Some of the most bizarre lifeforms on Earth lurk in the deeper realms of the ocean. There was so little known about one of these creatures that it took 20 years just to figure out what exactly it was. Things only got weirder from there.
The organism’s distinctive, glowing presence was observed by multiple deep-sea missions between 2000 to 2021 but was simply referred to as “mystery mollusk.” A team of Monterey Bay Aquarium Research Institute (MBARI) researchers has now reviewed extensive footage of past mystery mollusk sightings and used MBARI’s remotely operated vehicles (ROVs) to observe it and collect samples. They’ve given it a name and have finally confirmed that it is a nudibranch—the first and only nudibranch known to live at such depths.
Bathydevius caudactylus, as this nudibranch is now called, lives 1,000–4,000 meters (3,300–13,100 feet) deep in the ocean’s bathypelagic or midnight zone. It moves like a jellyfish, eats like a Venus flytrap, and is bioluminescent, and its genes are distinct enough for it to be classified as the first member of a new phylogenetic family.