Apple-Sized "Mystery Mollusk" Discovered In Ocean's Midnight Zone

A team of researchers at the Monterey Bay Aquarium Research Institute (MBARI) has discovered a glowing “mystery mollusk” within the ocean's midnight zone. The species, named Bathydevius Caudactylus, is similar to the size of an apple. Although it is classified as a sea slug, the marine animal is unlike any sea slug scientists have seen before, CNN reported.

The research on the new species was published in the journal Deep Sea Research Part I on Tuesday.

Senior scientists Bruce Robison and Steven Haddock, associated with the California-based research institute, first spotted the odd animal in February 2000 during a deep-water dive expedition offshore of Monterey Bay. For this, they used the remotely operated vehicle Tiburon, which is a subsea research robot, CNN states.

MBARI researchers have discovered a remarkable new species of sea slug in the deep sea. Nicknamed the "mystery mollusc," the nudibranch Bathydevius caudactylus swims through the midnight zone and lights up with brilliant bioluminescence.

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They have since then had over 150 sightings of what they call “mystery mollusk”. During this journey, they went through the challenge of extreme depth of the midnight zone to understand the unique animals surviving there.

The midnight zone is classified as the deep waters existing between 1,000-4,000 meters below the ocean's surface. It accounts for nearly 70% of seawater.

“We've invested more than 20 years in understanding the natural history of this fascinating species of nudibranch,” Robison, co-lead of the study, said.

He added that their discovery was a "new piece of the puzzle that can help better understand the largest habitat on Earth."

Haddock noted that Bathydevius, at first glance, looked more like a "megaphone with a feathered tail" than a sea slug. It has a massive bowl-shaped hooded structure on one end, and a flat tail that looks fringed with fingerlike projections on the other end. Its colourful internal organs are also on display.

It was named Bathydevius for its “devious” nature that fooled the scientists at first, while caudactylus refers to the dactyls -- the fingerlike projections on its tail.

Known for its large gelatinous hood and paddle-like tail, Bathydevius is a swimming sea slug, which glows with bioluminescence. It is also believed to be the first sea slug that lives in the deep ocean. Most of the other sea slugs survive on the seafloor or in coastal environments such as tide pools. Only a few species among them are known to live in open water near the surface.