in dorsal and ventral views. Vestibule separated from the body by a neat suture line. This vestibule is, in general, distinctly distinct from the body, over which it forms, at least in certain populations, a slight prominence, whereas in P. callida the vestibule is generally more closely integrated into the body, which gives the entire test an elliptical outline in dorsal view. The opening of the vestibule (distal orifice) in an arc of a circle or in a crescent, located in the anterior quarter of the sole and generally very difficult to see. Communication between body and vestibule ensured by an elliptical pseudostome, with a long axis parallel to the plane of the sole, located in the upper half of the diaphragm or septum separating the two cavities. In some cases, this pseudostome lies close to the dorsal wall and tends to assume a semi-elliptical shape. This orifice is generally blocked by an epiphragm formed of various debris agglomerated by mucus and similar to that of P. callida. The mineral part of the test is formed of altered, irregular siliceous platelets, incorporated into a yellowish medulla (or brownish in rich biotopes in iron oxide such as soils on decalcification clays).

Dimensions: Length mean 80 µm; width 50 µm; dorso-ventral (height) 34-40 µm.

Ecology: Soil. Xerophilic species, common in neutral or calcareous neosols with low organic matter content and medium C/N (more or less skeletal rendziniform soils). Worldwide distribution.