Everything about The Octopus totally explained
The
octopus (from
Greek Ὀκτώπους, 'eight-footed', with plural forms:
octopuses [ˈɒktəpəsɪs],
octopi [ˈɒktəpaɪ], or
octopodes [ˌɒkˈtəʊpədiːs], see
below) 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 around 300 recognized octopus
species, which is over one-third of the total number of known cephalopod species.
Biology
Octopuses are characterized by their eight
arms (not
tentacles), usually bearing suction cups. These arms are a type of
muscular hydrostat. 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
squids. 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're 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 span, 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 bound in
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, probably more intelligent 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. 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 (Scientific Procedures) Act 1986 and other
cruelty to animals legislation, extending to them protections not normally afforded to invertebrates.
A common belief is that when stressed, an octopus may begin to eat its own arms. However, limited research conducted in this area has revealed that the cause of this abnormal behavior, called
autophagy, may be a virus that attacks the octopus's
central nervous system. Thus this behavior may be more correctly labeled as a
neurological disorder.
Defense
Three defensive mechanisms are typical of octopuses:
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 dulls
smell, which is particularly useful for evading predators that are dependent on smell for hunting, such as
sharks.
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's provoked.
When under attack, some octopuses can
detach their own limbs, 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; this ability is also used in mating.
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. They have also been observed changing the texture of their mantle in order to achieve a greater camouflage. The mantle can take on the spiky appearance of seaweed, or the scraggly, bumpy texture of a rock, among other disguises.
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 after mating. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature. After they've 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 doesn't eat during the roughly one-month period spent taking care of the unhatched eggs. At around the time the eggs hatch, the mother dies and 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're ready to sink down to the bottom of the ocean, where the cycle repeats itself. In some deeper dwelling species, the young don't go through this period. This is a dangerous time for the larval octopuses; as they become part of the plankton cloud they're vulnerable to many plankton eaters.
Sensation
Octopuses have keen eyesight. Although their slit-shaped
pupils might be expected to afflict them with
astigmatism, it appears that this isn't a problem in the light levels in which an octopus typically hunts. Surprisingly, they don't appear to have
color vision, although they can distinguish the
polarization of light. 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's 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 isn't 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 doesn't possess
stereognosis; that is, it doesn't form a
mental image of the overall shape of the object it's handling. It can detect local texture variations, but can't 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. This is a standard evasive measure of the octopus that safely allows it to slowly meander away from a predator while presumably unnoticed. The octopus moves in synchronization with the cadence of underwater waves, thus giving the illusion of not moving and, more importantly, not resembling an octopus at all. Octopuses need such defensive strategies since their soft tissue and lack of bone structure make them extremely vulnerable to predators.
They 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
There are three forms of the plural of
octopus; namely,
octopuses,
octopi, and
octopodes. Currently,
octopuses is the most common form in the UK as well as the US;
octopodes is rare, and
octopi is often objected to.
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
octōpūs is a
second declension Latin noun, which it's not. Rather, it's (Latinized)
Greek, from
oktṓpous (ὀκτώπους),
gender masculine, whose plural is
oktṓpodes (ὀκτώποδες). If the word were native to Latin, it would be
octōpēs ('eight-foot') and the plural
octōpedes, analogous to
centipedes and
mīllipedes, as the plural form of
pēs ('foot') is
pedes. In modern, informal Greek, it's called
khtapódi (χταπόδι), gender neuter, with plural form
khtapódia (χταπόδια).
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 cognizant of the octopus, as evinced 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
Hawaiʻian 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.
As food
Many species of octopus are eaten as food by human cultures around the world. The arms and sometimes other parts of the body are prepared in various ways, often depending on the species being eaten.
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 (mostly in
South Korea). Octopus is also a common food in
Mediterranean cuisine. In
Galicia,
polbo á feira (fair style octopus) is a local delicacy. Restaurants which specialize or serve this dish are known as pulperías.
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.
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 intelligence, 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 the 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's 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
Class CEPHALOPODA
Further Information
Get more info on 'Octopus'.
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