3. The Tardigrade (aka, the Waterbear or Moss piglet)
The tardigrade is invincible. You could try to off this extremophile in a myriad of ways, and it would just look at you sleepily and say, "what next?" If you expose them to temperatures close to absolute zero, they'll smile and offer you a sweater. Likewise, they can withstand temperatures far hotter than boiling water, and endure pressures many times greater than those of the deepest ocean trenches. Radiation? No problem. Food and water? They can survive without it for 120 years. Most impressively, tardigrades can survive exposure to the vacuum of space. Think of that. If you channeled this little animal, your body would be a spaceship. Could a radioactive waterbear bite us already?