Octopus Trivia
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48 free Octopus trivia questions with answers — nature quiz, new questions added Aug 2026.
This octopus trivia quiz covers the ocean's strangest and smartest invertebrate. The easy questions handle the basics: how many arms and hearts it has, what colour its blood is, what it squirts at predators, how it changes colour and how long it lives. The harder end goes deeper: why two-thirds of its neurons live in its arms, the copper protein that makes its blood blue, the hectocotylus arm and the grim end that follows mating, the giant Pacific octopus and its 180,000 eggs, the tetrodotoxin of the blue-ringed octopus, coconut-carrying veined octopuses, the dumbo octopus photographed 6,957 metres down, the octopus plural argument, Hokusai's infamous print, and Paul, who picked World Cup winners. Every answer was checked against the encyclopaedia entry before publishing and the supporting sentence is stored with each question. Our ocean, sea creatures and animal quizzes are the natural next stop.
30 of 48 questions with answers and explanations. Play the quiz
Q 01To which class of molluscs do octopuses belong, along with squid, cuttlefish and nautiluses?
Cephalopoda
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.
Q 02How many hearts does an octopus have?
Three
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.
Q 03Which copper-based protein carries oxygen in octopus blood?
Haemocyanin
Haemocyanin carries oxygen on copper atoms, which is what turns octopus blood blue; it outperforms iron-based haemoglobin in cold, low-oxygen water.
Q 04Roughly how many neurons does an octopus have, about the same as a dog?
Over 500 million
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.
Q 05What fraction of an octopus's neurons are located in its arms rather than its brain?
Two-thirds
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.
Q 06Which is the only kind of octopus known to be deadly to humans?
Blue-ringed
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.
Q 07What toxin in the venom of the deadliest octopus causes paralysis by blocking nerve impulses to muscles?
Tetrodotoxin
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.
Q 08Which species is usually cited as the largest octopus?
Giant Pacific
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.
Q 09Which species, weighing under a gram as an adult, is the smallest known octopus?
O. wolfi
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.
Q 10Even large octopuses can squeeze through a gap of roughly what size?
A little over 2.5 cm
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.
Q 11What is the specially adapted arm a male octopus uses to transfer sperm packets called?
The hectocotylus
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.
Q 12What happens to a male octopus after mating?
He becomes senescent and dies
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.
Q 13Which animal is the octopuses' closest living relative, sharing the superorder Octopodiformes?
The vampire squid
Q 21What is an octopus's fastest way of moving?
Jet propulsion, swimming backwards
It is exhausting: the mantle pressure needed is so high it stops the main heart, so octopuses mostly crawl.
Q 22What extra sense do an octopus's suckers give its arms?
Taste whatever it touches
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.
Q 23Which organs in an octopus's head detect gravity and acceleration, and possibly sound?
Statocysts
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.
Q 14How long do most octopus species live?
One to two years
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.
Q 15Which organs, when removed, let an octopus keep feeding and live longer after reproducing?
The optic glands
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.
Q 16What is the main pigment in octopus ink?
Melanin
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.
Q 17Which specialised skin cells give an octopus its rapid camouflage?
Chromatophores
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.
Q 18What is the octopus display called in which waves of dark colour ripple across the body?
The passing cloud
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.
Q 19Which octopus of Indo-Pacific sand and mud flats was formally described as a species in 2005?
Mimic
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.
Q 20The veined octopus is famous for collecting and carrying what to build a shelter?
Discarded coconut shells
It 'stilt-walks' with the stacked shells tucked under it, a celebrated example of tool use.
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.
Q 24Roughly what share of a resting octopus's oxygen is absorbed through its skin?
About 41%
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.
Q 25Octopuses sometimes hunt cooperatively with fish, and keep their partners in line by doing what?
Punching them
They regulate both the make-up of the hunting group and their partners' behaviour this way.
Q 26Which octopus has been described as particularly social, living in groups of up to 40?
Larger Pacific striped
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.
Q 27In 2020 a dumbo octopus was filmed at what record depth in the Java Trench?
6,957 metres
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.
Q 28Cirrate octopuses such as the dumbo octopus differ from most octopuses in what way?
They have fins and swim with them rather than jetting
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.
Q 29Which habitat has no known octopus species at all?
Fresh water
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.
Q 30The argonaut or paper nautilus rides in a thin white 'shell'; what is it really?
A secreted egg case
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.