What the heck is a tardigrade?

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A tardigrade is a cute eight-legged invertebrate first discovered in 1773, also called a water bear. There are about 400 species, and they have an entire Phylum all to themselves. The biggest species are a tad over a millimeter long, but most are smaller. All are basically aquatic, though some live in the surface film of moisture on lichens and mosses instead of in a pond or an ocean. They have the distinction of being some of the hardiest organisms on earth; when times are bad, they can dry up into a little barrel called a tun, which is amazingly resistant to just about everything--high vacuum, high pressure, high radiation, high temperatures, low temperatures, and long times. This lets them live in just about every habitat on earth, from the Arctic Ocean to tropical forests. Live tardigrades have been regenerated from dried up mosses more than 100 years after being collected.