Jellyfish

Almost transparent, they drift through the sea and consist almost exclusively of water: jellyfish are among the strangest animals on earth.

Characteristics

What do jellyfish look like?

Jellyfish belong to the cnidarian phylum and subdivision of coelenterates. Your body consists of only two layers of cells: an outer one that covers the body and an inner one that lines the body. There is a gelatinous mass between the two layers. This supports the body and serves as storage for oxygen. The body of a jellyfish is 98 to 99 percent water.

The smallest species measure a millimeter in diameter, the largest several meters. Jellyfish usually look umbrella-shaped from the side. The stomach stick protrudes from the bottom of the umbrella, on the underside of which is the mouth opening. The tentacles are typical: Depending on the species, they are a few centimeters up to 20 meters long. They are used by the jellyfish to defend themselves and catch their prey.

The tentacles are equipped with up to 700,000 stinging cells, from which the animals can release a paralyzing poison. Jellyfish don’t have a brain, only sensory cells located in the outer cell layer. With their help, the jellyfish can perceive stimuli and control their actions and reactions. Only some types of jellyfish, such as the box jellyfish, have eyes.

Jellyfish have a very good ability to regenerate: if they lose a tentacle, for example, it grows back completely.

Where do jellyfish live?

Jellyfish can be found in all oceans of the world. The colder a sea is, the fewer different jellyfish species there are. The most poisonous jellyfish live mainly in tropical seas. Jellyfish live only in water and almost exclusively in the sea. However, some species from Asia are at home in freshwater. Many jellyfish species live in the uppermost layers of water, while the deep-sea jellyfish can be found at depths of up to 6,000 meters.

What types of jellyfish are there?

About 2,500 different species of jellyfish are known to date. The closest relatives of jellyfish are, for example, sea anemones.

How old do jellyfish get?

When jellyfish have produced offspring, their life cycle is usually complete. The tentacles recede and all that is left is a jelly disc, which is eaten by other sea creatures.

Behavior

How do jellyfish live?

Jellyfish are among the oldest creatures on earth: they have been inhabiting the seas for 500 to 650 million years and have hardly changed since then. Despite their simple physique, they are true survivors. Jellyfish move by contracting and releasing their umbrella. This allows them to move upwards at an angle, similar to squid, using a kind of recoil principle. Then they sink back down a bit.

Jellyfish are very exposed to ocean currents and often let themselves be carried along by them. The fastest jellyfish are the cross jellyfish – they move back at up to 10 kilometers per hour. Jellyfish hunt with their tentacles. If prey gets caught in the tentacles, the stinging cells “explode” and hurl tiny needles into their victim. The paralyzing nettle poison gets into the prey through these tiny poisonous harpoons.

The whole process happens at lightning speed, it only takes a hundred-thousandth of a second. If we humans come into contact with a jellyfish, this nettle poison burns like stinging nettles, and the skin turns red. With most jellyfish, such as stinging jellyfish, this is painful for us, but not really dangerous.

However, some jellyfish are a danger: for example the Pacific or the Japanese compass jellyfish. The most poisonous is the Australian sea wasp, its poison can even kill people. It has 60 tentacles that are two to three meters long. The poison of the so-called Portuguese galley is also very painful and sometimes deadly.

If you come into contact with a jellyfish, you should never clean your skin with fresh water, otherwise, the nettle capsules will burst open. It is better to treat the skin with vinegar or to clean it with damp sand.

Friends and foes of jellyfish

The natural enemies of jellyfish include various sea creatures such as fish and crabs, but also hawksbill turtles and dolphins.

How do jellyfish reproduce?

Jellyfish reproduce in different ways. They can reproduce asexually by shedding parts of their bodies. The whole jellyfish grow from the sections. But they can also reproduce sexually: Then they release egg cells and sperm cells into the water, where they fuse with each other. This gives rise to the planula larva. It attaches itself to the ground and grows into a so-called polyp. It looks like a tree and consists of a stalk and tentacles.

The polyp reproduces asexually by pinching off mini jellyfish from its body, which grows into jellyfish. The alternation of sexual and asexual reproduction is called the alternation of generations.

Care

What do jellyfish eat?

Some jellyfish are carnivores, others like cross jellyfish are herbivores. They usually feed on microorganisms such as algae or animal plankton. Some even catch fish. The prey is paralyzed by the jellyfish’s nettle venom and then transported into the mouth opening. From there it gets into the stomach. This can be seen in the gelatinous mass of some jellyfish. It is in the form of four horseshoe-shaped semicircles.

Keeping of jellyfish

Jellyfish are very difficult to keep in aquariums as they always need a water flow. Water temperature and food must also be just right for them to survive.