“Mysterious mollusk” whose skin is transparent and wears a hood to capture prey

What a slug.

This line could be used, for example, as an insult to a member of a sports team who isn’t working hard enough. After all, this notoriously slow-moving mollusk isn’t exactly known for its liveliness. But for a team of scientists who have discovered an amazing creature that literally goes beyond the depths of traditional slugs, that line is a huge compliment.

when Monterey Bay Aquarium Research Institute (MBARI) researchers sent a remote-controlled submersible to the ocean floor 8,576 feet off the coast of Northern California on a general “fishing expedition,” but they weren’t looking for anything in particular. But they discovered something special. It is a slug-like creature that “wears” a hood that it uses to capture prey. Shiny, translucent skin that reveals the colorful internal organs. They walk with appendages that resemble snail legs.

The strange combination of gastropod and mollusk earned it the nickname “mystery mollusk.” In the more than 20 years since its initial discovery, the MBARI team has encountered the creature more than 185 times and analyzed it using multiple techniques. A detailed description of this curious creature can be found at report in Deep sea research part I.

A confusing new discovery

Many aspects of this creature caused both surprise and confusion. “At first I had no idea what it was all about,” he says. bruce robisonMBARI senior researcher who led the research.

There were many reasons for that confusion. First, its closest apparent relative, a soft-bodied marine gastropod called a nudibranch, typically lives in shallower waters. Secondly, there is the issue of its unusual appearance.

“They’re very interesting creatures,” Robison said. “It looks like it was made from spare parts from other animals.”

That level of novelty caused scientists to postpone publication. “There were a lot of experts in the ship’s control room, and they were all scratching their heads,” Robison said. “It’s kind of flimsy. It’s transparent. It’s a soft, slow-moving, gelatinous creature. And when it comes to sea slugs, very few sea slugs have that characteristic.”

They waited more than 20 years between their initial discovery and writing because they wanted to use many tools to analyze the creature’s many unusual features and provide as complete a description as possible. After studying the creature’s body physiology, habitat, and genome, we discovered that this is no ordinary slug.

Bastidevius cordactylus in the deep sea

This creature was such a biological outlier that scientists developed special tools to study it. For example, measurements of respiration tend to be a good proxy for metabolism. It is usually done in a laboratory. But the researchers wondered if bringing these deep-sea creatures up to the surface and exposing them to varying temperatures, pressures, and light would stress them and make their measurements less reliable. So they asked engineers to find a way to monitor the creatures’ breathing while they were on the ocean floor.

Its depth was the mystical aspect of this discovery. Most known slugs live in shallower waters. Discovering the creature at that depth was “like finding a hummingbird on Mount Everest,” Robison says. “We never expected to find this type of creature there.”

This creature has many unusual aspects, which is why they named it Bathydevius caudactylus and that Genomic analysis became necessary. Scientists compared three important genes with their closest relatives.

“There is no question that it is separate from all other nudibranchs,” Robison says. “There’s nothing else genetically similar to it.”

The deep sea holds mysteries worth preserving

This discovery highlights that there are still many mysteries remaining deep down. Several other research groups have sent submersibles to the region’s ocean floor, both with and without humans.

”“This region is some of the best-studied deep ocean in the world, but we’re still discovering new things,” says Robison. “There are things happening in the world that we can’t even imagine yet because they have no precedent.”

This lack of knowledge should come with an environmental warning to industry. Disturbances of the deep seafloor can have unexpected effects on many species.

“There are a lot of really compelling resources out there,” Robison said. “There’s no question that we actually track them, but how we do it is important. What are we disrupting or the ecosystems we’re working with?” If we just push through without understanding how we’re impacting the system, it’s going to come back and bite us in the butt.