The Cephalopoda include such creatures as the Squid, Nautili, Octupus and Cuttlefish. Excepting the Nautilus, these animals are unique within the Mollusca as they do not have shells. Also unlike most shelled molluscs the Cephalopoda have adapted to a lifestyle swimming within the water column. There are over 500 species of Squid. Squid are the most variable of all the cephalopods and range from the tiniest at 6cm long up to the Giant squid Architeuthis which legend reports at 100feet long and has been found up to 16m long.
All cephalopods swim by jet propulsion, however squid are the most efficient at it.
The flying squid has such a strong escape propulsion that its long tapered bodies fly out of the water from the power of it. Before the escape propulsion Cephalopods release and ink jet which causes a cloud of black murky water and temporarily confuses the predator. Many of the Cephalopods first avenue of defence is camoflage, which they achieve by altering their appearance. Special cells called Chromatophores in the skin can expand or contract, changing the colour pattern of the octupus, squid. This Chromatophore manipulation can achieve extremely rapid and complex changes and is also used in communications during territory and mating rituals.