Lip (gastropod)

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).

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.

When the lip is bent into an "s" curve it is called sinuous, as is the case in the sigmoidal margin of Janthina exigua.