Researchers in California have discovered a new species of sea slug off the Pacific coast in an area of deep sea known as the midnight zone.
A team with the Monterey Bay Aquarium Research Institute first came across the creature, which they dubbed the “mystery mollusc” in 2000 at 8,576ft (2,613 meters), and spent years documenting the sea slug in order to “prepare the most comprehensive description of a deep-sea animal ever made”.
“We’ve invested more than 20 years in understanding the natural history of this fascinating species of nudibranch,” said Bruce Robison, a senior scientist with the institute. “Our discovery is a new piece of the puzzle that can help better understand the largest habitat on Earth.”
The researchers published their findings about the creature, the Bathydevius caudactylus, in the December volume of the journal Deep Sea Research Part I.
Sea slugs, also called nudibranchs, generally live on the sea floor, but the mystery mollusc is the first documented occupying the deep water column, a large area about 3,300-13,100ft under the surface. The ocean’s deep interior is an unexplored frontier, Robison and Steven Haddock, a senior scientist at the research institute, noted in the publication.
The creature has a transparent, gelatinous body with a large hood, a flat tail “fringed with … finger-like projections”, a foot similar to a snail, and brilliant bioluminescence, according to a statement from the research institute.
Since first observing the sea slug in February 2000 using the institute’s remotely operated vehicle, the team has encountered more than 100 of the creatures. They collected a specimen that allowed them to more closely examine the animal’s anatomy and genetics, confirming it is a new species of sea slug.
“What is exciting to me about the mystery mollusc 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.”
