In the common imagination, the octopus is certainly not one of the most sociable and playful sea creatures. The intelligent cephalopod leads a solitary existence, with sporadic two-person meetings aimed only at reproducing. For the rest, except for some territorial struggle, each on his own way.

Not so fast, though: US researchers have discovered in the Bay of Jervis, off the east coast of Australia, a submerged city inhabited by 15 specimens of the octopus Octopus tetricus. A novella underwater Atlantis in which the creatures cohabit, communicate indirectly, mate and - above all - they quarrel, but without seemingly getting away.

Metropolitan area. Octlantis, as the site was called at 10-15 meters depth, is the second octopus marine settlement observed in nature. The first, called Octopolis, was identified in 2009 in the same bay, a few hundred meters away, as biologists at the University of Illinois tell in the magazine Marine and Freshwater Behavior and Physiology.

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Houses and neighborhoods. Octopolis housed 16 specimens, collected in objects abandoned by man: the hypothesis, then, had been that the octopuses needed artificial structures to form stable congregations.

The discovery of the new city leads to a review of this theory. The assemblage that develops on 18 meters of length, in fact includes shelters in the rock, burrows drawn in the sand and skyscrapers formed by heaps of shells and other shells of consumed preys.

Vicious neighbors. Its inhabitants have often been seen interacting at a tentacle distance, even if "in their own way": the most frequent contacts were couplings, territorial struggles, manifestations of aggression with color changes, attempts to appropriate others' den. An antagonistic attitude that biologists have not yet been able to fully explain, but which could depend on the population density of the space. Analyzes of the 10-hour video footage of Octlantis captured by GoPro (still being examined by scientists) will provide some of the answers.