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Even cannibals can be caring. Crabs that live near hydrothermal vents 3,500 metres deep have been seen eating each other.

But they also seem to clean each other at other times, presumably eating bacteria off each other’s shells.

New footage shows a crab grooming another crab. “He was literally grooming this smaller shell, just in the same way that you would see chimpanzees for instance picking bugs off of the hair of a mate,” says , a marine biologist at the University of Southampton.

The behaviour was captured by a robotic submarine launched from the research vessel Falkor, which is exploring hydrothermal vent sites in the Mariana region of the Pacific.

The crabs, from the species Austinograea williamsi, have no eyes, and little is known about their biology or behaviour.

They certainly aren’t picky eaters – they’ve been seen feeding on anemones, snails, other crabs and bacteria. It’s likely that the crabs feed off bacteria on surfaces, and in this case the surface was another crab’s shell. But rather than move away, the smaller crab was letting the larger one groom it.

We can’t yet say if the grooming represents a social relationship, but the resemblance to primate behaviour is fascinating, says Bates, who is on board the Falkor. “It’s incredible to see that same type of behaviour in crabs that are 3,500 metres under the sea.”

Read more: Mysterious deep-sea swarm of thousands of crabs caught on camera