Mystery mollusk: Glowing sea slug found in the deep sea

Researchers recently revealed a stunning new species of sea slug glowing in the ocean’s darkest depths. Known as the “mystery mollusk” or Bathydevius caudactylus, this nudibranch inhabits the ocean’s midnight zone, one of Earth’s least-explored realms.

This discovery is more than just a new name on a species list – it’s an illuminating dive into our planet’s vast, hidden ecosystems.

Mystery mollusk in the midnight zone

The “mystery mollusk,” Bathydevius caudactylus as the scientists officially named it, inhabits the ocean’s deep abyss, also known as the midnight zone.

But this isn’t just about a new species – it’s about an exciting lifeline into understanding our planet’s largest habitat in more depth.

Monterey Bay Aquarium Research Institute (MBARI) Senior Scientist Bruce Robison steered this explorative venture.

“Thanks to MBARI’s advanced underwater technology, we were able to prepare the most comprehensive description of a deep-sea animal ever made,” noted Robison.

“We’ve invested more than 20 years in understanding the natural history of this fascinating species of nudibranch. Our discovery is a new piece of the puzzle that can help better understand the largest habitat on Earth.”

Identifying the mystery mollusk

This unusual sea creature was first spotted in the year 2000, during an expedition using the institute’s remotely operated vehicle (ROV) named Tiburon. It was found gliding through the waters offshore of Monterey Bay at a depth of 2,614 meters (8,576 feet).

Confusion arose when the team initially struggled to identify this creature due to its anomalous appearance – a voluminous hood, a flat tail fringed with numerous, finger-like projections, and a set of colorful internal organs.

But after years of research and countless ROV sightings, the mystery was solved – this strange creature is, in fact, a nudibranch or sea slug.

A nudibranch unlike any other

The mystery mollusk isn’t your ordinary nudibranch. It’s the first of its kind known to dwell in the immense open waters of the bathypelagic zone, a region 1,000 to 4,000 meters (3,300 to 13,100 feet) below the ocean surface.

Also, the sightings of this fascinating creature span the Pacific coast of North America, from Oregon to as far south as Southern California. Plus, similar creatures spotted by NOAA researchers in the Mariana Trench hint at the mollusk’s potentially widespread existence.

Survival techniques of the sea slug

Surviving in such harsh environments is no easy feat. How does the mystery mollusk manage? Interestingly, it has evolved unique survival strategies.

For instance, unlike most sea slugs that feed by rasping prey off the seafloor, it uses its cavernous hood to trap crustaceans, much like a Venus flytrap plant would do.

Moreover, to avoid predators, it has a clear body that blends with the surrounding waters and can emit a bright bioluminescence to deter and distract hungry predators.

“When we first filmed it glowing with the ROV, everyone in the control room let out a loud ‘Oooooh!’ at the same time. We were all enchanted by the sight,” said MBARI senior scientist Steven Haddock.

“Only recently have cameras become capable of filming bioluminescence in high-resolution and in full color. MBARI is one of the only places in the world where we have taken this new technology into the deep ocean, allowing us to study the luminous behavior of deep-sea animals in their natural habitat.”

Nudibranch family tree expands

Beyond its captivating appearance and survival tactics, what really stood out during the research was the mollusc’s genetic uniqueness.

Detailed examination of specific gene sequences emphasized that the mystery mollusk is distinct enough from other known nudibranchs to merit the creation of a new family, Bathydeviidae.

“What is exciting to me about the mystery mollusk is that it exemplifies how much we are learning as we spend more time in the deep sea, particularly below 2,000 meters,” said Haddock.

“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 catalog this vast environment. The more we learn about deep-sea communities, the better we will be at ocean decision-making and stewardship.”

Wealth of deep-sea discoveries

This discovery is just one exciting piece in the puzzle of deep-sea exploration. MBARI’s state-of-the-art technology has unveiled over 250 previously unknown deep-sea species to date, encouraging us to plunge deeper into these fascinating, otherworldly realms.

“Deep-sea animals capture the imagination. These are our neighbors that share our blue planet. Each new discovery is an opportunity to raise awareness about the deep sea and inspire the public to protect the amazing animals and environments found deep beneath the surface,” said Robison.

Indeed, each new discovery brings us one step closer to fully understanding and protecting our fascinating blue planet. And with this latest revelation of the mystery mollusk, we get to marvel at another fascinating dweller of the deep.

The study is published in the journal Deep Sea Research.

Image/ Video Credit: MBARI

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