The Tardigrade’s Extraordinary Weirdness Continues

The mystery of the tardigrade—a.k.a. moss piglet, a.k.a. water bear—is one step closer to a solution. Scientists studying the microscopic animals' DNA say the tough, many-legged creatures may be distantly related to nematodes and other "wormy things." The researchers published their findings in the journal PLOS Biology.

Tardigrades are some of the strangest, most badass organisms on Earth. Don't be fooled by their tiny size—these animals are anything but delicate. They can survive in the most brutal conditions, from dehydration and starvation to burning heat, blistering cold, intense radiation, and even the vacuum of space.

How they pull off this near-invincibility is, naturally, a question of some interest among biologists (and to Mental Floss—links to our many articles about these amazing creatures are found throughout this story).

The authors of one 2015 study made headlines when they announced that one-sixth of the tardigrade's genetic blueprint had been swiped from bacteria and other organisms. This horizontal gene transfer (HGT) is not unheard of in nature, but other tardigrade experts, including a team at the University of Edinburgh, felt that 17.5 percent seemed suspiciously high, even for a maverick like the tardigrade.

The skeptics were right. Additional investigation into the tardigrade genome confirmed the presence of a few horizontally transferred genes. Just a few.

HGT aside, there's still plenty to discover in the tardigrade's genes. Tardigrades have been tardigrades for hundreds of millions of years. No fossils remain from their early days to tell us what they might have been before. We don't really know where they came from, evolutionarily speaking, or who their relatives are.

To find out, Edinburgh researcher Mark Blaxter and his colleagues picked apart the genomes of two tardigrade species, Ramazzottius varieornatus and Hypsibius dujardini. They found something unexpected: The armored, many-legged tardigrades seemed more closely related to worms than to insects.

If these findings are accurate, Blaxter told Mental Floss in an email, they challenge the very structure of the Panarthropoda family tree, which assumes "the leggy moulting animals are more closely related to each other than they are to wormy things like nematodes."

But he notes that there's lots more research to be done before issuing that challenge: "We have only looked at a tiny fraction of the 10 or more million species on Earth. Every new group, and possibly every species, will have something exciting in it we haven't seen before, and didn't imagine."