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95 free Jellyfish trivia questions with answers — nature quiz, new questions added Aug 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 95 questions correctly?
30 of 95 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 small drifting animals are the staple; jellyfish eat and excrete through the same opening, and other jellyfish are on the menu too.
Q 05Which class of jellyfish, all of them marine, gets 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 06The jelly that forms most of a jellyfish's bell is at least what percentage water?
95%
95% water or more, which is why a beached jellyfish shrinks to almost nothing in the sun, and why species eaten in East Asia are pressed and salted.
Q 07What unique ability is attributed to the 'immortal jellyfish' (Turritopsis dohrnii)?
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; box jellyfish add an inward-folded rim, the velarium, that sharpens the jet and lets them outswim bigger species.
Q 11What is the non-living jelly that makes up most of a jellyfish's bell called?
Mesoglea
Mesoglea is the animal's hydrostatic skeleton, sandwiched between the outer epidermis and inner gastrodermis, with collagen and wandering amoebocytes that mop up debris.
Q 12How is a jellyfish's body arranged around its central axis?
Radially
Radially: a jellyfish has no left, right, front or back; its oral arms, gastric pouches and rim sense organs are spaced evenly around the central mouth.
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 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.
Q 22The 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 23The genus name Physalia comes from the Greek for what?
Bubble or bladder
Bubble or bladder: Physalia comes from the Greek physalis, a bubble, describing the gas-filled float; Linnaeus described the species in the 1758 tenth edition of Systema Naturae.
Q 14Which jellyfish, with tentacles past 30 metres, is arguably the longest animal alive?
Lion's mane
Lion's mane tentacles reach 36.5 metres, though most are far smaller; the Portuguese man o' war is not a true jellyfish but a colonial siphonophore.
Q 15Jellyfish have existed for at least how many years, making them the oldest multi-organ animal group?
500 million
At least 500 million years: unambiguous medusa fossils come from the Cambrian, and molecular estimates push the group's origin back 700 million years or more.
Q 16What is a group of jellyfish called?
A smack
A smack is the traditional collective noun for jellyfish, with 'smuck' an accepted variant; a mass seasonal gathering is usually called a bloom.
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: each of the four club-shaped rhopalia holds six eyes, two image-forming lens eyes plus pit and slit eyes that act as light meters, 24 in all.
Q 19The record-length jellyfish measured off Massachusetts in 1865 had tentacles how long?
36.6 metres
36.6 metres (120 feet) of tentacle, recorded by Alexander Agassiz in Massachusetts Bay, with a bell 210 cm across; it is often cited as the longest animal ever measured.
Q 20The bell of Cyanea capillata is divided into how many lobes, giving it a star-like look?
Eight
Eight lobes, each carrying 70 to 150 tentacles in four rows, for about 1,200 tentacles in total.
Q 24The immortal jellyfish achieves its trick through which cell process?
Transdifferentiation
Transdifferentiation lets specialised cells of a stressed, sick or old medusa convert into other cell types, so the animal drops back to the polyp stage; most are eaten first.
Q 25How big is an adult Irukandji jellyfish?
About one cubic centimetre
About one cubic centimetre: Carukia barnesi has a bell barely a centimetre across with four thin tentacles, yet its stings cost north Queensland millions each year in tourism and hospital bills.
Q 26How did Jack Barnes prove in 1964 that Carukia barnesi causes Irukandji syndrome?
He let it sting himself, his son and a lifeguard
He let it sting himself, his son and a lifeguard, and all three ended up in hospital; the syndrome had been named by Hugo Flecker in 1952.
Q 27Irukandji syndrome takes its name from what?
An Aboriginal people near Cairns
An Aboriginal people near Cairns: the Irukandji, or Yirrganydji, whose country runs along the coast north of Cairns, gave the syndrome its name when Hugo Flecker described it in 1952.
Q 28In 2009, a Japanese trawler capsized off Chiba while hauling a net full of which giant species?
Nomura's
Nomura's jellyfish, Nemopilema nomurai, reaches two metres across; the trawler Diasan Shinsho-maru went over while its three crew tried to haul in a net full of them.
Q 29Nemopilema nomurai is named after a fisheries station director in which Japanese prefecture?
Fukui
Fukui: Kan'ichi Nomura, director of the Fukui Prefectural Fisheries Experimental Station, shipped a specimen to Professor Kishinouye in a 72-litre wooden tank in 1921.
Q 30Which jellyfish did NASA fly on shuttle Columbia in 1991 to study development in microgravity?
Moon jellyfish
Moon jellyfish: more than 2,000 Aurelia polyps rode Columbia's STS-40 mission in June 1991 so researchers could watch their gravity-sensing organs develop without gravity.