Lip (gastropod)

In the shell of

In dextral (right-handed) shells (most snail shells are right-handed), the right side or outer side of the aperture is known as the outer lip (labrum). The left side of the aperture is known as the inner lip or columellar lip (labium) if there is a pronounced lip there. In those species where there is no pronounced lip, the part of the body whorl that adjoins the aperture is known as the parietal wall.

The outer lip is usually thin and sharp in immature shells, and in some adults (e.g. the land snails Helicella and Bulimulus). However, in some other land snails and in many marine species the outer lip is thickened (also called callused), or reflected (turned outwards). In some other marine species it is curled inwards (inflected), as in the cowries such as Cypraea. It can also be expanded, as in Strombus; it can have finger-like processes (digitate) or it can be fringed with spines (foliated), as in Murex.

The lip is called emarginate when it is incised or slit, as in