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There are dozens of different ways of defining a species, and none are universally accepted. That said, de Santana says that his team “used many lines of evidence to prove that there’s more than one electric eel species.” This trinity differs not only in physique, but also in genetics, habitat, and electric power. Tellingly, the eels’ DNA suggests that they last shared a common ancestor 7 million years ago, which means that they started to diverge well before brown bears and polar bears, lions and tigers, and even humans and chimpanzees.

One of the trio retains the original name Electrophorus electricus, and de Santana now calls it Linnaeus’s electric eel, after the legendary Swedish taxonomist who classified it. The two others are now Volta’s electric eel (Electrophorus voltai), after the Italian physicist who built a battery based on the animal, and Vari’s electric eel (Electrophorus varii), after Richard Peter Vari, a famous ichthyologist who was part of de Santana’s team until his death in 2016. (Most of the eels used in previous research are likely to be Vari’s eels, since they’re the only species from Peru, the only country from which these animals can be legally exported.)

“These findings do not surprise me,” says Graciela Unguez from New Mexico State University. As researchers sample electric fishes from more parts of South America, she adds, they’re almost bound to find that currently known species harbor more diversity than people suspected.

The same goes for unusual animals whose outward distinctiveness can mask subtler differences that become clear only through genetic analyses. Such studies have shown that there are likely four distinct species of giraffe, three species of mola mola, and two species of African elephants. “We sort of lump the weirdos together,” says Prosanta Chakrabarty from Louisiana State University. “Oh, obviously, this thing is that thing, and no one looks more carefully. We all thought that an electric eel is an electric eel.”

Contrary to appearances, they’re not even eels. They’re knife fishes—a group of mostly small, gill-breathing species that have flattened bodies and that produce weak electric fields for navigation and communication. The misnamed eels buck all these trends—weirdos, even within their own family. They breathe by rising to the surface and gulping air, which makes them one of the only fish that you can drown. Their thick, cylindrical, meaty bodies can reach seven feet in length. And the electric organs that make up 80 percent of that length can produce shocks that are strong enough to incapacitate a human or a horse.

Read: The stunning case of leaping electric eels

Collecting these animals from the wild, as de Santana did, is not easy. “I do it by myself, or with the help of really experienced fishermen,” he says. “I don’t allow students to do it. It’s never safe.” Even if he wears rubber gloves, the sweat that builds up inside them eventually links up with the water outside them, creating a continuous conductive layer. Bottom line: You can’t collect electric eels without suffering shocks, which de Santana compares to getting hit with a Taser. It’s even worse in the dry season, when more than 10 individuals can occupy a single stream. “When one starts to discharge, the others do too,” says de Santana. “You just get used to it. You do what you have to do.”