Everything about Peristome totally explained
The word
peristome is derived from the
Greek peri, meaning 'around' or 'about', and
stoma, 'mouth'. It is a term used to describe various structures in
plants and
invertebrate animals, such as
molluscs, that surround an opening to an organ.
Moss peristomes
In
mosses, 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) which falls off when the
spores 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 specially thickened
cell 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 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. The first is termed
haplolepidous and consists of a single circle of 16 peristome teeth. The second type is the
diplolepidous peristome fround 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 don't fully develop.
Other peristomes
In
pitcher 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 in
Cephalotus) possesses sharp, overhanging 'teeth' which aid in prey retention. It is often studded with nectar secreting glands, hence its popular name, 'nectar roll'.
The peristome is the margin of the
aperture of a
gastropod shell.
Further Information
Get more info on 'Peristome'.
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