an ocean world where vast underwater cities house an advanced civilization of aquatic beings with mushroom house

ocean world underwater cities advanced civilization aquatic beings mushroom house atlantis marine subaqueous submerge metropolis species fungi dwelling undersea urban submerged colony waterworld seafaring maritime abyssal pelagic benthic hydrothermal architecture oceanic coral reefs seaweed submarine azure merfolk finfolk hydrophilic mollusks aquatica sponges starfish gilled creatures barnacle encrusted cephalopod depth oyster