The Water Bear

The tardigrade is also known as the water bear.

A polyextremophile is an organism that can survive many types of extreme environments. One of the most complex polyextremophiles is the tardigrade, which can live in just about every environment possible here on earth, plus some not on Earth (more on that later). Tardigrades are about a millimeter long when fully grown. They are short and plump with eight tubular legs, each with 4-8 bear-like claws. Given that they also move like a lumbering bear, tardigrades have earned the nickname water bear.
   Tardigrades typically live in marine, fresh water, or semiaquatic environments, but you can also find them in the mosses and lichens found in forested areas. As long as there is some water around, they can thrive. They feed on the fluids found in plant and animal cells. Their mouth is able to pierce the cell walls so that they can then suck out and ingest the inner parts of the cell. 
   Tardigrades can survive being completely desiccated for nearly 10 years as well as exposure to high levels of chemical toxins. They can survive extreme heat (150 °C) for a few minutes and extreme cold (-200 °C) for a few day. When exposed to extreme cold their body composition changes from 85% water to only 3% which keeps their body from being damaged by ice crystal formation. 

   The can survive extreme pressures far greater than that found at the Mariana trench. In 2007, tardigrades were sent into space on the Russian/EU satellite Foton-M3 for ten days. Even after being exposed to the vacuum of space for this long, most of the samples survived after being rehydrated back on Earth, some of which had also been fully exposed to the Sun’s radiation. Tardigrades were also sent into space on the final flight of Space Shuttle Endeavour where experiments showed that cosmic radiation and microgravity did not significantly affect their survival, confirming their usefulness in space research.
   You’re probably wondering just how these creatures could be so resilient. They rely on cryptobiosis—a state of suspended animation that they can enter in response to adverse environmental conditions where all metabolic processes stop. Their bodies dehydrate into a dense, mummified disc called a tun. They can remain in this state indefinitely until their environment becomes hospitable once again. When this happens, the tun plumps back up and the tardigrade return to its previous metabolic state.