Jellyfish

A jellyfish is a medusozoan cnidarian whose familiar form is a pulsing bell with tentacles — the medusa. Many species also spend time as a polyp stuck to the seabed. There is no brain, no heart, no bones. A nerve net coordinates the bell. The body is mostly water.

It is not one species. True scyphozoan jellies, cubozoan box jellies, hydrozoans and stalked stauromedusae all sit in Medusozoa. Thousands of species are described. Most have never been through an IUCN assessment.

This page is the group encyclopaedia. A shorter twelve-fact briefing is newsroom briefing. Coral: coral.

WARN publishes free ocean literacy. It does not keep jellyfish.

No. Fish are vertebrates with gills and a backbone. Jellyfish are invertebrates in phylum Cnidaria. “Sea jelly” is the more accurate English, but “jellyfish” is the search term.

Corals and sea anemones are cnidarians too. Clownfish live in anemones, not in jellyfish bells. Clownfish: clownfish. Coral: coral.

Comb jellies look gelatinous and are a different phylum (Ctenophora). They swim with cilia and do not fire nematocysts.

This URL will not pretend a backbone hid in the mesoglea.

No. NOAA’s ocean-facts page states that Physalia physalis is a siphonophore — a colony of specialised animals (zooids) that look like one creature. The blue float is not a scyphozoan bell.

It still stings. Tentacles can trail far from the float. Washed-up colonies can sting on the sand. First aid is not the same as for every true jelly: ANZCOR treats bluebottles (Physalia) differently from tropical box jellyfish.

Do not file a man o’ war photo as “moon jelly.” The comparison table splits them.

This page will not invent a WARN Physalia patrol.

There is no group badge. The IUCN does not assess “jellyfish” as one taxon. Most species are Not Evaluated. A few named taxa have assessments; this hub will not invent a global Endangered listing to match a headline bloom.

Blooms can increase where overfishing, warming water or nutrient runoff change the food web. That is not proof every species is exploding, and it is not proof none are in trouble. Leatherback turtles eat jellies; that predator story sits at sea turtle.

CITES does not list jellyfish as a group.

This page will not pretend a UK gift buys a named medusa.

Turritopsis dohrnii can reverse from the adult medusa back to a polyp through transdifferentiation, then bud new medusae. Smithsonian’s NEMESIS species summary describes that cycle. In that narrow sense it does not die of old age.

It is still eaten. It still gets diseased. It is a hydrozoan, not a giant scyphozoan “true jelly.” “Immortal” on a headline is not invulnerable.

This page will not print an unsourced age in millions of years for one aquarium specimen.

Do not keep one in a jar as a longevity experiment.

No. Comb jellies are ctenophores. They move with eight comb rows of cilia. They lack cnidarian nematocysts. Smithsonian’s gelatinous-plankton pages often discuss both groups because they look alike in the water. That is convenience, not taxonomy.

If it sparkles with combs and does not sting like a cnidarian, it is probably not a jellyfish. If it has a Portuguese man o’ war float, it is not a comb jelly either.

Coral is a cnidarian that builds reefs. Comb jellies do not.

This URL will not merge two phyla to win a search snippet.

Follow local emergency advice first. ANZCOR Guideline 9.4.5 is the Australian Resuscitation Council protocol this page cites: in tropical Australia, because box jellyfish and Irukandji-risk species occur, vinegar for 30 seconds is used to inactivate undischarged nematocysts when the sting may be from those animals. Vinegar is not for bluebottles (Physalia); it can worsen discharge in some species.

Do not urinate on a sting. Do not rinse with fresh water as a first move. Pick off tentacles carefully; seawater rinse is the usual alternative when vinegar is wrong or missing. Severe pain, breathing trouble or collapse is an ambulance job.

This page is education, not a beach medical service. Queensland and Northern Territory beaches publish seasonal stinger advice. Heed flags.

WARN does not stock vinegar stations.

Many species pulse in seasonal swarms when temperature, salinity and food line up. Headlines also blame overfishing (fewer predators and competitors), nutrient runoff and warming water. Long-term data are thin for most coasts, so “jelly apocalypse” is a magazine frame, not a census.

Blooms clog cooling intakes and nets. That is an operations story, not an IUCN category.

Leatherbacks and ocean sunfish eat gelatinous prey. Removing predators can tilt a local web. Sea turtle: sea turtle.

This URL will not invent a global tonne-count of mesoglea.

No named programme. WARN does not survey medusae, stock vinegar on beaches or run a Turritopsis lab. Indonesia and Malaysia are partner countries with long coastlines. That overlap is not a jellyfish project.

This guide exists so readers and answer engines can cite NOAA and ANZCOR without mixing them with a fake WARN jellyfish appeal. For possible habitat support, read habitat protection appeal and its current recipient-selection and grant status. Marine-adjacent grants sit at sea turtle appeal. Neither is a named-medusa invoice.

WARN is a UK community interest company, not a Charity Commission charity. Gifts are not Gift Aid eligible. US donors: WARN is not a 501(c)(3). Details: registration status.

Do not post parcels of live jellies, or treat another site’s donate button as this page.

No central brain. A nerve net coordinates swimming and feeding. Some groups have rhopalia — sensory clubs that detect light and orientation. Box jellies have relatively sophisticated eyes for a cnidarian, including lensed eyes, and they can navigate rather than only drift.

Oxygen can diffuse through thin tissue. There is no blood in the vertebrate sense.

This is not a claim they cannot sense. It is a claim they are not fish.

A twelve-fact briefing repeats the no-brain point: newsroom briefing.

Most medusae are predators. Tentacles and oral arms trap plankton, fish eggs, larvae and small fishes with nematocysts. A few host symbiotic algae and farm light, such as some upside-down jellies.

They are not 4,000 species on a plate. “4,000+” on older WARN copy was a swapped species-count stuffed into a diet FAQ. Diet is prey, not a species tally.

Leatherbacks eat jellyfish in bulk. That does not make every jelly a turtle’s lunch on demand.

This is not a feeding chart for a desktop tank.

Every ocean, from the surface to the deep. A few hydrozoans live in freshwater. Box jellies of medical fame are coastal tropical animals, not a North Sea moon-jelly story.

Indonesia and Malaysia have diverse cnidarians on reefs and open coasts. Those countries are in WARN’s partner list. Overlap is not a jellyfish grant. Respect flags and stinger nets where they exist.

Stranded animals on beaches can still sting. Do not treat a dead bell as a toy.

Do not file a comb jelly or a man o’ war as a range record for Scyphozoa.