Portal:Crustaceans

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edit   The Crustaceans Portal Crustaceans (Subphylum Crustacea) form a very large group of arthropods, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at 0.1 mm (0.004 in), to the Japanese spider crab with a leg span of up to 14 ft (4.3 m) and a mass of 44 lb (20 kg). Like other arthropods, crustaceans have an exoskeleton, which they moult in order to grow. They are distinguished from other groups of arthropods, such as insects, myriapods and chelicerates by the possession of biramous (two-parted) limbs, and by the nauplius form of the larvae. Most crustaceans are free-living aquatic animals, but some are terrestrial (e.g. woodlice), some are parasitic (e.g. fish lice, tongue worms) and some are sessile (e.g. barnacles). The group has an extensive fossil record, reaching back to the Cambrian, and includes living fossils such as Triops cancriformis, which has existed apparently unchanged since the Triassic period. More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, the majority of it being shrimps and prawns. Krill and copepods are not as widely fished, but may be the animals with the greatest biomass on the planet, and form a vital part of the food chain. | Go to random article edit   Selected article Seychellum alluaudi is a species of freshwater crab endemic to the Seychelles, and the only true freshwater crab in that country. It lives in rainforest streams on the archipelago's granitic high islands. Although it may be abundant, little is known about its biology, and it is currently listed as Least Concern on the IUCN Red List. Adults are dark yellow to brown in colour, and have a quadrangular carapace with a width of around 50 mm (2 in). The claws are unequal in size. S. alluaudi was described as a species of Deckenia in 1893 and 1894, and later split off into the monotypic segregate genus Seychellum. Its closest relatives are the two species currently in Deckenia, both of which are found in East Africa. Several hypotheses have been published to explain how Seychellum reached its isolated location; some means of transport across the open ocean is considered the most likely explanation. Seychellum differs from Deckenia in a number of characters, including the lengths of the legs and antennae, and the fact that Deckenia species have flattened legs, compared to those of Seychellum. edit   Did you know? ... that the crab Dyspanopeus sayi (pictured) may have lived in the Venetian Lagoon for 15 years before it was discovered? ... that the long-nosed spider crab, Libinia dubia, disguises itself by sticking bits of unpalatable seaweed and invertebrates on its carapace? ... that colour markings, considered rare among fossil crabs, have been found on Avitelmessus? ... that the sea anemone Calliactis tricolor is often attached to shells occupied by the hermit crabs Dardanus venosus and Clibanarius vittatus? edit   Selected biography Charles Robert Darwin FRS (February 12, 1809 – April 19, 1882) was an English naturalist who established that all species of life have descended over time from common ancestors, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection. In 1846, Darwin returned to a fascination in marine invertebrates, dating back to his student days with Robert Edmond Grant, by dissecting and classifying the barnacles (Cirripedia) he had collected on his voyages. In the following eight years of work on barnacles, Darwin's theory of natural selection helped him to find homologies, showing that slightly changed body parts served different functions to meet new conditions, and in some genera he found minute males parasitic on hermaphrodites, showing an intermediate stage in the evolution of distinct sexes. In 1853, this work earnt Darwin the Royal Society's Royal Medal, and it made his reputation as a biologist. Even without publication of his works on evolution, Darwin would have had a considerable reputation as the author of The Voyage of the Beagle, as a geologist who had published extensively on South America and had solved the puzzle of the formation of coral atolls, and as a biologist who had published the definitive work on barnacles. edit   Selected picture The hermit crab Dardanus calidus can grow to a length of 12 centimetres (4.7 in), and protects itself with a large gastropod shell, which it often decorates with one or more sea anemones of the genus Calliactis. edit   Crustacean lists List of Atlantic decapod species List of crabs of New Zealand List of crustaceans of the Indiana Dunes List of Cumacea literature List of prehistoric barnacles List of prehistoric malacostracans List of woodlice of the British Isles edit   Categories edit   Related portals Portal:Arthropods Portal:Insects Portal:Marine life Portal:Animals Portal:Biology Portal:Paleontology edit   Associated Wikimedia What are portals? 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