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A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. The shell is part of the body of the animal. Empty seashells are often found washed up on
beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc s ...
es by
beachcombers ''The Beachcombers'' is a Canadian comedy-drama television series that ran on CBC Television from October 1, 1972, to December 12, 1990. With over 350 episodes, it is one of the longest-running dramatic series ever made for English-language Can ...
. The shells are empty because the animal has died and the soft parts have decomposed or been eaten by another animal. A seashell is usually the
exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...
of an
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chorda ...
(an animal without a backbone), and is typically composed of calcium carbonate or
chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
. Most shells that are found on beaches are the shells of
marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
s, partly because these shells are usually made of calcium carbonate, and endure better than shells made of chitin. Apart from mollusk shells, other shells that can be found on beaches are those of
barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosiv ...
s,
horseshoe crab Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to ar ...
s and brachiopods. Marine
annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
worms in the family Serpulidae create shells which are tubes made of calcium carbonate cemented onto other surfaces. The shells of sea urchins are called "
test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...
s", and the moulted shells of
crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all th ...
s and lobsters are exuviae. While most seashells are external, some
cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, a ...
have internal shells. Seashells have been used by humans for many different purposes throughout history and prehistory. However, seashells are not the only kind of shells; in various habitats, there are shells from freshwater animals such as freshwater mussels and freshwater snails, and shells of land snails.


Terminology

When the word "seashells" refers only to the shells of marine mollusks, then studying seashells is part of
conchology Conchology () is the study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs; however, malacology is the study of molluscs as whole organisms, whereas conchology is confined to the study of their shells. It includ ...
. Conchologists or serious collectors who have a scientific bias are in general careful not to disturb living populations and habitats: even though they may collect a few live animals, most responsible collectors do not often over-collect or otherwise disturb ecosystems. The study of the entire molluscan animal (as well as the shell) is known as malacology; a person who studies mollusks is known as a malacologist.


Occurrence

Seashells are commonly found in beach drift, which is natural detritus deposited along strandlines on
beach A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc s ...
es by the
wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (re ...
s and the
tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...
s. Shells are very often washed up onto a beach empty and clean, the animal having already died. Empty seashells are often picked up by beachcombers. However, the majority of seashells which are offered for sale commercially have been collected alive (often in bulk) and then killed and cleaned, specifically for the commercial trade. This type of large-scale exploitation can sometimes have a strong negative impact on local
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s, and sometimes can significantly reduce the distribution of rare species.


Shell synthesis

Seashells are created by the
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is est ...
s that use them for protection. Molluscs have an outside layer of tissues on their bodies the
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
which creates the shell material and which connects the shell to the mollusc. The specialized cells in the mantle form the shell using different
minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
and
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s. The proteins are then used to create the framework that supports the growing shell. Calcium carbonate is the main compound of shell structure, aiding in
adhesion Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can ...
.


Molluscan seashells

The word ''seashell'' is often used to mean only the shell of a
marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
. Marine mollusk shells that are familiar to beachcombers and thus most likely to be called "seashells" are the shells of marine species of bivalves (or clams),
gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
s (or
snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...
s), scaphopods (or tusk shells), polyplacophorans (or
chiton Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as gumboots or sea cradles or coat-of-mail she ...
s), and
cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s (such as nautilus and spirula). These shells are very often the most commonly encountered, both in the wild, and for sale as decorative objects. Marine species of gastropods and bivalves are more numerous than land and freshwater species, and the shells are often larger and more robust. The shells of marine species also often have more
sculpture Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable ...
and more color, although this is by no means always the case. In the
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
and sub-tropical areas of the planet, there are far more species of colorful, large, shallow water shelled marine mollusks than there are in the temperate zones and the regions closer to the poles. Although there are a number of species of shelled mollusks that are quite large, there are vast numbers of extremely small species too, see micromollusks. Not all mollusks are marine. There are numerous land and freshwater mollusks, see for example
snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...
and
freshwater bivalves Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves. The majority of species of bivalve molluscs l ...
. In addition, not all mollusks have an external shell: some mollusks such as some cephalopods (squid and octopuses) have an internal shell, and many mollusks have no shell, see for example
slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a ...
and nudibranch.


Bivalves

Bivalves are often the most common seashells that wash up on large sandy beaches or in sheltered
lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into '' coastal lagoons'' (or ''barrier lagoons ...
s. They can sometimes be extremely numerous. Very often the two valves become separated. There are more than 15,000 species of bivalves that live in both marine and freshwater. Examples of bivalves are clams, scallops, mussels, and oysters. The majority of bivalves consist of two identical shells that are held together by a flexible hinge. The animal's body is held protectively inside these two shells. Bivalves that do not have two shells either have one shell or they lack a shell altogether. The shells are made of calcium carbonate and are formed in layers by secretions from the mantle. Bivalves, also known as pelecypods, are mostly filter feeders; through their gills, they draw in water, in which is trapped tiny food particles. Some bivalves have eyes and an open circulatory system. Bivalves are used all over the world as food and as a source of pearls. The larvae of some freshwater mussels can be dangerous to fish and can bore through wood.
Shell Beach, Western Australia Shell Beach is a beach in the Shark Bay region of Western Australia, located south-east of Denham. Situated on the northeastern side of the Taillefer Isthmus along the L'Haridon Bight, the beach is covered with shells for a stretch to a de ...
, is a beach which is entirely made up of the shells of the cockle '' Fragum erugatum''.


Gastropods

Certain species of gastropod seashells (the shells of sea snails) can sometimes be common, washed up on sandy beaches, and also on beaches that are surrounded by rocky marine habitat.


Polyplacophorans

Chiton Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as gumboots or sea cradles or coat-of-mail she ...
plates or valves often wash up on beaches in rocky areas where chitons are common. Chiton shells, which are composed of eight separate plates and a girdle, usually come apart not long after death, so they are almost always found as disarticulated plates. Plates from larger species of chitons are sometimes known as "butterfly shells" because of their shape.


Cephalopods

Only a few species of
cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s have shells (either internal or external) that are sometimes found washed up on beaches. Some cephalopods such as '' Sepia'', the cuttlefish, have a large internal shell, the
cuttlefish bone Cuttlebone, also known as cuttlefish bone, is a hard, brittle internal structure (an internal shell) found in all members of the family Sepiidae, commonly known as cuttlefish, within the cephalopods. In other cephalopod families it is cal ...
, and this often washes up on beaches in parts of the world where cuttlefish are common. '' Spirula spirula'' is a deep water squid-like cephalopod. It has an internal shell which is small (about 1 in or 24 mm) but very light and buoyant. This chambered shell floats very well and therefore washes up easily and is familiar to beachcombers in the tropics. '' Nautilus'' is the only genus of cephalopod that has a well-developed external shell. Females of the cephalopod genus '' Argonauta'' create a papery egg case which sometimes washes up on tropical beaches and is referred to as a "paper nautilus". The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common in certain areas as
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s.


Molluscan seashells used by other animals

Empty molluscan seashells are a sturdy, and usually readily available, "free" resource which is often easily found on beaches, in the
intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species ...
, and in the shallow subtidal zone. As such they are sometimes used
second-hand Used goods mean any item of personal property offered for sale not as new, including metals in any form except coins that are legal tender, but excluding books, magazines, and postage stamps. Risks Furniture, in particular bedding or upholstere ...
by animals other than humans for various purposes, including for protection (as in hermit crabs) and for construction.


Mollusks

* Carrier shells in the family
Xenophoridae Xenophoridae, commonly called carrier shells, is a family of medium-sized to large sea snails, marine gastropod mollusks in the clade Littorinimorpha. According to the taxonomy of the Gastropoda by Bouchet & Rocroi (2005) the family Xenophor ...
are marine shelled gastropods, fairly large sea snails. Most species of xenophorids cement a series of objects to the rim of their shells as they grow. These objects are sometimes small pebbles or other hard detritus. Very often shells of bivalves or smaller gastropods are used, depending on what is available on the particular substrate where the snail itself lives. It is not clear whether these shell attachments serve as
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
, or whether they are intended to help prevent the shell sinking into a soft substrate. * Small
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
es sometimes use an empty shell as a sort of cave to hide in, or hold seashells around themselves as a form of protection like a temporary fortress.


Invertebrates

* Almost all genera of hermit crabs use or "wear" empty marine gastropod shells throughout their lifespan, in order to protect their soft abdomens, and in order to have a strong shell to withdraw into if attacked by a predator. Each individual hermit crab is forced to find another gastropod shell on a regular basis, whenever it grows too large for the one it is currently using. :Some hermit crab species live on land and may be found quite some distance from the sea, including those in the tropical genus '' Coenobita''.


Conchology

There are numerous popular books and
field guide A field guide is a book designed to help the reader identify wildlife (flora or fauna) or other objects of natural occurrence (e.g. rocks and minerals). It is generally designed to be brought into the "field" or local area where such objects e ...
s on the subject of shell-collecting. Although there are a number of books about land and freshwater mollusks, the majority of popular books emphasize, or focus exclusively on, the shells of marine mollusks. Both the science of studying mollusk shells and the hobby of collecting and classifying them are known as
conchology Conchology () is the study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs; however, malacology is the study of molluscs as whole organisms, whereas conchology is confined to the study of their shells. It includ ...
. The line between professionals and amateur enthusiasts is often not well defined in this subject, because many amateurs have contributed to, and continue to contribute to, conchology and the larger science of malacology. Many shell collectors belong to "shell clubs" where they can meet others who share their interests. A large number of amateurs collect the shells of marine mollusks, and this is partly because many shells wash up empty on beaches, or live in the intertidal or sub-tidal zones, and are therefore easily found and preserved without much in the way of specialized equipment or expensive supplies. Some shell collectors find their own material and keep careful records, or buy only "specimen shells", which means shells which have full collecting
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
: information including how, when, where, in what habitat, and by whom, the shells were collected. On the other hand, some collectors buy the more widely available commercially imported exotic shells, the majority of which have very little data, or none at all. To
museum A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make th ...
scientists, having full collecting data (when, where, and by whom it was collected) with a specimen is far more important than having the shell correctly identified. Some owners of shell collections hope to be able to donate their collection to a major natural history or zoology museum at some point, however, shells with little or no collecting data are usually of no value to science, and are likely not to be accepted by a major museum. Apart from any damage to the shell that may have happened ''before'' it was collected, shells can also suffer damage when they are stored or displayed. For an example of one rather serious kind of damage see
Byne's disease Byne's disease, more accurately known as Bynesian decay, is a peculiar and permanently damaging condition resulting from an ongoing chemical reaction which often attacks mollusk shells and other calcareous specimens that are in storage or on di ...
.


Shell clubs

There are a number of clubs or societies which consist of people who are united by a shared interest in shells. In the US, these clubs are more common in southerly coastal areas, such as
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...
and
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
, where the marine fauna is rich in species.


Identification

Seashells are usually identified by consulting general or regional shell-collecting
field guide A field guide is a book designed to help the reader identify wildlife (flora or fauna) or other objects of natural occurrence (e.g. rocks and minerals). It is generally designed to be brought into the "field" or local area where such objects e ...
s, and specific scientific books on different taxa of shell-bearing mollusks (
monograph A monograph is a specialist work of writing (in contrast to reference works) or exhibition on a single subject or an aspect of a subject, often by a single author or artist, and usually on a scholarly subject. In library cataloging, ''monogra ...
s) or "iconographies" (limited text – mainly photographs or other illustrations). (For a few titles on this subject in the US, see the list of books at the foot of this article.) Identifications to the species level are generally achieved by examining illustrations and written descriptions, rather than by the use of Identification keys, as is often the case in identifying plants and other phyla of invertebrates. The construction of functional keys for the identification of the shells of marine mollusks to the species level can be very difficult, because of the great variability within many species and families. The identification of certain individual species is often very difficult, even for a specialist in that particular family. Some species cannot be differentiated on the basis of shell character alone. Numerous smaller and more obscure mollusk species (see micromollusk) are yet to be discovered and named. In other words, they have not yet been differentiated from similar species and assigned scientific (binomial) names in articles in journals recognized by the International Commission on Zoological Nomenclature (ICZN). Large numbers of new species are published in the scientific literature each year. There are currently an estimated 100,000 species of mollusks worldwide.


Non-marine "seashells"

The term ''seashell'' is also applied loosely to mollusk shells that are not of marine origin, for example by people walking the shores of lakes and rivers using the term for the freshwater mollusk shells they encounter. Seashells purchased from tourist shops or dealers may include various freshwater and terrestrial shells as well. Non-marine items offered may include large and colorful tropical land snail shells, freshwater
apple snail Ampullariidae, commonly known as the apple snails, is a family of large freshwater snails, aquatic gastropod mollusks with a gill and an operculum. These snails simultaneously have a gill and a lung as functional respiratory structures, which ...
shells, and pearly freshwater
unionid mussel The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at its most diverse ...
shells. This can be confusing to collectors, as non-marine shells are often not included in their reference books.


Cultural significance


Currency

Seashells have been used as a medium of exchange in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean. * The most common species of shells to be used as currency have been '' Monetaria moneta'', the "money cowry", and certain dentalium tusk shells, used in North Western North America for many centuries. * Many of the tribes and nations all across the continent of Africa have historically used th
cowry
as their media of exchange. The cowry circulated, historically, alongside metal coins and goods, and foreign currencies. Being durable and easy to carry the cowry made a very favorable currency. * Some tribes of the
indigenous peoples of the Americas The Indigenous peoples of the Americas are the inhabitants of the Americas before the arrival of the European settlers in the 15th century, and the ethnic groups who now identify themselves with those peoples. Many Indigenous peoples of the A ...
used shells for wampum and
hair pipe A Hair pipe is a term for an elongated bead, more than 1.5 inches long, which are popular with American Indians, particularly from the Great Plains and Northwest Plateau. History In 1878, Joseph H. Sherburne became a trader to the Ponca people. ...
s. The Native American '' wampum belts'' were made of the shell of the
quahog The hard clam ('' Mercenaria mercenaria''), also known as the round clam, hard-shell (or hard-shelled) clam, or the quahog, is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince ...
clam.


Tools

Seashells have often been used as
tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates b ...
s, because of their strength and the variety of their shapes. * Giant clams (Family Tridacnidae) have been used as bowls, and when big enough, even as bathtubs and
baptism Baptism (from grc-x-koine, βάπτισμα, váptisma) is a form of ritual purification—a characteristic of many religions throughout time and geography. In Christianity, it is a Christian sacrament of initiation and adoption, almost ...
al fonts. * ''
Melo melo ''Melo melo'', common name the Indian volute or bailer shell, is a very large edible sea snail, a marine gastropod mollusc in the family Volutidae, the volutes. Distribution The distribution of this species is restricted to Southeast Asia, fr ...
'', the "bailer volute", is so named because Native Australians used it to bail out their canoes. * Many different species of bivalves have been used as scrapers, blades, clasps, and other such tools, due to their shape. * Some marine gastropods have been used for oil lamps, the oil being poured in the aperture of the shell, and the siphonal canal serving as a holder for the wick.


Horticulture

Because seashells are in some areas a readily available bulk source of calcium carbonate, shells such as
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
shells are sometimes used as soil conditioners in
horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
. The shells are broken or ground into small pieces in order to have the desired effect of raising the pH and increasing the
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
content in the soil.


Religion and spirituality

Seashells have played a part in religion and spirituality, sometimes even as ritual objects. * In Christianity, the scallop shell is considered to be the symbol of Saint James the Great, see '' Pecten jacobaeus''. * In
Hinduism Hinduism () is an Indian religion or '' dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the world's third-largest, with over 1.2–1.35 billion followers, or 15–16% of the global p ...
, left-handed shells of ''
Turbinella pyrum ''Turbinella pyrum'', common names the chank shell, sacred chank or chank, also known as the divine conch, sometimes referred to simply as a conch, is a species of very large sea snail with a gill and an operculum, a marine gastropod mollusk i ...
'' (the sacred
shankha A Shankha ( conch shell) has religious ritual importance in Hinduism. It is the shell of any suitable sea snail which had a hole made for the performer's embouchure. In Hindu history, the shankha is a sacred emblem of The Hindu preserver god ...
) are considered to be sacred to the god
Vishnu Vishnu ( ; , ), also known as Narayana and Hari, is one of the principal deities of Hinduism. He is the supreme being within Vaishnavism, one of the major traditions within contemporary Hinduism. Vishnu is known as "The Preserver" withi ...
. The person who finds a left-handed chank shell (one that coils to the left) is sacred to Vishnu, as well. The chank shell also plays an important role in
Buddhism Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and ...
. * Cowries have often been considered to be symbols of female fertility. They were often treated as actual fertility charms. The dorsum of the shell resembles a pregnant belly, and the underside of the shell resembles a
vulva The vulva (plural: vulvas or vulvae; derived from Latin for wrapper or covering) consists of the external female sex organs. The vulva includes the mons pubis (or mons veneris), labia majora, labia minora, clitoris, vestibular bulbs, vulv ...
. In the South Indian state of Kerala, cowries are used for making astrological predictions. * In the
Santería Santería (), also known as Regla de Ocha, Regla Lucumí, or Lucumí, is an African diasporic religion that developed in Cuba during the late 19th century. It arose through a process of syncretism between the traditional Yoruba religion of We ...
religion, shells are used for
divination Divination (from Latin ''divinare'', 'to foresee, to foretell, to predict, to prophesy') is the attempt to gain insight into a question or situation by way of an occultic, standardized process or ritual. Used in various forms throughout history ...
. * The Moche culture of ancient
Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...
worshipped animals and the sea, and often depicted shells in their art. * In Christianity, the top of the sand dollar represents the Star of Bethlehem that led the Wise Men to the manger of Christ. Outside the "star" you will see the Easter Lily, a sign of Jesus' Resurrection. There are four holes that represent the holes in the Lord's hands and feet. The center hole is the Wound to His Sacred Heart by the spear of Longinus. On the other side of the sand dollar, you will see Poinsettia. Lastly, if you break open the sand dollar, five doves will come out, the doves of Peace and Joy.


Musical instruments

Seashells have been used as musical instruments,
wind instruments A wind instrument is a musical instrument that contains some type of resonator (usually a tube) in which a column of air is set into vibration by the player blowing into (or over) a mouthpiece set at or near the end of the resonator. The pit ...
for many hundreds if not thousands of years. Most often the shells of large sea snails are used, as trumpets, by cutting a hole in the
spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires a ...
of the shell or cutting off the tip of the spire altogether. Various different kinds of large marine gastropod shells can be turned into "blowing shells", however the most commonly encountered species used as "
conch Conch () is a common name of a number of different medium-to-large-sized sea snails. Conch shells typically have a high spire and a noticeable siphonal canal (in other words, the shell comes to a noticeable point at both ends). In North Am ...
" trumpets are: * The sacred chank, ''
Turbinella pyrum ''Turbinella pyrum'', common names the chank shell, sacred chank or chank, also known as the divine conch, sometimes referred to simply as a conch, is a species of very large sea snail with a gill and an operculum, a marine gastropod mollusk i ...
'', known in India as the
shankha A Shankha ( conch shell) has religious ritual importance in Hinduism. It is the shell of any suitable sea snail which had a hole made for the performer's embouchure. In Hindu history, the shankha is a sacred emblem of The Hindu preserver god ...
. In
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...
it is known as "dung-dkar". * The Triton shell also known as "Triton's trumpet" '' Charonia tritonis'' which is used as a trumpet in Melanesian and Polynesian culture and also in
Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic ...
and Japan. In Japan this kind of trumpet is known as the horagai. In Korea it is known as the nagak. In some Polynesian islands it is known as "''pu''". * The
Queen Conch ''Aliger gigas,'' originally known as ''Strombus gigas'' or more recently as ''Lobatus gigas'', commonly known as the queen conch, is a species of large sea snail, a marine gastropod mollusc in the family of true conches, the Strombidae. This s ...
'' Lobatus gigas'', has been used as a trumpet in the Caribbean. Children in some cultures are often told the myth that you can hear the sound of the ocean by holding a seashell to ones ear. This is due to the effect of seashell resonance.


Personal adornment

Whole seashells or parts of sea shells have been used as jewelry or in other forms of adornment since prehistoric times. Mother of pearl was historically primarily a seashell product, although more recently some mother of pearl comes from freshwater mussels. Also see
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
. * Shell necklaces have been found in Stone Age graves as far inland as the
Dordogne Dordogne ( , or ; ; oc, Dordonha ) is a large rural department in Southwestern France, with its prefecture in Périgueux. Located in the Nouvelle-Aquitaine region roughly half-way between the Loire Valley and the Pyrenees, it is named ...
Valley in France. * Seashells are often used whole and drilled, so that they can be threaded like beads, or cut into pieces of various shapes. Sometimes shells can be found that are already "drilled" by predatory snails of the family Naticidae. Fine whole shell necklaces were made by Tasmanian Aboriginal women for more than 2,600 years. The necklaces represent a significant cultural tradition which is still practised by Palawa women elders. The shells used include pearly green and blue-green maireener (rainbow kelp) shells, brown and white rice shells, black cats' teeth shells and pink button shells. * Naturally-occurring, beachworn, cone shell "tops" (the broken-off spire of the shell, which often has a hole worn at the tip) can function as beads without any further modification. In
Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
these natural beads were traditionally collected from the beach drift in order to make puka shell jewelry. Since it is hard to obtain large quantities of naturally-occurring beachworn cone tops, almost all modern puka shell jewelry uses cheaper imitations, cut from thin shells of other species of mollusk, or even made of plastic. * Shells historically have been and still are made into, or incorporated into, necklaces, pendants, beads, earrings, buttons, brooches, rings, hair combs, belt buckles and other uses. * The shell of the large "bullmouth helmet" sea snail, scientific name ''
Cypraecassis rufa ''Cypraecassis rufa'' is a species of large sea snail, a marine gastropod mollusc in the family Cassidae. It is commonly known as the bullmouth shell or red helmet shell, and also as the cameo shell. Distribution This species is found off t ...
'', was historically, and still is, used to make valuable cameos. * Mother of pearl from many seashells including species in the family Trochidae, Turbinidae, Haliotidae, and various pearly bivalves, has often been used in jewelry, buttons, etc. * In London, Pearly Kings and Queens traditionally wear clothing covered in patterns made up of hundreds of "pearl buttons", in other words, buttons made of mother-of-pearl or
nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...
. In recent years however, the majority of "pearl buttons" are imitations that are made of pearlescent plastic.


Creating Crafts

" Sailor's Valentines" were late 19th-century decorative keepsakes which were made from the Caribbean, and which were often purchased by sailors to give to their loved ones back home for example in England. These valentines consisted of elaborate arrangements of small seashells glued into attractive symmetrical designs, which were encased on a wooden (usually octagonal) hinged box-frame. The patterns used often featured heart-shaped designs, or included a sentimental expression of love spelled out in small shells. The making of shell work artifacts is a practice of Aboriginal women from La Perouse in
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mounta ...
, dating back to the 19th century. Shell work objects include baby shoes, jewelry boxes and replicas of famous landmarks, including the Sydney Harbour Bridge and the
Sydney Opera House The Sydney Opera House is a multi-venue performing arts centre in Sydney. Located on the foreshore of Sydney Harbour, it is widely regarded as one of the world's most famous and distinctive buildings and a masterpiece of 20th-century architec ...
. The shellwork tradition began as an Aboriginal women's craft which was adapted and tailored to suit the tourist souvenir market, and which is now considered high art.


Architectural decoration

Small pieces of colored and iridescent shell have been used to create
mosaic A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and were particularly pop ...
s and
inlay Inlay covers a range of techniques in sculpture and the decorative arts for inserting pieces of contrasting, often colored materials into depressions in a base object to form Ornament (art), ornament or pictures that normally are flush with th ...
s, which have been used to decorate walls, furniture and boxes. Large numbers of whole seashells, arranged to form patterns, have been used to decorate mirror frames, furniture and man-made
shell grotto A shell grotto is a type of folly, a grotto decorated with sea shells. The shell grotto was a popular feature of many British country houses in the 17th and 18th centuries. It suited the Baroque and Rococo styles (which used swirling motifs sim ...
s.


Art

A very large outdoor sculpture at Akkulam of a gastropod seashell is a reference to the sacred chank shell ''
Turbinella pyrum ''Turbinella pyrum'', common names the chank shell, sacred chank or chank, also known as the divine conch, sometimes referred to simply as a conch, is a species of very large sea snail with a gill and an operculum, a marine gastropod mollusk i ...
'' of India. In 2003, Maggi Hambling designed a striking 13 ft (4 m) high sculpture of a scallop shell which stands on the beach at
Aldeburgh Aldeburgh ( ) is a coastal town in the county of Suffolk, England. Located to the north of the River Alde. Its estimated population was 2,276 in 2019. It was home to the composer Benjamin Britten and remains the centre of the international Ald ...
, in England. The goddess of love,
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
or
Aphrodite Aphrodite ( ; grc-gre, Ἀφροδίτη, Aphrodítē; , , ) is an ancient Greek goddess associated with love, lust, beauty, pleasure, passion, and procreation. She was syncretized with the Roman goddess . Aphrodite's major symbols incl ...
, is often traditionally depicted rising from the sea on a seashell. In '' The Birth of Venus'', Botticelli depicted the goddess
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
rising from the ocean on a scallop shell.


Poultry feeds

Sea shells found in the creek and backwater of the coast of west India are used as an additive to poultry feed. They are crushed and mixed with jowar maize and dry fish.


Use

Seashells, namely from bivalves and gastropods, are fundamentally composed of calcium carbonate. In this sense, they have potential to be used as raw material in the production of lime. Along the
Gulf Coast of the United States The Gulf Coast of the United States, also known as the Gulf South, is the coastline along the Southern United States where they meet the Gulf of Mexico. The coastal states that have a shoreline on the Gulf of Mexico are Texas, Louisiana, Missi ...
,
oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
shells were mixed into
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixe ...
to make "shellcrete" which could form bricks, blocks and platforms. It could also be applied over logs. A notable example is the 19th-century Sabine Pass Lighthouse in Louisiana, near Texas.


Shells of other marine invertebrates


Arthropods

Many
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s have sclerites, or hardened body parts, which form a stiff exoskeleton made up mostly of
chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
. In
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...
s, especially those of the class
Malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, lobs ...
(crabs, shrimps and lobsters, for instance), the plates of the exoskeleton may be fused to form a more or less rigid
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
. Moulted carapaces of a variety of marine malacostraceans often wash up on beaches. The
horseshoe crab Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to ar ...
is an arthropod of the family Limulidae. The shells or exuviae of these arachnid relatives are common in beach drift in certain areas of the world.


Echinoderms

Some
echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...
s such as sea urchins, including heart urchins and sand dollars, have a hard "test" or shell. After the animal dies, the flesh rots out and the spines fall off, and then fairly often the empty test washes up whole onto a beach, where it can be found by a beachcomber. These tests are fragile and easily broken into pieces.


Brachiopods

The brachiopods, or lamp shells, superficially resemble clams, but the phylum is not closely related to mollusks. Most lines of brachiopods ended during the Permian-Triassic extinction event, and their ecological niche was filled by bivalves. A few of the remaining species of brachiopods occur in the low
intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species ...
and thus can be found live by beachcombers.


Annelids

Some polychaetes, marine annelid worms in the family Serpulidae, secrete a hard tube made of calcium carbonate, adhering to stones or other shells. This tube resembles, and can be confused with, the shell of marine gastropod mollusks in the family Vermetidae, the worm snails.


Other more atypical kinds

A few other categories of marine animals leave remains which might be considered "seashells" in the widest possible sense of the word.


Chelonians

Sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhe ...
s have a
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...
and plastron of bone and
cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...
which is developed from their
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s. Infrequently a turtle "shell" will wash up on a beach.


Hard corals

Pieces of the hard skeleton of
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
s commonly wash up on beaches in areas where corals grow. The construction of the shell-like structures of corals are aided by a
symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or para ...
relationship with a class of
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
, zooxanthellae. Typically a coral polyp will harbor particular species of algae, which will
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
e and thereby provide energy for the coral and aid in calcification, while living in a safe environment and using the carbon dioxide and nitrogenous waste produced by the polyp.
Coral bleaching Coral bleaching is the process when corals become white due to various stressors, such as changes in temperature, light, or nutrients. Bleaching occurs when coral polyps expel the zooxanthellae ( dinoflagellates that are commonly referred to as ...
is a disruption of the balance between polyps and algae, and can lead to the breakdown and death of coral reefs.


Soft corals

The skeletons of soft corals such as gorgonians, also known as sea fans and sea whips, commonly wash ashore in the
tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also refer ...
after storms.


Plankton and protists

Plant-like diatoms and animal-like radiolarians are two forms of
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...
which form hard
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
te shells.
Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...
and
coccolithophore Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the king ...
s create shells known as "
tests Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...
" which are made of calcium carbonate. These shells and tests are usually microscopic in size, though in the case of foraminifera, they are sometimes visible to the naked eye, often resembling miniature mollusk shells.


See also

* Bailey-Matthews Shell Museum *
Marine biogenic calcification Marine biogenic calcification is the process by which marine organisms such as oysters and clams form calcium carbonate. Seawater is full of dissolved compounds, ions and nutrients that organisms can use for energy and, in the case of calcificati ...
* Mollusk shell *
Ocean acidification Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...
* Seashell resonance * Seashell surface, a mathematical construct * Shell growth in estuaries * Shell purse * Small shelly fauna


References


Citations


Sources

; Books * Abbott R. Tucker & S. Peter Dance, 1982, ''Compendium of Seashells, A full color guide to more than 4,200 of the World's Marine shells'', E.P. Dutton, Inc, New York, . * Abbott R. Tucker, 1985, ''Seashells of the World: a guide to the better-known species'', 1985, Golden Press, New York, . * Abbott, R. Tucker, 1986, ''Seashells of North America'', St. Martin's Press, New York, . * Abbott, R. Tucker, 1974, ''American Seashells'', Second edition, Van Nostrand Rheinhold, New York, .


External links

{{wikiquote
Hohlman Shell Collection, Florida Institute of Technology
Zoology Mollusc shells Mollusc products Collecting