For more than two decades, deep-sea researchers have been observing an elusive, glowing creature they’ve only known as the “mystery mollusk.” Between 2000 and 2021, its unusual bioluminescent presence was recorded on different deep-sea missions, yet scientists struggled to identify it until now. But a team from the Monterey Bay Aquarium Research Institute (MBARI) finally discovered, after several years of studying, that it is an entirely new species of nudibranch-a type of sea slug. Bathydevius caudactylus has been given its name and is the very first-and only-nudibranch species known to this day that thrives at depth in the ocean’s midnight zone, which spans 1,000 to 4,000 meters (3,300 to 13,100 feet).
How does Bathydevius caudactylus move?
Bathydevius caudactylus is not a typical sea slug. Instead of crawling along the ocean floor like most other nudibranchs, this species swims more like a jellyfish. Using an oral hood similar to that found in jellyfish, it produces a jet propulsion to push itself through the water backward. Such a locomotion system enables them to effortlessly float through the deep ocean, avoiding predators and maneuvering through the dark of their habitat with little exhaustion.
What does this animal eat?
This is the Venus flytrap-like method that Bathydevius caudactylus uses to capture its prey of small crustaceans, moving it afterward into its mouth, in order to feed on it. This species is unique in being one of the very few nudibranchs that do not eat cnidarians like jellyfish. In addition, on having a unique diet, it lacked the traditional radula, that tonguelike structure that most nudibranchs possess.
What Makes This Nudibranch Bioluminescent?
One of the most intriguing characteristics about Bathydevius caudactylus is that it is bioluminescent. The creature radiates a blue color as an adaptation to the dark bottom depths, where red light cannot go very far. This glowing trait is very rare among the nudibranch, as Bathydevius caudactylus has only been recorded as the third species of the bioluminescent sea slug known. It was just its glowing body against the blackness of space at that depth.
How Does This Nudibranch Differ from Others?
While its bioluminescence and way of feeding are unique, so is Bathydevius caudactylus genetic constitution from other nudibranchs. From here, the researchers found that in great degree, the DNA constituting this creature was different from other species of nudibranchs and hence is considered to fall under a new phylogenetic family. Its similarity with a close general named Melibae leonina seems to be only related through convergent evolution-unnatural development of similar traits by two unrelated species.
Are there any more weird species out there?
The discovery of Bathydevius caudactylus emphasizes how much mystery there is within our planet’s deep oceans. As the closest thing we have to an alien environment, the deep ocean remains largely unexplored. Many creatures-just as strange and fascinating as this glowing nudibranch-might still be hiding in the darkness, waiting to be discovered. Protection of these ecosystems could lead to further discoveries, giving us a deeper understanding of the strange and wondrous lifeforms that lurk beneath the surface.
