Watch: Scientists Stunned by Glowing ‘Mystery Sea Slug’ That Sheds Body Parts

Researchers have identified a unique mollusk, described as a “mystery sea slug,” in the ocean’s midnight zone. Known as *Bathydevius caudactylus*, this nudibranch, or sea slug, is the first of its kind discovered in such deep waters. It stands out with a glowing, apple-sized body, a paddle-like tail, and a large, gelatinous hood. Nudibranchs are generally soft-bodied marine mollusks, yet this one possesses features unseen in other sea slugs.

The discovery, made by scientists at the Monterey Bay Aquarium Research Institute, has been published in *Deep Sea Research Part I*. Unlike typical nudibranchs, which inhabit coastal areas and the seafloor, this new species was found over 7,220 feet deep in the Pacific Ocean, marking it as the first sea slug identified in such extreme conditions.

Researchers Bruce Robison and Steven Haddock first encountered *Bathydevius caudactylus* in 2000 using a robotic submersible during a deep-sea dive. Since then, it has been observed more than 150 times.

Exploring the deep midwater region has long presented challenges due to its depth, but scientists hope that studying *Bathydevius* and its unique adaptations will shed light on the mysteries of the midnight zone, which spans 70% of all ocean water and is the planet’s largest habitat.

Robison, co-author of the study, noted that this discovery adds valuable insights to our understanding of Earth’s largest ecosystem. The bioluminescent body of *Bathydevius* displays its internal organs clearly through translucent skin, and it activates a glowing defense when threatened. Remarkably, the slug has a unique survival tactic: one of its tail tendrils glows, rotates, and detaches when in danger, much like a lizard’s tail.

This fascinating trait, combined with its bioluminescence, highlights the creature’s extraordinary adaptations to life in the deep sea.