Editing Peristome

'''Peristome''' (from the [[Greek language|Greek]] ''peri'', meaning 'around' or 'about', and ''stoma'', 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Some [[plant]]s, [[fungi]], and shelled [[gastropods]] have peristomes.

==In mosses==
[[File:Dicranella varia sporogon.jpeg|left|thumb|Arthrodontous capsule of the [[moss]] ''Dicranella varia'']]
[[File:Bryum capillare peristome.jpg|thumb|upright|Peristome of ''[[Bryum capillare]]'']]
In [[moss]]es, the peristome is a specialized structure in the [[sporangium]] that allows for gradual [[spore]] discharge, instead of releasing them all at once.  

Most mosses produce a capsule with a lid (the [[operculum (botany)|operculum]]) which falls off when the [[spore]]s inside are mature and thus ready to be dispersed.  The opening thus revealed is called the ''stoma'' (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 thickened [[cell wall]]s.  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 termed '''arthrodontous''' and is found in the moss subclass [[Bryopsida]].  In other groups of mosses, the capsule is either '''nematodontous''' with an attached operculum (as in the [[Polytrichopsida]]), or else splits open without operculum or teeth.

There are two subtypes of arthrodontous peristome.<ref>Edwards, S.R. (1984). "Homologies and inter-relationships of moss peristomes", pages 658–695 ''in'' R. M. Schuster (Ed.) ''New Manual of Bryology''. (Japan: The Hattori Botanical Laboratory). {{Listed Invalid ISBN|49381633045}}.</ref>  
# The first is termed '''haplolepidous''' and consists of a single circle of 16 peristome teeth.  
# The second type is the '''diplolepidous''' peristome found in subclass [[Bryidae]].  In this type, there are two rings of peristome teeth—an inner '''endostome''' (short for ''endoperistome'') and an '''exostome'''.  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.

==In pitcher plants==
[[File:Sarracenia pitcher anatomy basic.jpg|thumb|right|Diagram showing the location of the peristome on a ''[[Sarracenia]]'' ([[North America]]n [[pitcher plant]])]]
In [[pitcher plant]]s, 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 in ''[[Cephalotus]]'' and ''[[Nepenthes]]'') possesses sharp, overhanging 'teeth' which aid in prey retention. It is often studded with nectar secreting glands, hence its popular name, '''nectar roll'''.

==In fungi==
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.<ref>Pegler, D.N. et al. 1995. ''British Puffballs, Earthstars and Stinkhorns''. (Kew: Royal Botanic Gardens)</ref>
[[File:Geastrum pectinatum 135825.jpg|thumb|left|The earthstar ''[[Geastrum pectinatum]]'' showing a beaked peristome]]

==In shelled gastropods==
[[File:Cepaea nemoralis unten.jpeg|thumb|The ventral surface of a shell of ''[[Cepaea nemoralis]]''. The peristome is thickened and dark in an adult snail.]]

{{main|Lip (gastropod)}}

The peristome is the margin of the [[Aperture (mollusc)|aperture]] of a [[gastropod 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.

==In other invertebrates==
The peristome is any of the structures or sets of parts that surround the [[mouth]] or invertebrates such as [[echinoderm]]s or [[earthworm]]s.<ref>[https://www.collinsdictionary.com/dictionary/english/peristome Peristome] Collins Dictionary. </ref>

==References==
<references/>

==External links==
* [http://dictionary.reference.com/browse/Peristome Dictionary definition]

{{Gastropod anatomy}}

[[Category:Plant anatomy]]
[[Category:Mollusc anatomy]]
[[Category:Fungal morphology and anatomy]]