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Marine invertebrates

Octopuses

Blue-ringed octopusBlue-ringed octopus Octopuses belong to a family of molluscs called cephalopods, a group which also includes squid, cuttlefish and nautiluses. They have bag-shaped bodies and eight arms. Octopuses live in all of the world’s seas and oceans. The smallest species are only the size of a fingernail, while the largest have an arm span of up to 9 metres (30 feet). Octopuses use their sucker-covered arms to clamber around the seabed and seize their prey of crabs and lobsters. They have large eyes and excellent eyesight, the best of any invertebrate. Like humans, they can see in colour, which many other sea creatures cannot. Octopuses are considered the most intelligent of all invertebrates.


Arms

Pacific octopus gripping its prey, a crabPacific octopus gripping its prey, a crabOctopuses have eight muscular arms used for gripping, touching, fighting and walking along the seabed. Suckers along the underside of these arms help them to grip prey and force it into their beak-like mouth.
 

Octopus's beak.Octopus's beak.

Beak

An octopus's mouth is in the centre of its body. Instead of jaws it has a hard, sharp beak, like a parrot's. This beak is tough enough to break open crab shells. Octopuses normally inject their prey with a paralysing saliva before breaking it up into small pieces with their beaks. They have rough tongues, called radulas, which grate their food and draw it down towards their stomachs.

Octopus comes from the Greek word, oktapous, meaning "eight-footed".

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