48 Fun Facts About Octopus

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

Octopuses belong to the class Cephalopoda, the 'head-foot' molluscs whose arms ring the mouth; squid, cuttlefish and nautiluses are the other living cephalopod groups.

How many hearts does an octopus have?

An octopus has three hearts: one systemic heart pumps blood round the body while two branchial hearts push it through the gills, and the systemic heart pauses while the animal swims.

Which copper-based protein carries oxygen in octopus blood?

Haemocyanin carries oxygen on copper atoms, which is what turns octopus blood blue; it outperforms iron-based haemoglobin in cold, low-oxygen water.

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

An octopus has over 500 million neurons, comparable to a dog; the central brain sits in a cartilaginous capsule, and a large share of the neurons lie in the arms, which act semi-independently.

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

About two-thirds of an octopus's neurons lie in its arms rather than its central brain, which is why a severed arm can keep moving and reacting to touch for a while.

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

Blue-ringed octopuses, genus Hapalochlaena, are the only octopuses known to have killed people; every octopus is venomous, but no antivenom exists for a blue-ringed bite.

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

Tetrodotoxin, made by symbiotic bacteria in the octopus's salivary glands, blocks sodium channels so nerves cannot fire; death comes by respiratory failure, but patients kept breathing artificially usually recover within 24 hours.

Which species is usually cited as the largest octopus?

The giant Pacific octopus, Enteroctopus dofleini, is the species usually called the largest; adults commonly weigh 10 to 50 kg and can have an arm span of around 4 metres or more.

Which species, weighing under a gram as an adult, is the smallest known octopus?

Octopus wolfi, the star-sucker pygmy octopus of the western Pacific, is the smallest known octopus; an adult weighs less than a gram and can sit on a fingertip.

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

An octopus can pass through any gap wider than its beak, the only hard part of its body, so even a large animal can fit through a hole a little over 2.5 cm across.

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

The hectocotylus, usually the third right arm, has a spoon-shaped tip for passing sperm packets to the female; Cuvier mistook a detached one for a parasitic worm and named it as such.

What happens to a male octopus after mating?

After mating a male octopus becomes senescent: he stops eating, weakens and dies within a few months, while the female dies after brooding her eggs.

Which animal is the octopuses' closest living relative, sharing the superorder Octopodiformes?

The vampire squid, Vampyroteuthis infernalis, is the octopuses' closest living relative; together they form the superorder Octopodiformes, with eight arms plus the vampire squid's two retractile filaments.

How long do most octopus species live?

Most octopus species live only one to two years; the common octopus completes its whole life cycle in roughly that span, and even the largest species seldom exceed five years.

Which organs, when removed, let an octopus keep feeding and live longer after reproducing?

The optic glands, on the optic stalks behind the eyes, release the hormones that start senescence; in Jerome Wodinsky's 1977 experiment, females whose optic glands were removed resumed eating and lived months longer.

What is the main pigment in octopus ink?

Melanin, the same pigment that darkens human skin and hair, is the main pigment in octopus ink; the ink mixes with mucus and leaves the funnel as a dark blob that works as a decoy or smokescreen.

Which specialised skin cells give an octopus its rapid camouflage?

Chromatophores are elastic pigment sacs in the skin, holding yellow, orange, red, brown or black, that muscles stretch open or shut in an instant; iridophores and leucophores beneath add shimmer and white.

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

The passing cloud display sends bands of dark pigment sweeping across the body like cloud shadows moving over ground; it is thought to startle prey into moving or to confuse predators.

Which octopus of Indo-Pacific sand and mud flats was formally described as a species in 2005?

The mimic octopus, Thaumoctopus mimicus, was discovered off Sulawesi in 1998 and described in 2005; it impersonates lionfish, sea snakes, flatfish and eels by reshaping its body and changing colour.

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.

What extra sense do an octopus's suckers give its arms?

Chemoreceptors in the suckers let an octopus taste whatever it touches; the same sensors recognise the animal's own skin, which is what stops its arms sticking to one another.

Which organs in an octopus's head detect gravity and acceleration, and possibly sound?

Statocysts, paired organs beside the brain, hold a tiny stone on sensory hairs to register gravity and acceleration; with them the common octopus can also detect sounds of roughly 400 to 1,000 Hz.

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

At rest about 41% of an octopus's oxygen uptake happens through the skin; the share falls to roughly 33% while swimming and as low as 3% while the animal digests a meal.

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?

The larger Pacific striped octopus, first watched off Panama by Arcadio Rodaniche, lives in groups of up to 40 and mates beak to beak; most octopuses are solitary den-dwellers ringed by middens of leftovers.

In 2020 a dumbo octopus was filmed at what record depth in the Java Trench?

In 2020 Alan Jamieson and Michael Vecchione reported a Grimpoteuthis filmed at 6,957 metres in the Java Trench, the first indisputable sighting of an octopus in the hadal zone below 6,000 metres.

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

Cirrate octopuses have a pair of fins on the mantle and swim with them rather than by jetting; they also carry cirri beside their suckers, lack an ink sac and keep a small internal shell.

Which habitat has no known octopus species at all?

No octopus, and no cephalopod, lives in fresh water; by contrast some survive at -1.8 C off Antarctica and Vulcanoctopus hydrothermalis lives at around 2,000 metres beside hydrothermal vents.

The argonaut or paper nautilus rides in a thin white 'shell'; what is it really?

The argonaut's 'shell' is a secreted egg case: the female builds it with two specialised arms, broods her eggs inside and traps air in it for buoyancy; it is not a true molluscan shell.

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

H. W. Fowler's Modern English Usage (1926) ruled that 'octopuses' is the only acceptable plural: 'octopi' wrongly treats the word as a Latin second-declension noun when it is Greek.

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

Octopus comes from the Greek oktōpous, 'eight foot', from oktō (eight) and pous (foot); the two rear arms are the ones used most for walking along the sea floor.

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

William Elford Leach, a zoologist at the British Museum, named the order Octopoda in 1818, having first grouped the animals as Octopoida in 1817.

How many rows of suckers run along each arm of a common octopus?

A common octopus carries two rows of suckers along each arm, each sucker a muscular cup that grips by suction; single-row genera such as Eledone, the curled octopus, are the exception.

Which genetic process do octopuses and squid use far more than any other animals?

Coleoid cephalopods use RNA editing on a huge scale, recoding thousands of messenger RNAs, mostly in nervous tissue; this flexibility comes at the cost of slower evolution of the surrounding DNA.

Which ancient Greek described the octopus's colour change and mating arm in Historia animalium?

Aristotle described the octopus's colour change and its mating arm in Historia animalium; his idea that the arm served reproduction was ignored until Japetus Steenstrup confirmed it in 1856.

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

The kraken of Norwegian legend, described by Bishop Erik Pontoppidan in 1752, was later pictured as a giant octopus or squid; the Ainu people's Akkorokamui is another octopus-like monster.

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

Katsushika Hokusai, best known for The Great Wave, made The Dream of the Fisherman's Wife in 1814 for his shunga book Kinoe no Komatsu; it later inspired a 1903 drawing by Picasso.

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

Toilers of the Sea, Victor Hugo's 1866 novel set on Guernsey, has its hero Gilliatt battle a giant octopus, a scene that made the word pieuvre famous in French.

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

Paul, a common octopus at Sea Life Oberhausen in Germany, picked the winner of all seven of Germany's 2010 FIFA World Cup matches plus the final by choosing food from flagged boxes.

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

San-nakji is small octopus (nakji) cut into pieces and served while the arms still wriggle; the active suckers can stick to the throat, so diners are warned to chew thoroughly.

Galicia's pulpo a la gallega is traditionally served on what?

Pulpo a la gallega, or pulpo á feira, is boiled octopus sliced onto a wooden plate and finished with olive oil, coarse salt and paprika, the classic dish of Galicia's fairs.

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

The United Kingdom's Animals (Scientific Procedures) Act 1986 was extended to the common octopus in 1993, the only invertebrate covered until a 2012 amendment brought in all cephalopods under an EU directive.

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

Peter Godfrey-Smith, in Other Minds (2016), called meeting an octopus the closest we will come to meeting an intelligent alien, because its mind evolved on a branch separate from ours for some 600 million years.

Which Bronze Age civilisation's Marine Style pottery, around 1500 BCE, featured sprawling octopuses?

The Minoans of Bronze Age Crete painted sprawling octopuses on Marine Style pottery around 1500 BCE, such as the Palaikastro flask; the motif later spread to Mycenaean Greek pottery of about 1200 BCE.

Roughly how many octopus species make up the order Octopoda?

The order Octopoda holds about 300 species in two suborders, Cirrina and Incirrina, the latter holding nearly all familiar shallow-water species; most grow fast, mature early and die young.

As of 2020, what was the live mass of the heaviest scientifically documented octopus?

The heaviest scientifically documented octopus weighed 71 kg, a specimen of the largest species; adults of that species usually weigh 10 to 50 kg, and a 600 lb claim was never verified.

For roughly how long does a female of the largest octopus species guard her eggs?

A female of the largest octopus species guards and aerates her eggs for about five months without eating, then dies; in colder Alaskan waters the eggs can take up to ten months.