92 Fun Facts About Jellyfish

Which organ do jellyfish manage without entirely?

No jellyfish has a brain; a loose nerve net in the epidermis and a ring nerve around the bell coordinate swimming and feeding instead.

Jellyfish belong to which phylum, a group they share with the corals?

Cnidaria, from the Greek knide for 'nettle', unites jellyfish with corals and hydroids through the stinging cells, the cnidocytes, that every member carries.

Which of these represents a free-swimming larval stage in the life cycle of many jellyfish?

The planula, a tiny cilia-covered larva, swims briefly, then settles as a polyp, which buds off ephyrae that grow into medusae.

What do most jellyfish mainly eat?

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.

Which class of jellyfish is traditionally called the 'true jellyfish'?

Scyphozoa, with roughly 200 described species, carries the 'true jellyfish' label by convention; hydrozoan and cubozoan medusae are no less jellyfish.

Only about what share of a jellyfish's body is solid matter and not water?

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.

What ability earned Turritopsis dohrnii the nickname 'immortal jellyfish'?

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.

Which jellyfish carry multiple complex eyes, as many as 24 in some species?

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.

What are the harpoon-like stinging capsules on jellyfish tentacles called?

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.

How do most jellyfish propel themselves through the water?

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.

What is the jelly that makes up most of a jellyfish's bell called?

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.

A jellyfish has no left or right side, so how are its body parts arranged around its mouth?

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.

A jellyfish's stalked polyp stage looks most like which other sea creature?

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.

Which jellyfish, among the largest known, trails tentacles that can stretch 30 metres or more?

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.

Fossils show jellyfish have drifted through the seas for at least how many years?

At least 500 million years, and perhaps 700 million, which would make jellyfish roughly three times as old as the first dinosaurs.

What is a group of jellyfish called?

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.

Jellyfish swarms cause problems for power and desalination plants by doing what?

Clogging their cooling water intakes happens when swarms are sucked in with the seawater; the same blooms fill and damage fishing nets.

In cubozoans, the eyes are set in clusters at the ends of sensory structures called what?

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.

Which fictional detective solves a seaside death caused by a giant jellyfish in a 1926 short story?

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.

The Portuguese man o' war is not a true jellyfish but what kind of animal?

A siphonophore: a colony of genetically identical zooids, each specialised for floating, feeding, defence or reproduction, that functions as one individual.

The man o' war's gas-filled float is called what?

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.

Physalia, the Portuguese man o' war's genus, takes its name from the Greek for what?

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.

The immortal jellyfish achieves its trick through which cell process?

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.

The Irukandji jellyfish, whose sting can put a swimmer in hospital, has a bell about how wide?

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.

How did Jack Barnes prove that the jellyfish Carukia barnesi causes Irukandji syndrome?

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.

Irukandji syndrome takes its name from what?

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.

In 2009, a fishing trawler capsized while hauling a net full of which giant jellyfish?

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.

Many deep-sea jellyfish are bright red instead of see-through, so why does that colour hide 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.

Which jellyfish did NASA fly on shuttle Columbia in 1991 to study development in microgravity?

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.

Jellyfish Lake, where golden jellyfish cross the water every day, lies in which island nation?

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.

What do Jellyfish Lake's golden jellyfish get from the algae living in their tissues?

Sugars from photosynthesis: the golden jellyfish Mastigias papua hosts symbiotic zooxanthellae, which is why it migrates across the lake each day following the sun.

Why is a dead jellyfish on a beach still dangerous to touch?

Its stinging cells fire by themselves: each is a self-contained capsule that shoots out its barb in about 700 nanoseconds when triggered, even on a torn-off tentacle or a dead animal.

Which household liquid is kept on northern Australian beaches to pour on box jellyfish stings?

Vinegar stops stinging cells still stuck to the skin from firing, though it does nothing for venom already injected, so jugs of it stand ready along tropical Australia's swimming beaches.

Which nickname is given to Chironex fleckeri, the deadly box jellyfish of northern Australia?

Sea wasp: its tentacles, up to three metres long, carry some of the most potent venom known, and a bad sting can kill a swimmer within minutes.

In which country have people fished jellyfish for the table for at least 1,700 years?

China: jellyfish have been caught and cured there since about AD 300, and today fisheries in some 15 countries land hundreds of thousands of tonnes a year, mostly for Asian tables.

Comb jellies belong to which phylum, separate from the true jellyfish?

Ctenophora row themselves along with eight bands of comb plates and catch prey with sticky glue cells instead of stingers.

Which jellyfish is trawled off the US southeast coast and exported as food?

Cannonball jellyfish caught off Georgia are dried, packed and shipped to dinner tables across Asia; the firm, dome-shaped bell is about the size of the shot it is named for.

How does a jellyfish take in oxygen?

Diffusion through the body surface: with no gills, heart or blood, a jellyfish's thin epidermis and gastrodermis swap oxygen and carbon dioxide directly with the surrounding water.

A jellyfish fossil described in 2023 as the oldest swimming medusa known came from which Canadian fossil bed?

Burgess Shale: the British Columbia site is prized for preserving soft bodies, which is how its bell-shaped Burgessomedusa survived when jellyfish, with no hard parts, almost never fossilise.

The rainbow shimmer that ripples along a comb jelly's body is caused by what?

Light scattered by its beating cilia makes the rainbow; it is not bioluminescence at all, though many comb jellies can also make their own light in the dark.

A jellyfish has just one body opening, so its mouth also has to serve as what?

Its anus: food goes in and waste comes back out through the same opening, which sits at the tip of a stalk called the manubrium hanging beneath the bell.

The jellyfish Tripedalia cystophora steers by looking up through the water's surface at what?

The mangrove canopy: Tripedalia's upward-facing lens eyes watch the trees above its Caribbean lagoons, and the animals swim back toward the canopy's edge when moved away from it.

Sea turtles sometimes swallow which floating litter, mistaking it for jellyfish?

Plastic bags drifting in the water look much like jellyfish to a hungry turtle, and even a small amount of swallowed plastic can block its gut and kill it.

The rarely seen deep-sea jellyfish Stygiomedusa goes by which common name?

Giant phantom jelly: it trails four ribbon-like arms, up to 10 metres long, which scientists think it uses to ensnare its prey.

Which process sees a jellyfish polyp split into a stack of discs that break away as young ephyrae?

Strobilation turns one polyp into a tower of plate-like segments that break free one by one, and laboratories can set it off on demand by adding a little iodine to the water.

In moon jellies, fertilised eggs lodge in pits on which body part while they develop?

The oral arms: the male sheds strands of sperm into the water, the female takes them in, and pits on her frilly arms then serve as brood chambers until the larvae swim away.

Which seabed animal sometimes carries a live upside-down jellyfish on its back as a shield?

A crab: carrier crabs grip another animal over their backs with specially adapted rear legs, more often a spiny sea urchin, but a jellyfish's stinging cells make just as good a shield.

A 2017 Caltech study found upside-down Cassiopea jellyfish doing what, a first for any jellyfish?

Sleeping: the jellyfish pulsed less at night, were slow to react when disturbed, and dragged the next day if kept awake, the three hallmarks of true sleep.

What makes the water around an upside-down jellyfish burn the skin?

Stinger-laden mucus: the jellyfish sheds microscopic balls of stinging cells, named cassiosomes, into its mucus, where they can kill small prey; the cause of this 'stinging water' was only pinned down in 2020.

Which sea turtle lives almost entirely on jellyfish?

Leatherback: with no hard beak for crushing shells, it relies on sharp-edged jaws and a throat lined with backward-pointing spines that stop slippery jellyfish from sliding back out.

Jellyfish were blamed for a 1999 blackout across Luzon, the main island of which country?

The Philippines: the Sual power plant tripped on 10 December 1999 and took Luzon's grid down with it; its managers blamed a mass of jellyfish, and one Manila columnist asked why nobody had photographed them.

Why did Linnaeus name the adult jellyfish 'medusa' after the Gorgon?

Tentacles like her snakes: Linnaeus chose the name in 1758 because the long tentacles suggested the Gorgon's snaky hair, and 'medusa' is now the everyday word for a jellyfish in Spanish and Italian.

Cooks prize cured jellyfish mainly for what?

Its crunch: cured jellyfish has almost no flavour of its own, but weeks in salt and alum draw out the water and firm up the jelly, so it is sliced into strips to give a dish some bite.

Pliny the Elder wrote that a walking stick rubbed with jellyfish slime would do what?

Glow like a torch: his Natural History says wood rubbed with 'pulmo marinus', the sea lung, looks as if it were on fire, and many jellyfish do make their own light when touched.

Osamu Shimomura spent summers netting which glowing jellyfish for his Nobel-winning research?

Crystal jelly: at Friday Harbor in Washington state he cut the glowing rim from each bell and squeezed out the liquid, in which he found the proteins that make the jellyfish shine.

In which animated film do the heroes flee a forest of jellyfish by bouncing on their tops?

Finding Nemo: Dory has just named a tiny jellyfish Squishy when a whole forest of them closes in, and though Marlin spots that the tops don't sting, both fish are stung unconscious on the way out.

Green fluorescent protein, a jellyfish discovery, lets biologists do what?

Tag living cells: its gene can be joined to another protein's, so the pair glows green under blue light and researchers can watch nerve cells grow or cancer cells spread, work that won the 2008 Chemistry Nobel.

Popular advice says to urinate on a jellyfish sting, but what is that more likely to do?

Make the pain worse: urine is often dilute enough to act like fresh water, which can make the stingers left on the skin shoot out more venom, and no study has ever backed the cure.

Box jellyfish can jet along at four knots to do what?

Hunt fish: where true jellyfish wait for food to blunder into their tentacles, box jellyfish go after it, pumping the bell to jet along at up to two metres a second.

The deep-sea Atolla jellyfish answers an attack with rings of blue flashes thought to do what?

Lure in a bigger predator, one more interested in eating the attacker than the jellyfish: the trick has earned Atolla the nickname 'alarm jellyfish'.

Which undersea cartoon has a hero who spends his days off 'jellyfishing' with a net?

SpongeBob SquarePants: SpongeBob and his friend Patrick net them for sport in a meadow called Jellyfish Fields, and one of the show's first episodes, 'Jellyfishing', has them take their neighbour Squidward along.

In Hawaii, box jellyfish arrive off Waikiki Beach on a schedule that follows what?

The phases of the Moon: the swarms turn up roughly 8 to 12 days after every full moon, regularly enough that the Waikiki Aquarium publishes a calendar of the dates to watch.

A box jellyfish's stinging cells are set off by which trigger?

Chemicals on the skin: the stinging cells along each tentacle are triggered not by a mere touch but by the presence of a chemical on the outer layer of the animal they meet.

The 2019 Sydney search for a Chironex fleckeri antidote relied on which gene-editing tool?

CRISPR: Greg Neely's team knocked out human genes across the genome to find the ones the venom needs to kill a cell, and a drug that already existed then blocked pain and scarring in mice when given within 15 minutes.

The deadly box jellyfish genus Chironex ends in the Latin word 'nex', which means what?

Murder: nex is Latin for a violent death, a fair label for an animal whose worst stings can stop a swimmer's heart within minutes.

A single Australian box jellyfish is said to carry enough venom to kill about how many adults?

60 adults is the usual estimate, yet a 13-year study of confirmed stings in northern Australia found that most were not life-threatening; the rare deaths came within minutes.

Which sitcom's 1997 season opener has a beach jellyfish sting treated with a folk remedy?

Friends: in 'The One with the Jellyfish', Monica is stung at the beach, Joey remembers a tip from a nature documentary, and one of her two rescuers has to pee on her leg.

Irukandji syndrome is notorious for which strange symptom?

Impending doom: victims are gripped by a feeling that something terrible is about to happen, thought to come from a flood of adrenaline-type stress hormones that also brings sweating, vomiting and soaring blood pressure.

Australians know the Portuguese man o' war's Indo-Pacific form, a common beach hazard, by which name?

Bluebottle: at the mercy of the wind, the small blue floats are driven onto eastern Australian beaches by summer north-easterlies, sometimes stranding in huge numbers.

Experiments with Portuguese man o' war venom aboard the Prince of Monaco's yacht led to the Nobel-winning discovery of what?

Anaphylaxis: Charles Richet expected a small first dose of toxin to protect his dogs, but a second dose weeks later set off a violent reaction, the reverse of immunity, and the finding won him the 1913 Nobel Prize.

Cotylorhiza tuberculata, a common Mediterranean jellyfish, is nicknamed after which breakfast food?

A fried egg: a raised golden dome sits in the middle of a pale rim, a look so distinctive that several different jellyfish around the world have earned the same nickname.

The compass jellyfish of European coasts gets its name from what?

Brown V-shaped marks on its bell fan out from the centre like the points of a compass; the handsome summer visitor gives a nasty sting, so the advice on British beaches is to look but not touch.

A moon jelly is easily recognised by four horseshoe-shaped what, visible through the bell?

Gonads: the four horseshoe-shaped rings are its reproductive organs, and in place of long trailing tentacles it has a short, fine fringe that gathers food caught in the mucus on its bell.

The golden jellyfish of Jellyfish Lake vanished completely in the late 1990s, most likely because of what?

El Niño warming: the heated lake lost every one of its golden medusae for a time, and it happened again after the 2015-16 El Niño, when they stayed away until the water finally cooled in late 2018.

The oxygen-free deep layer of Jellyfish Lake is laced with which poisonous gas?

Hydrogen sulfide fills the water below about 15 metres, beneath a band of bacteria that soaks up the last of the light, so everything that needs oxygen, the jellyfish included, lives in the layer above.

Which emperor was also a published marine biologist who named new species of hydrozoans, the jellyfish's close relatives?

Hirohito of Japan kept a laboratory in the grounds of the Tokyo Imperial Palace, wrote several books on marine biology and described dozens of hydrozoan species new to science.

Japanese biologist Shin Kubota, keeper of immortal jellyfish colonies since the 1990s, became known for promoting his research how?

Singing songs about them: Kubota, who tended his colonies daily for decades, wrote his own numbers, among them an 'immortal jellyfish ondo' in the style of a festival dance, and released them on CD.

Turritopsis is thought to be spreading around the world mainly by what route?

Ship ballast water: the tiny jellyfish are thought to be drawn into the tanks that keep ships stable and pumped out again an ocean away, an invasion so quiet that it went unnoticed for years.

The jellyfish Craspedacusta sowerbii is unusual for living where?

Fresh water: native to pools along the Yangtze, it probably hitch-hiked abroad on ornamental water plants and now turns up in lakes, reservoirs and flooded quarries far from any sea.

Stalked jellyfish, the staurozoans, break the usual jellyfish rule by spending their adult lives how?

Attached to rocks or seaweed: these small, trumpet-shaped animals are in effect medusae that never break free, sitting stalk-down with their tentacles held upward, the other way up from a swimming jellyfish.

Pelagia noctiluca is usually known in English by which common name?

Mauve stinger: rated the most venomous jellyfish in the Mediterranean, it carries stinging cells on its bell as well as its tentacles, and when its swarms wash in, tourists stay off the beaches.

Pelagia noctiluca's species name combines the Latin words for which two things?

Night and light: Latin noctiluca meant a lantern, a fitting name for a jellyfish that glows in the dark and is sometimes called the night-light jellyfish.

Swarms of Pelagia noctiluca have been recorded wiping out entire what?

Fish farms: in November 2007 a swarm spread over some ten square miles drifted into Northern Ireland's only salmon farm and killed more than 100,000 fish, so densely packed that rescue boats could not reach the cages.

Britain's largest jellyfish, the barrel jellyfish, grows so wide that it is also named after which household object?

A dustbin lid: up to 90 cm across, it is the largest jellyfish in British waters, yet it eats only plankton and its sting poses no serious threat to people.

The sea nettle genus Chrysaora shares its name with Chrysaor, who sprang from the slain Medusa alongside which sibling?

Pegasus: in Hesiod's telling, when Perseus cut off Medusa's head the winged horse leapt out together with Chrysaor, who was named for the golden blade he held.

What does the blue dragon sea slug do with its prey's stingers?

Stores them: the little slug eats the Portuguese man o' war and moves the unfired stinging cells into its own tissues, so anyone who picks up a stranded blue dragon can get a very painful sting.

What finally reined in the sea walnut's Black Sea takeover?

A predatory comb jelly: Beroe, a relative that swallows other comb jellies whole, reached the Black Sea in its turn and began eating the invader's numbers down.

The comb jelly Mnemiopsis leidyi invaded the Black Sea in the 1980s and crashed catches of which fish?

Anchovy: the comb jelly bred so fast that it stripped the sea of the plankton, eggs and larvae the fish depend on, and within a decade the anchovy fishery had collapsed.

A Japanese dairy found a use for troublesome giant jellyfish by dicing them into what?

Ice cream: swarms of the giant jellyfish damage nets and spoil catches along Japan's coast, which is why people there have looked for ways to turn the pest into a resource.

The Portuguese man o' war takes its common name from its resemblance to what?

A warship under full sail: a man-of-war was a fighting ship, and the likeness goes further, since the animal cannot swim and goes wherever wind and current push it, often in fleets of a thousand or more.

The 'kreisel' tanks that public aquariums build for jellyfish are typically what shape?

Circular: 'kreisel' is German for a spinning top, and the tank sends a slow current round and round so the fragile animals stay suspended in mid-water, clear of corners and plumbing.

Ernst Haeckel named the jellyfish Desmonema annasethe after whom?

His late wife Anna Sethe died in 1864, and the trailing tentacles reminded him of her long flowing hair.