This is a tardigrade. When fully grown, they reach only 1mm in length. Also known as moss piglets or water bears(they walk slowly, with a gait resembling a bear), these poly-extremophiles live in water and survive extremely hot or cold temperatures. There are over 1500 species of tardigrades found all over the planet, from the Himalayas, to equatorial regions, to the extreme deeps of the ocean (6000+ meters). They can be chilled for days below -200C or heated above 150C (but only for a few minutes). In 2007 an experiment on the International Space Station discovered that a handful of tardigrade embryos survived full solar radiation and grew up as healthy adults. Most tardigrades are planet eaters, while some feed on bacteria. A handful of species are also known to be predatory.
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