https://www.wired.com/2013/04/animal-superpowers/

Tardigrade, aka Water Bear (Tardigrada) These tiny, adorable creatures grow to be only a millimeter long but may be the hardiest organism on the planet (or perhaps any planet). Tardigrades are virtually indestructible[pdf]. They are polyextremophiles, meaning they thrive in multiple kinds of extreme environments. Among the things they are known to survive: Freezing temperatures as low as -200 C (-328 F), scorching temperatures up to 150 C (302 F), outer space, no food or water for over a century (or only a decade if you are a spoilsport scientist), ionizing radiation up to 570,000 roentgens (a dose of just 500 roentgens would kill you), solar radiation, gamma radiation, ultraviolet radiation, high salinity and lack of oxygen. How can a creature so tough be so cute and cuddly looking at the same time? It hardly seems fair. Image: NASA