Common cuttlefish (Sepia officinalis)
The cephalopods (meaning 'head-footed'), a group of molluscs containing the octopuses, squid and cuttlefish, are probably the most intelligent of all invertebrates. They have well-developed heads, with large eyes and mouths that feature beak-like jaws. The body of the common cuttlefish is flattened and broad, and is therefore oval in cross-section. A fin runs around the body from behind the head. Encircling the mouth there are eight 'arms' with suckers, which are used to manipulate prey, there are also two tentacles with flattened paddle-like tips, which can be rapidly extended and are used to catch prey. This species has excellent camouflage; it is able to change its colour to match its surroundings. Colour is therefore extremely variable, but is typically blackish-brown, mottled or striped, usually with paler underparts. Cuttlefish have an internal shell known as a cuttlebone, which is filled with gas and aids buoyancy; these shells are found washed ashore, and are often given to pet birds as a source of calcium and other minerals.