The idea of undiscovered underwater cities isn’t as far-fetched as you might think. It just turns out they’re built by octopuses.
Earlier this month, scientists published a paper describing a site in Australia’s Jervis Bay, near Sydney, where 10 to 15 gloomy octopuses (yes, that’s really what they’re called) live at “high density” and exhibit “complex social interactions” towards one another. The species, also known as Octopus tetricus, communicate, fight and even “evict” one another from their dens in a settlement formed around exposed rock patches.
In other words, it’s basically an octopus city, which biologists are calling “Octlantis,” according to The Guardian.
The study, a collaboration between multiple scientists from Australia and the United States, was published on Sept. 1 in the journal Marine and Freshwater Behaviour and Physiology. Thursday, Business Insider published a video that reveals exactly what life in the octo-city looks like:
The discovery is significant because octopuses are typically believed to be solitary animals, meeting up only for mating. In 2009, scientists discovered a similar site — also in Jervis Bay — dubbed “Octopolis,” but it was widely considered to be an anomaly.
The existence of Octlantis, though, suggests that groups of octopuses living together are more common than people thought. Lead study author David Scheel, a marine biology professor at Alaska Pacific University, told Quartz that he doesn’t believe octopus group settlements are necessarily new. He thinks it’s more likely that better technology is now allowing humans to find them.
In Octopolis, the animals had settled around what appeared to be some sort of human-made metal object around a foot long, so researchers wondered how much human activity influenced the creation of the “city.” But in Octlantis, which is only a few hundred meters away, there is no such man-made object.
So what does Octlantis look like? The settlement, which is about 60 feet by 13 feet, surrounds three exposed patches of rock emerging from the sea floor. It includes octopus dens made from digging into the sand itself, or constructed out of piles of discarded shells from the creatures that the octopuses eat.
“These shell piles, or middens, were further sculpted to create dens, making these octopuses true environmental engineers,” said Stephanie Chancellor, a Ph.D. student at the University of Illinois Chicago who was one of the study authors.
Chancellor added that since little is known about how octopuses interact socially, some of their behavior was hard to interpret. For instance, researchers observed the animals appearing to “evict” one another from their homes, but weren’t sure why they were doing it.
“Some of the octopuses were seen evicting other animals from their dens,” he said. “There were some apparent threat displays where an animal would stretch itself out lengthwise in an ‘upright’ posture and its mantle would darken. Often another animal observing this behavior would quickly swim away.”
That said, if aliens descended on Earth and observed humans, some of our behavior would be pretty hard to explain, too.
This article originally appeared on HuffPost.