But this deadliest of sea snakes has a secret: it’s actually two sea snakes.

By analysing the beaked sea snake’s genes, Kanishka Ukuwela from the University of Adelaide has shown that the Asian individuals belong to a completely different branch of the sea snake family tree than the Australian ones. They are two species, which have evolved to look so identical that until now, everyone thought they were the same. They’re a fantastic new example of convergent evolution, when different species turn up at life’s party wearing the same clothes.

More and more, scientists are using genetic studies to show that familiar animals are actually several different “cryptic species”, including killer whales and giraffes. Just last year, we learned that the famous Nile crocodile is actually two distinct crocodiles, a big one from east Africa and a small one from west Africa.

Like other members of this club, no one suspected that the beaked sea snake was actually two species. Bryan Fry from the University of Queensland, venom guru and co-author on the paper, had collected several individuals from Australia, to study their venom. (“They are the nastiest species of sea snake I’ve ever worked with,” he says. “That is another thing they both converge on!”)

As a matter of routine, he “barcodes” the DNA of every animal he collects, sequencing it at specific places that given away the identity of different species. Fry expected the genes of his Australian specimens to be similar to those of the Asian individuals. “When the first result came back, we thought we must have screwed up and ran a sample of [a different] sea snake,” says Fry. “So we re-ran it, and got the same results. That was when we started getting giddy.” And just like that, one sea snake became two.