‘Devious’ New Deep Sea Creature Hid Its Identity From Scientists

It took nearly 25 years for biologists to discover that a swimming and glowing organism in the ocean’s midnight zone was actually a sea slug.

Bruce Robison, a marine biologist, has long used robotic vehicles to explore the Monterey Canyon off California — a gargantuan rift of the Pacific seabed that descends rapidly from coastal shallows to a depth of more than two miles. In early 2000, he stumbled on a strange creature he had never seen before.

“We had no idea what it was,” Dr. Robison recalled.

The gelatinous blob had a giant hood at one end, fingerlike projections at the other and colorful internal organs in between. Baffled, Dr. Robison and a colleague at the Monterey Bay Aquarium Research Institute set out to discover what it was.

Now, a quarter-century later, having studied 157 of those enigmatic organisms in their dark habitats as well as in the laboratory, the two scientists are making their conclusions public. The newly identified creature, they report in a public release on Tuesday, turns out to represent a whole new family of living things that reside in the midnight world of the ocean’s vast midwaters — the largest and least explored part of the planet’s biosphere. Moreover, it looks and behaves unlike any of its closest relatives on the tree of life.

The discoverers say the creature is a surprising new kind of nudibranch, or sea slug. Nudibranchs (Latin for “naked gills”) get their name from that fact that they’re nude, unlike their snail cousins on land.

What sets the organism apart from its marine relatives — and what makes the discovery so astonishing — is that it swims. Up to now, most nudibranchs known to science were described as inching their way over coral reefs, sea grass beds, kelp forests, the deep seafloor and rocky tide pools.