Jellyfish
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92 free Jellyfish trivia questions with answers — nature quiz, new questions added Oct 2026.
14 free jellyfish trivia questions with answers. Dive into the depths of ocean knowledge with our comprehensive jellyfish trivia quiz! From their ancient origins to their unique biology, test your understanding of these mesmerizing creatures. Can you answer all 92 questions correctly?
30 of 92 questions with answers and explanations. Play the quiz
Q 01Which organ do jellyfish manage without entirely?
Brain
No jellyfish has a brain; a loose nerve net in the epidermis and a ring nerve around the bell coordinate swimming and feeding instead.
Q 02Jellyfish belong to which phylum, a group they share with the corals?
Cnidaria
Cnidaria, from the Greek knide for 'nettle', unites jellyfish with corals and hydroids through the stinging cells, the cnidocytes, that every member carries.
Q 03Which of these represents a free-swimming larval stage in the life cycle of many jellyfish?
Planula
The planula, a tiny cilia-covered larva, swims briefly, then settles as a polyp, which buds off ephyrae that grow into medusae.
Q 04What do most jellyfish mainly eat?
Zooplankton
Zooplankton and other tiny drifting animals are the staple, but jellyfish are carnivores that also take fish eggs, larvae, small fish and even other jellyfish.
Q 05Which class of jellyfish is traditionally called the 'true jellyfish'?
Scyphozoa
Scyphozoa, with roughly 200 described species, carries the 'true jellyfish' label by convention; hydrozoan and cubozoan medusae are no less jellyfish.
Q 06Only about what share of a jellyfish's body is solid matter and not water?
5%
5% or so is solid matter and the rest is water, which is why a jellyfish lifted out of the sea slumps into a shapeless blob.
Q 07What ability earned Turritopsis dohrnii the nickname 'immortal jellyfish'?
Reverting to a juvenile stage
Reverting to a juvenile stage means a stressed adult can collapse back into a colony of polyps and start over, escaping death by old age; predators still eat plenty.
Q 08Which jellyfish carry multiple complex eyes, as many as 24 in some species?
Box jellies
Box jellies carry 24 eyes in four clusters, including eight true lens eyes with retinas; the upward-facing lens eyes look through the surface to help the animal navigate.
Q 09What are the harpoon-like stinging capsules on jellyfish tentacles called?
Nematocysts
Nematocysts sit inside cells called cnidocytes and fire a barbed thread on contact to stun prey; true jellyfish carry them around the mouth and on gastric filaments too.
Q 10How do most jellyfish propel themselves through the water?
Pulsing contractions of the bell
Pulsing contractions of the bell push water out behind, and the elastic bell then springs back for free, making jellyfish among the most energy-efficient swimmers ever measured.
Q 11What is the jelly that makes up most of a jellyfish's bell called?
Mesoglea
Mesoglea sits between the outer and inner cell layers and is mostly water, with just enough structural protein to work as the animal's springy internal skeleton.
Q 12A jellyfish has no left or right side, so how are its body parts arranged around its mouth?
Radially
Radially, like the spokes of a wheel: its parts repeat around the central mouth, so a drifting jellyfish can meet food or danger from any direction.
Q 13A jellyfish's stalked polyp stage looks most like which other sea creature?
Sea anemone
Sea anemone: the polyp is a small stalked cup ringed with tentacles, just like its anthozoan cousin; it buds off stacks of ephyrae that swim away and grow into medusae.
Q 21The man o' war's gas-filled float is called what?
A pneumatophore
The pneumatophore is the gas-filled float; its sail is set left- or right-handed, so winds scatter the two mirror-image forms of a population in different directions.
Q 22Physalia, the Portuguese man o' war's genus, takes its name from the Greek for what?
Bubble or bladder
Bubble or bladder: the name fits the gas-filled float, which the animal can briefly let down to duck beneath the surface when something attacks from above.
Q 23The immortal jellyfish achieves its trick through which cell process?
Transdifferentiation
Q 14Which jellyfish, among the largest known, trails tentacles that can stretch 30 metres or more?
Lion's mane
Lion's mane tentacles work as a drifting net for fish and smaller jellyfish; the longest on record, from an 1865 Massachusetts specimen, were put at about 36.6 metres.
Q 15Fossils show jellyfish have drifted through the seas for at least how many years?
500 million
At least 500 million years, and perhaps 700 million, which would make jellyfish roughly three times as old as the first dinosaurs.
Q 16What is a group of jellyfish called?
A smack
A smack is the collective noun for jellyfish; when currents and rich feeding sweep vast numbers together the gathering is called a bloom, and some are thick enough to close beaches.
Q 17Jellyfish swarms cause problems for power and desalination plants by doing what?
Clogging their cooling water intakes
Clogging their cooling water intakes happens when swarms are sucked in with the seawater; the same blooms fill and damage fishing nets.
Q 18In cubozoans, the eyes are set in clusters at the ends of sensory structures called what?
Rhopalia
Rhopalia hang from the four sides of the bell; each holds six eyes, two of them built with a lens, retina and cornea much like a vertebrate's.
Q 19Which fictional detective solves a seaside death caused by a giant jellyfish in a 1926 short story?
Sherlock Holmes
Sherlock Holmes narrates the case himself: retired to the Sussex coast, he works out that the 'murderer' is a Cyanea capillata jellyfish washed into a bathing pool by a storm.
Q 20The Portuguese man o' war is not a true jellyfish but what kind of animal?
A siphonophore
A siphonophore: a colony of genetically identical zooids, each specialised for floating, feeding, defence or reproduction, that functions as one individual.
Transdifferentiation reprogrammes cells that have already specialised into quite different cell types, a feat so rare that researchers study it for ways to renew damaged human tissue.
Q 24The Irukandji jellyfish, whose sting can put a swimmer in hospital, has a bell about how wide?
About 1 cm
About 1 cm: an adult is roughly a cubic centimetre of jelly, and its sting can feel like little more than a mosquito bite before severe pain sets in up to two hours later.
Q 25How did Jack Barnes prove that the jellyfish Carukia barnesi causes Irukandji syndrome?
He let it sting himself and his son
He let it sting himself and his son, aged nine, along with a local lifeguard, and all three were rushed to hospital with the full syndrome.
Q 26Irukandji syndrome takes its name from what?
An Aboriginal people near Cairns
An Aboriginal people near Cairns: Hugo Flecker named the syndrome in 1952 after the Irukandji, or Yirrganydji, on whose coast the stings were common, years before anyone found the jellyfish behind it.
Q 27In 2009, a fishing trawler capsized while hauling a net full of which giant jellyfish?
Nomura's
Nomura's jellyfish can grow two metres across; the 10-tonne Japanese trawler went over off Chiba as its three crew hauled in a net full of them, and another boat pulled all three from the sea.
Q 28Many deep-sea jellyfish are bright red instead of see-through, so why does that colour hide them?
Red light never reaches them
Red light never reaches them: the red in sunlight does not penetrate to the depths, so down there a red animal simply looks black and is harder for predators and prey to spot.
Q 29Which jellyfish did NASA fly on shuttle Columbia in 1991 to study development in microgravity?
Moon jellyfish
Moon jellyfish: Aurelia polyps spent nine days in orbit and budded young that looked normal, yet far more of the space-born jellies pulsed abnormally than those raised on Earth.
Q 30Jellyfish Lake, where golden jellyfish cross the water every day, lies in which island nation?
Palau
Palau: snorkellers swim right through the lake's golden jellyfish, which do have stinging cells for catching tiny prey but sting too weakly for most people to feel.