Peristome (from theGreekperi, meaning 'around' or 'about', andstoma, 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Someplants,fungi, and shelledgastropods have peristomes.

Inmosses, the peristome is a specialized structure in thesporangium that allows for gradualspore discharge, instead of releasing them all at once.

Most mosses produce a capsule with a lid (theoperculum) which falls off when thespores inside are mature and thus ready to be dispersed. The opening thus revealed is called thestoma (meaning "mouth") and is surrounded by one or two peristomes. Each peristome is a ring of triangular "teeth" formed from the remnants of dead cells with thickenedcell walls. There are usually 16 such teeth in a single peristome, separate from each other and able to both fold in to cover the stoma as well as fold back to open the stoma. This articulation of the teeth is termedarthrodontous and is found in the moss subclassBryopsida. In other groups of mosses, the capsule is eithernematodontous with an attached operculum (as in thePolytrichopsida), or else splits open without operculum or teeth.

There are two subtypes of arthrodontous peristome.^[1]

1. The first is termedhaplolepidous and consists of a single circle of 16 peristome teeth.
2. The second type is thediplolepidous peristome found in subclassBryidae. In this type, there are two rings of peristome teeth—an innerendostome (short forendoperistome) and anexostome. The endostome is a more delicate membrane, and its teeth are aligned between the teeth of the exostome. There are a few mosses in the Bryopsida that have no peristome in their capsules. These mosses still undergo the same cell division patterns in capsule development, but the teeth do not fully develop.

Inpitcher plants, the peristome is a reflexed ring (or partial ring) of tissue that surrounds the entrance to the digestive tube in these plants. It often (for example inCephalotus andNepenthes) possesses sharp, overhanging 'teeth' which aid in prey retention. It is often studded with nectar secreting glands, hence its popular name,nectar roll.

Thebasidiocarps of somegasteroid fungi – such aspuffballs andearthstars – 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.^[2]

The peristome is the margin of theaperture of agastropod shell. It is the edge of the lip of the shell. 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 themouth or invertebrates such asechinoderms orearthworms.^[3]

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• Plant anatomy
• Mollusc anatomy
• Fungal morphology and anatomy

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