Coelenterates. Classes of coelenterates Respiratory system of coelenterates

Type Coelenterates are multicellular individuals, inhabitants of water spaces, mainly seas. Some species have adapted to a sedentary lifestyle (attached to the bottom or substrate), others actively move, covering long distances.

There are more than 10,000 species of coelenterates. The diversity of coelenterates is very great: there are small individuals up to a couple of millimeters, and huge representatives are cyanea jellyfish, about two meters wide, and the tentacles reach 15 meters in length.

Why did coelenterates get this name? Coelenterates have a two-layer body, so that a cavity is formed between the cells of the layers, which is equipped with one mouth opening. The cavity is called intestinal, and this is how the name coelenterates was formed.

Coelenterates are characterized by radial symmetry; if you draw a line from the lower edge to the upper, then the opposite parts of the body relative to the drawn axis will be identical. The polyp wall consists of three layers.

Epidermis

The first layer is the outer ball of epithelial cells (epidermis).

The ectoderm also includes:

• Contractile cells(provide movement);
• stinging which perform a protective function. The capsule of the stinging cells contains a paralyzing poison; when danger approaches, toxic substances enter a special channel, which is located in the stinging thread and is directed to the victim’s body. After the poison spills out, the cell dies, a new one from intermediate cells begins to form;
• intermediate cells capable of constant division and transformation into specialized ones, this is how the body regenerates;
• germ cells– eggs and sperm are formed in ectodermal tubercles.

Endoderm

The second layer is the inner layer (endoderm). The ball of cells lines the intestinal cavity and consists of two types of cells:

• Digestive– have flagella and pseudopods, with the help of which they capture food particles and carry out intracellular digestion;
• glandular- secrete enzymes to break down food in the gastric cavity.

Mesoglea

Mesoglea, which is located between the layers and is a jelly-like mass with collagen fibers, does not contain cells.

Coelenterates lack mesoderm - the middle germ layer.

Organs of coelenterates

All representatives are deprived of specialized respiratory, circulatory, and excretory organs. Nervous system coelenterates are represented by nerve cells that are connected into a nerve plexus. Jellyfish have nerve rings near the mouth and dome.

Digestion carried out in the intestinal cavity due to glandular cells; epithelial-muscle cells are responsible for intracellular digestion. Digested residues are removed through the mouth (closed digestive system).

Reproduction coelenterates go by budding; this is an asexual mechanism when the body is divided in the longitudinal or transverse directions. During sexual division, sperm and eggs enter the external environment, where they merge. First, the zygote is formed, and then the larva, the planula, emerges. After the transformation of the planula, either a polyp or a jellyfish can form from it.

Life cycle of coelenterates

Depending on the life cycle of coelenterates, two groups are distinguished: asexual generation (polyps) and sexual generation (jellyfish).

Polyps- These are single organisms or colonial ones, which unite from tens to thousands of individual individuals. Equipped with a mouth opening with tentacles, which passes into the gastric cavity. The lower part of the polyp is the sole, with which it is attached to underwater objects or the bottom.

The internal cavity is divided by septa, the number of which corresponds to the number of tentacles. Cilia extend from the septa, which are in constant motion and ensure a regular change of water inside the polyp.

The continuous movement of water ensures increased pressure in the intestinal cavity, so the polyps straighten out and remain in this position for a long time. When he gets tired, he changes his position by bending over or moving a short distance.

The body shape is similar to a bell, the contractile cells of which ensure the active movement of individuals in the water. Mesoglea is 98% water, the rest is connective tissue. Due to their high water content, jellyfish can easily stay in the aquatic environment.

At the bottom of the bell there is a mouth opening with oral lobes. With the help of the mouth, food is captured, which enters the intestinal cavity. It consists of many tubules that extend from the central cavity. In the mouth area there are stinging cells that serve to obtain food and protect against enemies.

Jellyfish have sensory organs; there are eyes on the surface of the body that perceive light rays. If a jellyfish washes ashore, it will die due to complete evaporation of the water.

What stage of the life cycle of coelenterates contributes to their dispersal?

The dispersal of animals across the sea occurs at the larval and medusoid stages. During these periods of life, they are able to move or are carried away by the current. During the entire period of its existence, a polyp can only move a couple of meters, and most are completely motionless.

Types of coelenterates

The following types of coelenterates are distinguished: hydroid, scyphoid and coral polyps.

Hydroid– have a relatively simple structure in comparison with other representatives of the type. They feed on plankton and small animals. In the spring-summer period, it reproduces asexually; buds develop on the body, which, when mature, leave the mother. In the fall, sexual reproduction occurs, with the formation of an egg, which in the spring will give birth to new organisms.

Scyphoid– a class of free-swimming jellyfish, the polyp stage is either absent or poorly developed. Reproduction is sexual, a scyphostoma is formed, from which jellyfish bud (the young form is ether).

Coral– organisms with an internal keratinized skeleton. They lead a sedentary lifestyle, reproduce by budding, and are not separated from the mother’s body, or sexually.

Comparative table of differences between flatworms and coelenterates
Characteristic	Type Coelenterates	Flatworms
Habitat	Water environment
Category	Multicellular
Body type	Radial symmetry	Bilateral symmetry
Wall structure	Two layers of cells	Three layers of cells
Organs and systems	The presence of only specialized cells: muscle, nerve, reproductive cells	Characteristic of all representatives

Flatworms have a more complex structure and advanced differentiation of tissues and organs. But representatives of the coelenterates have evolved significantly in comparison with the simplest organisms, which is manifested in their structure, way of life, and procreation.

Compare the vital functions of coelenterates and protozoa using the table provided.

Comparison of the life activities of coelenterates and protozoa
Characteristic	Coelenterates	Protozoa
Category	Multicellular	Unicellular
Habitat	Water environment	Soil, water
Movement	By contracting muscle cells	Due to flagella and contractile vacuoles
Specialized cells	Present	None
Nutrition	Heterotrophs
Reproduction	Sexual and asexual
Breath	Body surface

The role of coelenterates in nature

They participate in the regulation of the number of small fish and crustaceans, as they are food for coelenterates.

They are an integral part of the marine biocenosis.

They form coral reefs - massive accumulations of madrepore corals. They are located near islands, gradually growing upward, forming islands (atolls).

Atolls - islands made of coral reefs

Serve as raw material for lime extraction.

Coelenterate organisms can live in symbiosis with other animals. Sea anemones, which lead a sedentary lifestyle, often attach to crayfish and thus move faster. Cohabitation is also beneficial for cancer, since the sea anemone protects it from enemies.

The sea anemone's tentacles serve as a hiding place for small shrimp.

The importance of coelenterate organisms in human life

Widely used in the food industry (edible jellyfish - rootworms). Every year the Japanese catch several thousand tons of Ropilem jellyfish, from which they prepare various dishes.

Jewelry is made from the skeleton of a red coral polyp.

Coral reef islands become an obstacle to transport ships.

The poison, which is secreted by the stinging cells of coelenterates, is dangerous to human health and causes severe burns, as well as respiratory failure and cardiac arrhythmia.

One of the first groups of multicellular animals is the type Coelenterata. Grade 7, which includes a zoology course, examines in detail all the structural features of these amazing creatures. Let's remember once again what they are.

Type Coelenterates: biology

These animals received the name of the systematic unit due to the structure of the same name. It is called the intestinal cavity, and all representatives of the type have it: both polyps that lead an attached lifestyle and actively moving jellyfish. A characteristic of the coelenterate type is also the presence of specialized cells. But despite such a progressive structural feature, the body of these animals does not form real tissues.

Habitat and size

These first true multicellular animals can be found in fresh and salt water bodies of various climatic zones. The type Coelenterates (the 7th grade of a comprehensive school studies this topic in some detail) is represented by small individuals with a diameter of several millimeters, and giant jellyfish with tentacles up to 15 meters long. Therefore, the nature of the reservoir where they live may be different. Thus, small freshwater hydras live in small puddles, and coral polyps form huge colonies in tropical seas.

Type Coelenterates: general characteristics

The body of all coelenterates consists of several types of cells, each of which performs a specific function, like the organs of more complex animals.

The main characteristic of coelenterates is the presence. They consist of a capsule in which a thread with a sharp end is twisted. A sensitive hair is located on top of the cell. When it touches the victim's body, it spins and bites into it with force. As a result, it has a paralyzing effect. Next, using tentacles, representatives of this type place the victim into the intestinal cavity. And here the process of breakdown of organic substances begins. And the digestive and

The Coelenterate type is characterized by a high degree of regeneration. Scientists have proven that freshwater hydra can completely restore a body from 1/200 parts. And this is possible due to the presence of intermediate cells. They actively divide, giving rise to all other types. Coelenterates are also capable of sexual reproduction due to the fusion of eggs and sperm.

Nerve cells are scattered throughout the body, interconnecting the body with the environment and uniting it into a single whole. So, the movement of one of them is very interesting - the hydra. Thanks to the activity of the skin-muscle cells, she, like an acrobat, moves from the head to the sole, doing a real somersault.

Life processes of coelenterates

The phylum Coelenterata is characterized by a more complex physiology compared to its predecessors - protozoa and sponges. Although there are some common signs. For example, gas exchange still occurs through the integument, and there are no specialized structures for this.

Due to the presence of skin-muscle cells, jellyfish are capable of contracting. At the same time, their bell contracts, water is pushed out with force, causing a reverse push.

All coelenterates are carnivorous animals. With the help of tentacles, prey enters the body through the mouth opening. The effectiveness of the digestion process is proven by the simultaneous existence of two types of digestion: cavity and cellular.

Coelenterates are characterized by the presence of a response from their body to irritation - reflexes. They arise in response to mechanical or chemical influences from the environment. And jellyfish have special sensitive formations that ensure the maintenance of body balance and perception of light.

Life cycle

The phylum Coelenterata is also characterized by the fact that in many of its species there is an alternation of generations in the life cycle. For example, the aurelia polyp reproduces exclusively asexually using budding. Over time, the body of one of them is separated by transverse constrictions. As a result, small jellyfish appear. Visually, they resemble a stack of plates. One by one, they break away from above and move on to an independent and active lifestyle.

The alternation of sexual and asexual generations in the life cycle of coelenterates contributes to a rapid increase in their numbers and more efficient settlement.

Includes the type Coelenterate classes, the polyps of which are not shed off. They form colonies of bizarre shapes. These are coral polyps. There is no alternation of generations in freshwater hydra either. They reproduce in the summer by budding, and in the fall they proceed to sexual reproduction, after which they die. Fertilized eggs overwinter at the bottom of reservoirs. And in the spring, young hydras develop from them.

Diversity of coelenterates

The phylum Coelenterates in nature is represented by two life forms: polyps and jellyfish. One of the most interesting representatives of the first group is sea anemone. This is an inhabitant of warm tropical seas, which, thanks to its bright color, looks like a fantastic flower. Hence the second name for sea anemones - sea anemones. Among them there are predators and filter feeders. And some species of sea anemones can enter into mutually beneficial cohabitation with hermit crabs.

The polyp has the ability to move and feed on the remains of organic arthropod food. And the cancer is reliably protected by the stinging cells of the sea anemone. It is interesting that, changing the shell from time to time, he also transplants the polyp there. The cancer strokes the sea anemone with its claws, as a result of which it independently crawls to a new home.

And colonies of coral polyps form huge clusters. For example, the Great Barrier Reef stretches along the coast of Australia for a distance of about 2 thousand km.

The importance of coelenterates in nature and human life

Many coelenterates can be dangerous to animals and humans. The action of their stinging cells causes burns. Their consequences for humans can be convulsions, headaches, disturbances in the functioning of the heart and respiratory organs. If help is not provided in time, death is possible.

Polyps and jellyfish are an important link in the food chain of aquatic life. And corals in many countries are used to make jewelry, souvenirs and building materials.

So, the type Coelenterates, the general characteristics of which we have considered, is represented by two life forms. These are polyps and jellyfish. These animals are characterized by the presence of specialized cells and alternating generations in the life cycle.

In this article we will look at the features of the type of coelenterates. What animals belong to it? Why are they combined into this type? So, coelenterates are multicellular invertebrate animals living in an aquatic environment. This includes jellyfish (or scyphoid), coral polyps And hydra (hydroid). Their body, in a schematic simplification resembling a pouch, is formed from outer and inner layers of cells and is characterized by radial symmetry.

Coelenterates evolved from primitive multicellular organisms, consisting of two types of cells. They live exclusively in water, both salty and fresh. Coelenterates differ in whether they are prone to changing their place of residence. Jellyfish are free-swimming and move quite quickly, but coral polyps are attached forms that can live in colonies or alone. The freshwater hydra is an intermediate form - it usually leads a sedentary lifestyle, but is also capable of movement, albeit very slowly.

The structure of coelenterates

1. Coelenterates have only one “entrance”, that is, the oral cavity, and no “exit”. The mouth, lined with tentacles, leads into a blindly closed gastric (intestinal) cavity- hence the name.

2. The body consists of two cell layers: ectoderm(motor cells with flagella) and endoderm (digestive, forming pseudopods). Between them lies the noncellular layer mesoglea.

3. Diffuse nervous system the coelenterate was formed for the first time in the process of evolution. Nerve cells are randomly located throughout the ectoderm and touch each other with processes.

4. In jellyfish, nerve cells are collected in nodes - ganglia, forming a nerve ring.

5. Coelenterates do not have respiratory or excretory organs.

Nutrition of coelenterates

1. Coelenterates - predatory animals. Their food is a variety of living small things that the aquatic environment is chock full of.

2. Coral polyps are capable of two types of nutrition. At heterotrophic Typically, they capture food with their brightly colored tentacles, but with conventional “ autotrophs" they are helped by symbiotic algae living inside the polyps.

3. Coelenterates digest food both inside the gastric cavity (the so-called intracavitary digestion), and in endoderm cells ( intracellular digestion).

4. Undigested food is sent back to where it came from - through the oral cavity into the external environment.

Reproduction of coelenterates

1. Implemented reproduction coelenterates in two ways: asexual And sexual. Moreover, for many representatives these two options can replace each other - there is an alternation of generations.

2. Coelenterates are characteristic separation of the sexes, however, among them there are hermaphrodites, for example, ceriantharian corals and common hydra.

3. There are species with direct development, but there are also coelenterates that pass through larval stage.

The importance of coelenterates

1. Every predator has its own predator - coelenterates are food for marine life. For example, butterfly fish happily eat coral polyps. Jellyfish also serve as food for fish and sea turtles. Even humans do not disdain several species of jellyfish; in Asia, cornerotae, Stomolophus meleagris and others have long been held in high esteem.

2. Coral thickets are home to many living organisms. There is always food and shelter here.

3. Coral polyps filter water and thereby purify it.

4. Corals participate in the calcium cycle, form sedimentary rocks, fantastically beautiful coral reefs and islands.

5. Construction materials are made from corals. The product of their firing is lime.

6. Red and black corals have been used by humans for thousands of years as jewelry.

The most ancient and primitive multicellular animals. They evolved from primitive primordial multicellular organisms. All coelenterates are aquatic animals, most of which live in the seas and oceans. They inhabit seas from the surface to extreme depths, from tropical waters to polar regions. A small number of species live in fresh waters. About 9,000 species of coelenterates are now known. Among them there are solitary and colonial animals.

Common features of this type:

1. The body is sac-shaped, formed by two layers of cells: the outer - ectoderm, and the inner - endoderm, between which there is a structureless substance - mesoglea.
2. Radial, or radial, symmetry of the body, formed in connection with an attached or sedentary lifestyle.
3. Two life forms are characteristic: a sessile sac-like polyp and a free-swimming discoid jellyfish. Both forms can alternate in the life cycle of the same species.

4. Absence of tissue in most species (except coral polyps). The outer and inner layers of the body include several types of cells, different in structure and functions. Many vital processes in coelenterates occur at the cellular level.
5. The digestive system is primitive and consists of a blindly closed intestinal cavity and an oral opening. Digestion of food begins in the intestinal cavity under the action of enzymes, and ends in specialized cells of the endoderm, i.e. the digestion process is mixed. Undigested food remains are removed through the mouth.
6. The diffuse type nervous system that first appeared consists of nerve cells evenly distributed in the body, connected by processes and forming a nervous network.
7. Reproduction occurs both asexually and sexually. Incomplete asexual reproduction - budding - leads to the formation of colonies in a number of species. Many coelenterates are dioecious, but there are also hermaphrodites. Fertilization takes place in water, i.e. external. The vast majority of species develop with free-swimming larvae that have cilia.

Classification of Coelenterates

These are lower, mainly marine, multicellular animals, attached to the substrate or floating in the water column. Type Coelenterates combines three classes: Hydroid, Scyphoid and Coral polyps.

Hydroid class

• They live in fresh water bodies and the bottom of seas.
• The intestinal cavity is devoid of partitions.
• Lifestyle - attached; move slowly.
• Representatives: common hydra, brown hydra, green hydra

Class Scyphoid

• They live in deep sea water.
• The lifestyle is floating.
• Representatives: aurelia jellyfish, cyanea jellyfish, cornerotus jellyfish

Class Coral

• They live at the bottom of the sea.
• The intestinal cavity is divided into chambers.
• Lifestyle - attached; have an exoskeleton
• Representatives: sea anemone, red coral, black coral

The importance of coelenterates

The meaning of coelenterates:

• an important link in ecological food chains
• biological treatment of sea water
• participation in the calcium cycle and in the formation of sedimentary rocks
• raw materials for making jewelry and art objects
• raw materials for the production of biologically active substances
• danger to humans (some types of jellyfish)

Table “Coelenterates” (briefly)

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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
  • glandular cells that secrete digestive enzymes into the gastric cavity
  • 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

Subtype characteristics

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, without 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 the 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 ones, 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 observe 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.

• Cyanea jellyfish (Suapea) [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-nutrition product, but salted ropilem 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

Subtype characteristics

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.