The octopus is a cephalopod mollusc of the order Octopoda.
The molluscs compose the large phylum of invertebrate animals known as the Mollusca.
A cephalopod is any member of the molluscan class Cephalopoda.
It has two eyes and four pairs of arms and, like other cephalopods, it is bilaterally symmetric.
Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism.
All cephalopods possess flexible limbs extending from their heads and surrounding their beaks.
It has a beak, with its mouth at the center point of the arms.
All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages.
It has no internal or external skeleton, allowing it to squeeze through tight places.
The skeleton is the body part that forms the supporting structure of an organism.
Octopuses are among the most intelligent and behaviorally diverse of all invertebrates.
Intelligence has been defined in many different ways including as one's capacity for logic, understanding, self-awareness, learning, emotional knowledge, planning, creativity and problem solving.
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord.
Octopus is the largest genus of octopuses, comprising more than 100 species.
Octopuses inhabit diverse regions of the ocean, including coral reefs, pelagic waters, and the ocean floor.
Any water in a sea or lake that is neither close to the bottom nor near the shore can be said to be in the pelagic zone.
Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals.
An ocean is a body of saline water that composes much of a planet's hydrosphere.
They have numerous strategies for defending 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.
Deimatic behaviour in animals means any pattern of threatening or startling behaviour, such as suddenly displaying conspicuous eyespots, so as to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape.
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else.
In psychology and ethology, play is a range of voluntary, intrinsically motivated activities normally associated with recreational pleasure and enjoyment.
They trail their eight arms behind them as they swim.
All octopuses are venomous, but only one group, the blue-ringed octopus, is known to be deadly to humans.
The blue-ringed octopuses are three octopus species that live in tide pools and coral reefs in the Pacific and Indian Oceans, from Japan to Australia.
Venom is a form of toxin secreted by an animal for the purpose of causing harm to another.
Around 300 species are recognized, which is over one-third of the total number of known cephalopod species.
In biology, a species is one of the basic units of biological classification and a taxonomic rank.
The term 'octopus' may also be used to refer specifically to the genus Octopus.
A genus is a taxonomic rank used in the biological classification of living and fossil organisms in biology.