What is "operculum"

Operculum \O*per"cu*lum\, n.; pl. L. Opercula, E. Operculums. [L., a cover or lid, fr. operire to cover.]

1. (Bot.)

   1. The lid of a pitcherform leaf.

   2. The lid of the urnlike capsule of mosses.

2. (Anat.)

   1. Any lidlike or operculiform process or part; as, the opercula of a dental follicle.

   2. The fold of integument, usually supported by bony plates, which protects the gills of most fishes and some amphibians; the gill cover; the gill lid.

   3. The principal opercular bone in the upper and posterior part of the gill cover.

3. (Zo["o]l.)

   1. The lid closing the aperture of various species of shells, as the common whelk. See Illust. of Gastropoda.

   2. Any lid-shaped structure closing the aperture of a tube or shell.

1713, from Latin operculum "cover, lid," from operire "to cover, close" (see weir), with instrumental suffix *-tlom. Related: Opercular.

n. A covering flap or lidlike structure in plants and animals, such as a gill cover

1. n. a hard flap serving as a cover for (a) the gill slits in fishes or (b) the opening of the shell in certain gastropods when the body is retracted

2. [also: opercula (pl)]

An operculum is a small covering or lid, and is widely used in descriptions of animals and plants.

Operculum may refer to:

In human biology:

• Operculum (in pregnancy), the cervical mucus plug that blocks the cervix of the uterus after conception
• Operculum (brain), the part of the brain covering the insula
• Operculum (dentistry), a small flap of tissue which may cover an erupting or partially erupted molar

In animal biology:

• Operculum (animal), a structure resembling a lid or a small door that opens and closes
  • Operculum (fish), a flap of the bony fish covering the gills
  • Operculum (gastropod), a sort of trapdoor used to close the aperture of some snails
  • Operculum (bird), a structure which covers the nares of some birds
  • Operculum (bryozoa), a lid on the orifice of some bryozoans
  • Operculum, the anterior end of the fruit fly puparium, through which the adult fly emerges

In botany:

• Operculum (botany), various lids and flaps pertaining to plants, algae and fungi

In human brain anatomy, an operculum (Latin, meaning "little lid") (pl. opercula), may refer to the frontal, temporal, or parietal operculum, which together cover the insula as the opercula of insula. It can also refer to the occipital operculum, part of the occipital lobe.

The insular lobe is a portion of the cerebral cortex that has invaginated to lie deep within the lateral sulcus. It sits like an island (the meaning of insular) almost surrounded by the groove of the circular sulcus and covered over and obscured by the insular opercula.

A part of the parietal lobe, the frontoparietal operculum, covers the upper part of the insular lobe from the front to the back. The opercula lie on the precentral and postcentral gyri (on either side of the central sulcus). The part of the parietal operculum that forms the ceiling of the lateral sulcus functions as the secondary somatosensory cortex.

The operculum, meaning little lid, (plural: opercula or operculums) is a corneous or calcareous anatomical structure like a trapdoor which exists in many (but not all) groups of sea snails and freshwater snails, and also in a few groups of land snails. In other words, this structure is found in some marine and freshwater gastropods, and in a minority of terrestrial gastropods, including the families Helicinidae, Cyclophoridae, Aciculidae, Maizaniidae, Pomatiidae, etc.

The operculum is attached to the upper surface of the foot and in its most complete state, it serves as a sort of "trapdoor" to close the aperture of the shell when the soft parts of the animal are retracted. The shape of the operculum varies greatly from one family of gastropods to another. It is fairly often circular, or more or less oval in shape. In species where the operculum fits snugly, its outline corresponds exactly to the shape of the aperture of the shell and it serves to seal the entrance of the shell. A small air-hole may remain to aid respiration, especially during aestivation.

Many families have opercula that are reduced in size, and which are not capable of closing the shell aperture. Opercula have sometimes been modified: in the Strombidae the operculum is claw-shaped and is used to push into the substrate in a leaping form of locomotion.

Virtually all pulmonate snails are inoperculate, i.e. they do not have an operculum, with the exception of the Amphiboloidea. However, some terrestrial pulmonate species are capable of secreting an epiphragm, a temporary structure that can in some cases serve some of the same functions as an operculum. The epiphragm may be distinguished from the true operculum by its homogeneity and want of growth marks.

In ammonites (extinct shelled cephalopods), a calcareous structure known as the aptychus (plural aptychi) existed. When these were first described they were thought to be valves of a bivalve species, then for many years after that they were considered to be a form of paired or single operculum-like structures belonging to ammonites. More recently the aptychus or paired aptychi have been hypothesized to be a jaw apparatus of ammonites.

The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body.

The operculum is composed of four fused bones; the opercle, preopercle, interopercle, and subopercle. The posterior rim of the operculum is equipped with a flexible, ribbed structure which acts as a seal to prevent reverse water flow during respiration. The morphology of this anatomical feature varies greatly between species. For example, the bluegill (Lepomis macrochirus) has a posteriorly and dorsally oriented rounded extension with a small black splotch present. In some species, the operculum can push water from the buccal cavity through the gills.

For some fish, opercula are vital in obtaining oxygen. They open as the mouth closes, causing the pressure inside the fish to drop. Water then flows towards the lower pressure across the fish's gill lamellae, allowing some oxygen to be absorbed from the water.

Whereas the cartilaginous ratfishes have soft and flexible opercular flaps, the sharks, rays and relatives ( elasmobranch fishes) lack opercula completely and respire instead through a series of gill slits perforating the body wall. Without opercula, other methods of getting water to the gills are required, such as ventilation.

An operculum or (in plural) opercula are botanical terms describing a certain structure or structures of certain vascular plants, mosses, or fungi which act as a cap, flap, or lid. In vascular plants, an operculum may also be called a bud cap.

Examples of structures identified as opercula include:

• A flap of the sporangium of a moss, covering the peristome (appendages surrounding the mouth of a moss capsule).
• The cap of the ascus in certain ascomycetous fungi.
• A lid covering the aperture of pollen grains.
• The bud cap covering the flowers of Eucalyptus and Corymbia trees which falls off as they open.
• The covering of a pyxidium ( capsule whose upper part falls off when the seeds are released) of a plant, such as the plantain.
• The flared leaflet that prevents a pitcher plant from accumulating rainwater.

In the bryozoan order Cheilostomata, the operculum is a calcareous or chitinous lid-like structure that protects the opening through which the polypide protrudes.

Many species have modified the operculum in specialized zooids (avicularia) to form a range of mandibles (probably for defense) or hair-like setae (probably for cleaning, or in some unattached species, such as Selenaria, for locomotion).

The cylcostome family Eleidae also convergently evolved an opercular structure during the Early Cretaceous to Paleocene.

An operculum (animal) is an anatomical feature, a stiff structure resembling a lid or a small door that opens and closes, and thus controls contact between the outside world and an internal part of an animal. Examples include:

• An operculum (gastropod), a single lid that (in its most complete form) closes the aperture of the shell when the animal is retracted, and thus protects the internal soft parts of the animal that are not completely covered by the shell. The operculum lies on the top rear part of the foot. When the foot is retracted, the operculum is rotated 180° and closes the shell.
• An operculum (fish), a flap that covers the gills in bony fishes and chimaeras.
• The cover that rapidly opens a cnida of a cnidarian such as a jellyfish or a sea anemone. The lid may be a single hinged flap or three hinged flaps arranged like slices of pie.
• In insects, the operculum is the name for one or more lids covering the tympanal cavity. A subgenital operculum is exhibited in phasmoidea and grasshoppers and allies ( orthoptera).