California Scientists Discover New Species of ‘Mystery Mollusks’ in Ocean’s Depths

This undated photo provided by Monterey Bay Aquarium and Research Institute shows a mystery mollusk (Bathydevius caudactylus) observed by MBARI's remotely operated vehicle (ROV) Doc Ricketts in the outer Monterey Canyon at a depth of approximately 1,810 meters. MBARI via AP

California scientists have identified a new species dwelling in the ocean they have classified as a “sea slug.”

Monterey Bay Aquarium Research Institute (MBARI) science adviser Bruce Robison said in a Nov. 12 video statement that though MBARI’s deep-sea research has led to the discovery of “an astonishing array of animals,” this most recent finding “is one of the most remarkable yet.”

“Meet the mystery mollusk, Bathydevius caudactylus,” Robison said.

The mollusk was first encountered in early 2000 while exploring waters a mile and a half below the surface of the ocean, he said.

“We were mesmerized by the animal’s ethereal movements,” he said. “The curious combination of body features left us mystified.”

Researchers initially called the creature a “mystery mollusk” because of its muscular foot suggesting it might be a “swimming snail.”

However, its “voluminous hood on one end” with a “flat paddle-like tail with numerous finger-like projections on the other” continued to leave scientists perplexed, he said.

Its insides transparently revealed “vibrant internal organs,” he said.

Scientists weren’t sure how to classify the creature, Robison said.

“After gently collecting a specimen, we were able to take a closer look at the lab, and we got to work solving our mystery through detailed investigations of anatomy and genetics,” he said.

Scientists were able to confirm that the mystery mollusk was of the nudibranch marine gastropod family that dwells in the “bathypelagic depths in the eastern North Pacific Ocean.”

According to Robison, the nudibranch are known as “naked snails” that live in a “broad range of latitudes from the tropics to polar seas” and are commonly found on the seafloor.

This particular species of nudibranch is the first known to exist in the “deep water column” of the ocean’s midnight zone,” described by MBARI as “an expansive environment of open water 1,000 to 4,000 meters (3,300 to 13,100 feet) below the surface, also known as the bathypelagic zone.”

Unlike most sea slugs that use their “raspy tongue” to catch food on the seafloor, this mystery mollusk relies on its “cavernous hood to trap crustaceans like a Venus fly trap plant.”

“If threatened, the mystery mollusc can light up with bioluminescence to deter and distract hungry predators,” MBARI wrote. “On one occasion, researchers observed the animal illuminate and then detach a steadily glowing finger-like projection from the tail, likely serving as a decoy to distract a potential predator.”

Over the past 20 years, MBARI has recorded more than 150 sightings of the sea slug

“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 Bill Haddock, MBARI senior scientist and co-author with Robison on the paper published on the discovery. “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.”

The Associated Press contributed to this report.