A team of researchers has published a detailed description of the undersea creature previously dubbed the “mystery mollusk” due to its bizarre body.
The animal’s scientific name is Bathydevius caudactylus, and it was first observed in 2000 by a remotely operated vehicle (ROV) making a dive off California’s Monterey Bay. That’s right: This animal is so weird that it took nearly a quarter-century to nail down its branch on the tree of life. According to Bruce Robison, a senior scientist at the Monterey Bay Aquarium Research Institute, it’s “the most comprehensive description of a deep-sea animal ever made.”
The team published its description in Deep-Sea Research Part I and comes on the heels of over 150 additional sightings of the creature by MBARI ROVs. Researchers also recovered a specimen from the deep sea to investigate it in a lab setting. Following anatomical and genetic analyses, the researchers concluded that B. caudactylus is a nudibranch, a group of animals commonly known as sea slugs.
This particular nudibranch is the first known to live in the deep water column—the ocean’s midnight zone—between 3,300 feet and 13,100 feet deep (1,000 to 4,000 meters). But the most captivating aspect of the mystery mollusk is its bizarre morphology, which took a couple decades to fully investigate. The creature has a gelatinous hood, a fingered, paddle-like tail, and is bioluminescent—the creature glows. That makes it a rare example of a bioluminescent nudibranch.
The mystery mollusk brings to mind another famously confusing critter: the platypus. Indeed, when Western scientists first encountered the monotreme, they thought it was a hoax. Featuring the body of an otter, webbed feet, a beaver-like tail, a duck bill, and venomous spurs—it’s hard to blame them. If B. caudactylus wasn’t so foreign to our mammalian senses to begin with, you’d probably react the same way to it.
“When we first filmed it glowing with the ROV, everyone in the control room let out a loud ‘Oooooh!’ at the same time,” said Steven Haddock, a senior scientist at MBARI, in an institute release.
The team found that its bioluminescence comes from glowing granules throughout the creature’s hood and its tail. Sometimes, the animal will lose one of its glowing, finger-like appendages (or “dactyls”) on its tail, which the researchers believe is a way to distract predators. Don’t worry—the animal can regenerate its dactyls.
“Only recently have cameras become capable of filming bioluminescence in high-resolution and in full color,” Haddock added. “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.”
The 5.6-inch-long (14.5-centimeter) invertebrate eats crustaceans, which it pulls into its funnel-shaped mouth, located at the back of the animal’s elastic hood. It’s also hermaphroditic, and spawns on the seafloor—as deep as nine Empire State Buildings stacked on top of one another.
The animal also has a lower metabolism than other known nudibranchs; its respiration rates are more similar to those observed in deep-sea jellyfish. That’s a reflection of the way B. caudactylus goes about life in the deep sea: with the flow, as the animal is neutrally buoyant. When it swims, it does so slowly. Sometimes, it moves about the sea by simply drifting.
Earth’s oceans cover about 70% of its surface, but scientists have only mapped about a quarter of the global seafloor. There’s plenty of room for mystery in the average 12,080 feet (3,682 meters) of water between the surface and the bottom of the sea.
According to the National Oceanic and Atmospheric Administration, about 67% of the estimated million species in the ocean have yet to be identified—and that’s not counting the millions of microorganisms that eke out existence in some of its most mysterious depths. Just last month, a team coordinated by the Schmidt Ocean Institute identified animals living beneath the seafloor, stretching the known bounds of life on Earth.
The mystery mollusk is no longer an enigma to science, but still boasts an eye-popping range of morphological features. It’s a reminder that even when we learn more about our diverse Earth, it always has another surprise in store.
English (US) ·