Adult shell calcareous, with strongly truncated keel composed of conchiolin. Shell small (less than 2 mm) and helicoid. Spire slightly elevated and composed of about 3 whorls. Radula large, triangular. Central tooth monocuspid, with a large, low basal plate. Lateral teeth monocuspid with a low process on its inner side. Marginal teeth monocuspid. Eyes type a, and operculum type a.
In the Atlantic Ocean shells with two different spire morphologies are encountered, often in the same plankton tow samples. In the first morph the spire whorls are smooth; in the second a low spiral ridge is present, which appears just after the beginning of the second whorl, is centered on the whorl, and ends after about three-fourths of a turn in the third whorl. A less conspicuous, secondary spiral ridge is present inside of the primary ridge on the second whorl. In sediment trap samples from the Walvis Ridge in the eastern South Atlantic, specimens of Protatlanta souleyeti with a much stronger spiral sculpture prevail. This sculpture matches precisely that described by Issel (1911) for his Protatlanta sculpta. Since the spire sculpture is as variable in Protatlanta souleyeti as in a number of other atlantids, we conclude that Tesch (1949) was correct in not accepting Protatlanta sculpta as a valid species.
See the family Atlantidae for a discussion of the species groups.