Tuesday, February 26, 2019

Is freshwater pearls real?

Cultured freshwater pearls are pearls that are farmed and created using freshwater mussels. These pearls are produced in Japan and the United States on a limited scale, but are now almost exclusively produced in China.
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The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.
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This cavity is formed by the mantle skirt, a double fold of mantle which encloses a water space. This space contains the mollusc's gills, anus, osphradium, nephridiopores, and gonopores. The mantle cavity functions as a respiratory chamber in most molluscs. In bivalves it is usually part of the feeding structure.
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The mantle cavity is a central feature of molluscan biology. This cavity is formed by the mantle skirt, a double fold of mantle which encloses a water space. This space contains the mollusc's gills, anus, and organs for taste, excretion and reproductive organs.
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The fireplace mantel or mantelpiece, also known as a chimneypiece, originated in medieval times as a hood that projected over a fire grate to catch the smoke. The term has evolved to include the decorative framework around the fireplace, and can include elaborate designs extending to the ceiling.
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After a chiton dies, the individual valves which make up the eight-part shell come apart because the girdle is no longer holding them together, and then the platessometimes wash up in beach drift. The individual shell plates from a chiton aresometimes known as "butterfly shells" due to their shape.
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The mantle cavity functions as a respiratory chamber in most molluscs. In bivalves it is usually part of the feeding structure. In some molluscs the mantle cavity is a brood chamber, and in cephalopods and some bivalves such as scallops, it is a locomotory organ.
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The bivalve's two siphons are situated at the posterior edge of the mantle cavity. There is an inhalant or incurrent siphon, and an exhalant or excurrent siphon. ... Usually water enters the mantle cavity through the inhalant siphon, moves over the gills, and leaves through the exhalant siphon.
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Only those bivalves that burrow in sediment, and live buried in the sediment,need to use these tube-like structures. The function of these siphons is to reach up to the surface of the sediment, so that the animal is able to respire, feed, and excrete, and also to reproduce.
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A practical siphon, operating at typical atmospheric pressures and tube heights, works because gravity pulling down on the taller column of liquid leaves reduced pressure at the top of the siphon (formally, hydrostatic pressure when the liquid is not moving).
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Most bivalves are filter feeders, using their gills to capture particulate food such as phytoplankton from the water. The protobranchs feed in a different way, scraping detritus from the seabed, and this may be the original mode of feeding used by allbivalves before the gills became adapted for filter feeding.
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Common oyster predators include crabs, seabirds, starfish, and humans. Someoysters contain crabs, known as oyster crabs.
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Bivalves as a group have no head and they lack some usual molluscan organs like the radula and the odontophore. They include the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders.
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Oysters are filter feeders, drawing water in over their gills through the beating of cilia. Suspended plankton and particles are trapped in the mucus of a gill, and from there are transported to the mouth, where they are eaten, digested, and expelled as feces or pseudofeces.
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Fresh oysters must be alive just before consumption or cooking. There is only one criterion: the oyster must be capable of tightly closing its shell. Open oystersshould be tapped on the shell; a live oyster will close up and is safe to eat.
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Some crustaceans that are commonly eaten are shrimp, lobsters, crayfish, and crabs. Echinoderms are not as frequently harvested for food as molluscs and crustaceans; however, sea urchin roe is quite popular in many parts of the world. Most shellfish eat a diet composed primarily of phytoplankton and zooplankton.
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Oysters naturally grow in estuarine bodies of brackish water. When farmed, the temperature and salinity of the water are controlled (or at least monitored), so as to induce spawning and fertilization, as well as to speed the rate of maturation – which can take several years.
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Black cultured pearls from the black pearl oyster – Pinctada margaritifera – are not South Sea pearls, although they are often mistakenly described as black South Sea pearls. In the absence of an official definition for the pearl from the blackoyster, these pearls are usually referred to as "black pearls".
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Natural pearls are formed by nature, more or less by chance. On the other hand,cultured pearls are human creations formed by inserting a tissue graft from a donor oyster, upon which a pearl sac forms, and the inner side precipitates calcium carbonate, in the form of nacre or "mother-of-pearl".
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The Tahitian pearl (or black pearl) is an organic gem formed from the black lip oyster (Pinctada margaritifera). These pearls derive their name from the fact that they are primarily cultivated around the islands of French Polynesia, around Tahiti.
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Not all mussels and oysters produce pearls. In a haul of three tons, only three orfour oysters will produce perfect pearls.
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The nucleus bead in a beaded cultured pearl is generally a polished sphere madefrom freshwater mussel shell. Along with a small piece of mantle tissue from another mollusk (donor shell) to serve as a catalyst for the pearl sac, it is surgically implanted into the gonad (reproductive organ) of a saltwater mollusk.
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Oysters usually reach maturity in one year. They are protandric; during their first year, they spawn as males by releasing sperm into the water. As they grow over the next two or three years and develop greater energy reserves, they spawn as females by releasing eggs.
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Pearl powder is made from freshwater pearls or saltwater pearls below jewellery grade. These are sterilised in boiling water and then milled into a fine powder using stainless steel grinding discs or by milling with small porcelain balls in moist conditions. The powder is sold as such or mixed into creams.
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Nacre (/ˈneɪkÉ™r/ NAY-kÉ™r also /ˈnækrÉ™/ NAK-rÉ™), also known as mother of pearl, is an organic-inorganic composite material produced by some molluscs as an innershell layer; it also makes up the outer coating of pearls. It is strong, resilient, and iridescent.
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Fine quality natural pearls are very rare jewels. Their values are determined similarly to those of other precious gems, according to size, shape, color, quality of surface, orient and luster. Single natural pearls are often sold as collectors' items, or set as centerpieces in unique jewelry.
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The outer layer of pearls and the inside layer of pearl oyster and freshwater pearl mussel shells are made of nacre. Other mollusc families that have a nacreous inner shell layer include marine gastropods such as the Haliotidae, the Trochidae and the Turbinidae.
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The Pearl of Lao Tzu (also referred to as Pearl of Lao Tze and previously as Pearlof Allah) used to be the largest known pearl. The pearl was found in the Palawan sea, which surrounds the island of Palawan in the Philippines, and was found by a Filipino diver.
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Baroque pearls are pearls with an irregular non-spherical shape. ... Most cultured freshwater pearls are baroque because freshwater pearls are mantle-tissue nucleated instead of bead nucleated. Cultured saltwater pearls can also bebaroque, but tend to be more teardrop-shaped due to the use of a spherical nucleation bead.
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Tridacna is a genus of large saltwater clams, marine bivalve mollusks in the subfamily Tridacninae, the giant clams. They have heavy shells, fluted with 4 to 6 folds. The mantle is brightly coloured. They inhabit shallow waters of coral reefs in warm seas of the Indo-Pacific region.
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The largest A. vaccaria has been measured at 99 cm in length and weighing in at almost 14 kg). An extremely large species of fossil gastropod is Campanile giganteum. The overall height (also known as length) of the shell of S. aruanus is up to 91 cm (see also Hawaiian Shell News, 1982).
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The giant clams are the members of the clam genus Tridacna that are the largest living bivalve mollusks. There are actually several species of "giant clams" in the genus Tridacna, which are often misidentified for Tridacna gigas, the most commonly intended species referred to as “the giant clam”.
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Today the giant clam is considered neither aggressive nor particularly dangerous. While it is certainly capable of gripping a person, the shell's closing action is defensive, not aggressive, and the shell valves close too slowly to pose a serious threat.
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The color pearl is a pale tint of off-white. It is a representation of the average color of a pearl. The first recorded use of pearl as a color name in English was in 1604. The color used in interior design when an off-white tint is desired.
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