Glowing mysterious sea snail feeding like a Venus flytrap, captured in deep-sea footage for the first time

Hypnotic footage shows a never-before-seen swimming sea slug that eats using a large gelatinous hood and glows to defend itself from predators.

Living at depths between 3,300 and 13,100 feet (1,000 to 4,000 meters), the mysterious mollusk (Bathydevius caudactylus) is the first nudibranch species to occur in the deepwater column. Researchers first captured images of the animal using a remotely operated vehicle (ROV) off the coast of Monterey Bay in February 2000. Over the next twenty years, they learned more and gathered enough information to publish the most comprehensive description of a deep-sea animal to date.

Nudibranchs, or sea snails, usually live and feed on the seafloor, but the newly described bioluminescent species swims through the ocean’s midnight zone, deep below the surface. The newly discovered species is 14 centimeters long and has a huge gelatinous hood, a fringed tail, colorful organs visible through its translucent body, and a foot that resembles a snail.

MBARI researchers discover remarkable new swimming sea slug in the deep sea – YouTube

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At first, the researchers couldn’t figure out what this strange animal was, so they named it the “mystery mollusk.” When they brought it back to the lab, anatomical and genetic tests confirmed it was a slug.

It is so different from other known nudibranchs that the researchers have created a new family: Bathydeviuswhich refers to the way this ‘cunning’ animal fooled researchers with its unique features. It got its generic name caudactylus thanks to the finger-like projections, or dactyls, on its tail.

‘We were very surprised when we discovered that Bathydevius is a slug, partly because it doesn’t look like the others, but also because this is such an unusual habitat for a slug.” Bruce Robinsonsenior scientist at the Monterey Bay Aquarium Research Institute (MBARI), told LiveScience via email. Robison led efforts to describe the mysterious mollusk.

“Most nudibranchs live on the seabed in shallow water and feed on prey attached to them,” he said. “Entering the deep water column and feeding on free-swimming, fast-moving prey is a real challenge.”

A white mollusk sea snail (Bathydevius caudactylus) in the water column.

On November 12, researchers from MBARI published everything they know about this bizarre animal – through more than 150 observations over a period of twenty years – in the journal Deep Sea Research Part I.

The sea slug’s translucent body likely protects it from the sighting of predators, Robison said.

The scientists believe the mysterious mollusk uses its hood as a Venus flytrap to catch crustaceans to eat. The hunting technique is used by several other marine animals. “Several unrelated animals, including the large jellyfish Deepstaria and fragile comb jellies trap their prey in what appears to be a living shopping bag,” said co-author Steven Haddocksenior scientist at MBARI, told LiveScience via email. “It’s like throwing a rope net to stop an attacking lion.”

Although the mysterious mollusk feeds in a similar manner to the lion’s mane slug (Melibe leonina) and the veiled slug (Tethys fimbria), these species are only distantly related, so this is a case of convergent evolution.

“Given the genetic separation from all other slugs and their radically different body types, it seems clear that this is a successful evolutionary experiment,” Robison said.

When the mysterious mollusk is threatened, it uses bioluminescence to distract its predators. In one case, researchers saw it detach a bioluminescent limb as bait, similar to a lizard dropping its tail.

The mysterious mollusk is known to live in the northeastern Pacific Ocean, from Oregon to Southern California. However, experts believe its spread could be more widespread as NOAA researchers have spotted a similar-looking animal in the US Mariana Trench – the deepest part of the ocean, located in the western Pacific Ocean.

The experts still want to solve the puzzle of how this animal feeds. “We know what it eats, but we can’t figure out how this slow-moving sea slug can catch those very fast shrimp,” Robison said.