The octopus is a soft-bodied, eight-limbed mollusc of the order Octopoda. Around 300 species are known, and they occupy every ocean, from tidal shallows to the abyssal plain. An octopus has no internal or external skeleton, which allows it to squeeze through any gap larger than its beak — the only hard part of its body. Two thirds of its neurons sit not in the brain but in its arms, so each arm can taste, touch and act with a striking degree of independence. Octopuses change colour and skin texture in a fraction of a second using pigment sacs called chromatophores, despite being, as far as anyone can tell, colour-blind. They are among the most capable invertebrate problem-solvers: captive animals open jars, navigate mazes and recognise individual keepers. Most species live only one to two years, dying shortly after they reproduce. (Full article...)