Cephalopods

Octopus, squid and cuttlefish can all change colour in response to aggression, fear, sexual arousal or the need for camouflage. Octopus and cuttlefish can also change skin texture.
More about Octopus mating and Octopus netting prey

 
Octopus

In octopus the soft head and body are fused. Octopus have 8 long arms covered in suckers They have an advanced nervous system,good vision and acute senses of taste and touch, and can exhibit complex behaviours. They have nervous control of their vascular system. Blood flow to a severed limb can be constricted so as to decrease bleeding. Octopuses are usually found hiding under rocks.

Hapalochlaena fasciata, blue-lined octopus Octopus tetricus, Sydney octopus, gloomy octopus
Octopus cyanea, day octopus
 
Cuttlefish

Cuttlefish have an oval body supported by a cuttlefish bone which is used to regulate buoyancy by pumping liquidinto the tiny chambers within it. There are narrow fins arround the edge of the body. They have a relativley large head, which is partly fused with the body,8 short arms plus two long tentacles
Cuttlefish swim close to the bottom in search of prey.

Sepia mestus, reaper cuttlefish
 
 
Squid

Squid live in mid-water. They have a thin, lightweight transparent horny structure supports the tissue. They hunt fast moving fish.Squid can emit clouds of black ink when stressed