Claim: Octopuses can swim with their tentacles quickly through the water.

The octopus -LRB- -LSB- ˈɒktpəs -RSB- or ~ -LSB- əpʊs -RSB- -RRB- is a soft-bodied , eight-armed mollusc of the order Octopoda . The order is grouped within the class Cephalopoda with squids , cuttlefish and nautiloids . Like other cephalopods , the octopus is bilaterally symmetric with two eyes and a beak , with its mouth at the centre point of the arms . The soft body , with its lack of internal or external skeleton , can rapidly alter its shape , appearance and colour , enabling the octopus to squeeze through small gaps . The mantle cavity is used both for respiration and for locomotion , by expelling a jet of water . Octopuses have a complex nervous system and excellent sight , and are among the most intelligent and behaviourally diverse of all invertebrates .   Octopuses inhabit various regions of the ocean , including coral reefs , pelagic waters , and the seabed ; some occur in the intertidal zone and others at abyssal depths . Most species grow fast , mature early and are short-lived . During breeding , the male uses a specially adapted arm to deliver a bundle of sperm directly into the female 's mantle cavity , after which he goes into a decline . The female deposits fertilised eggs in a den and cares for them until they hatch , after which she also dies .   Octopuses have numerous strategies for to defend themselves against predators , including the expulsion of ink , the use of camouflage and deimatic displays , their ability to jet quickly through the water , and their ability to hide . They trail their eight arms behind them as they swim . All octopuses are venomous , but only one group , the blue-ringed octopuses , is known to be deadly to humans . Around 300 species are recognised .   Octopuses appear in mythology as sea monsters like the Kraken of Norway and the Akkorokamui of the Ainu , and probably the Gorgon of ancient Greece . A battle with an octopus appears in Victor Hugo 's book Toilers of the Sea , inspiring other works such as Ian Fleming 's Octopussy . Octopuses appear in Japanese erotic art , shunga . They are eaten by humans in many parts of the world , especially the Mediterranean and the Asian seas .