Type Coelenterates(Coelenterata), as well as sponges, the oldest of the multicellular organisms, are known from the Vendian (Vendian - the last epoch of the Proterozoic), in the Ordovician of the Paleozoic they were already represented by numerous groups. Coelenterates are predominantly marine, solitary or colonial organisms, characterized by two life forms: attached polyp and free-floating jellyfish. In many coelenterates, both forms alternate during the life cycle ( metagenesis), some coelenterates (hydra, coral polyps) do not have jellyfish, others (certain species of scyphoid jellyfish) have lost the generation of polyps.

The body of an individual coelenterate consists of two layers of tissue - ectoderm And endoderm, between which there is a layer of gelatinous mesoglea. The ectoderm consists mainly of epithelial-muscular cells, combining integumentary and motor functions, from those characteristic of coelenterates stinging cells, forming stinging capsules (nematocysts), and undifferentiated cells, giving rise to cells of all types. In the endoderm, in addition to epithelial-muscular and stinging cells, there are glandular digestive cells. Intestinal cavity, or gastric cavity, simple or divided into chambers (in polyps) or canals (in jellyfish). Mouth, surrounded tentacles, serves to capture food, as well as to remove undigested residues. Digestion is cavity and intracellular. Nervous system diffuse type. Jellyfish, in addition, have two

Drawing. Stinging cells characteristic only of Coelenterates.

nervous rings and sense organs - either photosensitive eyes, or statocysts, and in scyphojellyfish - Rhopalia.

Reproduction is sexual and asexual. Incomplete asexual reproduction in a number of species leads to the formation of large colonies. Many coelenterates are dioecious, some are hermaphrodites. In hydroids, reproductive products develop in the ectoderm, and in scyphoid and coral polyps, in the endoderm, after which they are released into the external environment, where fertilization occurs. A free-swimming larva develops from a fertilized egg - planula. A polyp (less commonly a jellyfish) is formed as a result of metamorphosis of the planula. Jellyfish usually bud on the body of polyps. In some species, development occurs in the mother's body, and young individuals are excreted through the mouth.

There are about 9 thousand species of modern coelenterates and about 20 thousand extinct species. Coelenterates are found in all seas, from the surface to extreme depths and on the bottom. There are freshwater species (hydra). All coelenterate predators feed on plankton and larger aquatic organisms, some are food competitors of fish, and some serve as food for other organisms.

Type Coelenterates are divided into 3 classes.

Class 1. Hydroid polyps, or Hydrozoans (3 thousand species). The most famous among hydroid polyps is Hydra. This is a small (up to 1-3 cm) polyp found in our fresh water bodies. It leads a sessile lifestyle, attaching itself to the substrate with its base, or sole. At the free end of the body there is a mouth opening, surrounded by a corolla of 6-12 tentacles, on which the bulk of the stinging cells are located. Hydra feeds mainly on small crustaceans - daphnia and cyclops. Reproduction occurs by both sexual and asexual (budding) methods. In the first case, a new hydra develops from a fertilized egg after a period of rest (in winter).

However, most hydroid polyps, unlike hydra, lead not a solitary, but a colonial lifestyle. At the same time, in such colonies special mobile individuals arise and bud off - the very jellyfish that are responsible for the dispersal of polyps. Jellyfish actively move and release mature germ cells into the environment. The larva that has developed from a fertilized egg also moves in the water column for some time, and then sinks to the bottom and forms a new colony.

The class Hydroid polyps from the subclass Siphonophora includes very interesting colonial animals from the genus Physalia. These are marine organisms that live mainly in the southern seas. Although outwardly Physalia looks like a solitary animal, but is actually a colony of organisms. In this colony, individual individuals are attached to a single trunk, in which a common gastric cavity is formed, communicating with the gastric cavity of each individual. The upper end of the trunk is swollen, this swelling is called air bubble, or a sail, or a float. The air bubble is one highly modified medusoid individual. Along the edges of the hole leading into the cavity of the bladder, a closing muscle is formed: the bladder can release gas from the hole (it is secreted by the glandular cells of the bladder, its composition is close to air), and thanks to this, Physalia capable of floating to the surface or sinking into the depths. Below the bladder there are other individuals specialized in feeding or reproduction, and there are also individuals with particularly abundant stinging tentacles. One of the most common physalia of the Pacific Ocean ( Physalia utriculus) one of the tentacles, the so-called lasso, longer than all the others, and can reach 13 or more meters in length. Along it are located thousands of stinging batteries, each of which consists of hundreds of microscopic stinging cells. When a fish encounters a tentacle, threads of stinging cells pierce the tissues of the victim, and the poison from the capsules is pumped through these channels. Thus, the lasso captures and paralyzes fairly large prey, and then pulls it towards the mouth.

If Physalia will sting a person who accidentally touches it, the consequences can be very serious. Burns Physalia are very painful, blisters appear on the victim’s skin, the lymph glands become enlarged, sweating increases, nausea appears, and it becomes difficult for the person to breathe.

A close relative of Physalia is interesting - Portuguese warship(Physalia physalis). It is found in the tropical Atlantic, Caribbean waters and Mediterranean Sea. Similar species of physalia live off the Hawaiian Islands and off the coast of southern Japan. Portuguese man of war got its name from its bright, multi-colored floating air bubble, reminiscent of the sail of a medieval Portuguese ship. Its ridged air bladder, approximately 35 cm long, is very colorful. The membrane of the bladder is colored iridescent blue, turning into mauve and then, at the top of the ridge, into pink (you have to imagine it). Boat colonies look like unusually elegant balls, often drifting in whole clusters on the surface of the ocean. From time to time, the boat dips its bladder in water so that the membrane does not dry out. Deadly poisonous tentacles stretch 10-15 m down from the bubble, capable of paralyzing even very large fish and pulling it up to the mouth opening. One researcher talked about his meeting with this cute boat: "...without thinking, I grabbed it, and roared in pain, frantically began to wash my fingers with sea water, but the sticky mucus did not lag behind. An attempt to wash off the mucus with soap was also unsuccessful. My hands burned and ached, my fingers bent with difficulty. Spraying with an anesthetic medicine from a special The atomizer relieved the pain for a few minutes, but it immediately returned with renewed vigor. The fingers could no longer bend, the pain began to spread to the shoulders and further to the heart area, the general state of health was disgusting. I took two tablets of analgin, validol, pyramidon, and, as they say, I fell into bed. I was shaking with chills... It subsided gradually. At first my right hand felt better, then my left one. The pain subsided only after five hours.

Drawing. Colonial hydroid polyps Physalia (with fish)

and Portuguese Man of War (right).

Although physalia are inhabitants of the open ocean, many of them, under appropriate currents and weather conditions, are carried to the shores of Northwestern Europe. Even washed ashore, they retain the ability to sting anyone who touches them. Sometimes Portuguese ships fall into the Gulf Stream and are carried by this current into the English Channel. When they accumulate off the coasts of England and France or, for example, near the beaches of Florida, television, radio and print warn the population of the danger.

Despite the toxicity of physalia, some sea turtles eat them in huge quantities. People, of course, do not eat physalia, but they also find uses for them. Their poison is unusually resistant to drying and freezing, and the tentacles, which lay in the refrigerator for six (!) years, perfectly retained their deadly properties. Farmers in Guadeloupe (Caribbean) and Colombia use dried physalia tentacles as rat poison.

Class 2. Scyphoid jellyfish, or Scyphozoa (200 species of different jellyfish). Scyphoid jellyfish are solitary, actively swimming inhabitants of the temperate and tropical waters of the World Ocean. The body of most jellyfish is transparent, which is due to the high (often up to 97.5%) water content in the tissues. In scyphoid jellyfish, the body has the shape of a rounded umbrella with long tentacles suspended from below. In all species, a gastrovascular system of varying complexity is formed: the oral opening, which is located on the lower side in the center of the umbrella, leads to a large stomach, from which the gastric canals diverge radially. A number of tentacles in jellyfish are modified, turning into so-called marginal bodies. Each of these bodies carries one statocyst (a formation involved in maintaining balance) and several ocelli, including some of a very complex structure.

Jellyfish go through two levels of development: sexual - this is the jellyfish itself, and asexual - this is the polyp. The common jellyfish reproduces sexually. Male reproductive products are released through the mouth into the water, after which they enter the female’s body, where fertilization occurs. The egg develops into a mobile larva - a planula, which is released into the water, goes to the bottom and attaches to underwater objects. Thus, it turns into a single polyp - scyphistoma. It grows, feeds, and then begins to reproduce by division (strobilation of scyphistoma). A mature polyp disintegrates into several discs, which turn into small jellyfish - ether. The ethers grow and turn into mature jellyfish.

In general, jellyfish are round like a ball, flat like a plate, elongated like a transparent airship. They can be quite small, such as Chironex, or sea ​​wasp(no more than 3 cm in diameter), and huge, like a giant of the Arctic waters, fiery red Cyanea, or Lion's mane, whose domed body grows up to two and a half meters in diameter, and bundles of writhing thread-like tentacles reaching 30 m in length can cover a five-story building! (The maximum recorded length of the tentacles of the giant Arctic jellyfish Cyanea was 36.5 m, and the diameter of the dome was 2.3 m. It washed ashore in North America in 1870. This specimen was greater than the maximum length of the blue whale, which is considered the most largest animals on the planet.)

Drawing. Scheme of the development of the Scyphoid jellyfish.

1 - egg, 2 - planula, 3 - scyphistoma, 4 - budding scyphistoma, 5 - strobilation, 6 - ether, 7 - adult jellyfish.

A much more modest jellyfish in size Pelagia, or Nochesvetka, amazes experienced sailors with a bright light in the middle of the night in the waters of the Mediterranean Sea, demonstrating the phenomenon of bioluminescence.

However, the beauty of most types of jellyfish can be very deceptive. After all, to a greater or lesser extent, all jellyfish are poisonous. The only difference is that some species are practically not dangerous to humans, others sting like nettles, and a painful burning sensation can be felt for several days, and others cause paralysis that can lead to death.

There are also jellyfish that are completely harmless to humans. This is the well-known glassy-white “eared” jellyfish - Aurelia. It lives in all tropical and moderately warm seas, including here in the Black Sea. Aurelia reaches 40 cm in diameter. Umbrella Aurelia translucent, most often colorless, sometimes there are umbrellas with a slight shade of blue, pink, purple. Aurelia- these are the animals of the summer season. Autumn storms bring death to them, so on the eve of cold weather, small, slightly more than a centimeter, lumps of living tissue settle to the bottom of the sea Aurelia, which carry hereditary information about this organism. These lumps are not afraid of either storms or cold snaps, and with the arrival of spring, tiny discs separate from them, which grow into adults in one summer. By the way, if you rub Aurelia’s body into human skin, it becomes immune to “stinging” jellyfish, such as, for example, the same Black Sea Rosistoma, or, in other words - Cornerot.

Drawing. Jellyfish Cyanea (A) and Jellyfish Aurelia aurita (B).

Cornerota can be recognized by the large size of the umbrella, up to 50 cm in diameter, and large fleshy root-like outgrowths. But these are not tentacles. U Cornerota there are no tentacles, their oral lobes branch, forming numerous folds fused together. The ends of the oral lobes do not form folds, but end in root-like outgrowths.

Cornerot- a predator that prefers small fish, worms, and small crustaceans. With its poison, it paralyzes prey and successfully eats it. However, mackerel fry travel in flocks together with the cornet jellyfish - they are not afraid of the stinging glands. But protection is an absolute plus of such a symbiosis.

In the Black Sea Cornerot widely spread. A particularly large number of individuals of this species appear on the coast in the second half of summer. This is far from the most pleasant part of the holiday, but it’s not dangerous either: the poison of one Cornerota is not fatal to humans, and the pain after a burn is not much stronger than nettle. Cornerot sensitive to changing weather conditions. For example, before a storm, jellyfish move away from the shore and go to the bottom.

Drawing. Black Sea jellyfish Cornerot.

Jellyfish Gonionema- a real baby among the whole multitude of sea jellyfish. Its size is no larger than a coin (3-4 cm in diameter), and its body has the shape of a flattened bell, along the edges of which there are many tentacles with suction cups, sometimes up to 70-80 pieces. Gonionema has a dome with four brown folds in the form of a cross on the concave side. This is why they called the jellyfish cross. Despite its small size, this baby is Jellyfish-little cross- in many ways even more dangerous than its larger brothers. It lives in the waters of the Pacific Ocean: in the Sea of ​​Japan - near Vladivostok, in the Tatar Strait, near the southern outskirts of Sakhalin, off the coast of Japan and the South Kuril Islands.

It lives in shallow water in algae thickets, so encounters with people are not uncommon. The danger of these jellyfish is not that their poison is particularly toxic, but that they live in shallow water, and their invasions are sometimes spontaneous. For example, in July 1966, a huge flock of Krestovichkov- thousands of vacationers were affected. There, in the summer of 1970, they received burns from Krestovichkov 1360 people, of which 116 had to be urgently hospitalized.

The poisonous apparatus of these jellyfish is located in the outer layer of the tentacles. These are chitinous capsules filled with poison. Each cell has a sensitive hair or the thinnest tube, the so-called stinging filament. Any touch causes a reflex release of a portion of poison. In case of accidental contact with Cross in water it is not so easy to get rid of it: as if afraid of losing its prey, it is firmly attached to the body. It has to be torn off with force.

Of course, it is impossible to die from touching one jellyfish, but the sensations are far from pleasant: at first you feel a tingling sensation, similar to those you get from touching nettles, but unlike a nettle burn, meeting with Cross entails serious consequences. Swelling, rash, burning sensation, itching appear at the site of the lesion; sharp pain in the lower back and joints, shortness of breath, dry cough, nausea, numbness of the arms and legs. Sometimes there are convulsions. I Krestovichka It often even affects the psyche. Usually, poor health lasts 4-6 days, but pain and discomfort may recur for about a month. Repeated meetings with Cross extremely dangerous. The whole point is that the human body does not develop immunity to its poison, but becomes even more sensitive to it.

It's most dangerous when Crosses attack in packs. The poisoning of the body is so great that instant death can occur. To avoid burns Krestovichkov you need to stay away from the algae thickets where these jellyfish live. When working near corals, do not touch them with your bare hands.

Drawing. Medusa-cross.

The most dangerous of all existing jellyfish - Sea wasps. They live in the warm waters of the Indian and Pacific oceans. It's hard to believe that this little blob of living mucus is actually a real killer. And meeting him is almost more dangerous than meeting a shark. I sea ​​wasp so strong that if it enters the bloodstream it can stop a person’s heart in a few minutes. In search of food, such as bottom-dwelling shrimp, these deadly creatures sometimes come very close to the shore. Large concentrations of small larvae are often observed in the coastal waters of Australia and the Philippine Islands Sea wasps, the local name is “stinging sea grass”, or “stinging pine needles”. Once caught in such a congestion, a person can suffer severe burns if his body is not protected by clothing.

Drawing. Jellyfish Sea wasp.

In the waters of the Sea of ​​Japan, the polypoid stage of jellyfish Navzitoi reefs and rocks are covered with continuous poisonous thickets. The Japanese call this polyp "iramo", which means stinging algae. It’s not for nothing that local fishermen and divers are afraid of such places. But some other slightly poisonous species of jellyfish are considered an exquisite delicacy in Japan and, after special processing, end up on the table... fried! This very exotic delicacy requires special cunning in preparation, especially considering that jellyfish consists of 90 percent sea water.

As you can see, an encounter with jellyfish can have very unpleasant consequences. Treatment required. During treatment, it is necessary to reduce pain, reduce spastic (convulsive) phenomena and eliminate local lesions (burns). It is recommended to administer analgesics to reduce pain. For local treatment, lotions with diluted ammonia, ethyl alcohol, and oil compresses are used. If cardiac or respiratory disorders develop, symptomatic treatment should be applied. Along with medications, it is advisable to use heat (heating pads, hot tea, rubbing hands and feet, etc.). For skin rashes, antihistamines must be administered.

Prevention consists of avoiding contact with poisonous jellyfish and siphonophores. During emergency underwater work in areas where these animals live, it is necessary to wear fairly thick clothing (wetsuits) and gloves. If there are large concentrations of small jellyfish, you should protect your eyes. In the event of a burn, the victim must get ashore or on board the ship as soon as possible. There are known cases where, as a result of burns, people lost consciousness from pain and drowned before help came to them.

Fishermen engaged in commercial fishing may come into contact with jellyfish when retrieving nets, disassembling the catch, and processing fish in production facilities.

The gelatinous body of a jellyfish, consisting almost entirely of water, is easily destroyed, and therefore whole specimens are not always preserved in the catch, by which one can determine whether a given jellyfish is dangerous or harmless. Therefore, any jellyfish that comes on board a vessel should be handled with care. Pieces of burning tentacles can stick to nets and ropes when hauling gear on board the vessel and, together with splashes of water, get on the face and, which is especially dangerous, in the eyes. Therefore, when working in habitats of poisonous jellyfish, it is necessary to use gloves (mittens) and safety glasses. Remains of jellyfish should be removed (washed off) from the deck and gear, since, once dry, they can get into the eyes in the form of fine dust and cause dangerous inflammation.

Class 3. Coral polyps(6 thousand species). Coral polyps (Anthozoa) are colonial (less often solitary) marine organisms. The body ranges in length from several millimeters to one meter and has six-ray or eight-ray symmetry. Due to the fact that fertilization in corals is internal, the planula larva develops in the gastric cavity of the polyp, which forms eggs. There is no jellyfish stage. The oral opening is connected to the gastric cavity by the pharynx. Polyps of one colony have a common gastric cavity, and food obtained by one of the polyps becomes the property of the entire colony.

There are about 6,000 species of coral polyps; they live in all seas with fairly high salinity; There are about 150 species in the northern and Far Eastern seas of Russia.

Madreporaceae, or reef-building corals (from the group of six-rayed corals) surround themselves with a massive calcareous skeleton. When a polyp dies, its skeleton remains and, growing over thousands of years, forms coral reefs and entire islands. Madrepore corals- These are reef-building corals. The largest existing reef, the Great Barrier Reef, stretches along the eastern coast of Australia for 2,300 km; its width ranges from 2 to 150 km.

The skeleton of madrepore corals is quite complex. It is built by the cells of the outer layer (ectoderm) of the polyp. At first, the skeleton looks like a small cup-like cell in which the polyp itself sits. Then, as radial partitions grow and form, the living organism finds itself, as it were, impaled on its skeleton. Colonies Madrepore corals are formed as a result of budding. Some corals have not one, but two or three polyps in each cell. In this case, the cell stretches out, becomes like a boat, and the mouths are arranged in one row, surrounded by a common rim of tentacles. In other species, dozens of polyps are already sitting in the limestone house. Finally, in corals of the genus Meandrins all polyps merge to form a single organism. The colony takes on the appearance of a hemisphere covered with numerous winding grooves. Such corals are called brain corals; the grooves on them are fused mouth slits lined with rows of tentacles.

Colonies of coral polyps grow quite quickly - branched forms, under favorable conditions, grow up to 20-30 cm per year. Having reached low tide, the tops of coral reefs stop growing and die, and the entire colony continues to grow from the sides. New colonies can grow from broken branches.

In order for coral polyps to grow calmly and build reefs, they need certain conditions. In shallow, well-heated lagoons, they can withstand water heating up to 35 °C and a certain increase in salinity. However, cooling water below 20.5 °C and even short-term desalination have a detrimental effect on them. Therefore, in cold and temperate waters, as well as where large rivers flow into the sea, coral reefs do not develop.

Coral reefs are unique ecosystems in which a huge number of other animals find shelter: mollusks, worms, echinoderms, fish. During the pre-glacial period, coral reefs fringed many islands. As sea levels began to rise, the polyps built up their reefs at an average rate of a centimeter per year. Gradually, the island itself disappeared under water, and in its place a shallow lagoon surrounded by reefs formed. The wind carried plant seeds to the reef. Then animals appeared, and the island turned into a coral atoll.

Coral reefs have existed since ancient geological eras, and more than 5,000 species of fossil corals have been described. Remains of corals were found in the Urals in deposits of the Cretaceous period (about 100 million years ago) and in the Moscow region (deposits more than 300 million years old). Fossil corals are reliable indicators of the age of sedimentary rocks. Many of them are associated with deposits of certain geological rocks, in particular coal. The discovery of such corals indicates the presence of this mineral in this place. For example, coal was discovered in the Donetsk basin.

By studying the structure of fossil corals, you can calculate the number of days in a year in different eras. The fact is that the walls of the calcareous tubes forming the skeleton of the colony grew in layers: their growth occurred only during the day and strictly obeyed the lunar (that is, ebb and flow) cycles. In addition, the annual growth rings also differ - dark stripes correspond to the winter season, light stripes correspond to the summer season. The width of the stripes depends on daily changes in illumination and water temperature. Analyzing the nature of the growth of tubes on the thinnest saw cuts, scientists calculated that, for example, in the Devonian period (about 400 million years ago), a calendar year, equal to the period of the Earth’s revolution around the Sun, lasted about 400 days - a day then was less than 22 hours. After 150 million years, the year already had 390 days. There is a gradual slowdown in the speed of rotation of the Earth around its axis.

Building stone containing coral remains is successfully used as a decorative material for interior and exterior decoration. This stone was once a shell rock and consisted of sedimentary rock, corals and mollusk shells. After hundreds of millions of years, it turned into solid rock. On its polished surface, corals form an intricate pattern, sometimes containing layers of different minerals. The fossils embedded in the stone give it a wavy texture. Such a structure has, for example, marble from deposits near Nizhny Tagil in the Urals.

Red noble coral Mediterranean Sea (Corallium rubrum) belongs to the eight-rayed corals and is not capable of forming reefs. Its colonies grow on the coastal slopes of the Mediterranean Sea at a depth of more than 20 m (usually from 50 to 150 m). Even in ancient times, divers used a special hook to extract corals from great depths. About the same Noble red coral, which has long been used for making jewelry, is still mined today.

Sea anemones, or Sea anemones- These are non-skeletal solitary coral polyps. Sea anemones coexist with hermit crabs, settling on their shells. Cancer is protected by stinging cells Sea anemones, and in return suffers cancer Sea anemone from place to place - to more favorable places for hunting. Other types Actinium cohabitates with a clown fish. Bright fish, immune to tentacle poison Sea anemones, attracts enemies, and sea ​​anemone grabs them and eats them. Something goes to the clown too. Separate Sea anemones live (in aquariums) up to 50–80 years.

DRAWINGS THAT SHOULD BE DONE IN THE ALBUM

(6 pictures in total)

Lesson topic: Sponge Type –Spongia

Type: Sponges

Class: Ordinary sponges

Order: Siliceous sponges Genus: Badyaga – Spongilla

Rice. 1. Badyaga. External building.

1-colony

2-substrate

Lesson topic: Sponge Type –Spongia

Type: Sponges

Class: Lime sponges

Genus: Sikon - Sycon

Rice. 2. The structure of a single Sicon sponge.

1-sole

3-osculum

4-outer layer of pinacocyte cells

5-inner layer of choanocyte cells

6-mesoglea

7-paragastric cavity

→ - direction of water flow

Lesson topic: Sponge Type –Spongia

Rice. 3. Morphological types of sponges.

Lesson topic: Sponge Type –Spongia

1-pinacocytes

2-collencytes

3-choanocytes

4-scleroblasts

5-spicule

6-amebocytes

7-ovum

8-mesoglea

Lesson topic: Type Coelenterates -Coelenterata

Type: Coelenterates

Class: Hydroid

Squad: Hydras

Type: Hydra - Hydra sp.

Rice. 5. Hydra stalked. External building.

2-tentacles

3-sole

5 mouth opening

6-substrate

Lesson topic: Type Coelenterates -Coelenterata

1-ectoderm

2-endoderm

3-support plate

4-gastric cavity

Coelenterates are the first two-layer ancient animals with radial symmetry, an intestinal (gastric) cavity and an oral opening. They live in water. There are sessile forms (benthos) and floating forms (plankton), which is especially pronounced in jellyfish. Predators feeding on small crustaceans, fish fry, and aquatic insects.

Coral polyps play a significant role in the biology of the southern seas, forming reefs and atolls that serve as shelters and spawning grounds for fish; at the same time they create a danger for ships.

Large jellyfish are eaten by people, but they also cause serious burns to swimmers. Reef limestone is used for decoration and as a building material. However, by destroying reefs, people reduce fish resources. The most famous reefs in the southern seas are along the coast of Australia, off the Sunda Islands, and in Polynesia.

Coelenterates are the oldest type of primitive two-layer multicellular animals. Deprived of real organs. Their study is of exceptional importance for understanding the epochulation of the animal world: ancient species of this type were the progenitors of all higher multicellular animals.

Coelenterates are predominantly marine, less often freshwater animals. Many of them attach to underwater objects, while others float slowly in the water. The attached forms are usually goblet-shaped and are called polyps. With the lower end of the body they are attached to the substrate; at the opposite end there is a mouth surrounded by a corolla of tentacles. The floating forms are usually bell- or umbrella-shaped and are called jellyfish.

The body of coelenterates has ray (radial) symmetry. Through it you can draw two or more (2, 4, 6, 8 or more) planes dividing the body into symmetrical halves. In the body, which can be compared to a two-layer sac, only one cavity is developed - the gastric cavity, which acts as a primitive intestine (hence the name of the type). It communicates with the external environment through a single opening, which functions as the oral and anal. The wall of the sac consists of two cell layers: the outer, or ectoderm, and the inner, or endoderm. Between the cell layers lies a structureless substance. It forms either a thin supporting plate or a wide layer of gelatinous mesoglea. In many coelenterates (for example, jellyfish), canals extend from the gastric cavity, forming, together with the gastric cavity, a complex gastrovascular (gastrovascular) system.

The cells of the body of coelenterates are differentiated.

• Ectoderm cells are presented in several types:
  • integumentary (epithelial) cells - form the covering of the body, perform a protective function

    Epithelial-muscle cells - in lower forms (hydroid) integumentary cells have a long process elongated parallel to the surface of the body, in the cytoplasm of which contractile fibers are developed. The combination of such processes forms a layer of muscular formations. Epithelial muscle cells combine the functions of a protective covering and a motor apparatus. Thanks to the contraction or relaxation of muscle formations, the hydra can shrink, thicken or narrow, stretch, bend to the side, attach to other parts of the stems and thus move slowly.

  • In higher coelenterates, muscle tissue is separated. Jellyfish have powerful bundles of muscle fibers.
  • star-shaped nerve cells. The processes of nerve cells communicate with each other, forming a nerve plexus, or diffuse nervous system.
  • intermediate (interstitial) cells - restore damaged areas of the body. Intermediate cells can form integumentary muscle, nerve, reproductive and other cells.
• stinging (nettle) cells - located among the integumentary cells, singly or in groups. They have a special capsule containing a spirally twisted stinging thread. The capsule cavity is filled with liquid. On the outer surface of the stinging cell, a thin sensitive hair is developed - the cnidocil. When a small animal touches, the hair is deflected, and the stinging thread is thrown out and straightened, through which paralyzing poison enters the body of the prey. After the thread is thrown out, the stinging cell dies. Stinging cells are renewed due to undifferentiated interstitial cells lying in the ectoderm. Endoderm cells
  • line the gastric (intestinal) cavity and perform mainly the function of digestion. These include
  • digestive cells with phagocytic function. Digestive cells (in lower forms) also have processes in which contractile fibers are developed, oriented perpendicular to similar formations of integumentary muscle cells. Flagella (1-3 from each cell) are directed from epithelial-muscular cells towards the intestinal cavity and outgrowths resembling false legs can form, which capture small food particles and digest them intracellularly in digestive vacuoles. Thus, coelenterates combine intracellular digestion characteristic of protozoa with intestinal digestion characteristic of higher animals.

The nervous system is primitive. In both cell layers there are special sensitive (receptor) cells that perceive external stimuli. A long nerve process extends from their basal end, along which the nerve impulse reaches multi-process (multipolar) nerve cells. The latter are located singly and do not form nerve nodes, but are connected to each other by their processes and form a nervous network. Such a nervous system is called diffuse.

The reproductive organs are represented only by the sex glands (gonads). Reproduction occurs sexually and asexually (budding). Many coelenterates are characterized by alternation of generations: polyps, reproducing by budding, give rise to both new polyps and jellyfish. The latter, reproducing sexually, produce a generation of polyps. This alternation of sexual reproduction with vegetative reproduction is called metagenesis. [show] .

Metagenesis occurs in many coelenterates. For example, the well-known Black Sea jellyfish - Aurelia - reproduces sexually. The sperm and eggs that arise in her body are released into the water. From fertilized eggs, individuals of the asexual generation develop - aurelia polyps. The polyp grows, its body lengthens, and then is divided by transverse constrictions (strobilation of the polyp) into a number of individuals that look like stacked saucers. These individuals separate from the polyp and develop into jellyfish that reproduce sexually.

Systematically, the phylum is divided into two subtypes: cnidarians (Cnidaria) and non-cnidaria (Acnidaria). About 9,000 species of cnidarians are known, and only 84 species of non-cnidarians.

SUBTYPE STINGING

Characteristics of the subtype

Coelenterates, called cnidarians, have stinging cells. These include the classes: hydroid (Hydrozoa), scyphoid (Scyphozoa) and coral polyps (Anthozoa).

Class hydroids (Hydrozoa)

An individual has the form of either a polyp or a jellyfish. The intestinal cavity of polyps is devoid of radial septa. The gonads develop in the ectoderm. About 2,800 species live in the sea, but there are several freshwater forms.

• Subclass Hydroids (Hydroidea) - bottom colonies, adherent. In some non-colonial species, polyps are able to float at the surface of the water. Within each species, all individuals of the medusoid structure are the same.
  • Order Leptolida - there are individuals of both polypoid and medusoid origin. Mostly marine, very rarely freshwater organisms.
  • Order Hydrocorallia (Hydrocorallia) - the trunk and branches of the colony are calcareous, often painted in a beautiful yellowish, pink or red color. Medusoid individuals are underdeveloped and buried deep in the skeleton. Exclusively marine organisms.
  • Order Chondrophora - a colony consists of a floating polyp and medusoid individuals attached to it. Exclusively marine animals. Previously they were classified as a subclass of siphonophores.
  • Order Tachylida (Trachylida) - exclusively marine hydroids, jellyfish-shaped, no polyps.
  • Order Hydra (Hydrida) - solitary freshwater polyps; they do not form jellyfish.
• Subclass Siphonophora - floating colonies, which include polypoid and medusoid individuals of various structures. They live exclusively in the sea.

Freshwater polyp Hydra- a typical representative of hydroids, and at the same time of all cnidarians. Several species of these polyps are widespread in ponds, lakes and small rivers.

Hydra is a small, about 1 cm long, brownish-green animal with a cylindrical body shape. At one end there is a mouth, surrounded by a corolla of very mobile tentacles, of which in different species there are from 6 to 12. At the opposite end there is a stem with a sole, which serves for attachment to underwater objects. The pole on which the mouth is located is called oral, the opposite pole is called aboral.

Hydra leads a sedentary lifestyle. Attached to underwater plants and hanging into the water with its mouth end, it paralyzes prey swimming past with stinging threads, captures it with tentacles and sucks it into the gastric cavity, where digestion occurs under the action of enzymes of glandular cells. Hydras feed mainly on small crustaceans (daphnia, cyclops), as well as ciliates, oligochaete worms and fish fry.

Digestion. Under the action of enzymes in the glandular cells of the endoderm lining the gastric cavity, the body of the captured prey disintegrates into small particles, which are captured by cells that have pseudopodia. Some of these cells are in their permanent place in the endoderm, others (amoeboid) are mobile and move. Digestion of food is completed in these cells. Consequently, in coelenterates there are two methods of digestion: along with the more ancient, intracellular one, an extracellular, more progressive method of food processing appears. Subsequently, in connection with the evolution of the organic world and the digestive system, intracellular digestion lost its significance in the act of nutrition and assimilation of food, but the ability for it was preserved in individual cells in animals at all stages of development up to the highest, and in humans. These cells, discovered by I. I. Mechnikov, were called phagocytes.

Due to the fact that the gastric cavity ends blindly and the anus is absent, the mouth serves not only for eating, but also for removing undigested food debris. The gastric cavity performs the function of blood vessels (moving nutrients throughout the body). The distribution of substances in it is ensured by the movement of flagella, which many endodermal cells are equipped with. Contractions throughout the body serve the same purpose.

Breathing and elimination carried out by diffusion by both ectodermal and endodermal cells.

Nervous system. Nerve cells form a network throughout the hydra's body. This network is called the primary diffuse nervous system. There are especially many nerve cells around the mouth, on the tentacles and sole. Thus, in coelenterates, the simplest coordination of functions appears.

Sense organs. Not developed. Touch with the entire surface, the tentacles (sensitive hairs) are especially sensitive, throwing out stinging threads that kill prey.

Hydra movement carried out due to transverse and longitudinal muscle fibers included in epithelial cells.

Hydra regeneration– restoration of the integrity of the hydra body after its damage or loss of part of it. A damaged hydra restores lost body parts not only after it has been cut in half, but even if it has been divided into a huge number of parts. A new animal can grow from 1/200 of a hydra; in fact, a whole organism is restored from a grain. Therefore, hydra regeneration is often called an additional method of reproduction.

Reproduction. Hydra reproduces asexually and sexually.

During the summer, hydra reproduces asexually - by budding. In the middle part of its body there is a budding belt, on which tubercles (buds) are formed. The bud grows, a mouth and a tentacle are formed at its apex, after which the bud laces at the base, separates from the mother’s body and begins to live independently.

With the approach of cold weather in the fall, germ cells - eggs and sperm - are formed in the ectoderm of the hydra from intermediate cells. The eggs are located closer to the base of the hydra, sperm develop in tubercles (male gonads) located closer to the mouth. Each sperm has a long flagellum, with which it swims in water, reaches the egg and fertilizes it in the mother's body. The fertilized egg begins to divide, becomes covered with a dense double shell, sinks to the bottom of the reservoir and overwinters there. In late autumn, adult hydras die. In the spring, a new generation develops from overwintered eggs.

Colonial polyps(for example, the colonial hydroid polyp Obelia geniculata) live in the seas. An individual colony, or the so-called hydrant, is similar in structure to a hydra. Its body wall, like that of hydra, consists of two layers: endoderm and ectoderm, separated by a jelly-like structureless mass called mesoglea. The body of the colony is a branched coenosarc, inside which there are individual polyps, interconnected by outgrowths of the intestinal cavity into a single digestive system, which allows the distribution of food captured by one polyp among members of the colony. The outside of the coenosarcus is covered with a hard shell - the perisarcoma. Near each hydrant, this shell forms an expansion in the form of a glass - a hydroflow. The corolla of the tentacles can be drawn into the expansion when irritated. The mouth opening of each hydrant is located on a growth around which the corolla of tentacles is located.

Colonial polyps reproduce asexually - by budding. In this case, the individuals that have developed on the polyp do not break away, like in the hydra, but remain associated with the maternal organism. An adult colony has the appearance of a bush and consists mainly of two types of polyps: gastrozoids (hydrants), which provide food and protect the colony with stinging cells on the tentacles, and gonozoids, which are responsible for reproduction. There are also polyps specialized to perform a protective function.

Gonozoids are elongated rod-shaped formations with an extension at the top, without a mouth opening and tentacles. Such an individual cannot feed on its own; it receives food from hydrants through the gastric system of the colony. This formation is called blastostyle. The skeletal membrane gives a bottle-shaped extension around the blastostyle - gonotheca. This entire formation as a whole is called gonangia. In the gongangium, on the blastostyle, jellyfish are formed by budding. They bud off from the blastostyle, emerge from the gonangium, and begin to lead a free lifestyle. As the jellyfish grows, germ cells are formed in its gonads, which are released into the external environment, where fertilization occurs.

From a fertilized egg (zygote), a blastula is formed, with the further development of which a two-layer larva, a planula, freely floating in water and covered with cilia, is formed. The planula settles to the bottom, attaches itself to underwater objects and, continuing to grow, gives rise to a new polyp. This polyp forms a new colony by budding.

Hydroid jellyfish have the shape of a bell or umbrella, from the middle of the ventral surface of which hangs a trunk (oral stalk) with a mouth opening at the end. Along the edge of the umbrella there are tentacles with stinging cells and adhesive pads (suckers) used for catching prey (small crustaceans, larvae of invertebrates and fish). The number of tentacles is a multiple of four. Food from the mouth enters the stomach, from which four straight radial canals extend, encircling the edge of the jellyfish umbrella (intestinal ring canal). The mesoglea is much better developed than that of the polyp and makes up the bulk of the body. This is due to the greater transparency of the body. The method of movement of the jellyfish is “reactive”; this is facilitated by the fold of ectoderm along the edge of the umbrella, called the “sail”.

Due to their free lifestyle, the nervous system of jellyfish is better developed than that of polyps, and, in addition to the diffuse nervous network, it has clusters of nerve cells along the edge of the umbrella in the form of a ring: external - sensitive and internal - motor. The sensory organs, represented by light-sensitive eyes and statocysts (equilibrium organs), are also located here. Each statocyst consists of a vesicle with a calcareous body - a statolith, located on elastic fibers coming from the sensitive cells of the vesicle. If the position of the jellyfish's body in space changes, the statolith shifts, which is perceived by sensitive cells.

Jellyfish are dioecious. Their gonads are located under the ectoderm, on the concave surface of the body under the radial canals or in the area of ​​the oral proboscis. In the gonads, germ cells are formed, which, when mature, are excreted through a rupture in the body wall. The biological significance of mobile jellyfish is that thanks to them, hydroids disperse.

Class Scyphozoa

An individual has the appearance of either a small polyp or a large jellyfish, or the animal bears characteristics of both generations. The intestinal cavity of polyps has 4 incomplete radial septa. The gonads develop in the endoderm of jellyfish. About 200 species. Exclusively marine organisms.

• The order Coronomedusae (Coronata) are predominantly deep-sea jellyfish, the umbrella of which is divided by a constriction into a central disk and a crown. The polyp forms a protective chitinoid tube around itself.
• Order Discomedusae - the umbrella of jellyfish is solid, there are radial canals. Polyps lack a protective tube.
• The order Cubomedusae - the umbrella of the jellyfish is solid, but lacks radial canals, the function of which is performed by the far protruding stomach pouches. Polyp without a protective tube.
• The order Stauromedusae are unique benthic organisms that combine in their structure the characteristics of a jellyfish and a polyp.

Most of the life cycle of coelenterates from this class takes place in the medusoid phase, while the polypoid phase is short-lived or absent. Scyphoid coelenterates have a more complex structure than hydroids.

Unlike hydroid jellyfish, scyphoid jellyfish are larger in size, have a highly developed mesoglea, and a more developed nervous system with clusters of nerve cells in the form of nodules - ganglia, which are located mainly around the circumference of the bell. The gastric cavity is divided into chambers. Channels extend radially from it, united by a ring channel located along the edge of the body. The collection of channels forms the gastrovascular system.

The method of movement is “jet”, but since scyphoids do not have a “sail”, movement is achieved by contracting the walls of the umbrella. Along the edge of the umbrella there are complex sensory organs - rhopalia. Each rhopalium contains an “olfactory fossa”, an organ of balance and stimulation of the movement of the umbrella - a statocyst, a light-sensitive ocellus. Scyphoid jellyfish are predators, but deep-sea species feed on dead organisms.

Sex cells are formed in the sex glands - gonads, located in the endoderm. The gametes are removed through the mouth and the fertilized eggs develop into a planula. Further development proceeds with alternation of generations, with the jellyfish generation predominating. The generation of polyps is short-lived.

The tentacles of jellyfish are equipped with a large number of stinging cells. The burns of many jellyfish are sensitive to large animals and humans. Severe burns with serious consequences can be caused by the polar jellyfish of the genus Cyanea, reaching a diameter of 4 m, with tentacles up to 30 m long. Bathers in the Black Sea are sometimes burned by the jellyfish Pilema pulmo, and in the Sea of ​​Japan - by gonionemus vertens.

Representatives of the class of scyphoid jellyfish include:

• Aurelia jellyfish (eared jellyfish) (Aurelia aurita) [show] .

  Eared jellyfish Aurelia aurita

  It lives in the Baltic, White, Barents, Black, Azov, Japanese and Bering regions, and is often found in large quantities.

  It gets its name from its mouth lobes, which are shaped like donkey ears. The umbrella of the eared jellyfish sometimes reaches 40 cm in diameter. It is easily recognized by its pinkish or slightly purple color and four dark ridges in the middle part of the umbrella - the gonads.

  In summer, in calm, calm weather, during low or high tide, you can see a large number of these beautiful jellyfish, slowly transported by the current. Their bodies sway calmly in the water. The eared jellyfish is a poor swimmer; thanks to the contractions of the umbrella, it can only slowly rise to the surface, and then, frozen motionless, plunge into the depths.

  At the edge of the aurelia umbrella there are 8 rhopalia bearing ocelli and statocysts. These sense organs allow the jellyfish to stay at a certain distance from the surface of the sea, where its delicate body will quickly be torn apart by the waves. The eared jellyfish captures food with the help of long and very thin tentacles, which “sweep” small planktonic animals into the jellyfish’s mouth. Swallowed food first goes into the pharynx and then into the stomach. This is where 8 straight radial canals and the same number of branching ones originate. If you use a pipette to introduce a solution of ink into the stomach of a jellyfish, you can see how the flagellar epithelium of the endoderm drives food particles through the channels of the gastric system. First, the mascara penetrates into the non-branching canals, then it enters the annular canal and returns back to the stomach through the branching canals. From here, undigested food particles are thrown out through the mouth.

  The gonads of the aurelia, having the shape of four open or complete rings, are located in the pouches of the stomach. When the eggs in them mature, the wall of the gonad ruptures and the eggs are thrown out through the mouth. Unlike most scyphojellyfish, Aurelia shows a peculiar kind of care for its offspring.

  The oral lobes of this jellyfish carry along their inner side a deep longitudinal groove, starting from the mouth opening and passing to the very end of the lobe. On both sides of the gutter there are numerous small holes that lead into small pocket cavities. In a swimming jellyfish, its oral lobes are lowered down, so that the eggs emerging from the mouth opening inevitably fall into the gutters and, moving along them, are retained in the pockets. This is where fertilization and egg development occurs. From the pockets, fully formed planulae come out. If you place a large female Aurelia in an aquarium, then within a few minutes you will notice a lot of light dots in the water. These are planulae that have left their pockets and float with the help of cilia.

  Young planulae tend to move towards the light source and soon accumulate in the upper part of the illuminated side of the aquarium. Probably, this property helps them get out of darkened pockets into the wild and stay close to the surface without going into the depths.

  Soon the planulas have a tendency to sink to the bottom, but always in bright places. Here they continue to swim briskly. The period of freely moving life of the planula lasts from 2 to 7 days, after which they settle to the bottom and attach their front end to some solid object.

• After two or three days, the settled planula turns into a small polyp - scyphistoma, which has 4 tentacles. Soon 4 new tentacles appear between the first tentacles, and then 8 more tentacles. Scyphistomas actively feed, capturing ciliates and crustaceans. Cannibalism is also observed - eating planulas of the same species by scyphistomas. Scyphistomas can reproduce by budding, forming similar polyps. Scyphistoma overwinters, and next spring, with the onset of warming, serious changes occur in it. The tentacles of the scyphistoma are shortened, and ring-shaped constrictions appear on the body. Soon the first ether is separated from the upper end of the scyphistoma - a small, completely transparent star-shaped jellyfish larva. By mid-summer, a new generation of eared jellyfish develops from the ether. [show] .

  

  The scyphoid jellyfish cyanea is the largest jellyfish. These giants among coelenterates live only in cold waters. The diameter of the cyanea umbrella can reach 2 m, the length of the tentacles is 30 m. Externally, cyanea is very beautiful. The umbrella is usually yellowish in the center, dark red towards the edges. The oral lobes look like wide crimson-red curtains, the tentacles are colored light pink. Young jellyfish are especially brightly colored. The venom of stinging capsules is dangerous to humans.

• rhizostoma jellyfish, or cornet (Rhizostoma pulmo) [show] .

  

  The scyphoid jellyfish cornerot lives in the Black and Azov Seas. The umbrella of this jellyfish is hemispherical or conical in shape with a rounded top. Large specimens of rhizostomy are difficult to fit into a bucket. The color of the jellyfish is whitish, but along the edge of the umbrella there is a very bright blue or purple border. This jellyfish has no tentacles, but its oral lobes branch in two, and their sides form numerous folds and grow together. The ends of the oral lobes do not bear folds and end with eight root-like outgrowths, from which the jellyfish got its name. The mouth of adult cornets is overgrown, and its role is played by numerous small holes in the folds of the oral lobes. Digestion also occurs here, in the oral lobes. In the upper part of the mouth lobes of the cornerotus there are additional folds, the so-called epaulettes, which enhance the digestive function. Cornerotes feed on the smallest planktonic organisms, sucking them along with water into the gastric cavity.

  Cornermouths are pretty good swimmers. The streamlined shape of the body and the strong muscles of the umbrella allow them to move forward with quick, frequent thrusts. It is interesting to note that, unlike most jellyfish, the cornerot can change its movement in any direction, including downward. Bathers are not very happy to meet a cornet: if you touch it, you can get a rather severe painful “burn”. Cornermouths usually live at shallow depths near the shores, and are often found in large numbers in the Black Sea estuaries.

• edible rhopilema (Rhopilema esculenta) [show] .

  Edible rhopilema (Rhopilema esculenta) lives in warm coastal waters, accumulating in masses near river mouths. It has been noticed that these jellyfish grow most intensively after the onset of the summer tropical rainy season. During the rainy season, rivers carry large amounts of organic matter into the sea, promoting the development of plankton, which jellyfish feed on. Along with Aurelia, Rhopilema is eaten in China and Japan. Externally, Rhopilema resembles the Black Sea Cornerot, differing from it in the yellowish or reddish color of the oral lobes and the presence of a large number of finger-like outgrowths. The mesoglea of ​​the umbrella is used for food.

  Ropylemas are inactive. Their movements depend mainly on sea currents and winds. Sometimes, under the influence of current and wind, clusters of jellyfish form belts 2.5-3 km long. In some places on the coast of Southern China in summer, the sea turns white from the accumulated ripples that sway near the surface.

  Jellyfish are caught with nets or special fishing gear that looks like a large bag of fine-mesh net placed on a hoop. During high or low tide, the bag is inflated by the current and jellyfish get into it, which cannot get out due to their inactivity. The oral lobes of captured jellyfish are separated and the umbrella is washed until the internal organs and mucus are completely removed. Thus, essentially only the mesoglea of ​​the umbrella goes into further processing. According to the figurative expression of the Chinese, the meat of jellyfish is “crystal”. Jellyfish are salted with table salt mixed with alum. Salted jellyfish are added to various salads, and also eaten boiled and fried, seasoned with pepper, cinnamon and nutmeg. Of course, jellyfish is a low-nutritive product, but salted ropilema still contains a certain amount of proteins, fats and carbohydrates, as well as vitamins B 12, B 2 and nicotinic acid.

  The eared jellyfish, the edible rhopilema and some closely related species of scyphojellyfish are, in all likelihood, the only coelenterates that are eaten by humans. In Japan and China there is even a special fishery for these jellyfish, and thousands of tons of “crystal meat” are mined there every year.

Class coral polyps (Anthozoa)

Coral polyps are exclusively marine organisms of a colonial or sometimes solitary form. About 6,000 species are known. Coral polyps are larger in size than hydroid polyps. The body has a cylindrical shape and is not divided into a trunk and a leg. In colonial forms, the lower end of the polyp body is attached to the colony, and in single polyps it is equipped with an attachment sole. The tentacles of coral polyps are located in one or several closely spaced corollas.

There are two large groups of coral polyps: eight-rayed (Octocorallia) and six-rayed (Hexacorallia). The former always have 8 tentacles, and they are equipped at the edges with small outgrowths - pinnules; in the latter, the number of tentacles is usually quite large and, as a rule, a multiple of six. The tentacles of six-rayed corals are smooth and without kicks.

The upper part of the polyp, between the tentacles, is called the oral disc. In its middle there is a slit-like mouth opening. The mouth leads into the pharynx, lined with ectoderm. One of the edges of the oral fissure and the pharynx descending from it is called the siphonoglyph. The ectoderm of the siphonoglyph is covered with epithelial cells with very large cilia, which are in continuous movement and drive water into the intestinal cavity of the polyp.

The intestinal cavity of a coral polyp is divided into chambers by longitudinal endodermal septa (septa). In the upper part of the body of the polyp, the septa grow with one edge to the body wall and the other to the pharynx. In the lower part of the polyp, below the pharynx, the septa are attached only to the body wall, as a result of which the central part of the gastric cavity - the stomach - remains undivided. The number of septa corresponds to the number of tentacles. Along each septum, along one of its sides, there is a muscular ridge.

The free edges of the septa are thickened and are called mesenteric filaments. Two of these filaments, located on a pair of adjacent septa opposing the siphonoglyph, are covered with special cells bearing long cilia. The cilia are in constant motion and drive water out of the gastric cavity. The joint work of the ciliated epithelium of these two mesenteric filaments and the siphonoglyph ensures a constant change of water in the gastric cavity. Thanks to them, fresh, oxygen-rich water constantly enters the intestinal cavity. Species that feed on tiny planktonic organisms also receive food. The remaining mesenteric filaments play an important role in digestion, as they are formed by glandular endodermal cells that secrete digestive juices.

Reproduction is asexual - by budding, and sexual - with metamorphosis, through the stage of a free-swimming larva - planula. The gonads develop in the endoderm of the septa. Coral polyps are characterized only by a polypoid state; there is no alternation of generations, since they do not form jellyfish and, accordingly, there is no medusoid stage.

The ectoderm cells of coral polyps produce horny substance or secrete carbon dioxide, from which the external or internal skeleton is built. In coral polyps, the skeleton plays a very important role.

Eight-rayed corals have a skeleton consisting of individual calcareous needles - spicules located in the mesoglea. Sometimes the spicules are connected to each other, merging or being united by an organic horn-like substance.

Among the six-rayed corals there are non-skeletal forms, such as sea anemones. More often, however, they have a skeleton, and it can be either internal - in the form of a rod of horn-like substance, or external - calcareous.

The skeleton of representatives of the madreporidae group reaches especially great complexity. It is secreted by the ectoderm of the polyps and at first has the appearance of a plate or low cup in which the polyp itself sits. Next, the skeleton begins to grow, radial ribs appear on it, corresponding to the septa of the polyp. Soon the polyp appears as if impaled on a skeletal base, which protrudes deeply into its body from below, although it is delimited throughout by ectoderm. The skeleton of madrepore corals is very strongly developed: soft tissues cover it in the form of a thin film.

The skeleton of coelenterates plays the role of a support system, and together with the stinging apparatus, it represents a powerful defense against enemies, which contributed to their existence over long geological periods.

• Subclass Eight-rayed corals (Octocorallia) - colonial forms, usually attached to the ground. The polyp has 8 tentacles, eight septa in the gastric cavity, and an internal skeleton. On the sides of the tentacles there are outgrowths - pinnules. This subclass is divided into units:
  • The order Sun corals (Helioporida) has a solid, massive skeleton.
  • Order Alcyonaria - soft corals, skeleton in the form of calcareous needles [show] .

    Most alcyonarians are soft corals that do not have a pronounced skeleton. Only some tubipores have a developed calcareous skeleton. In the mesoglea of ​​these corals, tubes are formed, which are soldered to each other by transverse plates. The shape of the skeleton vaguely resembles an organ, so tubipores have another name - organs. Organics are involved in the process of reef formation.

  • Order Horn corals (Gorgonaria) - skeleton in the form of calcareous needles, usually there is also an axial skeleton of horn-like or calcified organic matter passing through the trunk and branches of the colony. This order includes red or noble coral (Corallium rubrum), which is an object of fishing. Red coral skeletons are used to make jewelry.
  • The order Sea feathers (Pennatularia) is a unique colony consisting of a large polyp, on the lateral outgrowths of which secondary polyps develop. The base of the colony is embedded in the ground. Some species are able to move.
• Subclass Six-rayed corals (Hexacorallia) - colonial and solitary forms. Tentacles without lateral outgrowths; their number is usually equal to or a multiple of six. The gastric cavity is divided by a complex system of partitions, the number of which is also a multiple of six. Most of the representatives have an external calcareous skeleton; there are groups without a skeleton. Includes:

SUBTYPE NON-CHARGING

Characteristics of the subtype

Non-stinging coelenterates, instead of stinging ones, have special sticky cells on their tentacles that serve to capture prey. This subtype includes a single class - ctenophores.

Class Ctenophora- unites 90 species of marine animals with a translucent, sac-shaped gelatinous body in which the channels of the gastrovascular system branch. Along the body there are 8 rows of paddle plates, consisting of fused large cilia of ectoderm cells. There are no stinging cells. On each side of the mouth there is one tentacle, due to which a two-ray type of symmetry is created. Ctenophores always swim forward with the oral pole, using the paddle plates as an organ of movement. The oral opening leads to the ectodermal pharynx, which continues into the esophagus. Behind it is the endodermal stomach with radial canals extending from it. At the aboral pole there is a special organ of balance called the aboral. It is built on the same principle as the statocysts of jellyfish.

Ctenophores are hermaphrodites. The gonads are located on the processes of the stomach under the paddle plates. Gametes are expelled through the mouth. In the larvae of these animals, the formation of the third germ layer, the mesoderm, can be traced. This is an important progressive feature of ctenophores.

Ctenophores are of great interest from the point of view of the phylogeny of the animal world, since in addition to the most important progressive feature - the development between the ecto- and endoderm of the rudiment of the third germ layer - mesoderm, due to which in adult forms numerous muscle elements develop in the gelatinous substance of the mesoglea, they have a number of other progressive features , bringing them closer to higher types of multicellular organisms.

The second progressive sign is the presence of elements of bilateral (bilateral) symmetry. It is especially clear in the crawling ctenophore Coeloplana metschnikowi, studied by A.O. Kowalewsky, and Ctenoplana kowalewskyi, discovered by A.A. Korotnev (1851-1915). These ctenophores have a flattened shape and, as adults, lack paddle plates, and therefore can only crawl along the bottom of the reservoir. The side of the body of such a ctenophore facing the ground becomes ventral (ventral); the sole develops on it; the opposite, upper side of the body becomes the dorsal, or dorsal, side.

Thus, in the phylogenesis of the animal world, the ventral and dorsal sides of the body first became separated in connection with the transition from swimming to crawling. There is no doubt that modern crawling ctenophores have retained in their structure the progressive features of that group of ancient coelenterates that became the ancestors of higher types of animals.

However, in his detailed studies, V.N. Beklemishev (1890-1962) showed that despite the common structural features of ctenophores and some marine flatworms, the assumption about the origin of flatworms from ctenophores is untenable. Their common structural features are determined by the general conditions of existence, which lead to purely external, convergent similarity.

The importance of coelenterates

Colonies of hydroids, attached to various underwater objects, often grow very densely on the underwater parts of ships, covering them with a shaggy “fur coat”. In these cases, hydroids cause significant harm to shipping, since such a “fur coat” sharply reduces the speed of the vessel. There are many cases where hydroids, settling inside the pipes of a marine water supply system, almost completely closed their lumen and prevented the supply of water. It is quite difficult to fight hydroids, since these animals are unpretentious and develop quite well, it would seem, in unfavorable conditions. In addition, they are characterized by rapid growth - bushes 5-7 cm tall grow in a month. To clear the bottom of the ship from them, you have to put it in dry dock. Here the ship is cleared of overgrown hydroids, polychaetes, bryozoans, sea acorns and other fouling animals. Recently, special toxic paints have begun to be used; the underwater parts of the ship coated with them are subject to fouling to a much lesser extent.

Worms, mollusks, crustaceans, and echinoderms live in thickets of hydroids that live at great depths. Many of them, for example sea goat crustaceans, find refuge among hydroids, others, such as sea “spiders” (multi-articulated), not only hide in their thickets, but also feed on hydropolyps. If you move a fine-mesh net around hydroid settlements or, even better, use a special, so-called planktonic net, then among the mass of small crustaceans and larvae of various other invertebrate animals you will come across hydroid jellyfish. Despite their small size, hydroid jellyfish are very voracious. They eat a lot of crustaceans and are therefore considered harmful animals - competitors of planktivorous fish. Jellyfish need abundant food for the development of reproductive products. While swimming, they scatter a huge number of eggs into the sea, which subsequently give rise to the polypoid generation of hydroids.

Some jellyfish pose a serious danger to humans. In the Black and Azov Seas in the summer there are very numerous jellyfish, and if you touch them, you can get a strong and painful “burn.” In the fauna of our Far Eastern seas there is also one jellyfish that causes serious diseases upon contact with it. Local residents call this jellyfish a “cross” for the cross-shaped arrangement of four dark radial canals, along which four also dark-colored gonads stretch. The umbrella of the jellyfish is transparent, faint yellowish-green in color. The size of the jellyfish is small: the umbrella of some specimens reaches 25 mm in diameter, but usually they are much smaller, only 15-18 mm. At the edge of the umbrella of the cross (scientific name - Gonionemus vertens) there are up to 80 tentacles that can strongly stretch and contract. The tentacles are densely seated with stinging cells, which are arranged in belts. In the middle of the length of the tentacle there is a small suction cup, with the help of which the jellyfish attaches to various underwater objects.

Crossfishes live in the Sea of ​​Japan and near the Kuril Islands. They usually stay in shallow water. Their favorite places are thickets of sea grass Zostera. Here they swim and hang on blades of grass, attached with their suckers. Sometimes they are found in clean water, but usually not far from zoster thickets. During rains, when sea water off the coast is significantly desalinated, jellyfish die. In rainy years there are almost no of them, but by the end of the dry summer, crosses appear in droves.

Although crossfishes can swim freely, they usually prefer to lie in wait for prey by attaching themselves to an object. Therefore, when one of the tentacles of the cross accidentally touches the body of a bathing person, the jellyfish rushes in this direction and tries to attach itself using suction cups and stinging capsules. At this moment, the bather feels a strong “burn”; after a few minutes, the skin at the site of the tentacle’s contact turns red and becomes blistered. If you feel a “burn”, you need to immediately get out of the water. Within 10-30 minutes, general weakness sets in, pain in the lower back appears, breathing becomes difficult, arms and legs go numb. It’s good if the shore is close, otherwise you might drown. The affected person should be placed comfortably and a doctor should be called immediately. Subcutaneous injections of adrenaline and ephedrine are used for treatment; in the most severe cases, artificial respiration is used. The disease lasts 4-5 days, but even after this period, people affected by the small jellyfish still cannot fully recover for a long time.

Repeated burns are especially dangerous. It has been established that the poison of the cross not only does not develop immunity, but, on the contrary, makes the body hypersensitive even to small doses of the same poison. This phenomenon is known medically as anaphyloxia.

It is quite difficult to protect yourself from a cross. In places where a lot of people usually swim, to combat the crossworm, they mow down the zoster, fence the bathing areas with fine mesh, and catch the crossfish with special nets.

It is interesting to note that such poisonous properties are possessed by crossfish that live only in the Pacific Ocean. A very close form, belonging to the same species, but to a different subspecies, living on the American and European coasts of the Atlantic Ocean, is completely harmless.

Some tropical jellyfish are eaten in Japan and China and are called “crystal meat”. The body of jellyfish has a jelly-like consistency, almost transparent, contains a lot of water and a small amount of proteins, fats, carbohydrates, vitamins B1, B2 and nicotinic acid.

The most typical representative of the class is hydra(Fig. 7).

The first person to see the hydra was the inventor of the microscope and the greatest naturalist of the 17th – 18th centuries. A. Levenguk (1632 – 1723).

Looking at aquatic plants, he saw among the small organisms a strange creature with numerous “horns”. He also observed the growth of buds on its body, the formation of tentacles in them, and the separation of the young animal from the mother’s body.

Hydra is a freshwater single polyp with an oblong sac-like body about 1 cm long. The body consists of two layers of cells: outer - ectoderm, and internal - endoderm, lining the intestinal cavity. The two layers of cells are separated by a thin supporting plate - mesoglea. At the upper end of the hydra's body there is a mouth surrounded by a corolla of 6-12 tentacles. With their help, the hydra captures prey and directs it into its mouth. At the lower end of the body there is a sole, with the help of which the hydra is attached to underwater objects.

Part ectoderm includes cells of different types: epithelial-muscular, stinging, intermediate, nervous (Fig. 8).

Epithelial muscle cells form the basis of the ectoderm. Contractile fibers in the processes of their cells provide the movement of the tentacles and the entire body, which can stretch, contract, and walk like the caterpillars of moth butterflies.

Rice. 7. Schematic longitudinal section of the hydra: 1 - tentacle; 2 – mouth; 3 – ectoderm; 4 – endoderm; 5 - mesoglea; 6 – intestinal cavity; 7 – kidney; 8 – male gonad; 9 – female reproductive gland.

Among the epithelial-muscle cells, stinging cells are located singly or in groups. There are especially many of them on the tentacles. The hollow capsule of the cell contains a spirally coiled stinging filament. On the outer surface of the cell there is a sensitive hair, irritation of which (mechanical or chemical) causes the stinging thread to shoot out. The stinging cells are used only once and then die.

To replace the spent stinging cells, as well as other types of cells, new ones develop in the ectoderm - from numerous small, rapidly multiplying undifferentiated intermediate cells. Thanks to their presence, hydra has a well-expressed ability to regenerate lost or damaged cells and body parts.

Rice. 8. Hydra body cells: A– epithelial-muscular ectoderm cell; b– nerve cells connected to each other by processes; V- two stinging cells (1 – at rest; 2 – discharged).

Nerve cells are located evenly deep in the ectoderm; their processes form a network-like plexus - a diffuse nervous system. Irritation from one cell is transmitted to other nerve cells, and from them to skin-muscle cells. The response to external stimulation in the hydra is a simple unconditioned reflex.

Thus, ectoderm cells perform protective, motor and sensory functions.

The endoderm is formed by two types of cells: glandular and digestive. Glandular cells secrete digestive enzymes into the intestinal cavity. Digestive cells similar in structure to the epithelial-muscular cells of the ectoderm, but unlike them they are equipped with one or two flagella and are capable of forming pseudopods.

Consequently, endoderm cells specialize in performing digestive functions.

Hydra – predatory animal. With the stinging threads of its tentacles, it strikes small aquatic animals, paralyzing and swallowing them. In the intestinal cavity, food is semi-digested to a mushy state by enzymes secreted by the glandular cells of the endoderm. Small food particles are then captured by the rotational movements of the flagella of the digestive cells and are phagocytosed by their pseudopods. Undigested food remains are removed through the mouth.

Thus, hydra, like all coelenterates, has digestion mixed.

Reproduction hydra occurs in the warm season asexually - by budding. On the body of the hydra, a small tubercle is first formed - a bud, which is a protrusion outward of two layers of the body. The kidney increases in size, tentacles and a mouth opening are formed on it. Soon the young hydra separates from the mother.

With abundant nutrition, hydras reproduce by budding throughout the warm period of the year. With the onset of autumn cold, the hydra begins to sexual reproduction. Hydras of different species can be dioecious and hermaphrodite. Some intermediate ectoderm cells differentiate into male and female germ cells, which accumulate in the lower or middle part of the body and are called gonads or gonads. In the developing gonads, a large number of intermediate, undifferentiated cells accumulate, from which both future germ cells and “nutritional” cells are formed, due to which the future egg increases. In the first stages of egg development, these cells turn into mobile amoeboids. Soon one of them begins to absorb the others and increases significantly in size, reaching 1.5 mm in diameter. This large amoeboid, picking up pseudopodia, becomes rounded and becomes an egg. After it undergoes meiosis, the wall of the gonad bursts and the egg comes out, remaining, however, connected to the body of the hydra by a thin plasmatic stalk. Each female gonad produces one egg.

By this time, sperm develop in the testes of other hydras, which leave the gonad and swim in the water. One of them penetrates the egg, after which it immediately begins splitting up. The developing embryo is covered with two shells, the outer of which has dense chitinous walls and is often covered with spines.

Protected by a double shell - embryothecae– the embryo overwinters, while adult hydras die with the onset of cold weather. By spring, inside the embryotheca there is already a formed small hydra, which comes out through a rupture in its wall.

Rice. 9. Scheme of a longitudinal section of a hydroid jellyfish: On the left – a section in the plane of the radial canal: 1 – mouth opening; 2 – stomach; 3 – oral tentacles; 4 – radial channel;

5 – sail; 6 – marginal tentacle; 7 – motor nerve ring; 8 – peephole; 9 – sensitive nerve ring; 10 – gonad; on the right – a section between the radial canals: 11 – ectoderm, 12 – endoderm; 13 – mesoglea; 14 – ring channel. Hydroid jellyfish are much more complex (Fig. 9). Externally, the hydromedusa has the appearance of a transparent disk, umbrella or bell. An oral proboscis with a mouth at the end hangs from the inner center of the umbrella. The edges of the mouth may be smooth or equipped with four more or less fringed oral lobes. The mouth leads to the stomach, which occupies the entire cavity of the oral proboscis; four radial canals extend from the stomach to the periphery of the umbrella. At the edge of the umbrella they flow into a ring canal. The combination of the stomach and canals is called

gastrovascular system. Along the edge of the hydromedusa umbrella are tentacles and sensory organs. The tentacles are used for touching and catching prey; they are densely lined with stinging cells. Some hydromedusae have photosensitive organs - eyes, which are always located at the base of the tentacles and are clearly visible due to their dark color. The eye consists of two types of cells -

photosensitive and pigmented.

Jellyfish are dioecious; their gonads are located either in the ectoderm of the oral proboscis or in the ectoderm of the umbrella under the radial canals. Here they are closest to the nutrients necessary for the development of reproductive products. The structure of the cells of the ectoderm and endoderm of jellyfish is the same as that of polyps, but the mesoglea is undoubtedly more developed. It is rich in water and has a gelatinous nature, due to which hydromedusae are very transparent; many, even quite large, jellyfish are difficult to see in the water. The mesoglea in the umbrella is especially strongly developed.

The hydroid jellyfish belongs to the class of hydroids and coelenterates. The habitat is water. They are close relatives of polyps, but are a little more complicated. This type of jellyfish differs from others in that it can live forever, since the hydroid can regenerate from an adult to a child’s organism.

Jellyfish do not have a mouth, but they do have an oral proboscis. She can always trigger the revival mechanism. Fernando Boero reported about the degeneration of the jellyfish; while studying hydroids, he conducted experiments on them. He placed some of them in the aquarium, but, unfortunately, the experiment was disrupted, as a result of which the water dried up and Fernando discovered that the jellyfish did not die, but only threw off their tentacles, transforming into larvae.

Nutritional resources and eating process

Plankton, Artemia

The main resource in the food of hydroid jellyfish is plankton. For them, the basis of nutrition is Artemia, such jellyfish are considered predators. The tools for obtaining food are the tentacles, which are located on the edge of the umbrella body. The digestive system of these jellyfish is called gastrovascular. Jellyfish catch prey by passively moving their tentacles in the water, into which plankton falls, after which it begins active swimming. In such jellyfish, the nervous system consists of cellular networks that form 2 rings, one of them is the outer one, which is responsible for sensitivity, and the inner one is responsible for movement.

One of the hydroid jellyfish have light-sensitive eyes, which are located in the center of the tentacle. Hydra, by its nature, is a predator for food; it chooses ciliates, planktonic crustaceans, and also fry. They wait for prey by clinging to an aquatic plant and at the same time open their tentacles wide. When at least one tentacle reaches the prey, then all the other tentacles completely envelop the victim. And it quickly swallows its prey whole; when the hydra is satiated, its tentacles contract.

Reproduction

Reproduction of hydroid jellyfish is more often external than internal. Mature germ cells move outward, after which blastula is formed and some of the cells end up inside, forming endoderm. After some time, several cells degenerate to form a cavity. After this, the egg turns into larvae - a planula, and then into a hydropolyp, which buds into other polyps, as well as small jellyfish. After which the little ones grow up over time and begin to develop independently.

Hydra is one of the most convenient objects for conducting experiments, with the help of which scientists studying regeneration in animals. When the hydra is cut in half, after some time it itself restores the missing parts. Also, this type of surgery is easy to perform without anesthesia and there is no need to use special instruments. Hydra has the property of restoring not only from half, but even from the smallest pieces many polyps are revived.

Hydra habitats

Hydroid jellyfish are not always found, but in large concentrations carried by the current. The benthic class includes stages of polyps that lead a sedentary life, the exception to which is class of planktonic hydroid polyps. Hydroid species are also capable of grouping with the help of the wind into huge groups, but hydroid polyps, when clustered, seem to be one whole. If the jellyfish and the polyp are hungry, their movement will be aimed only at obtaining food, but when the body is saturated, their tentacles will begin to contract and be pulled towards the body.

Habitat zones

Jellyfish move depending on the presence or absence of hunger. In general, all species occupy a specific habitat, this can be either a lake or an ocean. They do not deliberately seize new territories for themselves. Alone prefer to live in warmth, while others, on the contrary, are in the cold. They can also be located both below at depth and on the surface of the water. Hydroid jellyfish can be found in the littoral zone, and they do not have a fear of the surf. Most of these jellyfish have a polyp, which is protected from impact by a skeletal cup (theca). The structure of the theca is thicker than that of other species that live deeper, where the perceptibility of the wave is much less.

At greater depths, a special type of hydroids lives, which is unlike littoral hydroids. At this depth there are colonies, having the form such as:

• tree,
• Christmas tree,
• feather,
• and there are also types of colonies that look like ruff.

Such species grow from 15 to 20 cm and cover the entire seabed with dense forest. Some species, for example, like the sea spider, live in these forests and eat hydropolyps.

Hydra can very rarely live in less saline waters, such as in the Gulf of Finland for such species, the salinity of the inhabited space should not exceed 0.5%. The hydroid jellyfish often lives close to the shore and in brighter places. This type of jellyfish does not have a tendency to be mobile; they most often attached to a plant branch or rock. One of the most favorite states of the hydroid jellyfish is to be upside down and have some tentacles hanging down.

Dangerous types of jellyfish for humans

But not all can be safe for human life. One of the most beautiful species called "Portuguese man-of-war" may cause harm to humans. The bell, which is present in it and has a beautiful appearance, attracting attention, can cause harm.

Physalia, which is found in Australia, as well as on the coasts of the Indian and Pacific Oceans and even the Mediterranean, is one of the huge hydroid species. Physalia's bubble can reach a length of 15 to 20 cm. But Physalia's tentacles can be much scarier, since their length and depth can extend to thirty meters. Physalia can leave burns on the victim's body. An encounter with a Portuguese man-of-war is especially harmful for people with weakened immune systems and people prone to allergies.

But most hydroid jellyfish will not harm humans, unlike scyphoids. There is a so-called white algae from the genus polyps, which was previously used as decorative jewelry. Some of the hydroid species act as laboratory animals - these are polyps from the Hydra class, which are even used in schools around the world.