An octopus is a cephalopod mollusc in the order Octopoda in its broadest sense, but also will refer more narrowly to groups of organisms within the family Octopodidae, or even more specifically the genus Octopus.
Generally less actively swimming than fellow cephalopods squid and cuttlefish, an octopus has eight flexible suckered arms, used for grasping rocks and prey as well as propelling the octopus. These are often inaccurately referred to as "tentacles", but in fact that term refers specifically to two longer extremities which cuttlefish and squid have at the front of their bodies but octopuses do not. To move, it may pull itself over the sea bed with its arms, but when in a hurry, it shoots a jet of water out of its body, thrusting it through the water.
Octopuses use chromatophores to perfectly camouflage themselves against their background. When threatened, they can eject a cloud of ink to mask their escape. They can compress their bodies to fit through minute apertures.
Octopuses as food
Octopuses in popular culture
The Octopus is also the name of novel by Frank Norris.
While "octopi" is the popularly used plural form of "octopus" and is sometimes listed as such in dictionaries , it is incorrect  because the word does not derive from Latin; the strictly accepted plurals are "octopuses" and "octopodes". Scholars working with cephalopods have settled on the usage of "octopuses" as plural for "octopus" in the narrow sense referring to species within the family Octopodidae and "octopods" the plural to refer more broadly to all species within the order Octopoda.
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