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The octopus is a cephalopod
of the order Octopoda that inhabits many diverse regions of the
ocean, especially coral reefs. The term may also refer to only
those creatures in the genus Octopus. In the larger sense, there
are 289 different octopus species, which is over one-third the
total number of cephalopod species. Octopuses are characterized
by their eight arms, usually with sucker cups on them. Unlike
most other cephalopods, octopuses have almost entirely soft bodies;
they have neither a protective outer shell like the nautilus,
nor any vestige of an internal shell or bones, like cuttlefish
or squids. A beak, similar in shape to a parrot's beak, is their
only hard part. This enables them to squeeze through very narrow
slits between underwater rocks, which is very helpful when they
are fleeing from morays or other predating fish.
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Three defensive
mechanisms are typical of octopuses: ink sacs, camouflage, and
autonomising limbs. Most octopuses can eject a thick blackish
ink in a large cloud to aid in escaping from predators. They also
have specialized skin cells both for color changing (chromatophores)
and light reflection and refraction (iridophores and leucophores).
They use this ability to blend into the environment to hide, as
communication with other octopuses, or as a warning: the very
poisonous Blue-ringed Octopus becomes bright yellow with blue
rings when it is provoked. When under attack, some octopuses can
detach and autonomise their limbs, in a similar manner to skinks
and other lizards. The crawling arm serves as a distraction to
would-be predators; this ability is also used in mating.
Above Images Come From The National Undersea Research
Program
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