By Stephen Beech via SWNS
A “remarkable” new sea slug nicknamed the “mystery mollusk” has been discovered swimming deep in the ocean’s “midnight” zone.
The species has “unique” adaptations for life in the pitch-black depths including a large gelatinous hood to trap prey, a paddle-like tail and the ability to light up, say American scientists.
The 5.6-inch (14.5 cm) hermaphrodite species, given the scientific name Bathydevius caudactylus, was discovered by boffins from Monterey Bay Aquarium Research Institute (MBARI) in California.
MBARI senior scientist Dr Bruce Robison said: “Thanks to MBARI’s advanced underwater technology, we were able 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.
“Our discovery is a new piece of the puzzle that can help better understand the largest habitat on Earth,”
MBARI researchers first observed the mystery mollusk in February 2000 during a dive with the institute’s remotely operated vehicle (ROV) Tiburon offshore of Monterey Bay at 8,576 feet (2,614 meters) deep.
The team used state-of-the-art underwater technology to gather extensive information about the mystery mollusk.
After reviewing more than 150 sightings from MBARI’s ROVs over the past 20 years, they have published a detailed description of the creature in the journal Deep-Sea Research.
With a voluminous hooded structure at one end, a flat tail fringed with numerous finger-like projections at the other, and colorful internal organs in between, the team initially struggled to place the animal in a group.
Because it also had a foot like a snail, they nicknamed it the “mystery mollusk.”
After gently collecting a specimen, MBARI researchers were able to take a closer look at the animal in the lab.
Through detailed investigations of anatomy and genetics, they began to solve the mystery, finally confirming that it is a nudibranch.
The researchers explained that most nudibranchs, also known as sea slugs, live on the seafloor.
They are common in coastal environments – such as tide pools, kelp forests, and coral reefs – and a few species are known to live on the abyssal seafloor. Some live in open waters near the surface.
But the mystery mollusk is the first nudibranch known to live in the midnight zone, an expansive environment of open water 1,000 to 4,000 meters (3,300 to 13,100 ft) below the surface, also known as the bathypelagic zone.
The mystery mollusk is currently known to live in the waters offshore of the Pacific coast of North America, with sightings on MBARI expeditions as far north as Oregon and as far south as Southern California.
An observation of a similar-looking animal in the Western Pacific’s Mariana Trench suggests the mystery mollusk may have a more widespread distribution.
The researchers say it has evolved “unique” solutions to find food, safety, and companions to survive in the midnight zone.
While most sea slugs use a raspy tongue to feed on prey attached to the seafloor, the mystery mollusk uses a cavernous hood to trap crustaceans like a Venus fly trap plant.
A number of other unrelated deep-sea species use such a feeding strategy, including some jellies, anemones, and tunicates.
To avoid being eaten, the mystery mollusk hides in plain sight with a transparent body.
Scientists say rapidly closing the oral hood facilitates a quick escape, similar to the pulse of a jelly’s bell.
If threatened, the mystery mollusk can light up with bioluminescence to deter and distract hungry predators.
On one occasion, researchers saw it illuminate and then detach a steadily glowing finger-like projection from the tail, likely serving as a decoy to distract a potential predator.
MBARI senior scientist Dr. Steven Haddock said: “When we first filmed it glowing with the ROV, everyone in the control room let out a loud ‘Oooooh!’ at the same time.
He added: “We were all enchanted by the sight.
“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.”
Like other nudibranchs, the mystery mollusk is a hermaphrodite, possessing both male and female sex organs.
It appears to descend to the seafloor to spawn.
MBARI researchers observed some animals using their muscular foot to attach to the muddy seafloor in order to release their eggs.
Dr. Haddock said: “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.
“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 mystery mollusk is one of several fascinating discoveries made in the midnight zone by MBARI scientists.
To date, MBARI technology has been used to document more than 250 deep-sea species previously unknown to science.
Dr. Robison said: “Deep-sea animals capture the imagination.
“These are our neighbors that share our blue planet.”
He added: “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.”
