Peristome

Definition

The rim, collar, or ring of tissue surrounding an opening to an organ or body cavity; in arthropods, often refers to the cuticular margin encircling the mouth, spiracles, or genital aperture. Structurally, it may be simple, toothed, fringed, or elaborated into lobes, ridges, or sclerotized plates that serve in feeding, respiration, or copulation.

Etymology

From Greek peri- (around) + stoma (mouth)

Example

In many spiders (Araneae), the peristome forms a sclerotized ring around the base of the chelicerae, often bearing teeth or ridges that interlock with the fang when at rest. In some insect spiracles, the peristome is expanded into a filter plate or valve lip that regulates airflow.

Related Terms

• epistome
• stoma
• Spiracle
• gnathosoma
• podonotal shield
• peritreme

Usage Notes

In entomology and arachnology, peristome is most commonly encountered in descriptions of mouthpart architecture (especially Acari and Araneae) and spiracle morphology. It should be distinguished from peritreme, which specifically denotes the sclerotized rim of a spiracle or tracheal opening, whereas peristome is the broader anatomical term for any surrounding rim. In bryology and botany, the term has independent but analogous usage for structures surrounding sporangial or calyx openings—context determines which domain is intended.