95 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 small drifting animals are the staple; jellyfish eat and excrete through the same opening, and other jellyfish are on the menu too.

Which class of jellyfish, all of them marine, gets 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.

The jelly that forms most of a jellyfish's bell is at least what percentage water?

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.

What unique ability is attributed to the 'immortal jellyfish' (Turritopsis dohrnii)?

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; box jellyfish add an inward-folded rim, the velarium, that sharpens the jet and lets them outswim bigger species.

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

Mesoglea is the animal's hydrostatic skeleton, sandwiched between the outer epidermis and inner gastrodermis, with collagen and wandering amoebocytes that mop up debris.

How is a jellyfish's body arranged around its central axis?

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.

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, with tentacles past 30 metres, is arguably the longest animal alive?

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.

Jellyfish have existed for at least how many years, making them the oldest multi-organ animal group?

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.

What is a group of jellyfish called?

A smack is the traditional collective noun for jellyfish, with 'smuck' an accepted variant; a mass seasonal gathering is usually called a bloom.

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: 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.

The record-length jellyfish measured off Massachusetts in 1865 had tentacles how long?

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.

The bell of Cyanea capillata is divided into how many lobes, giving it a star-like look?

Eight lobes, each carrying 70 to 150 tentacles in four rows, for about 1,200 tentacles in total.

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.

The genus name Physalia comes from the Greek for what?

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.

The immortal jellyfish achieves its trick through which cell process?

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.

How big is an adult Irukandji jellyfish?

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.

How did Jack Barnes prove in 1964 that Carukia barnesi causes Irukandji syndrome?

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.

Irukandji syndrome takes its name from what?

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.

In 2009, a Japanese trawler capsized off Chiba while hauling a net full of which giant species?

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.

Nemopilema nomurai is named after a fisheries station director in which Japanese prefecture?

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.

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

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.

Jellyfish Lake, where millions of golden jellyfish migrate daily, is on which island nation?

Palau: Jellyfish Lake, Ongeim'l Tketau on Eil Malk in the Rock Islands, holds millions of golden jellyfish, Mastigias papua, that cross the lake each day.

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.

A 2006 study found a stinging cell fires in about 700 nanoseconds, reaching what acceleration?

Up to 5,410,000 g: Nüchter and colleagues clocked nematocyst discharge in Hydra at about 700 nanoseconds, one of the fastest movements known in nature.

How many known Australian deaths did the sea wasp Chironex fleckeri cause from 1884 to 2021?

At least 64 recorded Australian deaths: sea wasp venom attacks the heart, and an untreated victim can die within minutes, which is why vinegar and antivenom wait on northern beaches.

Chironex fleckeri is named after Hugo Flecker, who was a toxicologist and what else?

Radiologist: Hugo Flecker practised radiology in Cairns while cataloguing venomous animals; after a five-year-old boy died at Cardwell in 1955 he collected the animal Southcott named Chironex fleckeri.

How many tentacles trail from each of the four corners of a sea wasp's bell?

15 tentacles hang from each of the four pedalia at the bell's corners, contracting short while the animal swims and trailing long when it hunts.

In 2001 the annual global harvest of edible jellyfish was estimated at roughly how much?

321,000 tonnes a year, per a 2001 estimate; Rhopilema esculentum, the flame jellyfish, is the most commonly eaten species in China, Japan and Korea.

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

Ctenophora, the comb jellies, swim by beating rows of fused cilia and are the largest animals to do so; the ribbon-like Venus girdle reaches 1.5 metres.

The cannonball jellyfish's dome-shaped bell can reach roughly what diameter?

25 cm, about the size of an actual cannonball, and juvenile spider crabs often hitch a ride inside the bell.

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.

The oldest unambiguous free-swimming medusa fossil comes from which Canadian fossil bed?

Burgess Shale: Burgessomedusa phasmiformis, described in 2023 from the mid-Cambrian Burgess Shale of British Columbia, is the oldest unambiguous swimming medusa; soft bodies rarely fossilise, so jellyfish fossils are scarce.

Medusozoan body parts come in multiples of which number?

Four: the tetramerous plan shows up everywhere, in four oral arms, four gastric pockets, four pedalia at a box jelly's corners and four radial canals in many hydromedusae.

The stalk hanging from the centre of the bell that carries the mouth is called what?

Manubrium: the mouth at its tip doubles as the anus, and in box jellies the manubrium is mobile, likened to an elephant's trunk as it swings food inward.

Tripedalia cystophora box jellyfish steer by looking up through the 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.

The largest Nemopilema nomurai can weigh roughly how much?

200 kg: Nemopilema nomurai reaches two metres across, and bloom years such as 2005 sent millions drifting from the Yellow Sea into Japanese waters.

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

Giant phantom jelly: Stygiomedusa gigantea trails four ribbon-like oral arms instead of fine tentacles, and is seen so rarely that sightings are counted in the low hundreds.

Which process sees a polyp form ring-like constrictions that detach as ephyrae?

Strobilation: the polyp reabsorbs its tentacles, its body narrows into a stack of discs, and each ephyra that breaks free is only a millimetre or two across.

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

The oral arms: pits on a female moon jelly's oral arms hold the fertilised eggs as brood chambers until the larvae swim off to settle as polyps.

Why do upside-down jellyfish (Cassiopea) rest bell-down on the seabed?

To expose symbiotic algae to sunlight: Cassiopea hosts zooxanthellae in its tissues, so it lies upside down in sunlit mangrove shallows with its oral arms facing the surface.

Cassiopea jellyfish were the first animals without a central nervous system seen doing what?

Researchers saw quiescence, slower responses to stimuli and homeostatic regulation, the three hallmarks of a genuine sleep state.

Cassiopea xamachana releases stinging cell balls that scientists likened to microscopic what?

The self-propelling blobs, named cassiosomes, swim around the jellyfish stinging anything they touch, which explains 'stinging water' near them.

Cannonball jellyfish are a main food of which sea turtle?

Leatherback: the jellyfish-eating leatherback feeds heavily on cannonball jellyfish off the US southeast coast, one reason Georgia's jellyball trawls must carry turtle excluder devices.

Jellyfish caused a cascading power blackout in 1999 in which country?

Swarms also disabled California's Diablo Canyon plant in 2008; they can stop desalination plants and ships' engines the same way.

Aristotle wrote that jellyfish (sea-nettles) were eaten in winter in what form?

In a fish stew, as Aristotle notes in Parts of Animals; only about a dozen rhizostome species are harvested for the table, mostly in East and Southeast Asia.

Traditional jellyfish processing treats the umbrella with table salt and which other substance?

Alum lowers the pH and firms the texture while salt draws out water; the 20- to 40-day job is done by a 'jellyfish master'.

Pliny the Elder said the slime of a jellyfish produced light when rubbed on what?

A walking stick: Pliny's Natural History says a staff rubbed with the slime of his 'Pulmo marinus' glowed like a torch, an early record of jellyfish bioluminescence.

Besides GFP, which calcium-triggered photoprotein did Osamu Shimomura isolate from the crystal jellyfish?

Aequorin flashes blue when calcium binds it, and GFP converts that blue to green; both became standard markers in cell biology.

Who sequenced and cloned the gene for green fluorescent protein?

Douglas Prasher cloned and sequenced the GFP gene in 1992, thirty years after the protein was first isolated, yet was left out when the Nobel went to Shimomura, Chalfie and Tsien, who paid his way to the ceremony.

Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for GFP work in which year?

2008: the Chemistry Nobel honoured Shimomura's discovery, Chalfie's use of GFP as a genetic tag, and Tsien's engineering of brighter and differently coloured variants.

Contrary to popular belief, urinating on a jellyfish sting has been shown to do what?

Make the pain worse: urine can trigger unfired stinging cells to discharge; rinsing with seawater, plucking off tentacles, and vinegar for box jelly stings are what actually help.

Box jellyfish can swim at roughly how many nautical miles per hour?

4 knots, about two metres a second; they can also turn 180 degrees in a few bell contractions and actively hunt small fish rather than drifting like true jellyfish.

In the wild, a box jellyfish lives for up to about how long?

Three months is the typical wild lifespan of a box jellyfish; in a lab tank they can stretch to seven or eight months.

Some box jellyfish perform a 'wedding dance' to transfer which packages to females?

Spermatophores: in Copula sivickisi the male grips the female by the tentacles and passes her sperm packets, and the fertilised embryos are later released as strands.

In Hawaii, box jellyfish numbers near shore peak roughly how long after a full moon?

7 to 10 days after the full moon, Alatina box jellyfish come inshore to spawn, and the influx is sometimes heavy enough for lifeguards to close Hanauma Bay until it passes.

Pantyhose protect swimmers from box jellyfish because the stingers fire in response to what?

The old theory was that the stingers were simply too short to get through the fabric; it turned out the trigger is chemical, not touch.

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

CRISPR: Greg Neely's Sydney team switched off human cell genes one by one, which pointed to ATP2B1, and existing cholesterol drugs blocked pain and necrosis in mice if given within 15 minutes.

The genus name Chironex ends in the Latin 'nex', meaning what?

Murder: nex is Latin for a violent death, and chiro- is Greek for hand, so Chironex reads as 'hand of death' for its four clusters of tentacles.

The venom in a single sea wasp, the Australian box jellyfish, is said to be enough to kill how many adults?

60 adults' worth, and untreated a large sting can kill in two to five minutes, though most encounters end in mild envenomation.

About how much Chironex fleckeri tentacle is needed to deliver a fatal dose?

3 metres of tentacle contact, about the length a hunting tentacle extends; while swimming the tentacles contract to around 15 centimetres, and most fatalities involve large animals.

The cramps, sweating and racing heart of Irukandji syndrome come from a release of what?

Catecholamines: the venom triggers a surge of adrenaline and noradrenaline, and the full syndrome is delayed 5 to 120 minutes after a sting that barely hurts.

Linnaeus first described the man o' war in Systema Naturae under which name?

Holothuria physalis was Linnaeus's 1758 name in the tenth Systema Naturae; Lamarck moved the animal to his new genus Physalia in 1801.

Thanks to its left- or right-handed float, a man o' war sails about how far off the wind?

45 degrees: mirror-image left- and right-handed colonies get pushed to opposite sides of the wind, so at most half a population is blown toward any one coast.

Which of these names is also used for Cyanea capillata?

Arctic red jellyfish is one name for Cyanea capillata, alongside hair jelly and giant jellyfish; juveniles start tan or orange and darken to red and purple with age.

In 2010 fragments of one lion's mane jellyfish stung about 150 bathers in which US state?

New Hampshire: at Wallis Sands beach in Rye, pieces of a single 40-pound lion's mane stung around 150 people in one July 2010 afternoon.

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

Gonads: the four horseshoe-shaped reproductive organs show through the translucent bell, usually 25 to 40 cm across, and the animal feeds with short fine tentacles.

The golden jellyfish of Jellyfish Lake vanished in 1998; what was the most likely cause?

El Niño warming: a 1998 temperature spike killed the symbiotic algae in medusae and polyps and the medusae vanished for a time before recovering; a second crash followed the 2015-16 El Niño.

Scuba is banned in Jellyfish Lake partly because its oxygen-free deep layer holds which toxic gas?

Hydrogen sulfide below about 15 metres can be absorbed straight through a diver's skin, which is why visitors snorkel instead.

Turritopsis dohrnii honours Anton Dohrn, founder of a zoological station in which city?

Naples: Anton Dohrn founded the Stazione Zoologica there in 1872; Weismann named the species after him in 1883, and it was long lumped with T. nutricula.

Shin Kubota, who keeps a long-running Turritopsis dohrnii colony, famously ends his talks how?

Singing songs about them: Shin Kubota of Kyoto University's Shirahama lab performs his own immortal-jellyfish songs, often in costume, and is a regular on Japanese television.

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

Ship ballast water: polyps ride in tanks across oceans, and researcher Maria Pia Miglietta called the spread 'a worldwide silent invasion', unnoticed because the animal is tiny and harmless.

The freshwater jellyfish Craspedacusta sowerbii is native to which river basin?

Yangtze: native to the Yangtze basin of China, it has been introduced on every continent except Antarctica, turning up unpredictably in quarries, reservoirs and lakes.

Craspedacusta sowerbii is also known by which flowery common name?

Peach blossom jellyfish, from its Chinese name, is about 2.5 cm across and colourless, and its stinging cells have never been shown to pierce human skin.

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

Mauve stinger: unusually, its bell as well as its tentacles carries stinging cells, and it is the Mediterranean's most important stinging species.

Which life stage has Pelagia noctiluca dropped entirely from its life cycle?

Polyp: Pelagia's larvae turn straight into ephyrae in about a week, skipping the settled polyp stage, which suits an open-sea animal with nowhere to attach.

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

Fish farms: in November 2007 a bloom covering about 26 square kilometres swept through a Northern Ireland salmon farm and killed its entire stock of more than 100,000 fish.

A record-sized Phyllorhiza punctata washed up in 2007 on a beach in which US state?

North Carolina: the giant turned up at Sunset Beach in 2007, far above the species' usual 50 cm; native to the western Pacific, it has spread from Hawaii to the Gulf of Mexico and Mediterranean.

The barrel jellyfish Rhizostoma is nicknamed after which household object?

A dustbin lid: the barrel or dustbin-lid jellyfish has a solid, thick bell that can reach about 90 cm across, among the largest in British and Mediterranean waters.

The sea nettle genus Chrysaora is named for Chrysaor, the brother of which mythical figure?

Pegasus: Chrysaor and the winged horse both sprang from Medusa's severed neck; Chrysaor means 'he who has a golden armament', a nod to the goldenrod bell of the Pacific sea nettle.

Velella and Porpita are hunted by purple sea snails of which genus?

Janthina: the violet snails hang beneath rafts of mucus bubbles and share Velella and Porpita with blue dragon sea slugs of the genus Glaucus, all part of the surface-living neuston.

The comb jelly Mnemiopsis leidyi is also known by which nutty name?

Sea walnut: Mnemiopsis leidyi does not sting, and when disturbed it glows blue-green along its eight comb rows, separate from the rainbow shimmer its beating cilia make in daylight.

Mnemiopsis leidyi's 1980s Black Sea invasion crashed stocks of which commercial fish?

Anchovy: Mnemiopsis devoured the fish's eggs, larvae and plankton food, so Black Sea anchovy landings collapsed around 1989; another comb jelly, Beroe ovata, later arrived and grazed the invader down.

Japan's Tango Jersey Dairy made a vanilla-flavoured what with echizen kurage jellyfish?

Ice cream: the diced jellyfish was soaked in milk before going into the vanilla mix, and tasters described the result as 'slightly chewy'.

Jellyfish collagen has been studied as a treatment for which condition?

Rheumatoid arthritis: researchers have tested jellyfish collagen for it; collagen harvesting is a sideline to the food trade, where the US cannonball catch is shipped to Asia.

Professional jellyfish tanks such as Monterey Bay Aquarium's are typically what shape?

Circular: jellies drift with currents and get stuck in corners, so a round 'kreisel' tank keeps a gentle rotating flow that sweeps them away from the outflow screen.

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.