Researchers from the Monterey Bay Aquarium Research Institute (MBARI) in California recently identified a new species of sea slug living deep in the North Pacific Ocean.
The “Mysterious Mollusk” and Its Glowing Defense
Nicknamed the “mysterious mollusk,” this transparent creature has a wild survival trick — it lights up when it feels threatened. This glow-in-the-dark ability is called bioluminescence.
Meet Bathydevius caudactylus: A Rare Deep-Sea Resident
Officially named Bathydevius caudactylus, the sea slug was first spotted in February 2000 at a depth of 8,580 feet (2,614 meters) during an expedition with the remotely operated vehicle (ROV) Tiburon off the coast of Monterey Bay, California. Since then, over 150 sightings have been recorded, leading to the species’ formal description in November 2024.
Weird Anatomy Built for the Deep
This sea slug has a big hood used to trap prey and a flat, frilly tail with finger-like projections. Its see-through body reveals vibrantly colored internal organs.
Unexpected Presence in the Deepest Parts of the OceanNOAA scientists also found a similar creature in the Mariana Trench, over 36,000 feet (11,000 meters) deep — suggesting that Bathydevius may live across a much wider area than first believed.
The Glowing Defense of the Bathyal Zone
The bioluminescence of this species is especially fascinating. When it feels threatened, the slug gives off light, possibly as a defense mechanism to confuse predators or draw attention away from itself. This clever adaptation is key to its survival in the bathyal zone — a part of the ocean that’s in total darkness, located between 3,300 to 13,100 feet (1,000 to 4,000 meters) deep.
The Scientific and Environmental Value of the Discovery
The discovery of Bathydevius caudactylus expands our understanding of deep-sea biodiversity and shows how important it is to keep exploring these largely unknown environments. Finding new species like this one highlights the need to protect deep-sea ecosystems, which are home to undiscovered life forms and play a key role in maintaining the planet’s environmental balance.