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 calcified, many are somewhat irregular in shape. Many, but not all, oysters are in the superfamily Ostreoidea; some kinds of oysters are consumed cooked or raw and are regarded as a delicacy. Some kinds of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects. First attested in English during the 14th century, the word "oyster" comes from Old French oistre, in turn from Latin ostrea, the feminine form of ostreum, the latinisation of the Greek ὄστρεον, "oyster". Compare ὀστέον, "bone". True oysters are members of the family Ostreidae; this family includes the edible oysters, which belong to the genera Ostrea, Ostreola and Saccostrea. Examples include the Belon oyster, eastern oyster, Olympia oyster, Pacific oyster, the Sydney rock oyster.
All shell-bearing mollusks can secrete pearls, yet most are not valuable. Pearls can form in both freshwater environments. Pearl oysters are not related to true oysters, being members of a distinct family, the feathered oysters. Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels yield pearls of commercial value; the largest pearl-bearing oyster is the marine Pinctada maxima, the size of a dinner plate. Not all individual oysters produce pearls naturally. In fact, in a harvest of two and a half tons of oysters, only three to four oysters produce what commercial buyers consider to be absolute perfect pearls. In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. Over the years, the irritating object is covered with enough layers of nacre to become a pearl; the many different types and shapes of pearls depend on the natural pigment of the nacre, the shape of the original irritant. Pearl farmers can culture a pearl by placing a nucleus a piece of polished mussel shell, inside the oyster.
In three to seven years, the oyster can produce a perfect pearl. These pearls are not as valuable as natural pearls, but look the same. In fact, since the beginning of the 20th century, when several researchers discovered how to produce artificial pearls, the cultured pearl market has far outgrown the natural pearl market. A number of bivalve molluscs have common names that include the word "oyster" because they either taste like or look somewhat like true oysters, or because they yield noticeable pearls. Examples include: Thorny oysters in the genus Spondylus Pilgrim oyster, another term for a scallop, in reference to the scallop shell of St. James Saddle oysters, members of the Anomiidae family known as jingle shells Dimydarian oysters, members of the family Dimyidae Windowpane oysters In the Philippines, a local thorny oyster species known as Tikod Amo is a favorite seafood source in the southern part of the country; because of its good flavor, it commands high prices. Oysters are filter feeders.
Suspended plankton and particles are trapped in the mucus of a gill, from there are transported to the mouth, where they are eaten and expelled as feces or pseudofeces. Oysters feed most at temperatures above 10 °C. An oyster can filter up to 5 L of water per hour; the Chesapeake Bay's once-flourishing oyster population filtered excess nutrients from the estuary's entire water volume every three to four days. Today, that would take nearly a year. Excess sediment and algae can result in the eutrophication of a body of water. Oyster filtration can mitigate these pollutants. In addition to their gills, oysters can exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. A small, three-chambered heart, lying under the adductor muscle, pumps colorless blood to all parts of the body. At the same time, two kidneys, located on the underside of the muscle, remove waste products from the blood, their nervous system includes three pairs of ganglia. While some oysters have two sexes, their reproductive organs contain sperm.
Because of this, it is technically possible for an oyster to fertilize its own eggs. The gonads surround the digestive organs, are made up of sex cells, branching tubules, connective tissue. Once the female is fertilized, she discharges millions of eggs into the water; the larvae develop in about six hours and exist suspended in the water column as veliger larvae for two to three weeks before settling on a bed and maturing to sexual adulthood within a year. A group of oysters is called a bed or oyster reef; as a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live in the intertidal zone, while Ostrea is subtidal; the hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live. Hundreds of animals, such as sea anemones and hooked mussels, inhabit oyster reefs. Many of these animals are prey to larger animals, including fish, such as striped bass, black drum and croakers. An oyster reef can increase the surface area of a flat bottom 50-fold.
An oyster's mature shape depends on the type of bottom to which it is attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and t
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more they represent problematic species concepts. For example, the boundaries between related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, in a ring species. Among organisms that reproduce only asexually, the concept of a reproductive species breaks down, each clone is a microspecies. All species are given a two-part name, a "binomial"; the first part of a binomial is the genus.
The second part is called the specific epithet. For example, Boa constrictor is one of four species of the genus Boa. None of these is satisfactory definitions, but scientists and conservationists need a species definition which allows them to work, regardless of the theoretical difficulties. If species were fixed and distinct from one another, there would be no problem, but evolutionary processes cause species to change continually, to grade into one another. Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped. Charles Darwin's 1859 book The Origin of Species explained how species could arise by natural selection; that understanding was extended in the 20th century through genetics and population ecology. Genetic variability arises from mutations and recombination, while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures.
Genes can sometimes be exchanged between species by horizontal gene transfer. Viruses are a special case, driven by a balance of mutation and selection, can be treated as quasispecies. Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics. Early taxonomists such as Linnaeus had no option but to describe what they saw: this was formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts, is hard or impossible to test. Biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: agamospecies for asexual organisms biospecies for reproductively isolated sexual organisms ecospecies based on ecological niches evolutionary species based on lineage genetic species based on gene pool morphospecies based on form or phenotype and taxonomic species, a species as determined by a taxonomist.
A typological species is a group of organisms in which individuals conform to certain fixed properties, so that pre-literate people recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens would differentiate the species; this method was used as a "classical" method of determining species, such as with Linnaeus early in evolutionary theory. However, different phenotypes are not different species. Species named in this manner are called morphospecies. In the 1970s, Robert R. Sokal, Theodore J. Crovello and Peter Sneath proposed a variation on this, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms, it differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species is a group of sexually reproducing organisms that recognize one another as potential mates.
Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms. A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology, genes can move even between distantly related bacteria extending to the whole bacterial domain; as a rule of thumb, microbiologists have assumed that kinds of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA-DNA hybridisation to decide if they belong to the same species or not. This concept was narrowed in 2006 to a similarity of 98.7%. DNA-DNA hybri
Pteriidae called the feather oysters, is a family of medium-sized to large saltwater clams. They are marine bivalve molluscs in the order Pterioida; some of the species in this family are important economically as the source of saltwater pearls. Genera in the family Pteriidae include: Crenatula Lamarck, 1803 Electroma Stoliczka, 1871 Isognomon Lightfoot, 1786 - tree oysters Pinctada Röding, 1798 Pteria Scopoli, 1777 - winged oysters Vulsella Röding, 1798 Powell A. W. B. New Zealand Mollusca, William Collins Publishers Ltd, New Zealand 1979 ISBN 0-00-216906-1
Japan is an island country in East Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asian continent and stretches from the Sea of Okhotsk in the north to the East China Sea and the Philippine Sea in the south; the kanji that make up Japan's name mean "sun origin", it is called the "Land of the Rising Sun". Japan is a stratovolcanic archipelago consisting of about 6,852 islands; the four largest are Honshu, Hokkaido and Shikoku, which make up about ninety-seven percent of Japan's land area and are referred to as home islands. The country is divided into 47 prefectures in eight regions, with Hokkaido being the northernmost prefecture and Okinawa being the southernmost one; the population of 127 million is the world's tenth largest. 90.7 % of people live in cities. About 13.8 million people live in the capital of Japan. The Greater Tokyo Area is the most populous metropolitan area in the world with over 38 million people. Archaeological research indicates; the first written mention of Japan is in Chinese history texts from the 1st century AD.
Influence from other regions China, followed by periods of isolation from Western Europe, has characterized Japan's history. From the 12th century until 1868, Japan was ruled by successive feudal military shōguns who ruled in the name of the Emperor. Japan entered into a long period of isolation in the early 17th century, ended in 1853 when a United States fleet pressured Japan to open to the West. After nearly two decades of internal conflict and insurrection, the Imperial Court regained its political power in 1868 through the help of several clans from Chōshū and Satsuma – and the Empire of Japan was established. In the late 19th and early 20th centuries, victories in the First Sino-Japanese War, the Russo-Japanese War and World War I allowed Japan to expand its empire during a period of increasing militarism; the Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the Japanese surrender. Since adopting its revised constitution on May 3, 1947, during the occupation led by SCAP, the sovereign state of Japan has maintained a unitary parliamentary constitutional monarchy with an Emperor and an elected legislature called the National Diet.
Japan is a member of the ASEAN Plus mechanism, UN, the OECD, the G7, the G8, the G20, is considered a great power. Its economy is the world's third-largest by nominal GDP and the fourth-largest by purchasing power parity, it is the world's fourth-largest exporter and fourth-largest importer. Japan benefits from a skilled and educated workforce. Although it has renounced its right to declare war, Japan maintains a modern military with the world's eighth-largest military budget, used for self-defense and peacekeeping roles. Japan is a developed country with a high standard of living and Human Development Index, its population enjoys the highest life expectancy and third lowest infant mortality rate in the world, but is experiencing issues due to an aging population and low birthrate. Japan is renowned for its historical and extensive cinema, influential music industry, video gaming, rich cuisine and its major contributions to science and modern technology; the Japanese word for Japan is 日本, pronounced Nihon or Nippon and means "the origin of the sun".
The character nichi means "sun" or "day". The compound therefore means "origin of the sun" and is the source of the popular Western epithet "Land of the Rising Sun"; the earliest record of the name Nihon appears in the Chinese historical records of the Tang dynasty, the Old Book of Tang. At the end of the seventh century, a delegation from Japan requested that Nihon be used as the name of their country; this name may have its origin in a letter sent in 607 and recorded in the official history of the Sui dynasty. Prince Shōtoku, the Regent of Japan, sent a mission to China with a letter in which he called himself "the Emperor of the Land where the Sun rises"; the message said: "Here, I, the emperor of the country where the sun rises, send a letter to the emperor of the country where the sun sets. How are you". Prior to the adoption of Nihon, other terms such as Yamato and Wakoku were used; the term Wa is a homophone of Wo 倭, used by the Chinese as a designation for the Japanese as early as the third century Three Kingdoms period.
Another form of Wa, Wei in Chinese) was used for an early state in Japan called Nakoku during the Han dynasty. However, the Japanese disliked some connotation of Wa 倭, it was therefore replaced with the substitute character Wa, meaning "togetherness, harmony"; the English word Japan derives from the historical Chinese pronunciation of 日本. The Old Mandarin or early Wu Chinese pronunciation of Japan was recorded by Marco Polo as Cipangu. In modern Shanghainese, a Wu dialect, the pronunciation of characters 日本; the old Malay word for Japan, Japun or Japang, was borrowed from a southern coastal Chinese dialect Fukienese or Ningpo – and this Malay word was encountered by Portuguese traders in Southeast Asia in the 16th century. These Early Portuguese traders brought the word
Sri Lanka the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia, located in the Indian Ocean to the southwest of the Bay of Bengal and to the southeast of the Arabian Sea. The island is geographically separated from the Indian subcontinent by the Gulf of Mannar and the Palk Strait; the legislative capital, Sri Jayawardenepura Kotte, is a suburb of the commercial capital and largest city, Colombo. Sri Lanka's documented history spans 3,000 years, with evidence of pre-historic human settlements dating back to at least 125,000 years, it has a rich cultural heritage and the first known Buddhist writings of Sri Lanka, the Pāli Canon, date back to the Fourth Buddhist council in 29 BC. Its geographic location and deep harbours made it of great strategic importance from the time of the ancient Silk Road through to the modern Maritime Silk Road. Sri Lanka was known from the beginning of British colonial rule as Ceylon. A nationalist political movement arose in the country in the early 20th century to obtain political independence, granted in 1948.
Sri Lanka's recent history has been marred by a 26-year civil war, which decisively ended when the Sri Lanka Armed Forces defeated the Liberation Tigers of Tamil Eelam in 2009. The current constitution stipulates the political system as a republic and a unitary state governed by a semi-presidential system, it has had a long history of international engagement, as a founding member of the South Asian Association for Regional Cooperation, a member of the United Nations, the Commonwealth of Nations, the G77, the Non-Aligned Movement. Along with the Maldives, Sri Lanka is one of only two South Asian countries rated "high" on the Human Development Index, with its HDI rating and per capita income the highest among South Asian nations; the Sri Lankan constitution accords Buddhism the "foremost place", although it does not identify it as a state religion. Buddhism is given special privileges in the Sri Lankan constitution; the island is home to many cultures and ethnicities. The majority of the population is from the Sinhalese ethnicity, while a large minority of Tamils have played an influential role in the island's history.
Moors, Malays and the indigenous Vedda are established groups on the island. In antiquity, Sri Lanka was known to travellers by a variety of names. According to the Mahavamsa, the legendary Prince Vijaya named the land Tambapanni, because his followers' hands were reddened by the red soil of the area. In Hindu mythology, such as the Ramayana, the island was referred to as Lankā; the Tamil term Eelam, was used to designate the whole island in Sangam literature. The island was known under Chola rule as Mummudi Cholamandalam. Ancient Greek geographers called it Taprobanē from the word Tambapanni; the Persians and Arabs referred to it as Sarandīb from Cerentivu or Siṃhaladvīpaḥ. Ceilão, the name given to Sri Lanka by the Portuguese Empire when it arrived in 1505, was transliterated into English as Ceylon; as a British crown colony, the island was known as Ceylon. The country is now known in Sinhala in Tamil as Ilaṅkai. In 1972, its formal name was changed to "Free and Independent Republic of Sri Lanka".
In 1978 it was changed to the "Democratic Socialist Republic of Sri Lanka". As the name Ceylon still appears in the names of a number of organisations, the Sri Lankan government announced in 2011 a plan to rename all those over which it has authority; the pre-history of Sri Lanka goes back 125,000 years and even as far back as 500,000 years. The era spans the Palaeolithic and early Iron Ages. Among the Paleolithic human settlements discovered in Sri Lanka, which dates back to 37,000 BP, Batadombalena and Belilena are the most important. In these caves, archaeologists have found the remains of anatomically modern humans which they have named Balangoda Man, other evidence suggesting that they may have engaged in agriculture and kept domestic dogs for driving game. One of the first written references to the island is found in the Indian epic Ramayana, which provides details of a kingdom named Lanka, created by the divine sculptor Vishwakarma for Kubera, the Lord of Wealth, it is said that Kubera was overthrown by his demon stepbrother Ravana, the powerful emperor who built a mythical flying machine named Dandu Monara.
The modern city of Wariyapola is described as Ravana's airport. Early inhabitants of Sri Lanka were ancestors of the Vedda people, an indigenous people numbering 2,500 living in modern-day Sri Lanka; the 19th-century Irish historian James Emerson Tennent theorized that Galle, a city in southern Sri Lanka, was the ancient seaport of Tarshish from which King Solomon is said to have drawn ivory and other valuables. According to the Mahāvamsa, a chronicle written in Pāḷi, the original inhabitants of Sri Lanka are the Yakshas and Nagas. Ancient cemeteries that were used before 600 BC and other signs of advanced civilisation have been discovered in Sri Lanka. Sinhalese history traditionally starts in 543 BC with the arrival of Prince Vijaya, a semi-legendary prince who sailed with 700 followers to Sri Lanka, after being expelled from Vanga Kingdom (present-day Ben
Pteria is a genus of molluscs in the family Pteriidae. The species of the genus are sometimes referred to as winged oysters; the World Register of Marine Species includes the following species in the genus: Pteria admirabilis Wang, 2002 Pteria aegyptiaca Pteria avicular Pteria bernhardi Pteria broomei Huber, 2010 Pteria brunnea Pteria bulliformis Wang, 2002 Pteria colymbus — Atlantic wing-oyster Pteria cooki Lamprell & Healy, 1997 Pteria dendronephthya Habe, 1960 Pteria fibrosa Pteria formosa Pteria gregata Pteria heteroptera Pteria hirundo Linnaeus, 1758 Pteria howensis Lamprell & Healy, 1997 Pteria lata Pteria maura Pteria peasei ‒ swift wing oyster Pteria penguin — Penguin's wing oyster Pteria physoides Pteria saltata Pteria spectrum Pteria sterna Gould, 1851 — Pacific wing-oyster Pteria straminea Pteria tortirostris Pteria venezuelensis