Humans have pretty much traipsed over all the dry parts of the planet, but the vast oceans still hide plenty of secrets from us landlubbers. Deep-sea expeditions have recently discovered eerie "faceless" fish and hairy-chested "Hoff" crabs, nicknamed after a certain Baywatch star. And now, an ongoing study has identified a new species, the Mariana snailfish, which appears to be the deepest-dwelling fish in the world.

Officially known as Pseudoliparis swirei, the new snailfish gets its common name from its home, the Mariana Trench, which at a maximum depth of over 36,000 ft (11,000 m) is the deepest known part of the ocean. For comparison, Mount Everest could be comfortably fully submerged down there. While the pressure that far down would be fatal to most lifeforms, the Mariana snailfish uses that to its advantage.

"Snailfishes have adapted to go deeper than other fish and can live in the deep trenches," says Thomas Linley, co-author of a study describing the new species. "Here they are free of predators, and the funnel shape of the trench means there's much more food. There are lots of invertebrate prey and the snailfish are the top predator. They are active and look very well-fed."

The fish look pretty unassuming – small and pale with no scales, they resemble fleshy tadpoles. Exactly how they can thrive under that extreme water pressure is still a mystery for now, but these creatures have been sighted regularly at depths of around 26,200 ft (8,000 m) and down to a record-breaking depth of 26,830 ft (8,178 m), as captured on video by Japanese researchers earlier this year.

"This is the deepest fish that's been collected from the ocean floor, and we're very excited to have an official name," says Mackenzie Gerringer, lead author of the study. "They don't look very robust or strong for living in such an extreme environment, but they are extremely successful."

The fish was discovered during research trips in 2014 and 2017, when the team dropped traps down to the bottom of the trench to snap pictures, shoot video and capture specimens. In all, 37 specimens were brought up and subjected to DNA analysis and CT scans. By studying the structure of the creatures' skeletons and tissues, they were able to determine that they were indeed a new species.

"There are a lot of surprises waiting," says Gerringer. "It's amazing to see what lives there. We think of it as a harsh environment because it's extreme for us, but there's a whole group of organisms that are very happy down there."

The research was published in the journal Zootaxia.

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