The octopus (pronounced /??kt?p?s/, from Greek ?κτ?που? (oktapous), "eight-footed",[1][2] with plural forms: octopuses [??kt?p?s?z], octopi [??kt?pa?], or octopodes [??k?t??p?di?z], see below) is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. The term may also refer to only those creatures in the genus Octopus. In the larger sense, there are around 300 recognized octopus species, which is over one-third of the total number of known cephalopod species.An octopus has eight flexible arms, which trail behind it as it swims. Most octopuses have no internal or external skeleton, allowing them to squeeze through tight places. An octopus has a hard beak, with its mouth at the center point of the arms. Octopuses are highly intelligent, probably the most intelligent invertebrates. They are known to build "forts" and "traps" in the wild, and for rearranging tanks and burying other animals alive in domestication[citation needed]. For this reason, they are quite notorious among aquarium operators.[3] For defense against predators, they hide, flee quickly, expel ink, or use color-changing camouflage. Octopuses are bilaterally symmetrical, like other cephalopods, with two eyes and four pairs of arms.