Octopus
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The Octopus [1] is a cephalopod mollusc in the order Octopoda. Octopuses have two eyes and four pairs of arms equipped with suckers. An octopus has a hard beak, and its mouth is at the center point of the arms.
Most octopuses have no internal or external skeleton, allowing them to squeeze through tight places. Octopuses are intelligent predators with a taste for crabs.
The octopus inhabits many regions of the ocean, especially coral reefs. For defense against predators, they hide, flee quickly, expel ink, or use color-changing camouflage. They live rather short lives.
An octopus trails its eight arms behind it as it swims. All octopuses are venomous, but only the small blue-ringed octopuses are known to be deadly to humans.[2]
There are about 300 octopus species, which is over one-third of the total number of known cephalopods. The term octopus may also be used to refer only to those creatures in the genus Octopus.
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[change] Structure
Unlike most other cephalopods, most octopuses have only soft body with no internal skeleton. They have no protective outer shell like the nautilus, which is another type of cephalopod. A beak, similar in shape to a parrot's beak, is their only hard part.
Because of this, it is very easy for an octopus to squeeze through very narrow openings between rocks, for example squeezing through a hole as big as its eye.
[change] Intelligence
Octopuses are highly intelligent, probably more so than any other invertebrate. The exact extent of their intelligence and learning capability is much debated among biologists.[3][4][5] Maze and problem-solving experiments have shown that they do have both short and long-term memory. Their short lifespans limit the amount they can learn.
Some octopuses, such as the Mimic Octopus, can move their arms in ways which copy the movements of other sea creatures.
In laboratory experiments, octopuses can be readily trained to distinguish between different shapes and patterns. They have been seen in what some have described as play: repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them.[6] Octopuses often break out of their aquaria and sometimes into others in search of food. They have even boarded fishing boats and opened holds to eat crabs.[4]
In the UK, cephalopods such as octopuses are regarded as honorary vertebrates under the Animals (Scientific Procedures) Act 1986 giving them protection not normally afforded to invertebrates.[7]
The octopus is the only invertebrate which has been conclusively shown to use tools. At least four specimens of the Veined Octopus (Amphioctopus marginatus) have been seen picking up discarded coconut shells, and then reassembling them to use as shelter.[8][9]
[change] Food
Octopods are active and intelligent predators, with good eyesight and brains. They eat mostly crabs and some fish. Some species of octopuses eat other octopuses.
[change] Defences
Octopods have a variety of defences. They use active camouflage and mimicry, controlled by their nervous system. Most can eject black ink clouds to help escape, and some can shed an arm in extreme danger. It wriggles, and attracts the attacker.
[change] Eyes
Octopuses' eyes are complex. In fact, the octopus does not have a blind spot.[10] A blind spot is a special place in the eyes that is not able to sense light. So, when we look somewhere, part of what is there is not actually perceived (the brain 'fills in' so we do not notice). However, an octopus does not have this problem.
Octopus eyes' lens are movable. It moves back and forth to focus. This is the way a camera focuses. When a camera focuses on an object to take a picture, the lens moves back and forth until the image that the camera sees is in the right focus.[10]
[change] Colors
Some octopuses can use their chromatophores for more than camouflage. If they are not blending in with their surroundings, they can signal their feelings using color. When they are relaxed, for example, they are a dull, grayish brown or orange-tinged color. When they become angry, they can become red. If they feel scared, they may turn white.
[change] Reproduction and death
When octopuses reproduce, males use a specialized arm to put packets of sperm into the female's mantle cavity. Males die within a few months of mating. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature.
After they have been fertilized, the female lays about 200,000 eggs (this figure dramatically varies between species). The female cares for the eggs, guarding them against predators, and gently blowing currents of water over them so that they get enough oxygen. The female does not hunt during the roughly one-month period spent taking care of the unhatched eggs and may ingest some of her own arms for sustenance.
At around the time the eggs hatch, the mother leaves the lair and is too weak to defend herself from predators like cod, often succumbing to their attacks. The young larval octopuses spend a period of time drifting in clouds of plankton, where they feed until they are ready to descend to the ocean bottom, where the cycle repeats.
Octopuses have a relatively short life expectancy, and some species live for as little as six months. Larger species, such as the North Pacific Giant Octopus, may live for up to five years under suitable circumstances.
Reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch. They neglect to eat during the (roughly) one month period spent taking care of their unhatched eggs, but apparently they do not die of starvation. A biological explanation of these short lifespans (or rapid ageing) is not agreed at present.
Right: Ancient Greek black-figure amphora (vase), 530–520 BC. On the left, a hoplite with an octopus image on his shield. Staatliche Antikensammlungen, Munich, Germany
[change] References
- ↑ The plural of octopus is usually octopuses, sometimes octopods, but never octopi. (Greek: okto = eight; podes = feet).
- ↑ Unimelb.edu.au Tentacles of venom: new study reveals all octopuses are venomous, University of Melbourne, Media Release, Wednesday 15 April 2009
- ↑ NFW.org?, Is the octopus really the invertebrate intellect of the sea, by Doug Stewart. In: National Wildlife. Feb/Mar 1997, vol.35 no.2.
- ↑ 4.0 4.1 Giant Octopus—Mighty but Secretive Denizen of the Deep
- ↑ Slate.com, How smart is the Octopus?
- ↑ What behavior can we expect of octopuses? by Dr. Jennifer Mather, Department of Psychology and Neuroscience, University of Lethbridge and Roland C. Anderson, The Seattle Aquarium.
- ↑ United Kingdom Animals (Scientific Procedures) act of 1986
- ↑ "Octopus snatches coconut and runs". BBC News. 2009-12-14. http://news.bbc.co.uk/1/hi/sci/tech/8408233.stm. Retrieved 2010-05-20.
- ↑ http://www.edutube.org/video/coconut-shelter-evidence-tool-use-octopuses
- ↑ 10.0 10.1 Marion Nixon & J.Z. Young 2003. The brains and lives of cephalopods. New York: Oxford University Press. ISBN 0-19-852761-6
