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.

This shape usually corresponds roughly to the cross-section of the body whorl of the shell.

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:

Three views of a shell of Norelona pyrenaica with the apertural view in the center
A shell of Semicassis pyrum , which has a large aperture and a pronounced parietal callus
Scheme of an aperture of a gastropod showing terminology of teeth, plicae and folds [ 7 ]
The dentate aperture of Multidentula ovularis