Tardigrades are sponges for foreign genes. Does that explain why they are famously indestructible?
Ed Yong in The Atlantic:
The toughest animals in the world aren't bulky elephants, or cold-tolerant penguins, or even the famously durable cockroach. Instead, the champions of durability are endearing microscopic creatures called tardigrades, or water bears.
They live everywhere, from the tallest mountains to the deepest oceans, and from hot springs to Antarctic ice. They can even tolerate New York. They cope with these inhospitable environments by transforming into a nigh-indestructible state. Their adorable shuffling gaits cease. Their eight legs curl inwards. Their rotund bodies shrivel up, expelling almost all of their water and becoming a dried barrel called a “tun.” Their metabolism dwindles to near-nothingness—they are practically dead. And in skirting the edge of death, they become incredibly hard to kill.
In the tun state, tardigrades don't need food or water. They can shrug off temperatures close to absolute zero and as high as 151 degrees Celsius. They can withstand the intense pressures of the deep ocean, doses of radiation that would kill other animals, and baths of toxic solvents. And they are, to date, the only animals that have been exposed to the naked vacuum of space and lived to tell the tale—or, at least, lay viable eggs. (Their only weakness, as a researcher once told me, is “vulnerability to mechanical damage;” in other words, you can squish ‘em.)