The
octopus is a
cephalopod of the
order Octopoda. Octopuses
have two eyes and four pairs of arms and like other cephalopods are
bilaterally symmetric. An
octopus has a hard beak, with its mouth at the center point of the
arms. Most octopuses have no internal or external skeleton,
allowing them to squeeze through tight places. Octopuses are highly
intelligent, probably the most intelligent of all
invertebrates.
The octopus inhabits many diverse regions of the
ocean, especially
coral
reefs. For defense against predators, they hide, flee quickly,
expel ink, or use color-changing camouflage. An octopus trails its
eight arms behind it as it swims. All octopuses are venomous, but
only the small
blue-ringed
octopuses are deadly to humans.
In the larger sense, there are around 300 recognized octopus
species, which is over one-third of the
total number of known cephalopod species. The term octopus may also
be used to refer only to those creatures in the
genus Octopus.
Biology
Octopuses are characterized by their eight
arms, usually bearing
suction cups. The arms of octopuses are often
distinguished from the pair of feeding
tentacles found in
squid and
cuttlefish. Both types of limbs are
muscular hydrostats. Unlike most
other cephalopods, the majority of octopuses – those in the
suborder most commonly known,
Incirrina –
have almost entirely soft bodies with no internal
skeleton. They have neither a protective outer
shell like the
nautilus, nor any vestige of an internal shell or
bones, like cuttlefish or squid. A
beak, similar in shape to a
parrot's beak, is the only hard part of their body.
This enables them to squeeze through very narrow slits between
underwater rocks, which is very helpful when they are fleeing from
morays or other predatory fish. The
octopuses in the less familiar
Cirrina
suborder have two fins and an internal shell, generally reducing
their ability to squeeze into small spaces.
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. However,
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 they don't die of
starvation. Endocrine secretions from the two optic glands are the
cause of genetically-programmed death (and if these glands are
surgically removed, the octopus may live many months beyond
reproduction, until she finally starves).
Octopuses have three
hearts. Two pump blood
through each of the two
gills, while the third
pumps blood through the body. Octopus
blood
contains the
copper-rich protein
hemocyanin for transporting
oxygen. Although less efficient under
normal
conditions than the
iron-rich
hemoglobin of vertebrates, in cold conditions
with low oxygen pressure, hemocyanin oxygen transportation is more
efficient than hemoglobin oxygen transportation. The hemocyanin is
dissolved in the
plasma instead of
being carried within
red blood cells
and gives the blood a blue color. Octopuses draw water into their
mantle cavity where it passes through its gills. As
mollusks, octopuses have gills that are finely
divided and vascularized outgrowths of either the outer or the
inner body surface.
Intelligence
Octopuses are highly
intelligent,
likely more so than any other order of
invertebrates. The exact extent of their
intelligence and learning capability is much debated among
biologists, but 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 ultimately learn. There has
been much speculation to the effect that almost all octopus
behaviors are independently learned rather than instinct-based,
although this remains largely unproven. They learn almost no
behaviors from their parents, with whom young octopuses have very
little contact.
An octopus has a highly complex
nervous
system, only part of which is localized in its
brain. Two-thirds of an octopus's
neurons are found in the nerve cords of its arms,
which have a remarkable amount of autonomy. Octopus arms show a
wide variety of complex
reflex actions
arising on at least three different levels of the nervous system.
Unlike vertebrates, the complex motor skills of octopuses in their
higher brain are not organized using an internal somatotopic map of
its body. Some octopuses, such as the
Mimic Octopus, will move their arms in ways
that emulate the movements of other
sea
creatures.
In laboratory experiments, octopuses can be readily trained to
distinguish between different shapes and patterns. They have been
reported to practice
observational learning, although the
validity of these findings is widely contested on a number of
grounds. Octopuses have also been observed in what some have
described as play: repeatedly releasing bottles or toys into a
circular current in their aquariums and then catching them.
Octopuses often break out of their aquariums and sometimes into
others in search of food. They have even boarded
fishing boats and opened holds to eat
crabs.
In some countries, octopuses are on the list of
experimental animals on which surgery may not
be performed without
anesthesia. In the
UK, cephalopods such as octopuses are regarded as
honorary
vertebrates under the
Animals Act 1986
and other
cruelty to animals
legislation, extending to them protections not normally afforded to
invertebrates.
Defense
An octopus's main (primary) defense is to hide, either not to be
seen at all, or not to be detected as an octopus. Octopuses have
several secondary defenses (defenses they use once they have been
seen by a predator). The most common secondary defense is fast
escape. Other defenses include the use of
ink
sacs,
camouflage, and
autotomising limbs.
Most octopuses can eject a thick blackish
ink in a large cloud to aid in escaping from
predators. The main colouring agent of the ink is melanin, which is
the same chemical that gives humans their hair and
skin colour. This ink cloud is thought to
reduce the efficiency of olfactory organs, which would aid an
octopus's evasion from predators that employ
smell for hunting, such as
sharks. Ink clouds of some species might serve as
pseudomorphs, or decoys that the predator attacks instead.
An octopus's camouflage is aided by certain specialized skin cells
which can change the apparent color, opacity, and reflectiveness of
the epidermis.
Chromatophores contain
yellow, orange, red, brown, or black pigments; most species have
three of these colors, while some have two or four. Other
color-changing cells are reflective
iridophores, and
leucophores (white). This color-changing ability
can also be used to communicate with or warn other octopuses. The
very venomous
blue-ringed
octopus becomes bright yellow with blue rings when it is
provoked. Octopuses can use muscles in the skin to change the
texture of their mantle in order to achieve a greater camouflage.
In some species the mantle can take on the spiky appearance of
seaweed, or the scraggly, bumpy texture of a rock, among other
disguises. However in some species skin anatomy is limited to
relatively patternless shades of one color, and limited skin
texture. It is thought that octopuses that are day-active and/or
live in complex habitats such as coral reefs have evolved more
complex skin than their nocturnal and/or sand-dwelling
relatives.
When under attack, some octopuses can perform arm
autotomy, in a similar manner to the way
skinks and other
lizards detach
their tails. The crawling arm serves as a distraction to would-be
predators.
A few species, such as the
Mimic
Octopus, have a fourth defense mechanism. They can combine
their highly flexible bodies with their color changing ability to
accurately mimic other, more dangerous animals such as
lionfish,
sea snakes, and
eels.
Reproduction
When octopuses reproduce, males use a specialized arm called a
hectocotylus to insert
spermatophores (packets of sperm) into the
female's mantle cavity. The hectocotylus in
benthic octopuses is usually the third right arm.
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
families, genera, species and also individuals). The female hangs
these eggs in strings from the ceiling of her lair, or individually
attaches them to the
substrate
depending on the 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 on
copepods, larval
crabs and
larval
starfish until they are ready to
descend to the ocean bottom, where the cycle repeats. This is a
dangerous time for the larval octopuses; in the plankton cloud they
are vulnerable to plankton eaters. In some deeper dwelling species,
the young do not go through this period.
Sensation
Octopuses have keen eyesight. Although their slit-shaped
pupils might be expected to afflict them with
astigmatism, it appears that this is not a
problem in the light levels in which an octopus typically hunts.
Octopuses, like other cephalopods, can distinguish the
polarization of light.
Color vision appears to vary from species to
species, being present in
Octopus aegina but absent in
Octopus vulgaris. Attached to the brain are two special
organs, called
statocysts, that allow the
octopus to sense the orientation of its body relative to
horizontal. An
autonomic
response keeps the octopus's eyes oriented so that the pupil slit
is always horizontal.
Octopuses also have an excellent
sense of touch. An octopus's suction
cups are equipped with
chemoreceptors
so that the octopus can
taste what it is
touching. The arms contain
tension sensors so that the octopus
knows whether its arms are stretched out. However, the octopus has
a very poor
proprioceptive sense. The
tension receptors are not sufficient for the octopus brain to
determine the position of the octopus's body or arms. (It is not
clear that the octopus brain would be capable of processing the
large amount of information that this would require; the
flexibility of an octopus's arms is much greater than that of the
limbs of vertebrates, which devote large areas of
cerebral cortex to the processing of
proprioceptive inputs.) As a result, the octopus does not possess
stereognosis; that is, it does not form
a
mental image of the overall shape of
the object it is handling. It can detect local texture variations,
but cannot integrate the information into a larger picture.
The neurological autonomy of the arms means that the octopus has
great difficulty learning about the detailed effects of its
motions. The brain may issue a high-level command to the arms, but
the nerve cords in the arms execute the details. There is no
neurological path for the brain to receive feedback about just how
its command was executed by the arms; the only way it knows just
what motions were made is by observing the arms visually.
Locomotion
Octopuses move about by crawling or swimming. Their main means of
slow travel is crawling, with some swimming. Jet propulsion is
their fastest means of locomotion, followed by swimming and
walking.
They crawl by walking on their arms, usually on many at once, on
both solid and soft surfaces, while supported in water. In 2005 it
was reported that some octopuses (
Adopus
aculeatus and
Amphioctopus
marginatus under current taxonomy) can walk on two arms,
while at the same time resembling plant matter. This form of
locomotion allows these octopuses to move quickly away from a
potential predator while possibly not triggering that predator's
search image for octopus (food). Octopuses lack bones and are
extremely vulnerable to predators.
Octopuses swim by expelling a jet of water from a contractile
mantle, and aiming it via a
muscular
siphon.
Size
The
North Pacific Giant
Octopus,
Enteroctopus dofleini, is often cited as the
largest octopus species. Adults usually weigh around 15 kg
(33 lb), with an arm span of up to 4.3 m (14 ft).
The largest specimen of this species to be scientifically
documented was an animal with a live mass of 71 kg
(156.5 lb). The alternative contender is the
Seven-arm Octopus,
Haliphron
atlanticus, based on a 61 kg (134 lb) carcass
estimated to have a live mass of 75 kg (165 lb). However,
there are a number of questionable size records that would suggest
E. dofleini is the largest of all octopus species by a
considerable margin; one such record is of a specimen weighing
272 kg (600 lb) and having an arm span of 9 m
(30 ft).
Terminology
The term octopus, , is from
Greek
(
oktapous), "eight-footed",
Scientific
Latin from
Greek (also )
"eight-footed" > or [combination form of "eight"] and "foot".
Cf.
Modern Greek . with plural forms:
octopuses ,
octopi , or
octopodes . Currently,
octopuses is the
most common form in the US as well as the UK;
octopodes is
rare, and
octopi is often objectionable.
The
Oxford English
Dictionary (2004 update) lists
octopuses,
octopi and
octopodes (in that order); it labels
octopodes "rare", and notes that
octopi derives
from the mistaken assumption that is a
second declension Latin noun, which it is not.
Rather, it is a Latinization of
Greek
third-declension masculine ( , 'eight-foot'), plural ( ).
If the word were native to Latin, it would be , plural , after the
pattern of ('foot'), plural , analogous to "Centipede". The actual
Latin word for octopus and other similar species is , from Greek (
, 'many-foot'); usually the inaccurate plural is used instead of
.
In
modern Greek, the word is ( ),
plural ( ), from
Medieval ( ),
equivalent to
Classical ( ), variant
of .
Chambers 21st Century Dictionary and the
Compact
Oxford Dictionary list only
octopuses, although the
latter notes that
octopodes is "still occasionally used";
the
British National Corpus
has 29 instances of
octopuses, 11 of
octopi and 4
of
octopodes.
Merriam-Webster 11th Collegiate
Dictionary lists
octopuses and
octopi, in
that order;
Webster's New World College Dictionary lists
octopuses,
octopi and
octopodes (in that
order).
Fowler's Modern
English Usage states that "the only acceptable plural in
English is
octopuses," and that
octopi is
misconceived and
octopodes pedantic.
The term
octopod (plural
octopods or
octopodes) is taken from the
taxonomic order Octopoda but has no
classical equivalent. The collective form
octopus is
usually reserved for animals consumed for food.
Relationship to humans
Ancient
peoples of the Mediterranean
were aware of the octopus, as evidenced by certain
artworks and designs of prehistory. For example, a stone
carving found in the archaeological recovery from Bronze Age Minoan Crete
at Knossos
has a
depiction of a fisherman carrying an octopus.
The
Moche people of ancient Peru
worshipped
the sea and its animals; moreover, octopuses were often depicted in
their art.
In mythology
The
Hawaiian
creation myth relates
that the present cosmos is only the last of a series, having arisen
in stages from the wreck of the previous universe. In this
account, the octopus is the lone survivor of the previous, alien
universe.
In literature
The octopus has a significant role in
Victor
Hugo's book
Travailleurs de la mer (
Toilers of the Sea).
As food
Humans eat octopus in many cultures. The arms and sometimes other
body parts are prepared in various ways, often varying by
species.
Octopus is a common ingredient in
Japanese cuisine, including
sushi,
takoyaki, and
Akashiyaki. Some small species are sometimes
eaten alive as a novelty and
health food. Similarly, a live octopus may be
sliced up and the legs eaten while still squirming, which continues
for some minutes.
Octopus is
eaten regularly in Hawai
i, since many popular dishes are Asian in
origin. Locally known by their Hawaiian or Japanese names,
("he'e" and "tako" respectively) octopus is also a popular fish
bait.
Octopus is a common food in
Mediterranean cuisine and
Portuguese cuisine.
In Galicia
, polbo á feira
(market fair style octopus) is a local delicacy. Restaurants
which specialize or serve this dish are known as pulperías.
On the
Tunisian
island of Djerba
, local
people catch octopuses by taking advantage of the animals' habit of
hiding in safe places during the night. In the evening they
put grey ceramic pots on the sea bed. The morning of the following
day they check them for octopuses that sheltered there.
According
to the USDA
Nutrient Database (2007), cooked octopus contains
approximately 139 calories per three ounce portion, and is a source
of vitamin B3, B12, potassium,
phosphorus, and selenium.
Care must be taken to boil the octopus properly, to rid it of
slime, smell, and residual ink.
As pets
Though octopuses can be difficult to keep in captivity, some people
keep them as pets. Octopuses often escape even from supposedly
secure tanks, due to their problem solving skills, mobility and
lack of rigid structure.
The variation in size and life span among octopus species makes it
difficult to know how long a new specimen can naturally be expected
to live. That is, a small octopus may be just born or may be an
adult, depending on its species. By selecting a well-known species,
such as the
California
Two-spot Octopus, one can choose a small octopus (around the
size of a
tennis ball) and be confident
that it is young with a full life ahead of it.
Octopuses are also quite strong for their size. Octopuses kept as
pets have been known to open the covers of their aquariums and
survive for a time in the air in order to get to a nearby feeder
tank and gorge themselves on the fish there. They have also been
known to catch and kill some species of
sharks.
Classification
See also
References
- Unimelb.edu.au, Tentacles of venom: new study
reveals all octopuses are venomous, University of Melbourne, Media
Release, Wednesday 15 April 2009
- Norman, M. 2000. Cephalopods: A World Guide.
ConchBooks, Hackenheim. p. 15. "There is some confusion around the
terms arms versus tentacles. The numerous limbs
of nautiluses are
called tentacles. The ring of eight limbs around the mouth in
cuttlefish, squids and octopuses are called arms.
Cuttlefish and squid also have a pair of specialised limbs attached
between the bases of the third and fourth arm pairs [...]. These
are known as feeding tentacles and are used to shoot out
and grab prey."
- 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.
- Giant Octopus—Mighty but Secretive Denizen of the
Deep
- Slate.com, How Smart is the Octopus?
- Zullo L, Sumbre G, Agnisola C, Flash T, Hochner B. (2009).
Nonsomatotopic organization of the higher motor centers in octopus.
Curr Biol. 19(19):1632-6. PMID 19765993
- Octopus intelligence: jar opening
- What is this octopus thinking?. By Garry
Hamilton.
- 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.
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Secretive Denizen of the Deep
- United Kingdom Animals (Scientific
Procedures) act of 1986
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Behaviour. Cambridge University Press, Cambridge.
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Protecting Adult Octopus bocki from Predation by Green
Turtle (Chelonia mydas) Hatchlings." Pacific
Science 59(1): 69–72.
- Norman, M.D., J. Finn & T. Tregenza (2001). Proceedings
of the Royal Society 268: 1755–1758.
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(Thaumoctopus mimicus n. gen. et sp.), a new octopus from
the tropical Indo-West Pacific (Cephalopoda: Octopodidae).
Molluscan Research 25: 57–70. Abstract
- Kawamura, G., et al. (2001). . Nippon Suisan Gakkashi
67(1): 35–39.
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advanced invertebrate. London : Chapman and Hall ;
New York : distributed in the U.S.A. by Halsted Press, 1978.
- Locomotion by Abdopus aculeatus, C.L.
Huffard 2006
- Science, vol. 307, p. 1927
- Smithsonian National Zoological Park: Giant Pacific
Octopus
- Cosgrove, J.A. 1987. Aspects of the Natural History of
Octopus dofleini, the Giant Pacific Octopus. M.Sc. Thesis.
Department of Biology, University of Victoria (Canada), 101
pp.
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atlanticus (Mollusca : Octopoda) in New Zealand waters.
New Zealand Journal of Zoology 31(1):
7-13.
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gelatinous octopus. Biodiversity Update
5: 1.
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ConchBooks, Hackenheim. p. 214.
- High, W.L. 1976. The giant Pacific octopus. U.S. National
Marine Fisheries Service, Marine Fisheries Review
38(9): 17-22.
- Oktapous, Henry George Liddell, Robert Scott,
A Greek-English Lexicon, at Perseus
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Usage. Cambridge: Cambridge University Press. ISBN
0-521-62181-X, p. 388.
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October 22, 2007.
- Chambersharrap.co.uk, Retrieved October 19,
2007.
- Askoxford.com, Retrieved October 19, 2007.
- C. Michael Hogan. 2007 Knossos fieldnotes, The Modern
Antiquarian
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Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera.
New York: Thames and Hudson, 199 7.
- Octopus Calories And Nutrition
- Archived Google video of an octopus catching a
shark, from The Octopus Show by Mike deGruy
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