‘Devious’ new deep sea creature hid its identity from scientists

The newly identified creature turns out to represent a whole new family of living things that reside in the midnight world of the ocean’s vast midwaters.

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 2 miles. In early 2000, he stumbled on a strange creature he had never seen before.

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

The gelatinous blob had a giant hood at one end, fingerlike projections at the other and colorful internal organs in between. Baffled, 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 reported in a public release 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 the 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.

By contrast, Robison and his colleague, Steven Haddock, found that the newly identified creature is neutrally buoyant — that is, it can float effortlessly underwater, not sinking or rising. Striking video footage shows how, from that weightless state, it moves gracefully through its dark habitat, slowly undulating its entire body up and down.

More dramatically, the scientists found it can also expel water rapidly from its hood — producing jet-like bursts that send it moving quickly backward to escape predators.

The organism’s highly elastic hood, it turns out, is an oral cavity that can expand and contract to trap shrimp and other crustaceans, much as a Venus flytrap does with insects. The animal’s mouth is at the hood’s back.

The fingerlike projections turn out to be part of its paddle-like tail, the scientists report. They also note that the nudibranch, like many creatures of the midnight realm, can light up in brilliant displays of bioluminescence. The glow radiates from luminous dots that give the animal a starry look.

Long studies of the ocean’s sunless depths have shown that the reproductive behavior of abyssal creatures can, by human standards, get weird. That applies to the nudibranch, too: The scientists found that the new animal is a hermaphrodite, possessing both male and female sex organs. In the boundless immensities of the deep sea, they wrote, the bisexual lifestyle can “maximize the chances for reproductive success.”

While the hermaphroditic animals live a solitary existence in the sea’s dark expanse, the scientists report that they occasionally found spawning individuals in proximity to one another on the seabed. Apparently, the nudibranch goes there to release its eggs. The scientists say that the animal’s penis is usually withdrawn but at times protrudes from its genital duct.

The largest of the studied creatures measured about 6 inches from the oral hood to the tail. The creatures were observed traveling a half-mile to 2 miles down.

While the swimming nudibranch was sighted most often in the dark recesses of Monterey Canyon, the institute says its expeditions have found the creatures as far north as Oregon and as far south as Southern California.

Detailed studies of the nudibranch — including what its anatomy and physiology are like and how its genes compare with marine relatives — suggest it is unique enough to reside in a new classification of the taxonomic hierarchy at the family level, the scientists say. The diverse family category comes directly above the more restricted groupings of the genus and species levels.

The scientists propose that the new family name should be Bathydeviidae. The Greek word “bathys” means deep. The institute says the latter part of family name reflects the “devious” nature of an animal that fooled scientists with odd features that pointed to anything but what normally constitutes a nudibranch.

In the institute’s news release, Robison said the team’s discovery added “a new piece” to the midnight-zone puzzle, helping science understand not only unfamiliar aspects of the planet’s largest habitat but also the natural history of some of its fascinating residents.

He called them “neighbors that share our blue planet.”