Otherwise known as a [wiki]tardigrade[/wiki], it's a animal extremophile that is generally about a millimeter long when fully grown (so it is visible to the unaided human eye). It can survive in temperatures from nearly absolute zero to well above the boiling point of water, it can withstand pressures greater than those found in the deepest ocean trenches all the way to a vacuum, it can survive doses of radiation that are hundreds of times stronger than what a human can possibly survive, and they've been known to survive in these conditions for at least a decade, probably longer. The secret is that they dehydrate in these extreme conditions to 1% or so of their normal amount of water
and go into a state of stasis, which they come back out of when they rehydrate.
Apparently, they took these organisms into space and exposed them to vacuum for ten days, then rehydrated them, and more than 2/3 of the ones that were protected from solar radiation survived. Even more incredibly, some of them actually survived exposure to full solar radiation for that time frame.
Truly an impressive example of what life is capable of.