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| image = Waterbear.jpg | image_caption = ''Hypsibius dujardini'' | authority = Spallanzani, 1777 | subdivision_ranks = Classes | subdivision = }} Tardigrades (also known as water bears or moss piglets)〔 are water-dwelling, eight-legged, segmented micro-animals.〔 They were first discovered by the German pastor Johann August Ephraim Goeze in 1773. The name ''Tardigrada'' (meaning "slow stepper") was given three years later by the Italian biologist Lazzaro Spallanzani. They have been sighted in numerous locations, including mountaintops, the deep sea, tropical rain forests, and the Antarctic. Tardigrades are notable for being perhaps the most durable of known organisms; they are able to survive extreme conditions that would be rapidly fatal to nearly all other known life forms. They can withstand temperature ranges from to ,〔(''Wired'', Water bear )〕 pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. They can go without food or water for more than 10 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.〔 They are not considered extremophilic because they are not adapted to exploit these conditions. This means that their chances of dying increase the longer they are exposed to the extreme environments,〔 whereas true extremophiles thrive in a physically or geochemically extreme environment that would harm most other organisms.〔 Usually, tardigrades are about long when they are fully grown. They are short and plump with four pairs of legs, each with four to eight claws also known as "disks".〔 The first three pairs of legs are directed ventrolaterally and are the primary means of locomotion, while the fourth pair is directed posteriorly on the terminal segment of the trunk and is used primarily for grasping the substrate.〔(【引用サイトリンク】title= Florida Entomologist: On Water Bears )〕 Tardigrades are prevalent in mosses and lichens and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a very low-power microscope, making them accessible to students and amateur scientists. Tardigrades form the phylum ''Tardigrada'', part of the superphylum Ecdysozoa. It is an ancient group, with fossils dating from 530 million years ago, in the Cambrian period.〔(【引用サイトリンク】title=Tardigrada (water bears, tardigrades) )〕 About 1,150 species of tardigrades have been described.〔Degma, P., Bertolani, R. & Guidetti, R. 2009–2011. Actual checklist of Tardigrada species. Ver. 18: 27-04-2011. (tardigrada.modena.unimo.it )〕 Tardigrades can be found throughout the world, from the Himalayas〔Hogan, C. Michael. 2010. ("Extremophile" ). eds. E.Monosson and C.Cleveland. ''Encyclopedia of Earth''. National Council for Science and the Environment, washington DC〕 (above ), to the deep sea (below ) and from the polar regions to the equator. ==Description== Johann August Ephraim Goeze originally named the tardigrade ''kleiner Wasserbär'' (''Bärtierchen'' today), meaning 'little water bear' in German. The name ''Tardigrada'' means "slow walker" and was given by Lazzaro Spallanzani in 1776. The name ''water bear'' comes from the way they walk, reminiscent of a bear's gait. The biggest adults may reach a body length of , the smallest below 0.1 mm. Newly hatched tardigrades may be smaller than 0.05 mm. The most convenient place to find tardigrades is on lichens and mosses. Other environments are dunes, beaches, soil, and marine or freshwater sediments, where they may occur quite frequently (up to 25,000 animals per liter). Tardigrades, in the case of ''Echiniscoides Wyethi'', may be found on barnacles. Often, tardigrades can be found by soaking a piece of moss in water. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tardigrade」の詳細全文を読む スポンサード リンク
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