Mystery Octopuses That Look like Dumbo Found Living Deep Beneath the Sea

In the deep, deep ocean lives a group of rare and mysterious octopuses that are named after one of Disney's most iconic characters.

The group, commonly known as the Dumbo octopuses, are found around the world in deep-ocean habitats, thousands of feet below the surface, where they are rarely seen by humans.

Michael Vecchione, a cephalopod expert with the NOAA National Systematics Laboratory at the Smithsonian Museum of Natural History in Washington, D.C., told Newsweek here are different interpretations of what constitutes a dumbo octopus. Understanding exactly what they are is tricky.

Some researchers use that term only to refer to the genus (group of species) Grimpoteuthis, whereas Vecchione and other experts call the wider group of so-called "cirrate" octopods—which consists of about 45 recognized species in total—Dumbo octopuses.

The main feature that characterizes cirrates is that, unlike most octopuses, they have fins. These body parts, found on the sides of their bodies, resemble the ears of Dumbo—the cartoon elephant—hence the name.

The other feature that characterizes the Dumbo octopuses, according to Vecchione, are finger-like muscular projections called "cirri" that are found in between each of the suckers on their arms. This is where the name "cirrate" comes from.

"We don't really know what [the cirri] are used for but we presume it's got to do with handling the prey that they feed on," Vecchione said.

Cirrate octopuses also have webbed arms, and often, this webbing is quite extensive, reaching the tips of the arms.

These creatures are primarily found in the deep sea, although it is not unusual to find some in comparatively shallow waters up in the polar regions. Dumbo octopuses are the deepest living known cephalopods—the group of molluscs that includes squid, octopus and cuttlefish.

"[They] live all the way down into the upper parts of the trenches, which are the deepest parts of the ocean," Vecchione said. "They get down to probably around 7,000 meters deep [around 23,000 feet]. And the shallowest ones are up close to the edge of the continental shelf, so about 200 meters [256 feet]. So the range of the group in general is really broad."

Currently, it appears as if a large percentage of Dumbo octopus species are very broadly distributed. Despite this, sightings of these cephalopods are rare.

"There's a species down in the Antarctic, which in some places we've found to be pretty abundant. But in general, the Dumbos are rare and people get excited every time they see them with a sub. So, I would say that they are rare, except in a few limited areas," said Vecchione, whose research focuses on deep-sea and polar cephalopods.

One of the most unusual aspects of these octopuses is their curious ear-like fins, which they use to propel themselves through water, steering with the help of their arms.

"Their swimming behaviour is unusual. Most cephalopods swim with jet propulsion—they suck water into their body and then squirt it out through a little funnel. We don't think that cirrate octopods do that at all anymore. What they do is they swim either by flapping their fins or by using their arms and webs to swim sort of like a jellyfish swims," Vecchione said.

The way these octopuses catch prey—usually invertebrates that swim above the sea floor—is somewhat of a mystery, according to Vecchione.

"They have a web between the arms, so the arms are all connected together. And we think that they catch their prey by getting the animal inside that web, trapping it with the arms and then doing something with the cirri to get the prey to the mouth," he said. "It might involve secreting mucus, for instance, and then using the cirri to move the animal to the mouth. But that's just speculation right now."

Another unusual aspect of their behavior is the way they lay their tough eggs, which in some cases can measure up to around an inch in length.

"As far as we know, they attach their eggs to things like deep-sea corals. We know that's true for a few species, because we found the eggs and probably all of them have a similar behavior," Vecchione said.

"So, unlike shallow water octopods, where the female lays a whole bunch of eggs, and then sits there and takes care of them, these appear to just lay their eggs one at a time, attaching them to deep-sea corals, and maybe sponges too. Then, after they lay that one egg, they swim away. And again unlike the shallow water octopods, which spawn a whole bunch all at once, these seem to keep spawning over and over again, over a prolonged period of time."

Dumbo octopuses are highly specialized to life in the deep sea, where temperatures can be extremely cold and sunlight is often severely limited or absent altogether, depending on the depth. For example, in order to increase the chances of finding a mate and successfully reproducing in the vast blackness of the deep, females appear to always carry eggs in different stages of development, and can store sperm for a long period of time after mating.

As a result, the female can transfer the sperm to the most developed eggs whenever the environmental conditions are just right.

Because they rarely encounter predators in the deep sea, these octopuses generally do not have ink sacs. Many cephalopods are capable of squirting ink as a defense mechanism to escape from predators.

Given the kinds of environments they tend to inhabit, cirrate octopods are largely not threatened by human activities like fishing to the extent that other marine life is. But they could be facing threats from global climate change, according to Vecchione.

"The deep sea is warming and in some areas there's less and less oxygen in the water. So, the low oxygen areas are expanding. And both of those can be threats to these cirrate octopods. The third aspect of climate change is acidification. And the deep ocean is suffering from that as well. But I think that's less of a threat to them than it is to other deep-sea animals."