Off the coast of Monterey, California, and some two miles below the surface of the Pacific Ocean, scientists piloting a remotely-operated submersible saw something no one has ever seen before.

Octopuses. Hundreds of them. Huddled on a rocky outcrop at the base of an underwater mountain.

“We went down the eastern flank of this small hill, and that’s when—boom—we just started seeing pockets of dozens here, dozens there, dozens everywhere,” says Chad King, chief scientist on the Exploration Vessel Nautilus.

All in all, King estimates that more than 1,000 octopuses known as Muusoctopus robustus were nestled among the rocks, most of which appeared to be inverted, or turned inside out. For this species, that inside-out pose is common among females that