Aperture (mollusc)

In some prosobranch gastropods, the aperture of the shell can be closed, and even completely sealed, with a sort of door or operculum.

The aperture of a snail shell can have many other forms: semicircular, trilobate or auriculate.

In some gastropods, the aperture is narrowed by protruding plaits, which help make the soft parts of the animal less vulnerable to predation.

[citation needed] The shape of the aperture in a gastropod shell can be: The shells of juveniles in some species (especially some families of land snails) have a simple aperture with a sharp edge, but after reaching adult size the aperture of the shell finally acquires adult characters, consisting of a thickened, reflected, inflected or lipped edge, which is sometimes more or less contracted by inflected calcareous projections known as teeth.

The numbers refer to those in the diagram shown opposite: Folds or plicae Lamellae are named as follows: