What do jellyfish eat, what is their diet? Why are these animals dangerous? Jellyfish: a smart hunter, devoid of a brain What does a jellyfish eat

One of the most ancient living organisms that are found on our planet are jellyfish. They are present in almost any large body of salt water, so they can be found in almost all seas and oceans. What are the jellyfish of the Black Sea?

What are jellyfish?

As scientists say, jellyfish have existed on the planet for a very long time. They appeared before man arose. And during all this time their way of life has not changed. Even the appearance remained the same. Interestingly, the body of jellyfish is almost entirely composed of water. And to be more precise, 98% is water. Due to their appearance, some call them "water umbrellas", while others consider them "floating bells".

Due to their shape, these marine inhabitants can move very quickly in the water. Their muscles, which are watered connective tissue, begin to contract, which facilitates movement. In total, there are several thousand different types of jellyfish in the world. As for the Black Sea, there are only three types of such marine life. And every vacationer on the Black Sea coast immediately has a question: how dangerous are they, do they pose a threat, if not to human life, then to his health?

Jellyfish of the Black Sea: what is their danger to humans?

Any diver should take into account that there are several inhabitants in the Black Sea, a meeting with which is undesirable:

- medusa.

Although they do not pose a mortal danger, you should still beware of them. Why is a jellyfish dangerous, what troubles can you expect from it?

If we take into account all three types of jellyfish that live here, then their main weapon is stinging cells. They contain a special toxin. When it gets on the skin of a person, it can cause a kind of burn, something comparable to nettle. So after meeting with a jellyfish, although you won’t end up in a hospital bed, unpleasant memories will still be provided. Parents especially need to supervise their children. After all, jellyfish are often washed ashore by waves. And children have more sensitive skin than adults.

Types of jellyfish in the Black Sea

You need to know that most of the jellyfish on the Black Sea coast falls in the second half of summer. There are three varieties of them here, and each species has its own distinctive features. The description should begin with the jellyfish, which is most often found here.

1. Cornerot, which is called the Blue Jellyfish (Rhizostoma pulmo) for its appearance. It is believed that this is the most popular inhabitant of this sea. This is a marine predator that feeds not only on worms, but also on small fish. At first, he paralyzes them with his poison, and then calmly eats them. The jellyfish consists of an upper cap, reaching up to half a meter in size, as well as lower fleshy outgrowths. They act as the oral cavity. This is the most poisonous species of jellyfish that lives in the Black Sea. They are able to sting so that a tumor appears on the skin as from a thermal burn.

Medusa Cornerot
Photo: https://destepti.ro

2. Aurelia (Aurelia aurita), which poses little to no danger. Unless you try what this jellyfish tastes like. The skin will not feel contact with it, but a slight burning sensation and redness will appear on the mucous membrane. Most of these jellyfish appear just at the height of the swimming season. The diameter of their dome can reach up to 40 cm.

Medusa-Aurelia. Photo: http://fr.academic.ru

3. Mnemiopsis (Mnemiopsis leidyi) has absolutely no stingers or even tentacles. In fact, this jellyfish appeared here from afar - from the coast of America. But it has taken root here and now it is considered a semi-indigenous inhabitant of the Black Sea. This jellyfish is completely harmless to humans. Today, everything is being done to reduce its population.

Everyone who swam in the sea at least once saw jellyfish. These are extraordinary creatures, as if they came to us from fairy tales. How do they live, so light and airy, because you can see through them? We want to talk about what jellyfish eat, how their body is arranged and why they are dangerous.

What is a jellyfish made of?

Medusa is a very ancient animal, representing the next phase of the life cycle of cnidarian (aquatic multicellular animals) from the subtype medusozoa.

Looking at this creature, it seems that it is just water in an incomprehensible shell. In part, this is true. The gelatinous body of a creature 98% water covered with connective tissue similar to our skin. On its surface are sensitive little bodies that serve as a kind of sensors that can perceive the environment and its impulses, for example, light or vibrations around.

Of the organs, the stingers have:

Stomach;
Intestines;
mouth opening;
Eyes (different number).

And mouth lobes containing a scalding substance that is used for defense and food extraction.

The animal moves using its domed shape. It allows, by muscle contraction, to throw out bundles of water from under it, which push the hostess like a jet engine. But, despite this, even the largest individuals cannot resist the sea currents and always move with it.

How and what does it eat in the sea?

Jellyfish are intestinal and invertebrate creatures. This means that they are deprived of some specialized organs, including excretory organs. Food enters through the mouth opening, is digested here with the help of glandular cells, and the remains are excreted back in the same way, that is, in a vicious circle - through the mouth.

What is included in their diet? This predators, they eat small marine life:

Worms;
Plankton;
caviar;
crustaceans;
Sometimes even weaker brothers.

In this they are helped by tentacles equipped with stinging poisonous cells that paralyze the victim. They put food in their mouths.

Hunting tactics for different jellyfish are different. Some species pass water through themselves like a filter, leaving what they need. Others wait for the prey to swim up and grab it.

What do scyphoid jellyfish eat?

Scyphoid- marine organisms from the same type of striding, some of which reach very large sizes. Usually these are the very creatures that are shown in the programs, big bright and colorful.

In our country, scyphoid jellyfish are rare, but three species have been seen:

eared;
Lion's;
Cornerot.

Some of them were about a kilometer long.

Scyphoid - passive hunters, they wait for prey to swim up. Any living creature passing through the tentacles activates the work of poisonous cells. There is a release of toxins that paralyze the victim and kill her.

The main food resource of scyphoid is zooplankton - small crustaceans, animal larvae, fish eggs.

Is it possible to keep them in an aquarium and what to feed them?

Until recently, this was not possible. Animals died in conventional aquariums. But progress does not stand still. Carousel-type aquariums or "jellyfish tanks" appeared on the market. The principle of their operation is based on the fact that water does not stand still, but constantly rotates. In such a device, this creature has the ability to hang on the stream, not sink to the bottom and not float up.

The main thing that breeders should know about jellyfish is:

That the flow rate should be comfortable for the animals so that they do not sink or float;
That there should not be aeration. Air bubbles can harm the inhabitants, they accumulate under the body-dome and throw them up.

Feed your pets in a variety of ways. To do this, use special vitamin supplements. You can take minced seafood from the store and pour it into the water.

Why are jellyfish dangerous?

Everyone knows that some species can harm humans. While swimming, touching the stingers, you can get a severe burn and more.

In our country, there are also such, although in smaller quantities than in other seas:

Cornerot- the largest representative living in the Black Sea. Its lacy lobes are abundantly supplied with stinging cells. For humans, they do not pose a great danger. Only people with individual sensitivity to touch can develop burns that look like a "bite" of nettles. That is why it is sometimes called "sea nettle";
hairy cyanoea- Found in the Pacific. Her bell-shaped body has a variety of colors with a predominance of red tones. The long tentacles are a dense network densely packed with poisonous cells. Their toxins are capable of quickly killing small fish. For humans, they are not so dangerous, but her bite is felt on the skin, can cause allergies;
Gonionema - found in the Sea of Japan. A small inhabitant, through whose transparent umbrella one can see the drawing of a cross. The defeat of its cells is not fatal, but very painful. There are cases when people could not do without the help of doctors. This is due to the effect of the poison on the nervous system. The person may lose sensation in the limbs or have trouble breathing.

These are all representatives of the aspirants who can somehow cause harm. The rest are dangerous only for the inhabitants of the sea.

How to treat bites?

But, if this nevertheless happened and you were stung by a jellyfish, proceed as follows:

Wash off toxic substances with water;
Do not scratch or touch the bite site;
Apply cold or make a lotion. For this, apple cider vinegar or ammonia is suitable;
Take antihistamines;
Apply a remedy for insect bites or "Fenistil-gel", "Psilo-balm" on the wound;
Drink plenty of fluids;
Be sure to see a doctor.

Yes, the poisons of the animals living in our seas are not lethal. But be careful, they can cause severe allergies. Watch the victim closely for the first day, especially if it is a child.

Surprisingly, these beautiful creatures are real predators. Now, knowing what jellyfish eat, you can safely tell your friends about it. This animal is not just a bag of water, as some make them out to be. It is an organism that eats other animals. And sometimes their own kind.

Jellyfish feeding video

In this video, oceanologist Roman Vorotnikov will show how jellyfish feed in an aquarium:

The text of the work is placed without images and formulas.
The full version of the work is available in the "Job Files" tab in PDF format

Introduction.

Every person who has ever been to the sea has seen jellyfish. These unusual marine inhabitants leave no one indifferent, causing a variety of emotions from admiration and delight to disgust and fear.

I'm not an exception. Living in the Urals, jellyfish seemed to me to be mystical creatures that came to us from another world. So it is, they are from another world, from the underwater, so mysterious and alluring.

Jellyfish can be found in every sea, in every ocean, on the surface of the water or many kilometers deep. Even fresh jellyfish exist.

Problem. What do we know about the life of jellyfish? What do they eat? How are they arranged? Who eats them? Why are they?

Target. The answers to these questions will be covered in this work.

Solution. While searching for additional information, I came across many facts that were previously unknown.

Who is this medusa?

Jellyfish is an invertebrate animal belonging to the type Coelenterates.

Jellyfish are the oldest animals on the planet, their history goes back at least 650 million years. They appeared in the world long before crocodiles, dinosaurs, and sharks. In nature, there are over 200 species of jellyfish, but even now, the appearance of new ones, previously unfamiliar to mankind, is recorded annually.

Jellyfish can be both very large and very small. Both giant species with a dome diameter of more than 2 m, and tiny ones with a dome the size of a match head are described.

Despite their vulnerability and deceptive primitiveness, jellyfish exist quietly in the difficult conditions of the ocean. There are species that live at a depth of up to 10 km. But most of the jellyfish live at shallow depths. Large clusters of jellyfish are called "swarm" or "bloom".

The structure of the medusa.

At first glance, this is a completely shapeless and rather primitive animal. But in reality, everything is much more complicated. Jellyfish have a unique structure. Jellyfish tissue cells perform various functions. Jellyfish are made up of only three types of tissue. The ectoderm is the outer layer, the endoderm is the inner layer and the connective colorless adhesive tissue is the cerebellum. The body of a jellyfish consists of a jelly-like bell, tentacles and mouth cavities used to eat prey.

Fig1. Diagram of the structure of a jellyfish in a longitudinal section.

Jellyfish don't need a respiratory system. Medusa breathes with the whole body. It is able to absorb oxygen and release carbon dioxide.

The jellyfish has no brain, no heart, no bones. Some jellyfish have the ability to distinguish between obstacles, light, which can be equated with vision, but jellyfish do not have eyes as such. 24 sensitive little bodies (ropalia) protrude along the perimeter of the body, or they are also called "eyes", perceiving various impulses of the environment. It remains a mystery how jellyfish react to stimuli - danger, food, without having a brain to process these impulses.

The mouth opening serves the jellyfish both for eating food and for removing its remains. The remains of food, not fully digested, are excreted through the same hole.

More than 90% of a jellyfish is water. Therefore, if she is taken out of her usual habitat, she will soon die, since all the water in her body will evaporate.

Jellyfish food.

Despite their harmless appearance, jellyfish are wonderful hunters. Near the mouth opening, jellyfish have tentacles with stinging cells, with which they catch their prey. Inside each cage is a small harpoon. As a result of touch or movement, he straightens up and shoots at prey, injecting poison into it. The degree of toxicity of this toxin depends on the type of jellyfish. Jellyfish feed on plankton, fish, crustaceans or other jellyfish. The victim depends on the size of the jellyfish.

The jellyfish uses the same stinging cells for its defense, stinging a potential enemy. Reactions to poison can also be different: from a small rash to death.

Life cycle of jellyfish.

Jellyfish reproduce sexually. After the merger of the male and female, a larva is formed - a planula, settling at the bottom. A polyp grows out of the planula. When the polyp reaches full maturity, young jellyfish break away from it by budding.

Fig.2 The life cycle of a jellyfish. 1-11 - asexual generation (polyp);

11-14 - sexual generation (jellyfish).

Some female jellyfish can produce up to 45,000 planulas per day.

Jellyfish have a short life cycle. The most tenacious species live up to 6 months. These creatures usually die in sea waters or fall prey to other predators. But there are among the jellyfish and centenarians. For example, the species Turritopsis dohrnii are considered immortal, because they can turn into a sessile form of a polyp and back into a jellyfish.

Fig.3 Immortal jellyfish Turritopsis dohrnii.

Medusa locomotion.

Basically, jellyfish drift in the water column, carried away by the current. They can also actively swim, due to the muscular contractions of the bell. When the bell contracts, the water is thrown back and the animal moves forward.

Some jellyfish swim on their own, while others attach themselves to other objects, such as seaweed.

Fig.4 1-The bell is relaxed, flattened and ready to start a new movement. 2-The bell contracts, pushing out the water. 3-The bell is completely reduced, only a little water remains under it.

With the help of special bags located on the rim of the bell, jellyfish perfectly balance in the water. When the body of the jellyfish rolls over on its side, the bags cause the nerve endings to contract the muscles, and the body of the jellyfish straightens out.

Who from the animal kingdom eats jellyfish.

The sunfish and leatherback turtle are the most dangerous predators that feed on jellyfish. Scientists still do not know how turtles and fish can eat jellyfish along with poisonous tentacles without harming themselves.

Fig.5 Leatherback turtle hunting.

Fig.6 Fish-moon.

But these are not all predators that eat jellyfish as food. The structural features of the beak of the albatross allow it to hold slippery jellyfish. It eats only some harmless species.

Fig.7 Albatross.

The most dangerous jellyfish.

The most dangerous jellyfish is considered sea wasp (box jellyfish). Its toxins, located in stinging cells, are the fastest acting. The sting of a sea wasp can kill in 3 minutes. In a year, the sea wasp kills more people than any of the sea creatures. The venom of a sea wasp is enough to kill 60 people.

Fig.8 The box jellyfish is also known as the sea wasp.

The box jellyfish has the shape of a bell or a cube and is divided into segments. It was the cubic shape that gave the name "box". The box jellyfish has a transparent body of pale blue color, which can grow up to 20 cm and have a mass of 20 kg. A box jellyfish can have up to 15 tentacles on each side of the cube. These tentacles can reach a length of up to 3 m and are covered with stinging cells. Up to 5,000 of these cells can grow on each tentacle. The box jellyfish uses its tentacles to catch prey, such as small fish or crustaceans. Box jellyfish, unlike many other jellyfish, have four eyes. The sea wasp can swim at up to four knots (7.408 km/h).

Stinging cells release their venom when they detect the presence of certain chemicals, not when they come into contact with an object. Only in the presence of the right substances, such as human skin or fish scales, does the stinging cell immediately release poison into the victim's body.

Sea wasp stings can cause excruciating pain to humans. The tentacles stick to the skin and cannot be peeled off while they are still alive. The pain can last for weeks if left untreated, and the injection often leaves a scar. A sea wasp sting can be treated with vinegar by applying it to the remaining tentacles on the skin. This kills the tentacles and allows them to be safely retrieved. After a bite, you need to immediately get the help of doctors, as the right treatment and antidote are needed. Bites can lead to respiratory spasm or arrhythmia.

The wasp jellyfish is a real problem in Australia. where there is a jellyfish invasion season, which lasts from October to April.

Sea wasps are usually found in calm waters, so swimming and other water activities are not recommended. An ordinary wetsuit is not able to protect against the sting of sea wasps, you need a special suit with protection against them. People who can't afford such a suit have come up with their own trick: a sea wasp can't sting through nylon stockings. For this reason, you can often find Australian rescuers in stockings on their legs and arms. But a sea wasp can still sting on the head or neck if they are not well protected.

The biggest jellyfish.

The largest species of jellyfish is called Lion's Mane or Hairy Cyanea.

Fig. 9 Medusa Lion's mane.

These jellyfish got their name from their huge, entangled tentacles, which actually resemble a lion's mane. The habitat of this jellyfish is limited to the cold waters of the Arctic, North Atlantic and Pacific Oceans. Jellyfish of the same species live near Australia and New Zealand.

The largest specimen of a lion's mane, officially registered by scientists, was washed ashore by the surf. It was found in Massachusetts Bay in 1870. The bell had a diameter of 2.29 meters, and the tentacles were 37 meters long - that is, more than the length of a huge blue whale.

Jellyfish Lion's Mane vary greatly in size. Those of them that live in warmer latitudes grow to a modest size (their domes rarely exceed 50 centimeters in diameter), compared with their northern counterparts. The tentacles of huge individuals can stretch up to 30 meters or even more. These organs are very sticky and are grouped into eight clusters, each containing over a hundred tentacles. The bell itself is divided into eight parts, which makes it look like an eight-pointed star. Those tentacles that can be called the weapon of a jellyfish are defiantly tangled and brightly colored, while hiding in the center of the bell. In addition, poisonous goads are much shorter than the silvery, thin tentacles located at the edges of the bell. The size of the giant cyanide also affects the color of the jellyfish: larger specimens also have a brighter color - crimson or dark purple, but smaller animals have a lighter or orange color.

Medusa Nomura is the misfortune of humanity.

Medusa Nomura (lat. Nemopilema nomurai) reach impressive sizes.

Fig. 10 Medusa Nomura.

Growing up to 2 meters in diameter and weighing about 220 kg, the Nomura jellyfish lives mainly in the waters between China and Japan, mainly in the central Yellow Sea and the East China Sea.

Currently, the number of Nomura jellyfish in the world is growing. Scientists consider climate change, overexploitation of water resources and environmental pollution as possible causes of population growth.

Jellyfish Nomura has become a real "plague" of the Sea of Japan from 2005 to the present. A large number of jellyfish disrupt the fish balance, which is a consequence of the decline of the fishing industry. In addition, more than one Japanese fishing boat has been sunk off the coast of Japan when the ship's crew tried to lift fishing nets filled with many giant jellyfish.

In the modern world, there is an active catch of Nomura jellyfish in order to "cleanse" the sea from these dangerous giants, since the fish is inedible after being hit by poisonous bites, and there are also accidents with fishermen.

Fig. 11 Medusa Nomura in fishing nets, instead of fish.

The use of jellyfish by humans.

Mankind has learned to use jellyfish for its own benefit.

Some types of jellyfish are an excellent source of protein, which can play a big role in defeating hunger and malnutrition in the poor countries of the world. In some countries, such as Japan and China, jellyfish are a delicacy. Jellyfish, if dried, deteriorate in just a few hours, while in a dried state it can be stored for weeks.

Fig. 12 Eating jellyfish: harvesting, drying, selling.

Analyzing interesting facts about jellyfish, the researchers came to the conclusion that jellyfish can help a person in the fight against stress. For these purposes, they began to breed jellyfish in an aquarium. The slow and smooth movements of jellyfish have a calming effect on a person.

Fig.13 Jellyfish in aquariums.

Currently, scientists are developing to extract such medicinal substances from jellyfish that can help humanity in the fight against cancer and diabetes.

Conclusion.

So who are these jellyfish? Friends of fish that are susceptible to their poison - they can hide among their tentacles. Could this be a threat to fisheries in China and Japan? The misfortune of mankind or its salvation?

One thing is clear, these unique animals will surprise us for decades.

Personally, the question of studying jellyfish is very interesting to me. And I will definitely look for new information about these amazing animals.

Bibliography.

Henderson K. A book about the most unimaginable animals. - M.: Dynasty, 2015. - p.

Francis P. Ocean. Earth's last secret has been revealed. - M.: Publishing house AST Astrel, 2007. - 512 p.

Baranovskaya I.G. Undersea world. - M.: AST Publishing House, 2015.—159 p.

Koshevar D.V., Likso V.V. The whole underwater world. - M.: AST Publishing House, 2015. - 239 p.

Tikhonov A.V. Ocean life. - M.: AST Publishing House, 2016. - 221 p.

Abramovich A.I. etc. Complete encyclopedia of the schoolboy. - M.: ROSMEN, 2014. - 608 p.

http://aqinfo.ru

http://terramia.ru-- Internet magazine.

http://www.medusy.ru

http://www.nkj.ru- information portal Science and Life.

Jellyfish Invasion Documentary Director: Peter Yost. - National Geographic Television Production, 2007.

Documentary "Jellyfish Monsters" - National Geographic Television Production, 2010.

Among the most unusual animals on Earth, jellyfish are also among the oldest, with an evolutionary history dating back hundreds of millions of years. In this article, we bring you 10 essential facts about jellyfish, from how these invertebrates move through the water column to how they sting their prey.

1. Jellyfish are classified as cnidarians or cnidarians.

Named after the Greek word for "sea nettle," cnidarians are marine animals characterized by a jelly-like body structure, radial symmetry, and cnidocyte stinging cells on their tentacles that literally explode when they capture prey. There are about 10,000 species of cnidarians, about half of which are coral polyps, and the other half include hydroids, scyphoids, and box jellyfish (a group of animals that most people call jellyfish).

Cnidaria are among the most ancient animals on earth; Their fossil roots go back almost 600 million years!

2. There are four main classes of jellyfish

Scyphoid and box jellyfish - two classes of cnidarians, including classic jellyfish; the main difference between the two is that box jellyfish have a bell-like cube shape, and are slightly faster than scyphoid jellyfish. There are also hydroids (most of which do not go through the polyp stage) and staurozoa - a class of jellyfish that lead a sedentary lifestyle, attaching to a hard surface.

All four classes of jellyfish: scyphoid, cubomedusa, hydroid and staurozoa belong to the cnidarian subtype - medusozoa.

3. Jellyfish are one of the simplest animals in the world.

What can you say about animals without central nervous, cardiovascular and respiratory systems? Compared to animals, jellyfish are extremely simple organisms, characterized mainly by undulating bells (which contain the stomach) and tentacles with many stinging cells. Their almost transparent bodies consist of only three layers of the outer epidermis, the middle mesogley, and the inner gastroderm and water make up 95-98% of the total, compared to 60% in the average person.

4. Jellyfish form from polyps

Like many animals, the life cycle of jellyfish begins with eggs, which are fertilized by males. After that, things get a little more complicated: what emerges from the egg is a free-swimming planula (larva) that looks like a giant shoe ciliate. Then, the planula attaches itself to a hard surface (seabed or rocks) and develops into a polyp that resembles miniature corals or sea anemones. Finally, after several months or even years, the polyp detaches and develops into an ether that grows into an adult jellyfish.

5. Some jellyfish have eyes

Kobomedusas have a couple of dozen photosensitive cells in the form of an eye spot, but unlike other sea jellyfish, some of their eyes have a cornea, lenses and retinas. These compound eyes are arranged in pairs around the circumference of the bell (one pointing up and the other down, providing a 360-degree view).

The eyes are used to search for prey and protect against predators, but their main function is the correct orientation of jellyfish in the water column.

6. Jellyfish have a unique way of delivering venom

As a rule, they release their poison during a bite, but not jellyfish (and other coelenterates), which in the process of evolution have developed specialized organs called nematocysts. When the jellyfish's tentacles are stimulated, the stinging cells create enormous internal pressure (about 900 kg per square inch) and they literally explode, piercing the skin of the unfortunate victim to deliver thousands of tiny doses of poison. The nematocysts are so powerful that they can be activated even when the jellyfish is washed ashore or dies.

7. Sea wasp - the most dangerous jellyfish

Most people are afraid of poisonous spiders and rattlesnakes, but the most dangerous animal on the planet for humans may be the species of jellyfish - the sea wasp ( Chironex fleckeri). With a bell the size of a basketball and tentacles up to 3m long, the sea wasp prowls the waters off Australia and Southeast Asia and has killed at least 60 people in the last century.

A slight touch of the tentacles of a sea wasp causes excruciating pain, and closer contact with these jellyfish can kill an adult in a couple of minutes.

8 Jellyfish move like a jet engine

Jellyfish are equipped with hydrostatic skeletons, invented by evolution hundreds of millions of years ago. In essence, the jellyfish bell is a fluid-filled cavity surrounded by circular muscles that squirt water in the opposite direction of travel.

The hydrostatic skeleton is also found in starfish, worms, and other invertebrates. Jellyfish can move along with ocean currents, thereby saving themselves from unnecessary effort.

9. One species of jellyfish may be immortal

Like most invertebrates, jellyfish have a short lifespan: some smaller species only live for hours, while the largest species, such as the lion's mane jellyfish, can live for several years. It is debatable, but some scientists claim that the species jellyfish Turritopsis dornii immortal: adults are able to revert to the polyp stage (see point 4), and thus an infinite life cycle is theoretically possible.

Unfortunately, this behavior has only been observed in laboratory conditions, and Turritopsis dornii can easily die in many other ways (for example, becoming a dinner for predators or being washed up on the beach).

10. A group of jellyfish is called a "swarm"

Remember the scene from the cartoon Finding Nemo where Marlon and Dory have to make their way through a huge cluster of jellyfish? From a scientific point of view, a group of jellyfish, consisting of hundreds or even thousands of individuals, is called a "swarm". Marine biologists have noticed that large aggregations of jellyfish are becoming more common and may serve as an indicator of marine pollution or global warming. Swarms of jellyfish tend to form in warm water, and jellyfish are able to thrive in anoxic sea conditions that are not suitable for other invertebrates of this size.

Paula Weston

She has no heart, no bones, no eyes, no brain. It is 95% water, but it remains the most active marine predator.

This unusual creature is a jellyfish, an invertebrate animal belonging to the phylum Coelenterates (the same type as corals).

The body of a jellyfish consists of a jelly-like bell, tentacles and mouth cavities used to eat prey. Medusa got its name due to the resemblance to the mythical Gorgon Medusa, who had snakes sticking out of her head instead of hair.

There are more than 200 species of jellyfish (class Cubomedusa) of different sizes: from tiny Caribbean jellyfish to Arctic cyanides, the bell of which reaches 2.5 m in diameter, the length of the tentacles is approximately 60 m (2 times longer than the blue whale), and the weight is more than 250 kg.

How jellyfish move

Some jellyfish swim using jet propulsion, while others attach themselves to other objects, such as seaweed. Despite the use of jet propulsion, jellyfish are still not good enough swimmers to overcome the force of waves and currents.

The reactive movement of the jellyfish is due to the presence of coronal muscles lining the lower part of its bell. When these muscles push water out of the bell, recoil occurs, pushing the body in the opposite direction.

The jellyfish has no brain or eyes, so it relies entirely on nerve cells to help it move and respond to food and danger. The sense organs tell the jellyfish in which direction to move, and also determine the source of light.

Hunters

Despite their harmless appearance, jellyfish are wonderful hunters. They sting and kill their victims with special stinging cells, nematocysts. Inside each cage is a small harpoon. As a result of touch or movement, he straightens up and shoots at prey, injecting poison into it. The degree of toxicity of this toxin depends on the type of jellyfish. Reactions to poison can also be different: from a small rash to death.

Jellyfish do not prey on humans. They prefer to feed on microscopic organisms, fish and other jellyfish. People can only be accidentally harmed when jellyfish enter the coastal zone.

A jellyfish floating in the open sea can be both a predator and a prey. Due to its transparency, it is perfectly camouflaged and almost invisible in the water. This is important, because, despite the jet propulsion, these organisms are entirely at the mercy of the current, and in the open sea, as you know, there is nowhere to hide.

Life cycle

The beginning of the life cycle of jellyfish is very similar, although not completely, to the beginning. The larvae swim in the water until they find a hard surface (stone or shell) on which they attach. The attached larvae grow and transform into polyps, which at this stage resemble sea anemones.

Then horizontal grooves begin to form in the polyps. They deepen until the polyp turns into a stack of individual, pancake-like polyps. These flat polyps break off the stack one by one and float away. From this point on, the breakaway polyp looks like an adult jellyfish.

Jellyfish have a short life cycle. The most tenacious species live up to 6 months. These creatures usually die in sea waters or fall prey to other predators. Moonfish and leatherback turtles are the most dangerous jellyfish predators (Researchers do not know how turtles and fish can eat jellyfish along with poisonous nematocysts without harming themselves).

Despite their incredible fragility, jellyfish are quite complex. Respiration of these intestinal cavities is carried out through the entire surface of the body. It is able to absorb oxygen and release carbon dioxide.

Other "jellyfish"

Many other creatures live in the sea, which, although they are called jellyfish, are not. One of these species is very similar to a jellyfish.

Ctenophores look and act like jellyfish but are not "true jellyfish" because they do not have stinging cells. Jellyfish inhabit the seas and oceans around the world. Most often they live in coastal areas, although deep-sea species are also known to produce fantastic light through bioluminescence.

Evolutionary mystery

Given the complexity of the anatomical structure and the way these sea creatures hunt, it is difficult to imagine how transitional forms between non-jellyfish and modern jellyfish could survive. Jellyfish appear in the fossil record suddenly and without transitional forms.

All the features of a jellyfish are important for survival: sacs that help them swim in the right direction, sensory organs that warn them of the approach of a predator or prey, and stinging nematocysts. Therefore, it is quite logical to conclude that any transitional form, devoid of these fully developed characters, would quickly lead to the extinction of the species. Evidence indicates that jellyfish have always been jellyfish since they were created by God on Day 5 of Creation Week (Genesis 1:21).