We’re all aware that the deep ocean contains some pretty weird creatures – yet one has continued to baffle even the ocean researchers studying it. Now, scientists have cracked a decades-long mystery about a creature lurking 2,614 metres (8,576 feet) deep off the coast of California, in the US.
For 24 years, researchers have been scratching their heads over what the mysterious creature actually was. Its snail-like foot made the scientists think it was a mollusc, yet its bizarre finger-like projections and flat tail suggested otherwise – not to mention its glowing body. Now, experts confirm this 'mystery mollusc' is, in fact, a sea slug.
The Bathydevius caudactylus is unlike any other sea slug (known to scientists as nudibranchs). For the most part, these critters tend to lounge in tidal pools, coral reefs or the seafloor, while others drift near the surface of open waters.
But not this one. The creature, profiled for the first time in the journal Deep-Sea Research Part I, is the first nudibranch the US researchers have found in the ocean’s midnight zone. This is the part of the ocean permanently blanketed in complete darkness, starting 1km (3,300ft) below the surface and ending 4km (13,100ft) deep.
“Our discovery is a new piece of the puzzle that can help better understand the largest habitat on Earth,” said Dr Bruce Robison, senior scientist at the Monterey Bay Aquarium Research Institute (MBARI), who led the research.
“We were able to prepare the most comprehensive description of a deep-sea animal ever made.”
To work out what the creature was, the scientists had to get 150 different sightings of it using a remote-operated ocean vehicle.
That’s when things got really weird. As well as its strange finger-like projections and snail-like foot, the researchers discovered the animal has a flat tail and a bizarre 'oral hood'. They think this helps it catch prey, much like a Venus fly trap.
The scientists also discovered that the nudibranch combats the water’s permanent darkness with its bioluminescence, a phenomenon that allows creatures to emit light from their body through chemical reactions.
But most impressive of all is this glowing slug’s prowess at confusing its predators. It can hide in plain sight by making its colourful organs transparent, and even detach the weird finger-like parts of its tail from its glowing body to distract deep sea creatures trying to eat it.
“For there to be a relatively large, unique, and glowing animal that is in a previously unknown family really underscores the importance of using new technology to catalogue this vast environment,” said Dr Steven Haddock, senior scientist at MBARI.
“The more we learn about deep-sea communities, the better we will be at ocean decision-making and stewardship.”
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