See text Atlantidae is a family of sea snails, holoplanktonic gastropod molluscs in the clade Littorinimorpha.

The Atlantidae is a group of holoplanktonic gastropods, which all demonstrate a strong adaptation to pelagic life, in the form of a lenticular, laterally flattened, aragonitic shell, the surface of which is further enlarged by the presence of a wide, and very thin and fragile, double-walled keel.

[1] For the living animal the enlargement of the shell's surface serves 'to increase stabilization during swimming and sinking'.

The snails of this family can retract into their shell and close it off with a cartilaginous, flexible operculum.

[1] Additional fossil genera considered to belong in the Atlantidae are Bellerophina d'Orbigny, 1843 (Cretaceous), Eoatlanta Cossmann, 1888 (Paleocene-Eocene) and Mioatlanta di Geronimo, 1974 (Miocene).