The dark periostracum is flaking off this dried valve of Arctica islandica from Wales
The ocean quahog (Arctica islandica) is a species of edible clam, a marinebivalvemollusk in the family Arcticidae. This species is native to the North Atlantic Ocean, and it is harvested commercially as a food source. This species is also known by a number of different common names, including Icelandic cyprine,[1] mahogany clam, mahogany quahog, black quahog, and black clam.[2]
The typical Arctica islandica resembles the quahog, but the shell of the ocean quahog is rounder, the periostracum is usually black, and 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, and can only be collected by dredging. They grow to sizes exceeding 50mm or two inches shell height.[3]An individual specimen was reported to have lived 507 years, making it the longest-lived non-colonial metazoan whose age was accurately known.[4]
Right and left valve of the same specimen:
Right valve
Left valve
Life cycle and longevity
Arctica Islandica shows slower growth rate than other species of clams, it takes an average rate of 4 days for birth (embryo to larvae stage). Furthermore, it takes an average of 5.8 years for A. Islandica to reach maturity; at this point the somatic costs start going down. Dynamic Energy Models (DEM) predict that Arctica islandica's extreme longevity arises from lowered somatic maintenance costs and a low aging acceleration.[5] For individuals in populations in cold areas the growth rate is probably further slowed because growth only occurs in summer.[6] This slow life style results in 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.[4][7][8] It is unknown how long it could have lived if it had not been collected alive by an expedition in 2006.
This characteristic has proven useful in the science of sclerochronology, the study of periodic physical and chemical features in the hard tissues of animals that grow by accretion, and is especially valuable for modeling of paleoclimates. 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 highly 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.[9]
One study found that in animals aged 4–192 years, antioxidant enzymes declined rapidly 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.[10] In contrast to the exceptionally long-lived populations in relatively deep, cold parts of its range, more southern populations that experience greater seasonal variations in salinity and temperature are typically far shorter-lived. For example, A. islandica from the German Bay of Kiel typically only reach an age of about 30 years and those from the German Bight about 150.[11]
Feeding ecology
Like other clam species, Arctica islandica is a filter feeder. Feeding activity appears regulated by light levels, which can be used as a proxy for food availability. This means that at the northern extreme of the distribution, feeding is concentrated during eight months of the year, while during the rest of the year the clams only feed for a few days a month.[6]
↑ Hackney, Cameron R.; Thomas E. Rippen (2000). "The Molluscan Shellfish Industry". In Roy E. Martin; Emily Paine Carter Jr.; George J. Flick; Lynn M. Davis (eds.). Marine and Freshwater Products Handbook. CRC Press. pp.323–324. ISBN1-56676-889-6.
1 2 Butler, P.; Wanamaker, A. Jr.; Scourse, J.; Richardson, C.; Reynolds, D. (2013). "Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica". Palaeogeography, Palaeoclimatology, Palaeoecology. 373: 141–51. Bibcode:2013PPP...373..141B. doi:10.1016/j.palaeo.2012.01.016.
↑ Strahl, Julia (2011). Life strategies in the long-lived bivalve Arctica islandica on a latitudinal climate gradient – Environmental constraints and evolutionary adaptations. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, University of Bremen.
Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shells of equal size connected by two adductor muscles and have a powerful burrowing foot. They live in both freshwater and marine environments; in salt water they prefer to burrow down into the mud and the turbidity of the water required varies with species and location; the greatest diversity of these is in North America.
Bivalvia or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs that have laterally compressed soft bodies enclosed by a calcified exoskeleton consisting of a hinged pair of half-shells known as valves. As a group, bivalves have no head and lack some typical molluscan organs such as the radula and the odontophore. Their gills have evolved into ctenidia, specialised organs for feeding and breathing.
The Pacific geoduck is a species of very large saltwater clam in the family Hiatellidae. The common name is derived from the Lushootseed name, gʷidəq.
Clam shrimp are a group of bivalved branchiopod crustaceans that resemble the unrelated bivalved molluscs. They are extant and also known from the fossil record, from at least the Devonian period and perhaps before. They were originally classified in the former order Conchostraca, which later proved to be paraphyletic, due to the fact that water fleas are nested within clam shrimps. Clam shrimp are now divided into three orders, Cyclestherida, Laevicaudata, and Spinicaudata, in addition to the fossil family Leaiidae.
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The hard clam, also known as the round clam, hard-shellclam, or the quahog, is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves that in the United States are frequently referred to simply as clams. Older literature sources may use the systematic name Venus mercenaria; this species is in the family Veneridae, the venus clams.
Chione cancellata, is a species of medium-sized saltwater clam, a marine bivalve mollusc in the family Veneridae, the venus clams.
Freshwater bivalves are molluscs of the order Bivalvia that inhabit freshwater ecosystems. They are one of the two main groups of freshwater molluscs, along with freshwater snails.
The Atlantic surf clam, also called the bar clam, hen clam, skimmer or simply sea clam, is a very large, edible, saltwater clam or marine bivalve mollusk in the family Mactridae. It is one of the most commonly found species of bivalves in the western Atlantic Ocean. Able to reach sizes between 7.9 and 8.9 inches in length, Atlantic surf clams are much larger than Spisula solida, which also resides in the eastern Atlantic coastal waters. Atlantic surf clams reproduce in late summer, when the water temperatures peak.
Ming, also known as Hafrún, was an ocean quahog clam that was dredged off the coast of Iceland in 2006 and whose age was calculated by counting annual growth lines in the shell. Ming was the oldest individual (non-colonial) animal ever discovered whose age could be precisely determined.
The Arcticidae are a family of marine clams in the order Venerida. The only living species in the family is Arctica islandica. There are also many fossil species classified in a number of genera.
Negligible senescence is a term coined by biogerontologist Caleb Finch to denote organisms that do not exhibit evidence of biological aging (senescence), such as measurable reductions in their reproductive capability, measurable functional decline, or rising death rates with age. There are many species where scientists have seen no increase in mortality after maturity. This may mean that the lifespan of the organism is so long that researchers' subjects have not yet lived up to the time when a measure of the species' longevity can be made. Turtles, for example, were once thought to lack senescence, but more extensive observations have found evidence of decreasing fitness with age.
Astarte borealis or Tridonta borealis, the boreal astarte, is a species of bivalve mollusc in the family Astartidae. It can be found in the Arctic Ocean and in the northern Pacific and Atlantic Oceans.
Enigmonia is a genus of saltwater clams, a marine bivalve mollusc in the family Anomiidae, the jingle shells. Enigmonia aenigmatica, the mangrove jingle shell clam, is the only species in this monotypic genus. It is found living on mangroves in the Indo-Pacific Ocean.
Venerupis corrugata, the pullet carpet shell, is a species of bivalve mollusc in the family Veneridae. It is found buried in the sediment on the sea bed in shallow parts of the eastern Atlantic Ocean. It is harvested for human consumption in Spain and other parts of Western Europe.
Nuttallia obscurata, the purple mahogany clam, dark mahogany clam, varnish clam or savory clam, is a species of saltwater clam, a marine bivalve mollusk in the family Psammobiidae. It was first described to science by Lovell Augustus Reeve, a British conchologist, in 1857.
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Right valve
Left valve
