About Cephalopods:

• Cephalopods are the most intelligent, most mobile, and the largest of all molluscs.
• They are the most morphologically and behaviorally complex class in phylum Mollusca.
• Squid, octopuses, cuttlefish, the chambered nautilus, and their relatives display remarkable diversity in size and lifestyle with adaptations for predation, locomotion, disguise, and communication.
• These "brainy" invertebrates have evolved suckered tentacles, camera-like eyes, color-changing skin, and complex learning behavior.
• Their lengthy evolutionary history spans an impressive 500 million years and the abundant fossils they've left behind record repeated speciation and extinction events.
• Characteristics:
  • They are characterized by a completely merged head and foot, with a ring of arms and/or tentacles surrounding the head. The arms, tentacles, and funnel are all derivatives of the foot.
  • Locomotion in cephalopods is accomplished mainly by jet propulsion.
  • All cephalopods are carnivorous. Many are skilled hunters, but some feed passively on floating debris.
  • They possess well-developed nervous systems and complex sensory organs.
  • They contain pigment-rich cells in the epidermis surrounded by cells containing contractile fibers.
  • One of the highly complex behaviours that many cephalopods show is visual camouflage. They can open and close tiny sacs just below their skin that contain coloured pigments and reflectors, revealing specific colours. 
  • The Australian giant cuttlefish, Sepia apama, uses its chromatophores to communicate, creating patterns that attract mates and warn off aggressors.
  • This ability can also come in handy for hunting; many cephalopods are ambush predators that blend into the background or even lure their prey.
• Some Cephalopods live alone in the nearly featureless darkness of the deep ocean; others live socially on active, sunny coral reefs.
• Some cephalopods may be capable of more complicated forms of learning, such as reversal learning – learning to flexibly adjust behaviour when different stimuli signal reward.