The most badass species in the entire world is about a millimeter long. It's the Tardigrade, affectionately known as the "waterbear," and it can survive... anything. It is completely indestructible. Temperatures close to absolute zero? Waterbear don't care. Temperatures well past the boiling point? Pft, bring it on! Outer space? No problem. Seriously, waterbears go into suspended animation when exposed to the vacuum of space, and reanimate once they're back in favorable conditions. Their body is its own spaceship! Truly, the waterbear is the king of extremophiles.