50 Fun Facts About Octopus

To which class of molluscs do octopuses belong, along with squid, cuttlefish and nautiluses?

The order Octopoda holds around 300 species.

How many hearts does an octopus have?

One main heart pumps blood round the body; two branchial hearts push it through the gills, and the main one stops when the animal swims.

Octopus blood is blue because it carries oxygen with which copper-rich protein?

It works better than haemoglobin in cold, low-oxygen water, but is so viscous that blood pressure can top 75 mmHg.

Roughly how many neurons does an octopus have, about the same as a dog?

One part sits in a cartilaginous capsule around the brain; the rest is spread through the arms, which act with some independence.

What fraction of an octopus's neurons are located in its arms rather than its brain?

A severed arm can still move and respond to stimuli.

Which is the only kind of octopus known to be deadly to humans?

All octopuses are venomous, but only these can kill a person; there is no antidote.

What toxin in the venom of the deadliest octopus causes paralysis by blocking nerve impulses to muscles?

Death comes by respiratory failure, but if breathing is kept going artificially, patients recover within 24 hours.

Which species is usually cited as the largest octopus?

Adults typically weigh 10 to 50 kg with an arm span up to 4.8 metres; the biggest scientifically documented weighed 71 kg.

What is the smallest octopus species, at around 2.5 cm and under a gram?

At the other extreme, a seven-arm octopus carcass was estimated to have weighed 75 kg alive.

Even large octopuses can squeeze through a gap of roughly what size?

The only hard part of the body is the beak; everything else is soft tissue.

What is the specially adapted arm a male octopus uses to transfer sperm packets called?

Usually it is the third right arm, with a spoon-shaped tip; Cuvier once mistook a detached one for a parasitic worm.

What happens to a male octopus after mating?

Females die too, after brooding their eggs.

How many eggs can the largest octopus species lay in a single clutch?

The common octopus can lay 500,000; the female guards them for about five months without feeding.

What is the maximum lifespan of an octopus?

Some species finish their entire lifecycle in under six months.

Which organs trigger senescence, the fatal decline after an octopus reproduces?

During senescence the animal stops eating, weakens, develops lesions and literally degenerates.

What is the main pigment in octopus ink?

The ink is mixed with mucus on the way out and leaves the funnel as a thick, dark blob that acts as a decoy or smoke-screen.

What are the specialised skin cells that let an octopus change colour called?

They hold yellow, orange, red, brown or black pigments; iridophores and leucophores add reflection and white.

What is the octopus display called in which waves of dark colour ripple across the body?

The 'moving rock' trick is different: mimicking a rock and inching across open ground at the speed of the water.

Which octopus can impersonate more dangerous animals such as lionfish, sea snakes and eels?

It combines a flexible body with colour change to pull off the disguise.

The veined octopus is famous for collecting and carrying what to build a shelter?

It 'stilt-walks' with the stacked shells tucked under it, a celebrated example of tool use.

What is an octopus's fastest way of moving?

It is exhausting: the mantle pressure needed is so high it stops the main heart, so octopuses mostly crawl.

Octopus suckers are equipped with chemoreceptors, meaning the animal can do what?

The sensors also recognise octopus skin, which stops the arms sticking to each other.

Which sac-like organs let an octopus sense its orientation and possibly hear?

The common octopus can hear sounds between 400 and 1,000 Hz, best at around 600 Hz.

Roughly what share of a resting octopus's oxygen is absorbed through its skin?

That drops to about 33% while swimming and as low as 3% while digesting a meal.

How does an octopus get into a hard-shelled clam or crab?

An enzyme in the toxic saliva dissolves the calcium carbonate; it can take hours, then the prey dies almost instantly.

Octopuses sometimes hunt cooperatively with fish, and keep their partners in line by doing what?

They regulate both the make-up of the hunting group and their partners' behaviour this way.

Which octopus has been described as particularly social, living in groups of up to 40?

Most octopuses are solitary and hide in dens surrounded by middens of uneaten food.

A dumbo octopus (Grimpoteuthis) holds the depth record for octopuses, photographed at what depth?

It is the only indisputable record of an octopus in the hadal zone.

Cirrate octopuses such as the dumbo octopus differ from most octopuses in what way?

They also usually lack an ink sac and have an internal shell.

Which habitat has no known octopus species at all?

Some survive at -1.8 C off Antarctica, and Vulcanoctopus hydrothermalis lives at 2,000 m around vents.

Which octopus's female secretes a thin, cornucopia-shaped shell in which she lays her eggs and lives?

She is far larger than the male and broods the young while swimming in open water.

Which usage authority declared 'octopuses' the only acceptable plural, calling 'octopodes' pedantic?

'Octopi' wrongly treats the word as a Latin second-declension noun; it is actually Greek.

The word 'octopus' comes from Greek words meaning what?

Okto plus pous; the two rear limbs are still used mainly for walking on the sea floor.

Who first gave the order Octopoda its scientific name, in 1818?

He had classified them as Octopoida the year before.

Octopuses arose in which geological period?

Their soft bodies mean fossils are rare; cephalopods themselves date back to the Cambrian.

Octopuses and other coleoid cephalopods do more of what to their genetic transcripts than any other animals?

Much of it tunes the nervous system, at the cost of slower genome evolution.

Which ancient Greek noted the octopus's colour-changing and hectocotyl arm in Historia animalium?

His idea that the arm was used in reproduction was ignored until Japetus Steenstrup proved it in 1856.

Which Norwegian sea monster of legend is conceived as octopus-like?

The Ainu people's Akkorokamui is another giant octopus-like monster, worshipped in Shinto.

Which Japanese artist made the 1814 shunga print The Dream of the Fisherman's Wife?

It later inspired a 1903 erotic drawing by Pablo Picasso.

A battle with an octopus features in which Victor Hugo novel of 1866?

In Gravity's Rainbow, an octopus named Grigori attacks a woman on the beach.

Paul the Octopus became a celebrity for predicting winners at which event?

He picked matches from an aquarium in Germany.

Live octopus eaten as wriggling pieces is a Korean dish called what?

If badly prepared, the suckers on the severed arms can choke the diner, which killed at least one person in 2010.

In what year did the world octopus catch peak, at about 380,000 tons?

It had fallen by a tenth by 2012; attempts at commercial farming remain controversial.

Which country's animal-testing law protected only one invertebrate, the octopus, from 1993 to 2012?

In 2012 the Animals (Scientific Procedures) Act was extended to all cephalopods, in line with an EU directive.

Which philosopher compared octopuses to intelligent aliens, since their intelligence evolved independently?

Their intelligence and flexibility help them escape supposedly secure aquarium tanks.

On which ancient civilisation's coins was the octopus depicted, possibly as early as 1650 BCE?

It also appears on Mycenaean Greek pottery from around 1200 to 1100 BCE.

Roughly how many octopus species make up the order Octopoda?

Most grow fast, mature early and die young; the only indisputable record from the hadal zone is a single sighting.

What is the live mass of the heaviest scientifically documented octopus specimen?

A giant Pacific specimen; adults of that species usually weigh 10-50 kg, and an unverified claim put one at 600 lb.

For roughly how long does a female giant Pacific octopus guard her eggs until they hatch?

In colder waters off Alaska the eggs can take up to ten months to develop fully.

What is the octopus 'moving rock' trick?

Alongside camouflage and the 'passing cloud' display, it lets the animal cross exposed seabed without being spotted.