Octopus

Octopus
Octopus vulgaris,the common octopus
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Coleoidea
Superorder:	Octopodiformes
Order:	Octopoda
Suborder:	Incirrina
Family:	Octopodidae
Genus:	Octopus

Octopus incamouflage

MovingOctopus vulgaris

Octopusis agenusofcephalopodmolluscin theorderOctopoda.The genus is quite typical of most octopods. They have two, large eyes and eight limbs with suckers. They have a hard beak, with the mouth at the center point of the arms.

Octopods have no internal or external skeleton, allowing them to squeeze through tight places and hide. Many stays in cracks between rocks or corals when they are not hunting. They areintelligentpredatorswith a taste forcrabs.Octopuses have three hearts. Two pump blood to the gills, while the third pumps it to the rest of the body.

Octopods inhabit many regions of the ocean, especiallycoral reefs.For defense against predators, they hide, flee quickly, expel ink, or use colour-changingcamouflage.They live rather short lives.

An octopus trails its eight arms behind it as it swims. All octopods arevenomous,but only the small blue-ringed octopus is known to be deadly to humans.

There are about 300 octopodspecies,of which more than 100 are in the genusOctopus.Octopods make up over one-third of the total number of living cephalopods. The term 'octopus' may be used to refer to those in the genusOctopus.The term 'octopod' is correct for members of the order Octopoda in general.

Physiology: RNA editing

Octopods, like other advanced cephalopods, can edit theirgenome.They can adapt the nucleic acid sequence of the primary transcript ofRNAmolecules, more so than any other organisms.More than 60% of RNA transcripts forcoleoidbrains are recoded by editing, compared to less than 1% for a human orfruit fly.This has come at the cost of slower genome evolution.

Anatomy

Unlike most othercephalopods,most octopods have only soft body with no internalskeleton.They have no protective outer shell like thenautilus,which is another type ofcephalopod. Abeak,similar in shape to aparrot'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.

Eyes

Octopod eyes are complex. In fact, they do not have a blind spot.Ablind spotis 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.

The lens in octopod are movable. It moves back and forth to focus. This is the way acamerafocuses. 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.

Colours

Some octopuses can use theirchromatophoresfor more thancamouflage.If they are not blending in with their surroundings, they can signal their feelings using colour. When they are relaxed, for example, they are a dull, grayish brown or orange-tinged colour. When they become angry, they can become red. If they feel scared, they may turn white.

Behaviour

Intelligence

An octopus opening a container with a screw cap

Octopods are highlyintelligent,probably more so than any otherinvertebrate.The exact extent of their intelligence and learning capability is much debated among biologists.Mazeandproblem-solving experiments have shown that they do have both short and long-termmemory.Their short lifespans limit the amount they can learn.

Some octopods, such as themimic octopus,can move their arms in ways which copy the movements of othersea 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 asplay:repeatedly releasing bottles or toys into a circular current in their aquariums and then catching them.Octopuses often break out of their aquaria and sometimes into others in search of food.

The largest of the 300+ species of octopods, thegiant octopusEnteroctopus,is large indeed. Mature males average about 50 pounds and females about 33 pounds. Their arm spans are about eight feet. They have even boarded fishingboatsand opened holds to get in and eat crabs.

In the UK, cephalopods such as octopuses are regarded ashonorary vertebratesunder theAnimals (Scientific Procedures) Act 1986.This gives them protection not normally given to invertebrates.

Octopods are the only invertebrate which have been definitely shown to usetools.At least four specimens of the veined octopus (Amphioctopus marginatus) have been seen picking up discardedcoconutshells, and then reassembling them to use asshelter.

Octopods are active and intelligentpredators,with good eyesight and brains. They eat mostlycrabsand somefish.

Defences

Octopods have a variety of defences. They use activecamouflageandmimicry,controlled by theirnervous 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.

Reproduction and death

To reproduce, males use a specialized arm to put packets of sperm into the female'smantle cavity.Males die in a few months after mating. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs mature.

After they have been fertilized, the female lays about 200,000 eggs (this figure varies dramatically between species). The female cares for the eggs, guarding them against predators, and gently blows currents of water over them so they get enough oxygen. The female does not hunt during the 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 likecod,often succumbing to their attacks. The young larval octopuses spend time drifting in clouds ofplankton,where they feed until they are ready to descend to the ocean bottom, where the cycle repeats.

All octopods for which we have data have a relatively shortlife expectancy.Some species live for as little as six months. Larger species, such as theNorth Pacific giant octopus,may live for up to five years under suitable circumstances.

Reproduction is acause of death:males can only live for a few months aftermating,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. One idea is that the lifespan is limited by the number of safe niches in their environment. If adults lived longer, they would use up all the safe niches. In that case, the baby octopus would scarcely survive. It is known that the same niches are used by generations of octopods. They are usually in thecalcium carbonatereefswhich were formed in tropical waters.

Left:Vase from aMycenaean Greekcemetery at Prosymna,Argos,about 1500 BC
Right:Ancient Greekblack-figureamphora(vase), 530–520 BC. On the left, ahoplitewith an octopus image on his shield. Staatliche Antikensammlungen, Munich, Germany

Deep-sea octopod broods eggs

Off the coast ofCalifornia,marine biologistshave watched the same female octopus guarding her eggs for over four years. Their development took a long time because the water 1.4 kilometres down was very cold. They knew it was the same octopod because it had a characteristicscar.The research was done using a remote diving vehicle with cameras, lights and robotic arms.