Operculum (gastropod)
Encyclopedia
Corneous
Corneous is a biological and medical term meaning horny, in other words made out of a substance similar to that of horns and hooves in some mammals....
or calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
anatomical structure which exists in many (but not all) groups of sea snail
Sea snail
Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....
s and freshwater snail
Freshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....
s, and also in a few groups of land snail
Land snail
A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod mollusks that have shells, It is not always an easy matter to say which species are terrestrial, because some are more or less...
s. In other words, this structure is found in some marine and freshwater gastropods, and in a minority of terrestrial gastropods, including the families Helicinidae
Helicinidae
Helicinidae is a family of small tropical land snails which have an operculum. They are terrestrial operculate gastropod mollusks in the superfamily Helicinoidea....
, Cyclophoridae
Cyclophoridae
Cyclophoridae is a taxonomic family of small to large tropical land snails with an operculum, terrestrial gastropod mollusks in the informal group Architaenioglossa belonging to the clade Caenogastropoda .- Taxonomy :This family consists of the following subfamilies according to the taxonomy of...
, Aciculidae
Aciculidae
The Aciculidae are a family of minute land snails which have opercula. In other words, Aciculidae are terrestrial operculate gastropods....
, Maizaniidae
Maizaniidae
Maizaniidae is a family of minute land snails with an operculum, terrestrial gastropod mollusks in the superfamily Cyclophoroidea .- Genera:...
, Pomatiidae
Pomatiidae
The family Pomatiidae is a taxonomic family of small operculate land snails, terrestrial gastropod mollusks that can be found over the warmer parts of the Old World. In the older literature, this family is designated as Pomatiasidae....
, 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
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
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
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
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
Strombidae
Strombidae, commonly known as the true conchs, is a taxonomic family of medium-sized to very large sea snails, marine gastropod mollusks in the superfamily Stromboidea....
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
Amphiboloidea
Amphiboloidea is a taxonomic superfamily of air-breathing land snails.- 2005 taxonomy :According to the taxonomy of the Gastropoda , it is a superfamily in the informal group Basommatophora, within the Pulmonata....
. However, some terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
pulmonate species are capable of secreting an epiphragm
Epiphragm
An epiphragm is a temporary structure which can be created by many species of shelled, air-breathing land snails, terrestrial pulmonate gastropod mollusks. It can also be created by freshwater snails when temporary pools dry up....
, 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.
NOTE: in ammonite
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
s (extinct shelled cephalopods), a calcareous structure known as the aptychus
Aptychus
An aptychus is a type of marine fossil, a hard anatomical structure like a curved shelly plate, which was part of the body of an ammonite. Paired aptychi have, on rare occasions, been found at or within the aperture of ammonite shells....
(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
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
apparatus of ammonites.
Functions
Perhaps the most essential function of the operculum in gastropods is to allow snails to resist drying out, or desiccationDesiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
. This is very important in intertidal marine snails during low tide, and this also enables operculate freshwater and land snails to survive periods of drought and dry weather.
In those marine species where the operculum completely seals the shell, it can also serve as a protection against predators when the snail body is retracted.
Anatomy
Buccinum
Buccinum is a genus of medium-sized sea snails with an operculum, marine gastropod mollusks in the family Buccinidae, the true whelks.Snails in this genus are commonly called whelks, a name that is however shared with several related and unrelated species...
a layer of long cylindrical epithelial cells, with mostly distinct nuclei, and long divided processes enter between the muscular fibres. The operculum, a cuticular development of these cells, is composed, as may be seen in the corneous opercula of Murex
Murex
Murex is a genus of medium to large sized predatory tropical sea snails. These are carnivorous marine gastropod molluscs in the family Muricidae, commonly calle "murexes" or "rock snails"...
,
Purpura
Purpura (gastropod)
Purpura is a genus of sea snails, marine gastropod mollusks in the family Muricidae, the murex snails or rock snails.-Species:Species within the genus Purpura include:* Purpura bufo Lamarck, 1822* Purpura mancinella...
, Triton, of very thin superimposed layers. The cylindrical cells are attached with their head to the lowermost layer.
The operculum grows in size as the shell grows, such that the operculum remains in proportion to the apertural
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
size. In many species, when the animal is active and crawling, part of the underside of the shell rests on the outer surface of the operculum.
In many species of marine shelled snails which live subtidally, the operculum is greatly reduced in size, and no longer serves to seal the shell entrance. In a large number of families it has been eliminated completely.
In species of conch
Conch
A conch is a common name which is applied to a number of different species of medium-sized to large sea snails or their shells, generally those which are large and have a high spire and a siphonal canal....
es, the operculum is elongated and claw-shaped, and is used to dig into the sand to enable the conch to perform a leaping type of locomotion
Animal locomotion
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
.
The structure of the operculum can be described as follows:
- concentric: the nucleus is central or subcentral as in LithoglyphusLithoglyphusLithoglyphus is a genus of freshwater snails with gills and an operculum, a gastropod mollusk in the family Lithoglyphidae.- Taxonomy :Lithoglyphus is the type genus of the family Lithoglyphidae....
and Ampullaria, and in other the nucleus is near the parietal margin of the shell. - imbricated, or lamellar: when it grows only on one side, and the nucleus is marginal, as in Purpura, XenophoraXenophoraXenophora, common name carrier shells, is a genus of medium sized to large sea snails, marine gastropod mollusks in the family Xenophoridae, the carrier snails or carrier shells.-Description:...
, and PaludomusPaludomusPaludomus is a genus of tropical freshwater snails with an operculum, aquatic gastropod mollusks in the family Paludomidae.Paludomus is the type genus of the family Paludomidae.-Species:...
. - claw-shaped, or unguiculate: with the nucleus apical or in front, as in TurbinellaTurbinellaTurbinella is a genus of large sea snails with a gill and an operculum, marine gastropod mollusks in the family Turbinellidae. These species are sometimes known as "chanks" or "chank shells"...
and FususFususFusus is a genus of sea snail, a marine gastropod mollusk in the family Fasciolariidae, the spindle snails, the tulip snails and their allies. The name Fusus is a temporary name and has become invalid as a taxonomical name...
; it is claw-shaped and serrated in StrombusStrombusStrombus, common name the true conchs, is a genus of medium to large sea snails with an operculum, marine gastropod mollusks in the family Strombidae, the true conchs and their immediate relatives.... - spiral : when it grows only on one edge, and revolves as it grows ; it is always sinistral in dextral shells.
- paucispiral or oligogyrous: with few spirals as in LittorinaLittorinaLittorina is a genus of small sea snails, marine gastropod molluscs in the family Littorinidae, the winkles or periwinkles. These small snails live in the tidal zone of rocky shores.-Overview:...
. - subspiral or scarcely spiral, in ThiaraThiara (gastropod)Thiara is a genus of freshwater snails, aquatic gastropod mollusks in the family Thiaridae.-Species:Species with accepted names within the genus Thiara include:* Thiara rodericensis...
- multispiral or polygyrous: having many closely spaced spirals as in TrochusTrochusTrochus is a genus of medium-sized to very large sea snails. They are marine gastropod molluscs in the family Trochidae, the top snails....
where they sometimes amount to twenty; the number of turns which the operculum makes is not determined by the number of whorls in the shell, but by the curvature of the aperture, and the necessity that the operculum should revolve fast enough to fit it constantly.
- articulated, when it has a projection, as in NeritaNeritaNerita is a genus of medium-sized sea snails with a gill and an operculum, marine gastropod molluscs in the family Neritidae, the nerites.This is the type genus of the family Neritidae.-Distribution and habitat:...
- radiated is a modification of the articulated operculum in which the spiral is not so evident as in NavicellaNavicellaNavicella is a genus of fungi in the family Massariaceae. "Navicella" is Italian for "small ship", and also found in English in reference to a mosaic by Giotto in St Peter's, Rome, now so often restored as to be effectively lost. In the 19th century the genus of molluscs now called Septaria were...
There are two basic types of opercula in terms of their material composition:
- The most common kind of operculum is composed of a thin to rather thick corneous protein material, which is yellow to brownish in color and is usually somewhat translucent. This matter is supple when in its natural state but may become brittle when it is dried out. The operculum varies in shape, depending on the family of snails and the shape of the aperture of their shells.
- The other kind of operculum is restricted to a few families of gastropods including the TurbinidaeTurbinidaeTurbinidae, the turban snails, are a family of small to large marine gastropods. Turbinidae have a strong, thick calcareous operculum readily distinguishing them from the somewhat similar Trochidae or top snails, which have a corneous operculum...
. This operculum structure has a corneous base with a heavy calcareousCalcareousCalcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...
overlay. The calcareous surface in some genera has color or ornamentation of various kinds including, for example, pustules and incised grooves.
The different shapes of opercula can include ungulate (hooflike), claw-like, or ovate. The type and shape of the operculum is used to help identify and classify related groups (genera) of land operculates, and likewise some marine operculates.
Human uses
The oldest known human depiction of an operculum together with the shell of Charonia tritonisCharonia tritonis
Charonia tritonis, common name Triton's trumpet, is a species of very large sea snail, a marine gastropod mollusc in the family Ranellidae, the tritons.Also see Charonia or Triton .-Distribution:...
is a seal made by Minoan civilization
Minoan civilization
The Minoan civilization was a Bronze Age civilization that arose on the island of Crete and flourished from approximately the 27th century BC to the 15th century BC. It was rediscovered at the beginning of the 20th century through the work of the British archaeologist Arthur Evans...
.
As incense material
Opercula of certain gastropods, especially varieties from the Red SeaRed Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, have long served as an incense
Incense
Incense is composed of aromatic biotic materials, which release fragrant smoke when burned. The term "incense" refers to the substance itself, rather than to the odor that it produces. It is used in religious ceremonies, ritual purification, aromatherapy, meditation, for creating a mood, and for...
material in ancient Jewish tradition, as well as Arabian cultures. The operculum of conch species Strombus tricornis
Strombus
Strombus, common name the true conchs, is a genus of medium to large sea snails with an operculum, marine gastropod mollusks in the family Strombidae, the true conchs and their immediate relatives....
and Lambis truncata sebae
Conch
A conch is a common name which is applied to a number of different species of medium-sized to large sea snails or their shells, generally those which are large and have a high spire and a siphonal canal....
are most commonly used in regions near the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
. Opercula from these conches may be the onycha
Onycha
Onycha , along with equal parts of stacte, galbanum, and frankincense, was one of the components of the consecrated Ketoret which appears in the Torah book of Exodus and was used in the Jerusalem's Solomon's Temple. This formula was to be incorporated as an incense, and was not to be duplicated...
incense material which is described in the Book of Exodus.
Operculum powder is also an important ingredient in Chinese
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese incense making. Here it is called "bèi xiāng" (Chinese: 貝香; lit. sea shell fragrance) or "kai kou" (Japanese: 甲香, lit. shell/armour fragrance) respectively. Incense producers in these countries use the operculum of many conches and other marine snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s, including those found in Southeast Asia, South America, and East Africa. The opercula are traditionally treated with vinegar
Vinegar
Vinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...
, alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
in order to remove any fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
y smell. The clean opercula are then ground to a powder and used as a scent fixative, in a technique similar to that used in perfume
Perfume
Perfume is a mixture of fragrant essential oils and/or aroma compounds, fixatives, and solvents used to give the human body, animals, objects, and living spaces "a pleasant scent"...
s with certain plant resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
s.
When burnt on its own, high quality operculum reportedly smells of castoreum
Castoreum
Castoreum is the exudate from the castor sacs of the mature North American Beaver Castor canadensis and the European Beaver Castor fiber. Within the zoological realm, castoreum is the yellowish secretion of the castor sac in combination with the beaver's urine, used during scent marking of territory...
or other animal musk
Musk
Musk is a class of aromatic substances commonly used as base notes in perfumery. They include glandular secretions from animals such as the musk deer, numerous plants emitting similar fragrances, and artificial substances with similar odors. Musk was a name originally given to a substance with a...
s, while that of lower quality is reminiscent of burnt hair.
As a gemstone or decorative object
The operculum of certain species of TurbinidaeTurbinidae
Turbinidae, the turban snails, are a family of small to large marine gastropods. Turbinidae have a strong, thick calcareous operculum readily distinguishing them from the somewhat similar Trochidae or top snails, which have a corneous operculum...
is sometimes used as a very inexpensive organic "gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
" in rings, bracelets, amulets etc. These opercula are commonly known as "cats eye" (or more recently "Shiva's eye").
The turban snail Turbo petholatus
Turbo petholatus
Turbo petholatus is a species of sea snail, marine gastropod mollusk in the family Turbinidae....
is the species whose operculum is most widely used, although the operculum of other species of Turbo are sometimes used. The operculum is almost always given a solid setting, because it has one unattractive flat and corneous
Corneous
Corneous is a biological and medical term meaning horny, in other words made out of a substance similar to that of horns and hooves in some mammals....
side where it was attached to the animal, and one roughly hemispherical glossy side, which, in the case of T. petholatus has an attractive dark green area.
Opercula are often used in Northwest Coast Native art, as detailing in masks, panels and paddles. These objects are used to represent the teeth in masks, and are used as a decorative element in many of the objects which form an important part in the art and culture of Northwest Coast people, including dishes for food, bentwood boxes and rattles.
Friedrich Ratzel
Friedrich Ratzel
Friedrich Ratzel was a German geographer and ethnographer, notable for first using the term Lebensraum in the sense that the National Socialists later would.-Life:...
in The History of Mankind reported in 1896 that, in Oceania, chains and girdles composed of the coloured opercula of certain shells were considered valuable ornaments.
As paperweights
The largest opercula of Turbo marmoratusTurbo marmoratus
Turbo marmoratus, the marbled turban or great green turban, is a large species of marine gastropod with a calcareous operculum in the family Turbinidae, the turban snails. These large snails live in tropical reefs in the Indian and western Pacific oceans. They are nocturnal and feed on algae.The...
have been used as paperweights.
External links
- Pictures of diverse gastropod opercula. This site also provides fairly extensive material on the growth, development, and physiology of the gastropod operculum as well as dozens of pictures of both the operculum and its host shell.
- Photo of opercula of some BusyconBusyconBusycon is a genus of very large edible sea snails, marine gastropod mollusks in the family Buccinidae. These snails are commonly known in the United States as whelks or Busycon whelks....
and BusycotypusBusycotypusBusycotypus is a genus of very large sea snails, marine gastropod mollusks in the family Buccinidae. In the USA, these are commonly known as whelks.-Subgenera and species:Subgenera and species within the genus Busycotypus are as follows:...
' species