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Jellyfish are prehistoric sea creatures known to have been present in the oceans for the past millions of years.

Although they are generally not aggressive, these fish are known for their stinging abilities, which allow them to ward off any danger.

These fish use their tentacles to hunt. However, they do not have any bones, hearts or most other organs. Interestingly, most of their bodies are made of water.

They live about three to six months and can grow up to 7 feet tall.

jellyfish one


Do jellyfish have brains?

As beautiful as these sea creatures are, they don't have brains. Instead, the body is made up of a complex nervous system, which is where all motor functions and sensory activity take place. Through neurons in this system, the body tells the muscles when to contract, which is how they swim.

Incredible Jellyfish Facts!

  • No brains, hearts or eyes : these fish are composed mostly of water. They have no brains, hearts or eyes. They also have no bones, and their bodies are primarily controlled by the nervous system.
  • Ancient Prehistoric Creatures : Jellyfish have been known for millions of years – even before the dinosaurs!
  • Bioluminescence : These fish are bioluminescent – meaning they can glow.
  • Fast Digestion : When a jellyfish feeds, the digestion process doesn't take long. This quick process ensures they can float in water.
  • World Cuisine : Jellyfish are beloved not only by the predators that feed on them, but also by the global population.

taxonomic name

The scientific name of these animals is Scyphozoa and it belongs to the kingdom Animalia and the phylum Cnidaria. Scyphozoa comes from two Greek words – skuphos and zōion. skuphos means "water cup" and zōion means "animal". The name is an interpretation meaning that this animal contains water. The phylum Cnidaria is also interesting because it comes from the modern Latin word knidē, meaning "nettle".

As part of the taxonomy, these fish are from the subphylum Jellyfish and the class Jellyfish – which is the same scientific name for the jellyfish in the taxonomy. Medusozoa is derived from the Ancient Greek Μέδουσα, from the word "to rule" (μέδω).


Jellyfish are thought to have evolved from the phylum Cnidaria, which includes sea anemones and corals. Jellyfish may well have been the ocean's first muscle-powered swimmers. They originated in the Precambrian period, when ecological and geological changes led to the explosion of animal life in the late Cambrian period.

The more accepted theory is that the jellyfish changed from polyps that grew on the ocean floor to swimming jellyfish with spiny tentacles. Their shape-shifting abilities likely helped them survive multiple mass extinctions over a period of 500 million years.

A second explanation by some scientists is that cnidaria originally had a jellyfish life stage, distinguishing them from sea anemones and corals.

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cauliflower jellyfish
Jellyfish are thought to have originated in the Precambrian period, when ecology and geology changed.



Jellyfish are a large family of plankton, with recent studies suggesting at least 4,000 species have been found. Given the vastness of the ocean, scientists believe this number is a fraction of the actual number in the ocean.

Even with all of these species in the world, only 70 are considered a threat to humans. Some of these endangered species include Malo kingi and Chironex fleckeri , both of which belong to the box jellyfish family. The venom is powerful and painful enough to kill.

Some types are even kept as pets, mostly because they don't sting their owners. The most common pet jellyfish is the moon jellyfish, which lives about 15 months. Other species of jellyfish can live much longer.

A group of jellyfish is called a swarm, smack or bloom. Check out this article to learn more about jellyfish group names and their functions.

Immortal jellyfish

Turritopsis dohrnii – also known as the jellyfish of immortality – is a small, transparent jellyfish that interestingly reverts to an earlier stage of its life. This transition could return the animal to the state in which jellyfish lived as fertilized eggs when they colonized the ocean floor in later life.


Some of these animals are transparent, while others exist in bright colors like yellow, blue, and pink. These fish are bioluminescent, which means they glow.

Due to their appearance, their bodies may appear complex, but they are very simple. Jellyfish have smooth bodies and tentacles containing tiny cells that they use when they use their stinging abilities.

They have no bones, brains, hearts or eyes. Their mouth is located in the center of the body. They are usually about 0.5 to 16 inches long, can grow up to 7 feet, and usually weigh about 440 pounds.

yellow jellyfish in ocean
Some jellyfish are transparent, while others come in bright colors like yellow, blue and pink.

© Dan90266 / Creative Commons

jellyfish tentacles

The animals' tentacles are equipped with tiny stinging cells that are activated when the fish launch a stinging attack on their prey. These tentacles are used to paralyze and stun prey stung by jellyfish. These tentacles were found dangling from the jellyfish's body.

Although these tentacles are controlled by the nervous system, the sting is rarely fatal. Most box jellyfish have enough venom to kill their victims. The purpose of the tentacles is to impede the movement of prey, although they are also used as a way of protecting animals.

deadly jellyfish

While some species of jellyfish are quite harmless, as mentioned above (such as moon jelly or Aurelia aurita , which are particularly common in the UK), others are much deadlier.

The most dangerous jellyfish are usually found around the Indo-Pacific and northern Australia.

The deadliest of these is the Australian box jellyfish, or Chironex fleckeri . The largest of all the box jellyfish, it is easily recognizable by its tentacles reminiscent of shoelaces, which can grow up to 10 feet long, and by a pale blue skull-like dome.

These tentacles, like those of all other venomous jellyfish, are overgrown with millions of nematocysts that release poisonous darts when touched. Its venom is as painful as a branding iron, and the creature can kill in minutes.

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However, Chironex fleckeri is the turtle's favorite snack, and thanks to its thick skin, the turtle is able to ignore its spines, allowing the turtle to enjoy a tasty jellyfish lunch.

The deadliest jellyfish in the world - the box jellyfish
The most dangerous jellyfish are usually found around the Indo-Pacific and northern Australia, such as the Australian box jellyfish.

© Danza/

Distribution, Population and Habitat

They are found globally and can be found in every ocean on Earth. Many species choose to live in warm tropical waters or cold arctic waters. They can be found both on the bottom of the sea and on the surface of the water, making them very versatile.

While specific regions may vary, each species must live in salt water to thrive. As of 1990, there were 900 million tons of jellyfish in the Black Sea alone.

Even with this ability to survive in so many places, pollution is a huge threat to every species. Oil spills and chemicals dumped in water are easily absorbed by their skin, making them unable to reproduce. While pollution doesn't always kill them right away, most species don't live that long once exposed to the air.

jellyfish lake
Jellyfish can live on the bottom of the water as well as on the surface, which makes them very versatile.

©Ethan Daniels/

predator and prey

These animals face threats from a variety of marine and terrestrial life, including sea anemones, swordfish, turtles, tuna and penguins. When jellyfish wash up on beaches, they are often found and eaten by foxes and other birds and animals. If humans manage to catch them, it's not uncommon to cook them up as a delicacy.

These fish in turn feed on many different things such as planktonic eggs, small plants, small fish and larvae, fish eggs and other small marine animals.

what jellyfish eat
The main food of jellyfish includes plankton, fish, crustaceans and plants.


Jellyfish Sting

The tentacles of these animals are equipped with tiny stinging cells that fish use when hunting prey or sensing danger. They often use their barbed properties for protection and use their tentacles to inject venom into other creatures.

Stings can cause pain and irritation, and sometimes systemic illness. Some stings can even be life-threatening. The worst sting comes from the Australian box jellyfish, the deadliest jellyfish in the world. Their venom is so painful that it often causes shock victims to drown.

glowing jellyfish
Jellyfish use their stinging properties to protect themselves and use their tentacles to inject venom into other creatures.

© LanKS/

Reproduction and Lifespan

These animals are known to reproduce both sexually and asexually. While one of the species reproduces sexually, some other types reproduce asexually. However, for both processes, fertilized eggs settle to the seafloor after developing into multicellular floating bodies.

The average lifespan of jellyfish is three to six months, but some can live for two to three years. Jellyfish technically never die. They eventually settle on the seafloor and give birth to young jellyfish from their DNA. Essentially, jellyfish technically never "die".

The largest jellyfish - black sea nettle
Jellyfish generally live 3-6 months, but some can live 2-3 years.

©Ken Wolter/

Jellyfish in Fishing and Cooking

Jellyfish can be caught and eaten. More than 12 species of the plant are edible and tasted worldwide as a delicacy. These fish are rich in protein and fatty acids.

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A popular recipe is Sesame Jellyfish, which combines fish with soy sauce, vinegar, sesame oil, and sometimes chili oil.

Classification of Cnidaria

There are many species of jellyfish, grouped into four groups of cnidarians. We left out a fifth species of polyp, which includes sea anemones and corals:

  • Scyphozoa – There are 200 species of marine Scyphozoa, known as "true jellyfish". This description refers to the cup-shaped jellyfish. These jellyfish swim freely. Some of the individual species in this group include: moon jellyfish, barrel jellyfish, cannonball jellyfish, cassiopeia jellyfish, blue ray jellyfish, helmet jellyfish, and lion's mane jellyfish.
  • Hydrozoa – Hydrozoa is a taxonomy of 700 unique jellyfish species. They are small, either transparent or colored, and are mostly found seasonally in coastal habitats as well as in freshwater from late spring to early fall. Some freshwater jellyfish ( Craspedacusta sowerbyi ), freshwater polyps ( Hydra ), Obelia , Portuguese jellyfish ( Physalia physalis ), cartilaginous animals (Porpitidae), "air ferns" ( Sertularia argentea ) and pink-core hydra ( Tubularia ).
  • Cubozoa – There are 50 species of Cubozoa, or box jellyfish, which are characterized by their box shape when viewed from overhead. They have well-developed eyes and four evenly spaced tentacles or clusters of tentacles. The sting of many species of box jellyfish is very painful. Examples include: Australian sea bee ( Chironex fleckeri ), Carukia barnesi , and Malo kingi .
  • Staurozoa – Staurozoa jellyfish are known as "stalk jellyfish". Compared to their trumpet-shaped bodies, they grow upside down so that their tentacles protrude upwards and the stem sits in the center of the umbrella. Some species incl. Haliclystus antarcticus , Manania handi, Lucernaria quadricornis and Haliclystus octoradiatus .

Species of True Jellyfish ( Scyphozoa )

  • moon jelly
  • Cannonball jellyfish
  • dulse
  • barrel jellyfish
  • lion's mane jellyfish
  • Cassiopeia
  • Camellia pods
  • blue jellyfish
  • Nocturnal algae
  • Nomura's Jellyfish
  • Nigrass
  • scarab
  • jelly fat
  • crown jellyfish
  • scarab
  • Rhizobia
  • helmet jellyfish
  • Styx jellyfish
  • Fabaceae
  • speckled jelly
  • Chrysaora melanaster
  • Scarab
  • scarab
  • deep star
  • grossular garnet
  • Guanosauridae

See all 36 animals starting with J

Jellyfish are found in warm tropical and cold arctic waters around the globe.

One of the most interesting features of jellyfish is that this animal has no brain. In addition, they also lack hearts, bones and eyes.

Jellyfish eat small plants, small fish, eggs, larvae, and other small sea creatures.

This group of jellyfish is called smack.

Some species of jellyfish reproduce sexually, while others reproduce asexually.

Jellyfish usually live only three to six months. However, some types can live for two to three years, and some are even immortal.

Jellyfish belong to the animal kingdom.

Jellyfish belong to the class Jellyfish.

Jellyfish belong to the phylum Cnidaria.

Jellyfish belong to the Cyaneidae family.

Jellyfish belong to the order Jellyfish.

Jellyfish are covered with smooth skin.

Jellyfish have an average of 100 babies.

Tentacles hang from the jellyfish's body.

The biggest threats to jellyfish are sharks, birds, tuna and sea anemones.

In 1990, there were 900 million jellyfish left in the world.

Jellyfish can travel as fast as 5 miles per hour.