Lip (gastropod)

In the shell of gastropod mollusks (a snail shell), the lip is the free margin of the peristome (synonym: peritreme) or aperture (the opening) of the gastropod shell.

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.