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Octopus and squid are molluscs, related to mussels, snails and clams. However, they are in a class of their own - the cephalopods - and are very different from their slow moving relatives. They are efficient predators, masters of disguise and can dart about the seas by jet-propulsion. What's more, they are more intelligent than any other invertebrate.

Jetting About
Octopuses have boneless, sack-like bodies with eight tentacles, or arms. The main body, the mantle, is thick and muscular and protects the gills, and the digestive, circulatory and reproductive systems. It is also the chief swimming organ. The octopus usually crawls around rocks on its suckered tentacles but if it needs to get somewhere in a hurry, either to escape or to catch prey, it uses its turbo jets. The mantle contracts strongly forcing water through a moveable funnel, which sticks out from the edge of the mantle, and the octopus is propelled in any direction.

Smoke-Screens and Camouflage
Instead of a hard protective shell, the octopus relies on its ability to leave the scene of danger quickly. However, if threatened it can also release a cloud of ink from a special ink sac that opens into the funnel. The ink may either confuse the predator or provide a smoke-screen while the octopus makes its escape.

Cephalopods have the ability to change colour and the speed and complexity of the colour changes are quite remarkable. They can change colour according to mood and background - body colour changes are brought about by muscular contractions of pigment cells in the skin. The lesser octopus, for example, turns deep red when excited, white when alarmed, with red around the eyes when angry.

Eight-Armed Predator
Octopus have good eyesight, their eyes are almost as well developed as our own. This, combined with the ability to blend in with the surroundings, makes them very effective predators. The octopus usually hides in rock crevices during the day, coming out at night to pounce on crustacean prey. The prey is engulfed in the webbing at the base of the octopus's arms and held tight while it is pierced by sharp, beak-like jaws. The octopus secretes a substance to paralyse the prey and then consumes it at its leisure. An octopus's den may often be recognised by the remains of crabs scattered at the entrance.

Super Mum
At about 2 years of age, octopuses are ready to reproduce. After a courtship involving complicated colour changes, the male donates a spermatophore (a packet of sperm) and the female lays grape-like clusters of eggs. The female stays close to her eggs, guarding them and keeping them clear of debris and sediment. Since she doesn't feed whilst brooding her eggs, she gradually loses condition and is so weakened that she dies when the young hatch as miniature adults.


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