Darwin in his Origin of Species had coined the phrase 'survival of the fittest'. Little did he know that Tardigrades would be the answer in the quest for 'the fittest'. All them are not same in terms of features. There are various types of Tardis. Some are found in the ocean, some on land.
In 2007, when the European Space Agency had sent these wrinkled species to space, on ESA's orbital Foton-M3 mission for 12 days, they had reportedly survived temperatures as cold as -272 degrees Celsius, to temperatures shooting as high as +150 degrees Celsius.
The Milnesium tardigradium (M. Tardigradium) can live without water for ten years and are resistant to radiation explain the findings in a report published in Natural Science Journal. Add to this list, its ability to survive close to 5000 to 6200 Gy (Gamma rays). In fact researchers believe, that conditions such as an asteroid impact, supernovae or gamma ray bursts (GRB) are some of the few apocalyptic events that could probably take down these minuscule monsters. The Ozone layer needs to deplete before these Tardigrades are exposed to lethal doses of radiations which should take them down. Clearly, mankind would be long dead before one of these critters begin to collapse.
These invertebrates through a clever biological trickery can form themselves into 'tuns'. According to Plos Journal, Tardigrades are capable of anhydrobiosis, a process where the invertebrate dehydrates itself and its metabolism decreases. However, in favourable conditions it can rehydrate. It also produces glycerol, and form a layer which keeps them protected from freezing temperatures and forms a cocoon like protective covering. The species tuck in their legs and form a 'tun'. Such is the body resistance that these 8-legged creatures can persist to live for 100 years before they can rehydrate.