Stunning Footage of a Newly Discovered Bioluminescent Swimming Slug in the Midnight Zone of Monterey Bay

The Monterey Bay Aquarium Research Insitute (MBARI) captured absolutely stunning ROV footage of a new species of sea slug, Bathydevius caudactylus, who swims and uses bioluminescence to hide from predators in plain sight.

This unusual creature is completely transparent, employs a giant hood to trap prey and lives in the midnight zone of the Monterey Bay. At first researchers were unsure about what they were seeing, as the different features of this “mystery mollusc” defied definition, as most slugs live on the ocean floor.

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 this animal in a group. Because the animal also had a foot like a snail, they nicknamed this the “mystery mollusc.”

The Bathydevius caudactylus was first discovered by MBARI in 2000. For the past 24 years, researchers have been studying the habits of this new swimming slug and published a scientific paper on their findings.

The team first observed the mystery mollusc in February 2000 during a dive with the institute’s remotely operated vehicle (ROV) Tiburon offshore of Monterey Bay at 2,614 meters (8,576 feet) deep. They leveraged MBARI’s advanced and innovative underwater technology to gather extensive natural history information about the mystery mollusc. After reviewing more than 150 sightings from MBARI’s ROVs over the past 20 years, they published a detailed description of this animal.