Tardigrades, more commonly known as Water Bears, are microscopic relatives of arthropods. They are water dwellers with eight legs and segmented bodies. The phylum was first discovered in 1773 when the first member was described. There are currently 1,150 species known to science found throughout the world, from 20,000 feet above sea level to 13,000 feet below sea level and from the poles to the equator.
Adults range in size from 0.1 to 1.5mm with newly hatched larvae often smaller than 0.05mm in length. They are most often found in damp areas, preferring habitats such as lichens or mosses, and can be found in concentrations of up to 25,000 animals per liter of water. Their diet consists of the fluids of plant and animals cells. They access this fluid by puncturing the cell membrane (and wall in plants) with a stylet and then ingest the contents of the cell. Some species will eat organisms whole such as rotifers and other Tardigrades.
They are best known for their ability to survive extreme environments. They can survive temperatures close to absolute zero (−459 °F) and as high as 304 °F. They can withstand 1,000 times more radiation than any other animal and can go almost a decade without water. Starting 2007 Tardigrades were sent into outer space for survival experiments; they were able to survive the vacuum of outer space in low earth orbit.