Molluscs in culture
Culture consists of the social behaviour and norms in human societies transmitted through social learning. Molluscs play a variety of roles in culture, including but not limited to art and literature, with both practical interactions—whether useful or harmful—and symbolic uses. Practical interactions with molluscs range from their use as food, where species as diverse as snails and squid are eaten in many countries, to the employment of molluscs as shell money and to make dyestuffs and musical instruments, for personal adornment with seashells, pearls, or mother-of-pearl, as items to be collected, as fictionalised  sea monsters, and as raw materials for craft items such as Sailor's Valentines. Some bivalves are used as bioindicators to monitor the health of marine and freshwater environments. Harmful interactions with molluscs include the stings of cone snails and the venomous bites of certain octopuses; blue-ringed octopuses bite only when provoked, but their venom kills a quarter of the people bitten. Some snails are vectors of diseases such as schistosomiasis, a major tropical disease that infects some 200 million people; others are serious crop pests, and species such as the giant East African snail "Lissachatina fulica" have damaged  ecosystems in areas where they have been introduced. Mollusc shells have been widely used in art, whether carved directly, sometimes as cameos, or depicted in paintings. In popular culture, the snail is known for its stereotypical slowness, while the octopus and giant squid have featured in literature since classical times as monsters of the deep. Many-headed and tentacled monsters appear as the Gorgon and the Medusa of Greek mythology, and the kraken of Nordic legend. The taxonomist Carl Linnaeus named the Venus shell as "Venus dione", for the goddess of love and her mother, and named its parts using  overtly sexual descriptors. Context. Culture consists of the social behaviour and norms found in human societies and transmitted through social learning. Cultural universals in all human societies include expressive forms like art, music, dance, ritual, religion, and technologies like tool usage, cooking, shelter, and clothing. The concept of material culture covers physical expressions such as technology, architecture and art, whereas immaterial culture includes principles of social organization, mythology, philosophy, literature, and science. This article describes the roles played by molluscs in human culture, so defined. Useful interactions. Adornment. Seashells are admired and collected by conchologists and others for scientific purposes  and for their decorative qualities. Seashells have been used for personal adornment, such as the strings of cowries in the traditional dress of the Kikuyu people of Kenya, and the formal dress of the Pearly Kings and Queens of London. Most molluscs with shells can produce pearls, but only the pearls of bivalves and some gastropods, whose shells are lined with nacre, are valuable. The best natural pearls are produced by marine pearl oysters, "Pinctada margaritifera" and "Pinctada mertensi", which live in the tropical and subtropical waters of the Pacific Ocean. Natural pearls form when a small foreign object gets  stuck between the mantle and shell. Pearls for use as jewellery are cultured by inserting either "seeds" or beads into oysters. The "seed" method uses grains of ground shell from freshwater mussels, and overharvesting for this purpose has endangered several freshwater mussel species in the southeastern United States. The pearl industry is so important in some areas, significant sums of money are spent on monitoring the health of farmed molluscs. Musical instruments. Seashells including the sacred chank or shankha "Turbinella pyrum"; "Triton's trumpet" "Charonia tritonis"; and the Queen Conch "Strombus gigas" have been used as musical instruments around the  world. For craft items. Seashells have been made into craft items such as Sailor's Valentines in the 19th century. Souvenir items, now considered as serious art, are made by Aboriginal women from La Perouse in Sydney. As food. Many species of mollusc, including gastropods such as whelks, bivalves such as scallops, cockles, mussels, and clams, and cephalopods such as octopuses and squids are collected or hunted for food. Oysters, abalone, and several species of mussels are widely farmed; oyster farming began in Roman times. Many recipes from around the world are based on molluscs from all three major orders . Among cephalopod recipes, both octopus and squid are used in dishes such as the popular fried calamari, and in sushi and sashimi. Among bivalve recipes, clams are made into soups called chowders, or served as a sauce with pasta in dishes such as "spaghetti alle vongole", while mussels are widely eaten as "moules marinieres", nowadays often with "frites" (chips). Gastropod recipes include "escargot", terrestrial snails, in French cuisine, and whelks in cuisines around the world. Imperial purple. Tyrian or imperial purple, made from the ink glands of murex shells, "... fetched its weight in silver" in the fourth century BC, according  to Theopompus. The discovery of large numbers of "Murex" shells on Crete suggests the Minoans may have pioneered the extraction of "imperial purple" during the Middle Minoan period in the 20th–18th centuries BC, centuries before the Tyrians. Sea silk. Sea silk is a fine, rare, and valuable fabric produced from the long silky threads (byssus) secreted by several bivalve molluscs, particularly "Pinna nobilis", to attach themselves to the sea bed. Procopius, writing on the Persian wars "circa" 550 CE, "stated that the five hereditary satraps (governors) of Armenia who received their insignia from the Roman Emperor were given chlamys (or  cloaks) made from "lana pinna". Apparently, only the ruling classes were allowed to wear these chlamys." Shell money. Peoples of the Indian Ocean, Pacific Ocean, North America, Africa and the Caribbean have used shells as money, including "Monetaria moneta", the money cowrie in preindustrial societies. However, these were not necessarily used for commercial transactions, but mainly as social status displays at important occasions, such as weddings. When used for commercial transactions, they functioned as commodity money, as a tradable commodity whose value differed from place to place, often as a result of difficulties in transport, and which was vulnerable to  incurable inflation if more efficient transport or "goldrush" behaviour appeared. Among the Eastern Woodlands tribes of North America, shell beads known as wampum were kept on strings and used as money. Bioindicators. Bivalve molluscs are used as bioindicators to monitor the health of aquatic environments in both fresh water and the marine environments. Their population status and structure, physiology, behaviour and their levels of contamination with chemicals together provide a detailed indication of the status of the ecosystem. Because they are sessile, they serve as readily-monitored representatives of their environment. Harmful interactions. Stings and bites. A few species of  molluscs, including octopuses and cone snails, can sting or bite. Some present a serious risk to people handling them. However, deaths from jellyfish stings are ten times as common as those from mollusc bites. All octopuses are venomous, but only a few species pose a significant threat to humans. Blue-ringed octopuses ("Hapalochlaena") from Australia and New Guinea have a powerful venom and warning coloration. They bite humans only if severely provoked, but their venom kills a quarter of the people bitten. Another tropical species, "Octopus apollyon", causes severe inflammation that can last for over a month even if treated  correctly. The bite of "O. rubescens" can cause necrosis that lasts longer than one month if untreated, and headaches and weakness persisting for up to a week even if treated. All marine cone snails are venomous and can sting when handled. Their venom is a complex mixture of toxins, some fast-acting and others slower but deadlier. Many painful stings have been reported, and a few fatalities. Only a few larger species of cone snails are likely to be seriously dangerous to humans. The effects of individual cone-shell toxins on victims' nervous systems are so precise as to be  useful tools for research in neurology, and the small size of their molecules makes it easy to synthesize them. The traditional belief that giant clams can trap the leg of a person between its valves, thus causing drowning, is a myth. Vectors of disease. Molluscs are vectors of parasitic diseases such as schistosomiasis, a major tropical disease second only to malaria. It is caused by flukes, "Schistosoma" spp., and infects some 200 million people in 74 countries. The flukes have a complex life cycle with freshwater snails as intermediate hosts; people swimming or washing in the water are at risk  of infection. Molluscs can also carry angiostrongyliasis, a disease caused by the worms of the "Angiostrongylus" spp., which can occur after voluntarily or inadvertently consuming raw snails, slugs, other mollusks and even unwashed fruits and vegetables. Pests. Some snails and slugs are serious crop pests, and in new environments can unbalance local ecosystems. One such pest, the giant African snail "Lissachatina fulica", has been introduced to many parts of Asia and islands in the Indian and Pacific Oceans, reaching the West Indies in the 1990s. The predatory snail "Euglandina rosea" was disastrously introduced in an attempt to control it, as  the predator ignored "A. fulica" but extirpated several native snail species instead. Symbolic interactions. Epithets. The snail features in an animal epithet for its stereotypical slowness, while its shell-less relative the slug similarly denotes a person who is lazy and loathsome. Monsters of the deep. Cephalopod molluscs including the octopus and giant squid have featured as monsters of the deep since classical times. Giant squid are described by Aristotle (4th century BC) in his "History of Animals" and Pliny the Elder (1st century AD) in his "Natural History". The Gorgon of Greek mythology may have been inspired by the  octopus or squid, the severed head of Medusa representing the animal, the beak as the protruding tongue and fangs, and its tentacles as the snakes. The six-headed sea monster of the "Odyssey", Scylla, may have had a similar origin. The Nordic legend of the kraken may also have derived from sightings of large cephalopods; the science fiction writer Jules Verne told a tale of a kraken-like monster in his 1870 novel "Twenty Thousand Leagues Under the Sea". In art. Throughout the world, the nautilus is captured to carve the elegantly shaped shells, and for their nacreous inner shell  layer, a pearl substitute. Mother-of-pearl or nacre, which lines some mollusc shells, is used to make organic jewellery. It has traditionally been inlaid into furniture and boxes, particularly in China. It has been used to decorate musical instruments, watches, pistols, fans and other products. Shells have been used in Southern Italy as a cheaper alternative to layered stone when carving cameos. In the fine art of the Italian Renaissance, Sandro Botticelli's c. 1486 "The Birth of Venus" depicts the goddess Venus emerging from the waves on a scallop shell. In the Dutch Golden Age, still life painters  such as Adriaen Coorte often depicted ornate sea shells of varied kinds in their compositions. Linnaeus's Venus shell. In his 1758 "Systema Naturae", and then in his 1771 "Fundamenta Testaceologiae", the pioneering taxonomist Carl Linnaeus used a series of "disquieting[ly]" sexual terms to describe the Venus shell: "vulva", "anus", "nates" (buttocks), "pubis", "mons veneris", "labia", "hymen". Further, he named the species "Venus dione", for Venus, the goddess of love, and Dione, her mother. The evolutionary biologist Stephen Jay Gould called Linnaeus's description "one of the most remarkable paragraphs in the history of systematics". Some later naturalists found the  terms used by Linnaeus uncomfortable; an 1803 review commented that "a few of these terms however strongly they may be warranted by the similitudes and analogies which they express, ... are not altogether reconcilable with the delicacy proper to be observed in ordinary discourse", while the 1824 "Supplement to the Encyclopædia Britannica" criticised Linnaeus for "indulg[ing] in obscene allusions."