Peristome

Peristome (from the Greek peri, meaning 'around' or 'about', and stoma, 'mouth') is an anatomical feature that surrounds an opening to an organ or structure.

Most mosses produce a capsule with a lid (the operculum) which falls off when the spores inside are mature and thus ready to be dispersed.

The basidiocarps of some gasteroid fungi - such as puffballs and earthstars - release spores through an apical opening that is termed a peristome and is variously delimited, its features often being diagnostic when distinguishing closely related species.

This part is sometimes reflected (turned back) or thickened once the snail reaches adult size, and these qualities of the peristome can be diagnostic features of the shell which may aid in identification of the species.

The peristome is any of the structures or sets of parts that surround the mouth or invertebrates such as echinoderms or earthworms.