Animals

Sea-riously Cool Jellyfish Facts You’ll Never Forget

Jellyfish facts will make you wonder about the vibrant underwater world.
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If there is any animal in the world that inspires imagination and awe, the jellyfish is definitely one of them. With a jelly-like umbrella-shaped body and wavy tentacles, these underwater creatures of the ocean belong to the phylum Cnidaria which also includes other invertebrates such as corals, sea anemones, and Hydra.

The phylum Cnidaria as a whole consists of over 10,000 species, out of which, approximately 2,000 species are the Medusazoa or jellyfish. The jellyfish species are further divided across four groups - Scyphozoa, Hydrozoa, Cubozoa, and Staurozoa with differences in shape, anatomy, habitat, and behavior. Out of these, the most common and familiar jellies that we know of belong to the Scyphozoa group and have around 200 species.

The jellyfish are primarily freely-swimming creatures with unique features. There are different types of jellyfish that are found in both marine and freshwater environments. While it is unfeasible to name them all, some of the most well-known and striking ones include the moon jellyfish, lion's mane jellyfish (red jellyfish or giant jellyfish), blue jellyfish, cannonball jellyfish, and the box jellyfish.

If fun facts about jellyfish interest you, read on for more interesting facts about jellyfish. If you like reading jellyfish facts for kids, you will also enjoy reading about barnacles and freshwater mussels.

Jellyfish

Fact File

What do they prey on?

Fish eggs, fish larvae, small fish, crustaceans, and planktons

What do they eat?

Carnivores

Average litter size?

100

How much do they weigh?

330.7-440.9 lb (150-200 kg)

How long are they?

Largest: 6.5 ft (2m), smallest: 0.2-1 in (5-25 mm)

How tall are they?

N/A

What do they look like?

Mostly transparent, umbrella-like with tentacles

Skin Type

Jelly-like

What are their main threats?

Sea anemones, tunas, sharks, penguins, sea turtles

What is their conservation status?

Least Concern

Where you'll find them

Oceans, freshwaters, aquariums

Locations

Tropical, temperate, and Arctic waters

Kingdom

Animalia

Class

Scyphozoa, Hydrozoa, Cubozoa, Staurozoa

Scientific Name

Aurelia aurita

Family

Ulmaridae

Genus

Aurelia

Jellyfish Interesting Facts

What type of animal is a jellyfish?

The jellyfish is not a fish but a gelatinous (jelly-like) invertebrate belonging to phylum Cnidaria.

What class of animal does a jellyfish belong to?

Jellies are invertebrates (without a backbone) that are divided across the four classes of phylum Cnidaria - Scyphozoa, Hydrozoa, Cubozoa, and Staurozoa.

How many jellyfish are there in the world?

While there is no figure about the exact number of jellyfishes in the world, there are roughly 2,000 species of jellies that have been documented so far.

Where does a jellyfish live?

Jellies mostly live in the oceans, in both shallow and deep water. Some jellyfish also thrive in a freshwater environment. With proper care, they can also live in a jellyfish tank or aquarium.

What is a jellyfish's habitat?

The jellyfish habitat is quite diverse. The jellies can be found in all oceans of the world, from the warm waters of the tropics to the icy cold aquatic environment of the Arctic. While some jellies dwell at the bottom of the ocean, others may be found on the surface. The 'true jellyfish' belonging to class Scyphozoa are exclusively marine while some freshwater jellyfish are from class Hydrozoa. Some jelly species are also known to adapt to tidal flux where they ride the ocean currents and let the ebb and high tides carry them in the water.

Who do jellyfish live with?

Who jellies live with entirely depends on the species of jellyfish. Some live alone while others tend to stick around in groups. The general trend is that the larger the jelly, the more isolated is its habitat, and the smaller the jelly, the more it tends to live in groups, primarily for protection against predators.

How long does a jellyfish live?

The jellyfish lifespan depends on the species of jellyfish and can range from a few hours to several years. For instance, the lion's mane jellyfish has an average lifespan of one year, the moon jellies live for about 12-18 months, the flame jellyfish has a short lifespan of three months to a year, and the cannonball jellies are known to live for about three to six months in the wild. However, jellies may have a longer lifespan in captivity. The immortal jellyfish (Turritopsis dorhnii), a species of the jellies, has been observed to be immortal due to their ability to transform back to an earlier life stage and grow again, thus escaping death.

How do they reproduce?

Jellies transition between two distinct body forms - the polyp and the medusa. The polyps usually have tube-like bodies with one end attached to the substrate and the other end surrounded by the typical jellyfish tentacles. On the other hand, the medusa jellyfish are free-swimming with the characteristic umbrella-shaped body with tentacles on the edges.

The jellyfish life cycle is quite complicated with sexual as well as asexual phases. The medusa is the sexual phase in most cases. Reproduction in polyps takes place either by asexual budding or by the sexual formation of gametes (sperms and eggs). Fertilization of the eggs by the sperms leads to the formation of jellyfish larvae which subsequently develop into polyps, ephyrae, and finally form the adult medusa.

With an abundant supply of food in the environment, adult jellies spawn (release sperm and eggs) almost regularly. Jellies are mostly either male or female but hermaphrodites (produce both male and female gametes) exist as well. The mating behavior and fertilization of the eggs and the sperms differ with the species. Usually, adult jellies release the eggs and the sperms into the surrounding water where fertilization takes place. Subsequently, the larvae develop. In others, the sperms swim into the female's mouth and fertilization takes place inside the female's body. In moon jellies, the females have gastric pouches into which the sperms enter for subsequent fertilization.

What is their conservation status?

There has not been enough study on the jellyfish population around the world and as of now, they have not been accorded any conservation status in the International Union for Conservation of Nature (IUCN) Red List. However, there are many jellyfish across the planet so it can be assumed they would be in the Least Concern category. Though, certain rarer species are likely to be vulnerable.

Jellyfish Fun Facts

What do jellyfish look like?

The body of a jellyfish is radially symmetrical and comprises of the umbrella-shaped bell, oral arms, and stinging tentacles. In fact, the name 'jellyfish' is due to the jelly-like bell of these animals. The bell is basically a hollow structure made up of a transparent mesoglea and forms the hydrostatic skeleton (fluid pressure supported skeleton) of the jellies. The edges of the bell are adorned with several tentacles that radiate out on all sides and from underneath it radiate oral arms which contain the nematocysts or stinging cells.

The jellyfish has a single opening that serves both as the mouth and the anus and it opens into a central gastrovascular cavity in which digestion occurs and nutrients are absorbed. The bells may also have small radiating hair-like structures called cilia. While the umbrella-shaped medusa are free-floating, the polyps are tubular with tentacles on one end that are attached to a substrate. While some jellies are transparent and colorless to camouflage with the ocean water, others such as the deep sea jellyfish may be a dazzling orange or red in color. Bioluminescent jellyfish can produce green or blue light, a result of a complex biological phenomenon involving certain proteins in tissues.

Fun facts about jellyfish are informative as well.

How cute are they?

Jellyfishes do not really qualify as 'cute.' However, they definitely look extraordinarily beautiful, especially the bioluminescent or the brightly colored ones.

How do they communicate?

The jellyfish do not have brains. Instead, they have a network of neurons called the 'nerve net' that allows the animals to sense their surrounding water environment such as the presence of food or some predator. The nerve net is pretty unique because it has balance sensors called statocysts that help the animals to figure out whether they are facing up or down and light sensors called ocelli which can detect whether it is light or dark. Further, some jellyfish may have rhopalia, additional sensory structures that can detect chemicals, light, as well as movement. With respect to jellyfish eyes, it is worthwhile to mention that the box jellyfish have as many as 24 eyes per individual!

How big is a jellyfish?

The size of jellyfish varies and can range from a few millimeters to several feet in length. There are many candidates for the biggest jellyfish in the world, the most well-known being the lion's mane jellyfish (Cyanea capillata). It is indeed one of the largest jellyfish with a diameter that can go up to 6.5 ft (2 m) and tentacles as long as 120 ft (36.6 m). The smallest jellyfish is the Irukandji jellyfish with a diameter of 0.2-1 in (5-25 mm) and tentacles that go up to 3.3 ft (1 m) in length.

How fast can a jellyfish move?

Jellyfishes are efficient swimmers and typically swim at a rate of 47 in/min (2 cm/s).

How much does a  jellyfish weigh?

The largest jellyfish weighs about 330.7-440.9 lb (150-200 kg).

What are their male and female names of the species?

Male and female jellies do not have distinct names.

What would you call a baby jellyfish?

A baby jellyfish is the larval stage called planula.

What do they eat?

The jellyfish diet consists of fish eggs, fish larvae, small fish, crustaceans, and planktons.

Are they dangerous?

Jellyfish stings can be painful, but not every sting from a jellyfish is dangerous.

Would they make a good pet?

Keeping a pet jellyfish can be quite challenging. But, with proper care and the right environment (in a jellyfish aquarium) jellies can be good pets.

Did you know...

A jellyfish sting is painful because it pierces the skin and injects toxins, causing adverse reactions in humans.

A box jellyfish sting can be treated with 3% - 10% aqueous acetic acid (vinegar).

The blue button jellyfish is not a true jellyfish but a colony of polyps of the class Hydrozoa.

The blue bottle jellyfish, also known as the Portuguese man o' war or floating terror has a poisonous sting.

What is a group of jellyfish called?

A group of jellyfish is known by different names such as smack, bloom, and swarm.

Can a jellyfish kill you?

The fatality of jellyfish stings depends on the type of jellyfish. For example, stings from the box jellyfish, also known as the sea wasp, can be quite dangerous and even deadly. A box jellyfish sting is known to be the most fatal of all due to its potent venom.

Here at Kidadl, we have carefully created lots of interesting family-friendly animal facts for everyone to discover! Learn more about some other arthropods including sea snake, or water beetle.

You can even occupy yourself at home by drawing one on our jellyfish coloring pages.

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