Seashell

A seashell (or sea shell), also known simply as a shell, is a hard, protective outer layer usually made by an animal that lives in the sea. Most seashells are made by mollusks, such as snails, clams, and oysters, to protect their soft insides. Empty seashells are often found on beaches by beachcombers. The shells are empty because the animal has died and the soft parts have decomposed or been eaten.

A seashell is usually the exoskeleton of an invertebrate (an animal without a backbone), and is typically made of calcium carbonate or chitin. Most shells found on beaches are from marine mollusks because these shells last longer.

Seashells have been used by humans for many purposes throughout history. Besides mollusk shells, other shells on beaches come from barnacles, horseshoe crabs, and brachiopods. Marine annelid worms in the family Serpulidae make shells that are tubes of calcium carbonate. The shells of sea urchins are called "tests", and crabs and lobsters leave behind exuviae. While most seashells are outside the animal, some cephalopods have shells inside.

Seashells are fun to collect and study. They show the beautiful patterns nature can create and help scientists learn about ocean environments and past climates.

Terminology

When we talk about "seashells," we mean the hard shells made by animals called marine mollusks. Learning about these shells is part of a science called conchology. People who study seashells try to be careful not to hurt the animals or their homes in the ocean.

The science that studies all mollusks, including their shells, is called malacology. A person who works in this science is known as a malacologist.

Occurrence

Seashells are often found on beaches, where waves and tides leave them behind. People enjoy picking up these empty shells, which the animals leave after they die. Some seashells sold in stores come from shells that were collected while the animals were still alive. This can sometimes affect the local environment and reduce the number of rare shell types found in nature.

Shell synthesis

Seashells are made by animals called mollusks to protect themselves. These animals have a special layer of tissue called the mantle. This mantle makes the shell using minerals and proteins. The main part of seashells is calcium carbonate. It helps the shell stay strong and grow bigger over time.

Molluscan seashells

The word seashell usually means the shell of a sea mollusk. The shells most often called "seashells" are from bivalves (or clams), gastropods (or snails), scaphopods (or tusk shells), polyplacophorans (or chitons), and cephalopods (such as nautilus and spirula). These shells are commonly found on beaches and sold as decorations.

Marine species of gastropods and bivalves are more numerous than land and freshwater species, and their shells are often larger and stronger.

Bivalves

Bivalves are often the most common seashells that wash up on sandy beaches or in sheltered lagoons. They sometimes are found in very large numbers. Often the two parts of their shell become separated.

There are more than 15,000 species of bivalves that live in both sea and freshwater. Examples of bivalves are clams, scallops, mussels, and oysters. Most bivalves have two identical shells held together by a flexible hinge. The animal's body is safely inside these two shells. Bivalves that do not have two shells either have one shell or no shell at all. The shells are made of calcium carbonate and are formed in layers by secretions from the mantle. Bivalves are mostly filter feeders; they draw in water through their gills to trap tiny food particles.

Gastropods

Some species of gastropod seashells (the shells of sea snails) can sometimes be common on sandy beaches and on beaches with rocky areas.

There are more than 65,000 species of gastropods that live in marine, freshwater, and land environments. Examples of gastropods include snails, slugs, whelks, limpets, and abalones. Most gastropods have a single coiled shell made of calcium carbonate, secreted in layers by the mantle, although some species have smaller shells or no shell at all. A key feature of gastropods is their muscular foot, which they use for crawling, burrowing, or swimming. Many gastropods feed using a radula, a ribbon-like structure with tiny teeth, though some species filter feed or hunt other animals.

Polyplacophorans

Chiton plates or valves often wash up on beaches in rocky areas where chitons live. Chiton shells, made of eight separate plates and a girdle, usually fall apart after death, so they are almost always found as separate plates. Plates from larger chitons are sometimes called "butterfly shells" because of their shape.

Cephalopods

Only a few species of cephalopods have shells (either internal or external) that are sometimes found on beaches.

Some cephalopods such as Sepia, the cuttlefish, have a large internal shell, the cuttlefish bone, which often washes up on beaches in some parts of the world.

Spirula spirula is a deep water squid-like cephalopod. It has an internal shell that is small (about 1 in or 24 mm) but very light and buoyant. This shell floats 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 called a "paper nautilus".

The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common in certain areas as fossils.

Molluscan seashells used by other animals

Empty molluscan seashells are strong and usually easy to find on beaches, in the intertidal zone, and in shallow water. They are sometimes used second-hand by animals other than humans for various purposes, including for protection (as in hermit crabs) and for building.

Mollusks

• Carrier shells in the family Xenophoridae 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 bits. Very often shells of bivalves or smaller gastropods are used, depending on what is available where the snail lives. It is not clear whether these shell attachments serve as camouflage, or whether they are intended to help prevent the shell from sinking into soft sand.

• Small octopuses sometimes use an empty shell as a hiding place, or hold seashells around themselves as a form of protection.

Invertebrates

• Almost all hermit crabs use or "wear" empty marine gastropod shells to protect their soft bellies, and to have a strong shell to hide in if attacked by a predator. Each hermit crab must find another gastropod shell when it grows too big for the one it is using.

Some hermit crab species live on land and may be found far from the sea, including those in the tropical genus Coenobita.

Conchology

There are many popular books and field guides about shell-collecting. Although there are books about land and freshwater mollusks, most focus 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. The line between professionals and amateur enthusiasts is often not clear, 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. Many collectors of marine mollusk shells find them on beaches, in the intertidal or sub-tidal zones, and can collect and preserve them without special equipment or expensive supplies. Some collectors keep careful records, or buy only "specimen shells", which have full collecting data: information about how, when, where, in what habitat, and by whom, the shells were collected. Other collectors buy widely available commercially imported shells, most of which have little or no data. To museum scientists, having full collecting data with a specimen is more important than having the shell correctly identified. Some owners of shell collections hope to donate their collection to a major natural history or zoology museum, but shells with little or no collecting data are usually not valuable to science, and are likely not to be accepted by a major museum. Shells can also become damaged when stored or displayed.

Shell clubs

There are clubs or societies of people who share an interest in shells. In the US, these clubs are more common in coastal areas, such as Florida and California, where there are many species of marine life.

Identification

Seashells are usually identified by using general or regional shell-collecting field guides, and specific scientific books on different groups of shell-bearing mollusks (monographs) or "iconographies" (limited text – mainly photographs or other illustrations). Identifications to the species level are generally done by examining illustrations and written descriptions, rather than by using Identification keys, as is often done with plants and other invertebrates. Creating functional keys for identifying the shells of marine mollusks to the species level can be very difficult, because of the great variability within many species and families. Identifying some species is often very difficult, even for a specialist in that family. Some species cannot be told apart based on shell character alone.

Many smaller and less well-known mollusk species (see micromollusk) have not yet been discovered and named. In other words, they have not yet been separated from similar species and given scientific (binomial) names in journals recognized by the International Commission on Zoological Nomenclature (ICZN). Many new species are published in scientific journals each year. There are currently an estimated 100,000 species of mollusks worldwide.

Non-marine "seashells"

The term seashell is also used for mollusk shells that are not from the sea, for example by people walking the shores of lakes and rivers using the term for freshwater mollusk shells they find. Seashells sold in tourist shops may include various freshwater and land shells as well. Non-marine shells offered may include large and colorful tropical land snail shells, freshwater apple snail shells, and pearly freshwater unionid mussel shells. This can be confusing to collectors, as non-marine shells are often not included in their reference books.

Cultural significance

Seashells have been used as a way to trade in various places, including many Indian Ocean and Pacific Ocean islands, also in North America, Africa and the Caribbean.

The most common shells used as money have been Monetaria moneta, the "money cowry", and certain dentalium tusk shells, used in North Western North America for many centuries. Many tribes and nations across Africa have historically used the cowry as their way to trade. The cowry circulated alongside metal coins and goods, and foreign currencies. Durable and easy to carry, the cowry was a good form of money.

Some tribes of the indigenous peoples of the Americas used shells for wampum and hair pipes. The Native American wampum belts were made from the shell of the quahog clam.

Seashells have often been used as tools 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 baptismal fonts.

Melo melo, the "bailer volute", is named because Native Australians used it to bail out their canoes.

Many different kinds of bivalves have been used as scrapers, blades, clasps, and other tools, because of their shape.

Some marine gastropods have been used for oil lamps, the oil being poured into the opening of the shell, and the siphonal canal serving as a holder for the wick.

Because seashells in some areas are a ready source of calcium carbonate, shells such as oyster shells are sometimes used to improve soil in horticulture. The shells are broken or ground into small pieces to raise the pH and increase the calcium content in the soil.

Seashells have played a part in religion and spirituality, sometimes even as special objects.

In Christianity, the scallop shell is linked to Saint James the Great, see Pecten jacobaeus.

In Hinduism, left-handed shells of Turbinella pyrum (the sacred shankha) are sacred to the god Vishnu. The person who finds a left-handed chank shell is sacred to Vishnu, as well. The chank shell also has an important role in Buddhism.

In the Santería religion, shells are used for divination.

The Moche culture of ancient Peru honored animals and the sea, and often showed shells in their art.

In Christianity, the top of the sand dollar represents the Star of Bethlehem that guided the Wise Men to the baby Jesus. Outside the "star" you will see the Easter Lily, a sign of Jesus' Resurrection. There are four holes that represent the nails in Jesus' hands and feet. The center hole is where the spear hurt His heart. 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.

Seashells have been used as musical instruments, wind instruments for many hundreds or thousands of years. Most often the shells of large sea snails are used as trumpets, by cutting a hole in the top of the shell or cutting off the tip. Various kinds of large marine gastropod shells can be turned into "blowing shells"; however, the most commonly used as "conch" trumpets are:

The sacred chank, Turbinella pyrum, known in India as the shankha. In Tibet 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 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, 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 your ear. This is because of the effect of seashell resonance.

Whole seashells or parts of sea shells have been used as jewelry or in other forms of decoration since prehistoric times. Mother of pearl was historically mainly a seashell product, although more recently some mother of pearl comes from freshwater mussels.

Shell necklaces have been found in Stone Age graves as far inland as the Dordogne Valley in France.

Seashells are often used whole and drilled, so that they can be strung 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 top of the shell, which often has a hole worn at the tip) can function as beads without any further change. In Hawaii these natural beads were traditionally collected from the beach in order to make puka shell jewelry. Because it is hard to find enough naturally occurring beachworn cone tops, almost all modern puka shell jewelry uses cheaper imitations, cut from thin shells of other kinds of mollusk, or even made of plastic.

Shells have historically been and still are made into, or added to, necklaces, pendants, beads, earrings, buttons, brooches, rings, hair combs, belt buckles and other items.

The shell of the large "bullmouth helmet" sea snail, scientific name Cypraecassis rufa, has 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 of hundreds of "pearl buttons", meaning buttons made of mother-of-pearl or nacre. In recent years, most "pearl buttons" are copies made of shiny plastic.

"Sailor's valentines" were late 19th-century decorative keepsakes made in the Caribbean, often bought by sailors to give to loved ones back home, for example in England. These valentines were elaborate arrangements of small seashells glued into attractive symmetrical designs, placed inside a wooden (usually octagonal) hinged box-frame. The designs often included heart shapes, or a message of love spelled out in small shells.

Making shell work objects is a practice of Aboriginal women from La Perouse in Sydney, dating back to the 19th century. Shell work objects include baby shoes, jewelry boxes and copies of famous landmarks, including the Sydney Harbour Bridge and the Sydney Opera House. The shellwork tradition began as an Aboriginal women's craft which was changed to fit the tourist souvenir market, and is now considered high art.

Small pieces of colored and shiny shell have been used to make mosaics and inlays, used to decorate walls, furniture and boxes. Large numbers of whole seashells, arranged to make patterns, have been used to decorate mirror frames, furniture and human-made shell grottos.

A very large outdoor sculpture at Akkulam of a gastropod seashell refers to the sacred chank shell Turbinella pyrum 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, in England. The goddess of love, Venus or Aphrodite, is often shown rising from the sea on a seashell. In The Birth of Venus, Botticelli showed the goddess Venus rising from the ocean on a scallop shell.

Enormous seashell sculpture at Akkulam, Thiruvananthapuram, India

Large sculpture of a scallop on the beach at Aldeburgh, by Maggi Hambling, 2003

Illustration from an 18th-century book, edited by Albertus Seba. These decorative arrangements were a popular way to display seashells at the time

Portrait of the Shell Collector Jan Govertsen van der Aer, by Hendrick Goltzius (1603)

Seashells found in the creeks 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.

Seashells, from bivalves and gastropods, are made of calcium carbonate. They can be used as a material to make lime.

Along the Gulf Coast of the United States, oyster shells were mixed into cement to make "shellcrete" which could form bricks, blocks and platforms. It could also be put over logs. A well-known example is the 19th-century Sabine Pass Lighthouse in Louisiana, near Texas.

Main article: Conch (musical instrument)

Main articles: Shellcraft, Molluscs in culture

Shells of other marine invertebrates

Many small sea animals, such as arthropods, have hard parts on their bodies made of a substance called chitin. In animals like crabs, shrimps, and lobsters, these hard parts can form a shell-like cover. When these animals shed their shells, they sometimes wash up on beaches.

Some sea animals called echinoderms, like sea urchins and sand dollars, have hard shells too. After these animals die, their shells can often be found whole on beaches.

There are also animals called brachiopods, which look a bit like clams but are not closely related. Most of them no longer exist, but a few still live in shallow waters near beaches.

Some sea worms, called polychaetes, make hard tubes that look like shells and can be found stuck to rocks or other shells.

Atypical shells

Some sea creatures, besides snails and clams, leave behind pieces that people might call "seashells." Sea turtles have a hard shell made of bone and cartilage from their ribs. Sometimes, this shell can wash up on beaches.

Pieces of hard skeletons from corals often appear on beaches where corals grow. Corals build their skeletons with help from special algae that live inside them. These algae use sunlight to help the coral grow strong.

Soft corals, like sea fans and sea whips, also leave behind skeletons. These can wash ashore after storms, especially in warm tropical areas.

Tiny plants called diatoms and animal-like creatures called radiolarians form hard shells made of silicate. Other tiny organisms, such as foraminifera and coccolithophores, make shells called "tests" from calcium carbonate. These shells are usually very small, but sometimes you can see them without a microscope. They look a bit like tiny mollusk shells.

Main article: Protist shells