Worried about how proposals for deep sea mining might threaten the oceans, including the habitat and behavior of these mysterious octopuses, she set out to devise a system to tell them apart. And in a paper published this week in Marine Biology Research, Dr. Voight and her colleague, Jessica Kurth, a biologist at Pennsylvania State University, revealed how the distribution of warts on the bodies of at least two octopus species in this important genus might be their distinguishing feature.

There are a variety of ways to distinguish one species of octopus from another: the length of their arms, the size of their suckers, the texture of their skin, the tip of the male’s sex arm or colors of the skin or around the eyes.

“But not in this group. Nothing works in these guys,” Dr. Voight said.

Members of Graneledone are actually kind of cute. They have two dark, big eyes mounted on a bulbous, head-like thing called a mantle with eight sucker-lined arms sticking out. They have no ink sac. Their colors, vibrant or pale, don’t appear to be that important: Sometimes they’re pink or purple or orange. Dr. Voight has seen just half of the body of one blanch white when threatened.