The
octopus (
or
; plural:
octopuses,
octopodes or
octopi;
see below) is a
cephalopod mollusc of the
order Octopoda. It has two eyes and four pairs of arms and, like other cephalopods, it is
bilaterally symmetric. It has a
beak,
with its mouth at the center point of the arms. It has no internal or
external skeleton (although some species have a vestigial remnant of a
shell inside their
mantles),
[3] allowing it to squeeze through tight places.
[4] Octopuses are among the most intelligent and behaviorally diverse of all
invertebrates.
Octopuses inhabit diverse regions of the
ocean, including
coral reefs,
pelagic waters, and the
ocean floor. 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. 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.
[5]
Around 300
species
are recognized, which is over one-third of the total number of known
cephalopod species. The term "octopus" may also be used to refer
specifically to the
genus Octopus.
Etymology and pluralization
The
scientific Latin term
octopus was derived from
Ancient Greek ὀκτώπους (
oktōpous, "eight-footed"), a
compound form of
ὀκτώ (oktṓ, "eight") +
πούς (poús, "foot").
[6][7][8] Related to the word "octopus" are the terms "Octopoda" (the
taxonomic order of cephalopod molluscs that comprises the octopuses) and the adjectival
octopoid (with the suffix
-oid, which signifies a resemblance to, but distinction from, something).
[9]
The standard
pluralized form of "octopus" in the
English language is "octopuses"
/ˈɒktəpʊsɪz/,
[10] although the Ancient Greek plural "octopodes"
/ɒkˈtɒpədiːz/, has also been used historically.
[9] The alternative plural "octopi" – which
misguidedly assumes it is a
Latin "
-us"-word – is considered grammatically incorrect.
[11][12][13][14] It is nevertheless used enough to make it notable, and was formally acknowledged by the
descriptivist Merriam-Webster 11th Collegiate Dictionary and
Webster's New World College Dictionary. The
Oxford English Dictionary (2008 Draft Revision)
[15]
lists "octopuses", "octopi", and "octopodes", in that order, labelling
"octopodes" as rare and noting that "octopi" derives from the
apprehension that
octōpus comes from Latin.
[16] In contrast,
New Oxford American Dictionary
(3rd Edition 2010) lists "octopuses" as the only acceptable
pluralization, with a usage note indicating "octopodes" as being still
occasionally used but "octopi" as being incorrect.
[17]
Biology
Schematic lateral aspect of octopod features
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.
[18] Both types of limb are
muscular hydrostats.
Octopuses can be divided into two suborders, the
Incirrina (or Incirrata) and the
Cirrina (or Cirrata). The incirrate octopuses are distinguished from the cirrate octopuses by their absence of
"cirri"
filaments (found with the suckers), as well as by the lack of paired
swimming fins on the head. Unlike most other cephalopods, the majority
of octopuses – those in the
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. The
beak, similar in shape to a
parrot's beak, and made of
chitin,
is the only hard part of their bodies. This enables them to squeeze
through very narrow slits between underwater rocks, which is very
helpful when they are fleeing from
moray eels 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. These
cirrate species are often free-swimming and live in deep-water habitats,
while incirrate octopus species are found in reefs and other shallower
seafloor habitats.
Octopuses have a relatively short
life expectancy, with some species living for as little as six months. Larger species, such as the
giant pacific octopus,
may live for up to five years under suitable circumstances. However,
reproduction is a cause of death: males can live for only 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, eventually dying of starvation. In a scientific
experiment, the removal of both
optic glands after spawning was found to result in the cessation of
broodiness, the resumption of feeding, increased growth, and greatly extended lifespans.
[19]
Octopuses have three
hearts. Two
branchial hearts pump blood through each of the two
gills, while the third is a
systemic heart that 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 bluish color. The octopus draws water into its mantle cavity, where it passes through its gills. As
molluscs, octopuses have gills that are finely divided and vascularized outgrowths of either the outer or the inner body surface.
Intelligence
Octopuses are highly
intelligent, possibly more so than any other order of
invertebrates. The exact extent of their intelligence and learning capability is much debated among biologists,
[20][21][22][23] but maze and
problem-solving experiments have shown evidence of a memory system that can store both
short- and
long-term memory.
It is not known precisely what contribution learning makes to adult
octopus behavior. Young octopuses learn almost no behaviors from their
parents, with whom they have very little contact.
[24]
As stated above, even the octopuses that have the longest lifespan
(the Giant Pacific Octopus) simply don't live long enough after the
young are born to teach them very much. Approximately 6 weeks after
mating, the female lays 20,000–100,000 eggs over the course of several
days on the inner side of her rocky den. For the next 5–8 months she
tends the eggs, carefully cleaning and aerating them until they hatch.
The female does not leave her brood, even to eat, and will die within
weeks or months after they hatch, gradually becoming weaker as she dies
of starvation. The male dies shortly after mating. The typical life span
of the octopus is between 3–5 years.
The 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 limited functional autonomy. Octopus arms show a variety of complex
reflex actions that persist even when they have no input from the brain.
[25] Unlike vertebrates, the complex motor skills of octopuses are not organized in their brain using an internal
somatotopic map of its body, instead using a nonsomatotopic system unique to large-brained invertebrates.
[26]
Despite this delegation of control, octopus arms do not become tangled
or stuck to each other because the suction cups have chemical sensors
that recognize octopus skin and prevent self-attachment.
[27] Some octopuses, such as the
mimic octopus, will move their arms in ways that emulate the shape and 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,
[28] although the validity of these findings is widely contested on a number of grounds.
[20][21] 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.
[29] Octopuses often break out of their aquariums and sometimes into others in search of food.
[30][31][32] They have even boarded
fishing boats and opened holds to eat crabs.
[22]
Tool use
The octopus has been shown to
use tools. At least four specimens of the veined octopus (
Amphioctopus marginatus) have been witnessed retrieving discarded
coconut shells, manipulating them, and then reassembling them to use as shelter.
[33][34][35]
Protective legislation
Due to their intelligence, octopuses in some countries are on the list of
experimental animals on which surgery may not be performed without
anesthesia, a protection usually extended only to vertebrates. In the UK from 1993 to 2012, the common octopus (
Octopus vulgaris) was the only invertebrate protected under the
Animals (Scientific Procedures) Act 1986.
[36] In 2012, this legislation was extended to include all cephalopods
[37] in accordance with a general
EU directive.
[38]
Defense
The octopus's primary defense is to hide or to disguise itself through
camouflage and
mimicry.
[39]
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 distraction with the use of
ink sacs and
autotomising limbs.
Most octopuses can eject a thick, blackish
ink in a large cloud to aid in escaping from predators. The main coloring agent of the ink is
melanin, which is the same chemical that gives humans their
hair and
skin color. This ink cloud is thought to reduce the efficiency of olfactory organs, which would aid 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.
[40]
The octopus's camouflage is aided by certain specialized skin cells
which can change the apparent color, opacity, and reflectivity 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).
[41] This color-changing ability can also be used to communicate with or warn other octopuses. The highly 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 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.
[39]
When under attack, some octopuses can perform arm
autotomy, in a manner similar to the way
skinks and other
lizards
detach their tails. The crawling arm serves as a distraction to
would-be predators. Such severed arms remain sensitive to stimuli and
move away from unpleasant sensations.
[42]
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.
[43][44]
Reproduction
When octopuses reproduce, the male uses a specialized arm called a
hectocotylus to transfer
spermatophores (packets of sperm) from the terminal organ of the reproductive tract (the cephalopod "penis") into the female's mantle cavity.
[45] 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).
[citation needed]
Cohabitation
Pacific striped octopuses share food and habitation but most other octopuses are solitary outside of mating.
[46]
Senses
Octopuses have keen eyesight. Like other cephalopods, they can distinguish the
polarization of light.
Color vision appears to vary from species to species, being present in
O. aegina but absent in
O. vulgaris.
[47] 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 the pupil slit is always horizontal.
[citation needed]
Octopuses also have an excellent
sense of touch. The octopus's suction cups are equipped with
chemoreceptors so the octopus can
taste what it is touching. The arms contain
tension sensors so the octopus knows whether its arms are stretched out. However, it has a very poor
proprioceptive
sense. The tension receptors are not sufficient for the brain to
determine the position of the octopus's body or arms. (It is not clear
whether the octopus brain would be capable of processing the large
amount of information that this would require; the flexibility of the
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.
[48]
The neurological autonomy of the arms means 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
proprioceptive
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, i.e.
exteroception.
[48]
Octopuses might use the
statocyst
(a sac-like structure containing a mineralised mass and sensitive
hairs) to register sound. The common octopus can hear sounds between
400 Hz and 1000 Hz, and hears best at a frequency of 600 Hz.
[49]
Locomotion
Video of an octopus in its natural habitat
Octopuses swim with their arms trailing behind.
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.
[50]
They crawl by walking on their arms, usually on many at once, on both
solid and soft surfaces, while supported in water. In 2005, some
octopuses (
Adopus aculeatus and
Amphioctopus marginatus under current taxonomy) were found to walk on two arms, while at the same time resembling plant matter.
[51]
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).
[50] A study of this behavior conducted by the
Weymouth Sea Life Centre led to the suggestion that the two rearmost appendages may be more accurately termed "legs" rather than "arms".
[52] Some species of octopus can crawl out of the water for a short period, which they may do between
tide pools while hunting crustaceans or gastropods or to escape predators.
[53][54]
Octopuses swim by expelling a jet of water from a contractile
mantle, and aiming it via a muscular
siphon.
Bottom-dwelling octopuses eat mainly crabs,
polychaete worms, and other molluscs such as
whelks and
clams.
Open-ocean octopuses eat mainly prawns, fish and other cephalopods.
They usually inject their prey with a paralysing saliva before
dismembering it into small pieces with their beaks.
[55]
Octopuses feed on shelled molluscs either by using force, or by
drilling a hole in the shell, injecting a secretion into the hole, and
then extracting the soft body of the mollusc.
[56]
Large octopuses have also been known to catch and kill some species of
sharks.
[57] Seabirds have also been documented as prey.
[58]
The
giant Pacific octopus,
Enteroctopus dofleini,
is often cited as the largest known octopus species. Adults usually
weigh around 15 kg (33 lb), with an arm span of up to 4.3 m (14 ft).
[59] The largest specimen of this species to be scientifically documented was an animal with a live mass of 71 kg (156.5 lb).
[60] 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).
[61][62] However, a number of questionable size records would suggest
E. dofleini is the largest of all known octopus species by a considerable margin;
[63] one such record is of a specimen weighing 272 kg (600 lb) and having an arm span of 9 m (30 ft).
[64]
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 (1900 – 1100 BC) has a depiction of a fisherman carrying an octopus.
[65]
In classical Greece,
Aristotle (384 BC – 322 BC) commented on the colour-changing abilities of the octopus, both for camouflage and for
signalling, in his
Historia animalium:
[66]
The octopus ... seeks its prey by so changing its colour as to render
it like the colour of the stones adjacent to it; it does so also when alarmed.
Octopuses were often depicted in the art of the
Moche people of ancient
Peru, who worshipped the sea and its animals.
[67]
In mythology
The
Gorgon of
Greek mythology has been thought to have been inspired by the octopus or squid, the octopus itself representing the severed head of
Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes.
[68]
The
Kraken are legendary sea monsters of giant proportions said to dwell off the coasts of
Norway and
Greenland, usually portrayed in art as a giant octopus attacking ships.
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.
[69]
Akkorokamui is a gigantic octopus-like
monster from
Ainu folklore, which supposedly lurks in
Funka Bay in
Hokkaidō and has been sighted in several locations including Taiwan and Korea since the 19th century.
[70]
In Japanese mythology and folklore there is a
yokai called the
tako no nana ashi, that is an octopus with seven tentacles.
In literature
The octopus has a significant role in
Victor Hugo's book
Travailleurs de la mer (
Toilers of the Sea).
[71] Ian Fleming's 1966 short story collection
Octopussy and The Living Daylights, and the 1983
James Bond film partly inspired by Hugo's book.
In
John Steinbeck's novella
Sweet Thursday, the
marine biologist "Doc" is studying what the denizens of
Cannery Row call "
devilfish". Doc's study of octopuses to ascertain whether their behavior displays emotional responses similar to humans, such as
apoplexy, is a major plot device in the novella.
[72]
Ed Ricketts,
the marine biologist who was Steinbeck's friend and inspiration for the
character Doc, had an octopus as a trademark for products sold by his
Pacific Biological Laboratories.
Ringo Starr wrote a 2014 children's book based on his 1969 song "
Octopus's Garden". The book is illustrated by Ben Court.
[73]
In popular culture
In
Pixar's 2016 film
Finding Dory, a sequel to its highly successful 2003
Finding Nemo,
Hank the octopus plays a major role in helping Dory find her parent.
According to Pixar personnel, the character is based on a mimic octopus.
[74]
The Nrol-39 Patch depicting a grasping octopus. Octopi are commonly used as metaphors for sinister intelligence
As a metaphor
Due to having numerous arms that emanate from a common center, the
octopus is often used as a metaphor for a group or organization that is
perceived as being powerful, manipulative or bent on domination. Use of
this terminology is invariably negative and employed by the opponents of
the groups or institutions so described.
[75]
Octopus is eaten in many cultures. They are a common food in Mediterranean and Asian sea areas.
[76][77] The arms and sometimes other body parts are prepared in various ways, often varying by species or geography.
Live octopuses are eaten in several countries around the world, including the US.
[78][79] Animal welfare groups have objected to this practice on the basis that octopuses can experience pain.
[80] In support of this, since September 2010, octopuses being used for scientific purposes in the EU are protected by
EU Directive 2010/63/EU
which states "...there is scientific evidence of their [cephalopods]
ability to experience pain, suffering, distress and lasting harm.
[38]
In the UK, this means that octopuses used for scientific purposes must
be killed humanely, according to prescribed methods (known as "Schedule 1
methods of euthanasia").
[81]
Though octopuses can be difficult to keep in captivity, some people
keep them as pets. They often escape even from supposedly secure tanks,
due to their problem-solving skills, mobility and lack of rigid
structure.
[citation needed]
The variation in size and lifespan 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 it is young with a full life ahead of it.
[citation needed]
Classification
Cephalopods have existed for around 500 million years, although octopus ancestors were in the Carboniferous seas around 300 million years ago. The oldest octopus fossil, Pohlsepia, can be found at the Field Museum in Chicago.[82]
