The ocean quahog is a species of edible clam, a marine bivalve mollusk in the family Arcticidae. This species is native to the North Atlantic Ocean, it is harvested commercially as a food source; this species is known by a number of different common names, including Icelandic cyprine, mahogany clam, mahogany quahog, black quahog, black clam. The typical Arctica islandica resembles the quahog, but the shell of the ocean quahog is rounder, the periostracum is black, on the interior of the shell, the pallial line has no indentation, or sinus. Unlike the quahog, which lives intertidally and can be collected by clam digging, this species lives subtidally, can only be collected by dredging, they grow to sizes exceeding 50 mm shell height. An individual specimen was reported to have lived 507 years, making it the longest-lived non-colonial metazoan whose age was known; these animals show exceptional longevity with a highest reported age, for Ming the clam, of 507 years. This makes it the longest living non-colonial metazoan species with an authenticated lifespan.
It is unknown how long it could have lived if it had not been collected alive by an expedition in 2006. In 1868 one specimen, collected alive near Iceland, was 374 years old; the study of its growth rate and the oxygen isotope data showed that it had a variable growth at the peak of the Little Ice Age around 1550–1620 and mild climate near its end around 1765–1780 and had recorded the volcanic eruption of Mount Tambora in 1815. One study found that in animals aged 4–192 years, antioxidant enzymes declined in the first 25 years, which includes the growth and sexual maturity stages, but afterwards remained stable for over 150 years. Though more detailed studies are warranted, it appears this species is a case of negligible senescence. In contrast to the exceptionally long-lived populations in deep, cold parts of its range, more southern populations that experience greater seasonal variations in salinity and temperature are far shorter-lived. For example, A. islandica from the German Bay of Kiel only reach an age of about 30 years and those from the German Bight about 150.
According to the research done by Irene Ballesta-Artero, Starrlight Augustine, et al. they conducted experiments using a Dynamic Energy Model to test the extreme longevity of the A. Islandica; the A. Islandica species shows slower growth rate than other species of clams, it takes an average rate of 4-days for birth. Furthermore it takes an average of 5.8-years for the Arctica Islandica to reach maturity, at this point the somatic costs start going down. A. Islandica's extreme longevity arises from a lowered somatic maintenance costs and a low aging acceleration. List of long-living organisms Maximum life span Ming Ocean quahog, Arctica islandica, Life history and habitat from the NOAA. Climate records from a bivalved Methuselah
The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, named after Cambria, the Latinised name for Wales, where rocks from this age were first studied; the Precambrian accounts for 88% of the Earth's geologic time. The Precambrian is an informal unit of geologic time, subdivided into three eons of the geologic time scale, it spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, when hard-shelled creatures first appeared in abundance. Little is known about the Precambrian, despite it making up seven-eighths of the Earth's history, what is known has been discovered from the 1960s onwards; the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, fossils from the Precambrian are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain buried beneath Phanerozoic strata.
It is thought that the Earth coalesced from material in orbit around the Sun at 4,543 Ma, may have been struck by a large planetesimal shortly after it formed, splitting off material that formed the Moon. A stable crust was in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma; the term "Precambrian" is recognized by the International Commission on Stratigraphy as the only "supereon" in geologic time. "Precambrian" is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. As of 2010, the United States Geological Survey considers the term informal, lacking a stratigraphic rank. A specific date for the origin of life has not been determined. Carbon found in 3.8 billion-year-old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia. Probable fossils 100 million years older have been found in the same area.
However, there is evidence. There is a solid record of bacterial life throughout the remainder of the Precambrian. Excluding a few contested reports of much older forms from North America and India, the first complex multicellular life forms seem to have appeared at 1500 Ma, in the Mesoproterozoic era of the Proterozoic eon. Fossil evidence from the Ediacaran period of such complex life comes from the Lantian formation, at least 580 million years ago. A diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma; these are referred to as Vendian biota. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic eon. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale, including some which may represent stem groups of modern taxa; the increase in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life. While land seems to have been devoid of plants and animals and other microbes formed prokaryotic mats that covered terrestrial areas.
Tracks from an animal with leg like appendages have been found in what was mud 551 million years ago. Evidence of the details of plate motions and other tectonic activity in the Precambrian has been poorly preserved, it is believed that small proto-continents existed prior to 4280 Ma, that most of the Earth's landmasses collected into a single supercontinent around 1130 Ma. The supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch 2400–2100 Ma. One of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "Snowball Earth"; the atmosphere of the early Earth is not well understood. Most geologists believe it was composed of nitrogen, carbon dioxide, other inert gases, was lacking in free oxygen. There is, evidence that an oxygen-rich atmosphere existed since the early Archean. At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism.
This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis, sometimes called the oxygen catastrophe. At first, oxygen would have combined with other elements in Earth's crust iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed real dates to be assigned to specific formations and features; the Precambrian is divided into
Grooved carpet shell
The grooved carpet shell, or Palourde clam, Ruditapes decussatus, or Venerupis decussatus, is a clam or bivalve mollusc in the family Veneridae. It is distributed worldwide and due to its ecological and economic interest has been proposed as a bioindicator; this species is one of the most popular and profitable mollusc of lagoonal and coastal sites in the Mediterranean, where it was collected for a long time as food. It is canned; the shell is broadly oval to quadrate with the umbones distinctly anterior. The posterior hinge line is straight, the posterior margin truncate, the anterior hinge line grades into the down-sloping anterior margin, it is prominent posteriorly. The surface has a sculpture of fine concentric striae and bolder radiating lines. Growth stages are clear; the lunule and escutcheon are poorly defined. Each valve has three cardinal teeth: the centre one in the left valve, centre and posterior in right are bifid; the pallial line and adductor scars are distinct. The pallial sinus is U-shaped, not extending beyond the midline of the shell, but reaching a point below the posterior part of the ligament.
The lower limb of the sinus is distinct from the pallial line for the whole of its length. The inner surfaces of the shell are glossy white with yellow or orange tints, with a bluish tinge along the dorsal edge; the overall color is cream, yellowish, or light brown with darker markings. Despite improper management, some regions in the Atlantic coast of the Iberian Peninsula, of the Mediterranean basin, as well as Ireland have solid populations of Ruditapes decussatus. Ruditapes decussatus is cultured from the Atlantic coast of France, Portugal and in the Mediterranean basin, it is grown with other bivalves. Their main predators are shore crabs. An individual Carcinus maenas can consume 6 clams per day. Marine aquaculture production of grooved carpet shell in 2003 was 3,007 t in Portugal, which excludes non-aquaculture harvesting of the species. Between 1997 and 2001 total aquaculture production varied between 3,700 and 4,900 tonnes, from five countries. Most was produced by Portugal but France and Spain have been significant producers.
Global production seems to be declining. In 1985 the price for live Ruditapes decussatus was about €0.60/kg. In 2005, the price was about €15/kg, it is canned. Garcia, F. – 1993. Interprétation des stries valvaires pour l'évaluation de la croissance de Ruditapes decussatus L. Oceanologica Acta. 16: 199–203.. Poppe, G. T. & Goto, Y. – 1991. European seashells. Vol 1. Verlag Christa Hemmen. Rodriguez-Moscoso, E & Arnaiz, R – 1998. Gametogenesis and energy storage in a population of the grooved carpet-shell clam, Tapes decussatus, in northwest Spain. Aquaculture.. Vol. 162, no. 1–2, pp. 125–139.. Xie, Qiushi & Burnell, GM – 1994. A comparative study of the gametogenic cycles of the clams Tapes philippinarum and Tapes decussatus on the south coast of Ireland. Journal of Shellfish Research.. Vol. 13, no. 2, pp. 467–472
The smooth clam, Callista chione, is a rather large, marine, bivalve mollusc that inhabits sandy bottoms or with small pebbles in clean waters down to about 200 m from the British Isles to the Mediterranean. The shell can reach up to about 110 mm Ø, its outer side is smooth and ranges from light greenish creamy colour to medium brown varies to match the background; the concentric and radial growth lines are seen. Callista chione is edible, different dishes are prepared throughout the Mediterranean in Spain, France, the Balkan and the Magreb countries, it has been found that, as is the case with many bivalve molluscs, which are filter-feeders, that Callista chione, common in fish markets in the Mediterranean, concentrates toxins from dinoflagellates blooms associated with pollution events such as red tides, sewage water, old sediment dredging, ship ballast water dumping, etc. These toxins cannot be eliminated by the traditional cleansing of shellfish in clean water or by cooking, can be responsible for complex human health problems: respiratory ailments, skin rashes paralysis, etc. such as it is known now to have occurred in New Orleans, associated with the contact or ingestion of contaminated water, left by Katrina.
The commonest of these dangers is known as paralytic shellfish poisoning. En: Smooth or brown Venus-clam Fr: Vernis, grande palourde It: Fasolaro, Cappa liscia, cappa chione, venerechione De: Braune Venusmuschel Es: Almejón de sangre, almejón brillante, concha fina Ca: Petxinot de sang, lluenta Gr: Gyalisteri Hr: Lakirka, Klapun ^. Details about the species and its fisheries ^. A nice set of colour photographs from Callista chione shells can be seen at Conchology Inc. a collectors outlet in Belgium ^. See for instance R. A. Vollenweider, A. Rinaldi, R. Viviani and E. Todini. 1996. Assessment of the state of eutrophication in the Mediterranean sea. MAP Technical Reports Series No. 106. UNEP, Athens
The razor shell, Ensis magnus called razor clam, razor fish or spoot, is a bivalve of the family Pharidae. It is found on sandy beaches in northern Europe. In some locations, the common name "razor shell" is used to refer to members of the family Solenidae, including species of the genera Ensis and Solen, by some taxonomic classifications which include the family Pharidae within the family Solenidae, it prefers coarser sand than E. siliqua. It is known for its elongated, rectangular shape, whose similarity to the straight razor gives it its name; the razor shell has been known to reach 23 centimetres in length. The dorsal margin is straight, it can be confused with the shorter 15 centimetres and more curved E. ensis. Razor shells have a fragile shell, with open ends; the shell is smooth on the outside and whitish in color, with vertical and horizontal reddish-brown or purplish-brown markings separated by a diagonal line. The periostracum is olive-green; the inner surface is white with a purple tinge and the foot is creamy white with brown lines.
The razor shell lives under the sand. Its digging activity comprises six stages, repeated cyclically. A digging cycle involves integration of the muscular foot with the opening and closing of the valve and one end; the foot is inflated hydraulically, anchoring the animal. Deflation of the foot draws the shell down; the razor shell squirts water down into the sand, removing loose sand from its path. The foot is thought to exert a pressure of about 196kPa, its presence is revealed by a keyhole-shaped hole in the sand, made by its siphons during suspension feeding for plankton. In the razor shell sexual development is synchronous. During the summer, they are in the sexual rest stage, gametogenesis begins at the start of autumn. In winter and spring consecutive spawns take place, interrupted by gonadal restoration periods. Many intertidal populations of razor shell have declined as a result of overfishing. Razor shells are sensitive to minor perturbations in, for instance and temperature, they will emerge from their burrows if brine is poured in.
Razor shells have been found to be vulnerable to a variety of tumour. Razor shells in Norway Effect of dredging on razor shell populations
The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago, to the beginning of the Devonian Period, 419.2 Mya. The Silurian is the shortest period of the Paleozoic Era; as with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed fish and bony fish. Multi-cellular life began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes and coastlines, terrestrial arthropods are first found on land during the Silurian. However, terrestrial life would not diversify and affect the landscape until the Devonian; the Silurian system was first identified by British geologist Roderick Murchison, examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s.
He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, from the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, the germ of the modern geological time scale; as it was first identified, the "Silurian" series when traced farther afield came to overlap Sedgwick's "Cambrian" sequence, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was "Gotlandian" after the strata of the Baltic island of Gotland; the French geologist Joachim Barrande, building on Murchison's work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge.
He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, the stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils; the Llandovery Epoch lasted from 443.8 ± 1.5 to 433.4 ± 2.8 mya, is subdivided into three stages: the Rhuddanian, lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, the Telychian. The epoch is named for the town of Llandovery in Wales; the Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian and Homerian ages. It is named after Wenlock Edge in England. During the Wenlock, the oldest-known tracheophytes of the genus Cooksonia, appear; the complexity of later Gondwana plants like Baragwanathia, which resembled a modern clubmoss, indicates a much longer history for vascular plants, extending into the early Silurian or Ordovician.
The first terrestrial animals appear in the Wenlock, represented by air-breathing millipedes from Scotland. The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, the Ludfordian stage. It is named for the town of Ludlow in England; the Přídolí, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area. In North America a different suite of regional stages is sometimes used: Cayugan Lockportian Tonawandan Ontarian Alexandrian In Estonia the following suite of regional stages is used: Ohessaare stage Kaugatuma stage Kuressaare stage Paadla stage Rootsiküla stage Jaagarahu stage Jaani stage Adavere stage Raikküla stage Juuru stage With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe.
The high sea levels of the Silurian and the flat land resulted in a number of island chains, thus a rich diversity of environmental settings. During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late-Ordovician glaciation; the southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity; the continents of Avalonia and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica. When the proto-Europe coll