One species of wart-encrusted octopus looks very much like another — which is why zoologists are taking a good, hard look at those warts: turns out, they could help scientists tell these exceptionally bumpy octopods apart.

Remotely operated vehicles (also known as ROVs) are giving scientists an unprecedented peek at deep sea creatures. That includes these warty octopuses — collectively grouped under the genus Graneledone. But because the species look so similar, it’s hard for scientists to say whether the one glimpsed through a submersible’s viewfinder is a known species, a new one, or a known one in an unusual spot.

That information makes a difference when it comes to figuring out which species need protection, and where — something that could become more urgent as climate change and human activity threatens creatures we don’t even have names for. And it’s why having a way to tell octopus species apart is a big deal. “That’s important because we’re doing a lot of visual work in the deep sea now,” says Mike Vecchione, a zoologist with Smithsonian who was not involved in the study. “Having characters that you can use from visual observations is really helpful.”

The work started when Janet Voight, a zoologist at the Field Museum of Natural History in Chicago, saw warty octopuses in nature. “And suddenly it kind of occurred to me — I’m asking the question is this one species or two species, when in fact, I don’t know,” she says. “I’ve never seen another species.” So Voight and a student accumulated more than 70 (dead) museum specimens of one species that lives in the Northeast Pacific, called Graneledone pacifica, and another that lives in the North Atlantic — Graneledone verrucosa.

They discovered that G. pacifica is especially warty, with cartilaginous bumps stretching down its arms and covering its mantle — the muscular covering for the octopus’s organs. The warts stop in a line, right at the back edge. On G. verrucosa, the warts don’t extend quite as far down its arms, and they taper off towards the back of its mantle. So the density of bumps on the back of the mantle and the length they extend down the arms are good benchmarks for deciding whether a given octopus is G. pacifica or G. verrucosa, according to the paper Voight published in Marine Biology Research.

Granted, the two species are separated by a continent, making today’s study a proof-of-concept. The next step is to see if other species show clear wart differences too. If so, the wart-based ID method could be broadly applied to the entire genus. That would help us find out who else we’re sharing the Earth with. “The deep sea is the last frontier of our planet,” Voight told The Verge. “And we don’t even know what’s out there.”