Tardigrades (or water bears) are microscopic, water-dwelling, segmented animals with eight legs. They were first described by Johann August Ephraim Goeze in 1773. The name Tardigrada means “slow walker” and was given by Spallanzani in 1777. The name water bear comes from the way they walk, reminiscent of a bear’s. The biggest adults may reach a body length of 1.5 mm, the smallest below 0.1 mm. Freshly hatched larvae may be smaller than 0.05 mm. More than 1000 species of tardigrades have been described. 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. Tardigrades often can be found by soaking a piece of moss in spring water. Tardigrades are polyextremophiles and are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures close to absolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals such as humans, nearly a decade without water, and even the vacuum of space.
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