Basic Information
Jellyfish aren’t actually fish at all – they’re invertebrates (animals without backbones) that belong to a group called cnidarians!
Jellyfish
Don't want random?
Search name of person, animal, place, thing, etc.
Share
Facts About Jellyfish
Jellyfish have existed for over 500 million years, making them older than dinosaurs and even some of the earliest trees!
A jellyfish’s body is made up of 95% water, which is why they appear almost transparent!
Jellyfish don’t have brains, hearts, or bones, yet they’ve survived for hundreds of millions of years!
Instead of a brain, jellyfish have a simple nerve net that helps them sense their surroundings!
Some jellyfish species can glow in the dark through a process called bioluminescence, creating their own light through chemical reactions!
Jellyfish move by pulsing their bell-shaped bodies to push water behind them, allowing them to travel about 5 miles per hour (8 km/h)!
The smallest jellyfish species, called Irukandji, is only the size of a fingernail but has venom that is 100 times more powerful than a cobra’s!
The largest jellyfish species, the Lion’s Mane jellyfish, can have tentacles that reach 120 feet (37 meters) in length, longer than a blue whale!
Jellyfish have special stinging cells called nematocysts that they use to capture prey and defend themselves!
Scientific Classification
Scientists classify jellyfish in the phylum Cnidaria, which also includes sea anemones and coral!
There are over 2,000 different species of jellyfish that have been identified by scientists so far!
The scientific name for the group of true jellyfish is Scyphozoa, which comes from Greek words meaning “cup animals”!
Box jellyfish belong to the class Cubozoa, named for their cube-shaped bells!
Portuguese Man-of-War jellyfish aren’t actually single animals but colonies of specialized organisms working together as one!
The immortal jellyfish (Turritopsis dohrnii) belongs to the class Hydrozoa and is the only known animal that can revert back to an earlier life stage instead of dying!
Jellyfish are grouped into different orders based on the structure of their bells and tentacles, with some major orders including Semaeostomeae and Rhizostomeae!
The Moon jellyfish’s scientific name is Aurelia aurita, and it’s one of the most common jellyfish species found in ocean waters worldwide!
The upside-down jellyfish (Cassiopea) is unusual because it spends most of its time sitting upside-down on the ocean floor!
Jellyfish are related to tiny freshwater animals called hydra, which are only about 1.2 inches (30 millimeters) long!
Collective Nouns
A group of jellyfish is called a “bloom,” a “swarm,” or sometimes a “smack”!
A bloom of jellyfish can contain thousands or even millions of individuals all floating together!
When jellies gather in huge numbers, scientists call it a “jellyfish bloom event,” which can stretch for more than 10 miles (16 kilometers)!
Some jellyfish blooms are so large they can be seen from space via satellite images!
A jellyfish bloom can weigh more than 40 tons and contain up to 40 million jellyfish in a single square mile!
Jellyfish blooms can sometimes last for months, with new jellyfish constantly joining the group!
Many jellyfish in a bloom pulse their bells in the same rhythm, creating a synchronized swimming pattern!
Scientists track large jellyfish blooms because they can affect fishing, tourism, and even power plants that use ocean water for cooling!
In some places, like Jellyfish Lake in Palau, millions of jellyfish migrate together across the lake each day following the sun!
When jellyfish gather near beaches, scientists often call it an “invasion” rather than a bloom!
Geographic Distribution and Habitat
Jellyfish live in every ocean on Earth, from the surface waters to depths of 30,000 feet (9,000 meters)!
Some jellyfish species, like the Australian Box Jellyfish, prefer to live in shallow coastal waters, especially near river mouths!
There are even a few species of jellyfish that live in freshwater lakes and rivers instead of the ocean!
The Arctic Lion’s Mane jellyfish lives in the freezing waters of the Arctic, North Atlantic, and northern Pacific Oceans!
Jellyfish are found in greater numbers in areas with warm water temperatures and plenty of food!
The Irukandji jellyfish is found in the warm waters around Australia, particularly near the Great Barrier Reef!
Warmer ocean temperatures due to climate change have led to increasing jellyfish populations in many parts of the world!
Jellyfish can survive in waters with low oxygen levels where many other sea creatures cannot live!
Some jellyfish, like the upside-down jellyfish, live in mangrove swamps and muddy lagoons instead of the open ocean!
Lifespan
Most jellyfish have a lifespan of just a few months, but some species can live for 2–3 years in the wild!
In captivity, jellyfish typically live longer, with lifespans of 1–3 years when kept in proper conditions!
The immortal jellyfish (Turritopsis dohrnii) can theoretically live forever by reverting to an earlier life stage when it gets old or injured!
A jellyfish’s life cycle includes multiple stages, and they spend part of their life attached to the ocean floor as tiny polyps!
Moon jellyfish typically live about 12–15 months, but in aquariums, they can sometimes live up to 2 years!
The polyp stage of a jellyfish’s life can last for several years, with each polyp producing multiple jellyfish!
Some jellyfish species die after reproducing just once, while others can reproduce multiple times!
The box jellyfish has a lifespan of only about 2-3 months from when it transforms into its medusa (adult) stage!
Cold water jellyfish species generally live longer than warm water species, sometimes surviving for up to 3 years!
The ephyra (young jellyfish) stage lasts only about 2-4 weeks before the jellyfish grows into its adult form!
