Underwater 'city' built by octopuses found, named Octlantis

US-based researchers have discovered underwater dens with pilings of shells and holes dug into sand, home to about 15 octopuses, off the Australian coast. At the site, dubbed 'Octlantis', researchers observed mating and signs of aggression, with some octopuses seen evicting other animals. The site was a few hundred metres away from the first such site 'Octopolis', found in 2009.