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It’s like going back in time. NOAA’s Okeanos Explorer has completed more than two weeks of ocean exploration beginning near Pago Pago, the capital of American Samoa, and ending near Honolulu in Hawaii. Some of the animal behaviour it recorded has previously been documented only in fossils hundreds of millions of years old.

“For all of the places we went, it was the first time we were getting to have eyes down in the deep sea,” says , a deep-sea biologist at the University of Louisiana at Lafayette who was on the ship.

Those eyes come in the form of remote submersibles that light up the sea floor and transmit live video to the team and the public around the world.

“We saw brittle stars capturing a squid from the water column while it was swimming. I didn’t know that was possible. And then there was a tussle among the brittle stars to see who got to have the squid,” says France.

Living fossils

The team also saw snails attached to crinoids, sometimes called sea lillies for their graceful branches.

“We saw this amazing footage of the snail that seemed to be eating a crinoid. No one had seen this before,” says at North Carolina State University in Raleigh, a geologist on the ship. “A scientist from the Smithsonian said he had seen it in the fossil record, but never live.”

France says it was like seeing “a living fossil”. After the dive, he sought out examples of snails from the Palaeozoic Era – which ended 252 million years ago – feeding on the faeces of crinoids in the same manner.

The expedition has mapped the area and taken samples. “We now have an inventory of what the rocks look like and what the biology is. We can track through time to see if there are changes and any impacts to those ecosystems if, say, someone should start nearby mineral extraction,” Bohnenstiehl says.

Much of the underwater mountain landscape was covered in a black coating of manganese crust, says Bohnenstiehl. The remote vehicles used the arms and basket on their fronts, to collect samples for analysis.

In some places, the sea floor was covered in a forest of bamboo corals. “This was one of the coolest coral observations,” says France. There are only 12 continuous carpets of lush bamboo coral known in the world, one of which was found on a dive during this expedition, he says.

“It was totally unexpected in the area we found it. The few studies done suggested it would be a very unpopulated place,” he says. They also collected three sponge varieties that were unrecognised by the sponge experts on hand.

“You can go almost anywhere in the deep sea and you’d be the first person on Earth looking there because there’s so much that we haven’t explored,” France says. “What’s even cooler is that we’re making just the first inroads. Boy, I really hope we can go back some time.”

Read more: Never-before-seen sea creatures filmed in world’s deepest abyss, Watch creatures of the abyss in Earth’s deepest ocean trench