The cephalopods (meaning ‘head-footed) are a group of molluscs that contain the octopuses, squid and cuttlefish, and are probably the most intelligent of all invertebrates. They have well-developed heads, with large complex eyes and mouths that feature beak-like jaws. All octopuses have eight tentacle-like arms; indeed ‘octopus’ derives from the Greek for ‘eight-footed’. The common octopus usually measures around 60 centimetres in length, but it can grow up to 1 metre. It is able to change its colour depending on its mood and situation, but individuals are usually greyish-yellow or brownish-green with extensive mottling. They are often very well camouflaged. The body is warty, and the thick arms bear two rows of suckers.