True to its name, the Pacific giant octopus is the largest of all octopus species, and, along with other cephalopods (a group of molluscs that contain the octopuses, squid and cuttlefish), it is considered one of the most intelligent of all invertebrates. The body, or ‘mantle’, is generally reddish-brown, and it is usually darker in the male than in the female. During mating, white spots also become visible on the male’s mantle. When disturbed or threatened, special pigment cells in the skin, called chromatophores, may become activated, and cause the mantle to change colour to white or red.