Cephalopods
This entirely marine class includes such familiar animals as the octopus, cuttlefish and squid and also the so-called ‘living-fossil’ Nautilus and the extinct ammonites. As the name suggests the limbs are closely associated with the head, and in most cephalopods these limbs (arms and tentacles) possess numerous suckers which help to secure prey. Typically the shell is internalised (or absent as in octopods) but in Nautilus the animal occupies the last chamber of a spiral shell. Cephalopods have a powerful beak for killing crustaceans, fish or other molluscs, and use their radular teeth for processing ingested tissues. Many species use venoms to immobilise prey items and some such as the Blue-lined Octopus are capable of inflicting serious or even fatal injuries to humans. Many species of squid, octopus and cuttlefish are of major commercial importance (primarily as seafood).
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