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 type Coelenterates 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 Coelenterata 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.

TYPE Coelenterate

The type of coelenterates includes lower multicellular animals, the body of which consists of two layers of cells and has radial symmetry. They live in marine and fresh water bodies. Among them there are free-swimming (jellyfish), sessile (polyps), and attached forms (hydra).

The body of coelenterates is formed by two layers of cells - ectoderm and endoderm, between which there is mesoglea (non-cellular layer). Animals of this type have the appearance of an open sac at one end. The hole serves as a mouth, which is surrounded by a corolla of tentacles. The mouth leads into the blindly closed digestive cavity (gastric cavity). Digestion of food occurs both inside this cavity and by individual cells of the endoderm - intracellularly. Undigested food remains are excreted through the mouth. In coelenterates, a diffuse type nervous system appears for the first time. It is represented by nerve cells randomly scattered in the ectoderm, which touch with their processes. In swimming jellyfish, a concentration of nerve cells occurs and a nerve ring is formed. Reproduction of coelenterates is carried out both asexually and sexually. Many coelenterates are dioecious, but hermaphrodites are also found. The development of some coelenterates is direct, while in others it is with a larval stage.

There are three classes in the type:

1. Hydroid

2. Jellyfish

3. Coral polyps

Hydroid class

His representative is freshwater hydra. The body of the hydra is up to 7 mm long, the tentacles are up to several cm.

The bulk of the large number of different types of hydra cells are integumentary muscle cells, forming the integumentary tissue. There is no muscle tissue as such; its role is also played by skin-muscle cells.

The ectoderm contains stinging cells, which are mainly located on the tentacles. With their help, the hydra defends itself and also detains and paralyzes prey.

The nervous system is primitive, diffuse. Nerve cells (neurons) are evenly distributed in the mesoglea. Neurons are connected by strands, but do not form clusters. Sensory and nerve cells provide the perception of irritation and its transmission to other cells.

There is no respiratory system; hydras breathe through the surface of the body. There is no circulatory system.

Glandular cells secreting adhesive substances are concentrated mainly in the ectoderm of the sole and tentacles. They also synthesize enzymes that help digest food.

Digestion in hydra occurs in the gastric cavity in two ways - intracavitary, with the help of enzymes, and intracellular. Endoderm cells are capable of phagocytosis (capturing food particles from the gastric cavity). Some of the skin-muscle cells of the endoderm are equipped with flagella that are in constant motion, which rake particles towards the cells. They organize pseudopods, thereby capturing food. Undigested food remains are removed from the body through the mouth.

Between all these cells there are small undifferentiated intermediate cells that can, if necessary, turn into any other types of cells; regeneration (the process of restoring lost or damaged parts of the body) occurs due to these cells.

Reproduction:

· Asexual (vegetative). In summer, under favorable conditions, budding occurs.

· Sexual. In autumn, with the onset of unfavorable conditions. The gonads form as tubercles in the ectoderm. In hermaphroditic forms they are formed in different places. The testes develop closer to the oral pole, and the ovaries closer to the sole. Cross fertilization. The fertilized egg (zygote) is covered with dense membranes and falls to the bottom, where it overwinters. The following spring, a young hydra emerges from it.

Class scyphoid

The class of scyphoid jellyfish is found in all seas. There are species of jellyfish that have adapted to live in large rivers flowing into the sea. The body of scyphojellyfish has the shape of a rounded umbrella or bell, on the lower concave side of which an oral stalk is placed. The mouth leads to a derivative of the dermis - the pharynx, which opens into the stomach. Radial canals diverge from the stomach to the ends of the body, forming the gastric system.

Due to the free lifestyle of jellyfish, the structure of their nervous system and sensory organs becomes more complex: clusters of nerve cells appear in the form of nodules - ganglia, balance organs - statocysts, and light-sensitive eyes.

Scyphojellyfish have stinging cells located on the tentacles around the mouth. Their burns are very sensitive even for humans.

Reproduction:

Jellyfish are dioecious; male and female reproductive cells are formed in the endoderm. The fusion of germ cells in some forms occurs in the stomach, in others in water. Jellyfish combine their own and hydroid characteristics in their developmental features.

Among the jellyfish there are giants - Physaria or Portuguese man-of-war (from 3 m or more in diameter, tentacles up to 30 m).

Meaning:

· Consumed as food

· Some jellyfish are deadly and poisonous to humans. For example, when bitten by a cornet, significant burns can occur. When bitten by a cross, the activity of all systems of the human body is disrupted. The first encounter with a cross is not dangerous, the second is fraught with consequences due to the development of anophiloxia. A tropical jellyfish sting is fatal.

Class coral polyps

All representatives of this class are inhabitants of the seas and oceans. They live mainly in warm waters. There are both solitary corals and colonial forms. Their sac-like body, with the help of the sole, is attached to underwater objects (in solitary forms) or directly to the colony. A characteristic feature of corals is the presence of a skeleton, which can be either calcareous or consist of a horn-like substance and is located either inside the body or outside (the anemone has no skeleton).

All coral polyps are divided into two groups: eight-rayed and six-rayed. The former always have eight tentacles (sea feathers, red and white corals). In six-rayed species, the number of tentacles is always a multiple of six (anemones, madrepore corals, etc.).

Reproduction:

Coral polyps are dioecious animals; fertilization occurs in water. From the zygote a larva develops - a planula. The planula attaches to various underwater objects and turns into a polyp, which already has a mouth and a corolla of tentacles. In colonial forms, budding subsequently occurs, and the buds are not separated from the mother organism. Colonies of polyps participate in the formation of reefs, atolls, and coral islands.

Coelenterates lead an exclusively aquatic and, in most cases, marine lifestyle. Some of them are free-swimming, while others, no less numerous forms, are sessile animals attached to the bottom. Coelenterata includes about 9,000 species.

The structure of coelenterates is characterized by radial, or radiant, symmetry. In their body, one can distinguish one main longitudinal axis, around which various organs are located in a radial (radial) order. The order of radial symmetry depends on the number of repeating organs. So, if there are 4 identical organs around the longitudinal axis, then radial symmetry in this case is called four-ray. If there are six such organs, then the order of symmetry will be six-rayed, etc. Due to this arrangement of organs, several (2, 4, 6, 8 or more) planes of symmetry can always be drawn through the body of coelenterates, i.e. planes by which the body is divided into two halves, mirror images of each other. In this respect, coelenterates differ sharply from bilaterally symmetrical, or bilateral, animals (Bilateria), which have only one plane of symmetry, dividing the body into two mirror-like halves: right and left.

Radial symmetry is found in several widely separated groups of animals, which, however, have a common biological feature. All of them either currently lead a sedentary lifestyle, or led one in the past, i.e. come from attached animals. From this we can conclude that a sedentary lifestyle contributes to the development of radiant symmetry.

Biologically, this rule is explained by the fact that in sessile animals one pole usually serves for attachment, while the other, free, carries the mouth. The free oral pole of the animal in relation to surrounding objects (in the sense of the possibility of grasping food, touch, etc.) is placed in completely identical conditions on all sides, as a result of which many organs receive the same development at different points of the body located around the main axis, passing through the mouth to the opposite attached pole; the result of this is the development of radiative symmetry. The situation is completely different for crawling animals.

Coelenterates are two-layered animals (Diploblastica): during ontogenesis, only two germ layers are formed - ecto- and endoderm, which are clearly expressed in the adult animal. The ectoderm and endoderm are separated by a layer of mesoglea.

In the simplest case, the body of coelenterates looks like an open sac at one end. In the cavity of the sac, lined with endoderm, food is digested, and the opening serves as the mouth. The latter is usually surrounded by several or one corolla of tentacles that capture food. Undigested food remains are removed from the body through the mouth. In terms of structure, the most simply organized of the coelenterates can be reduced to a typical gastrula.

Depending on the lifestyle, this structure diagram may vary slightly. The closest to it are sessile forms, which are given a common name - polyps: free-swimming coelenterates usually experience a strong flattening of the body in the direction of the main axis - these are jellyfish. The division into polyps and jellyfish is not systematic, but purely morphological; sometimes the same species of coelenterates at different stages of the life cycle has the structure of either a polyp or a jellyfish. In the medusoid state, coelenterates are usually solitary animals. On the contrary, polyps are only in rare cases solitary. The vast majority of them, starting life as a single polyp, then form colonies consisting of hundreds and thousands of individuals through budding, which does not reach the end. Colonies consist of completely identical individuals (monomorphic colonies) or of individuals that have different structures and perform different functions (polymorphic colonies).

The most characteristic feature of the type is the presence of stinging cells. Movement is carried out by muscle contractions.

The coelenterates include more than 8 thousand species that lead an exclusively aquatic lifestyle. Among them there are free-floating forms and sessile organisms attached to the bottom or underwater objects (animals). 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.

The appearance of coelenterates in the seas dates back to the Proterozoic era, when the first representatives of this group of animals appeared.

The emergence of coelenterates was accompanied by major aromorphoses, which significantly expanded the capabilities of their owners in using their habitat:
1) multicellularity;
2) the formation of the first tissues - ecto- and endoderm;
3) radial symmetry;
4) differentiation of cells into a number of specialized cell types;
5) the emergence of a nervous system of a diffuse type, consisting of individual cells connected by processes;
6) the appearance of partially intracavitary digestion;
7) the appearance of germ cells specialized for reproduction.

The phylum of coelenterates includes the classes of hydroid, scyphoid (jellyfish) and coral polyps.

Hydroid class. Freshwater Lolip Hydra

Body structure. Double-layered aquatic animals. Radial symmetry. The body is sac-like, elongated up to 1.5 cm in length. At the anterior end of the body there is a mouth surrounded by tentacles carrying a large number of stinging cells. The posterior end is the sole, with which the hydra attaches to the substrate (stones, plants, etc.).

Wall bodies. The outer layer of the hydra's body is the ectoderm, consisting of stinging, musculocutaneous and nerve cells. Beneath the ectoderm is a noncellular basement membrane or mesoglea.

Digestive system closed. It is represented by the gastric cavity, beginning with the oral opening. The cavity is lined with endoderm, the cells of which are capable of phagocytosis. Digestion is both cavity and intracellular (digestive vacuoles). Undigested remains are expelled through the mouth.

Breath hydra. Oxygen dissolved in water is absorbed by the entire surface of the body.

Selection. The end products of dissimilation are excreted through the ectoderm.

Nervous system consists of stellate nerve cells connected by their processes.

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

Reproduction. Asexual budding predominates. Animals are hermaphrodites; eggs and sperm develop in the ectoderm. Cross fertilization.

Development. From the zygote a two-layered larva with the rudiment of the intestinal cavity is formed - planula, which moves in water and winters at the bottom of the reservoir. Adult hydras die in the fall.

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- These are multicellular invertebrate animals living in the 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 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. For every predator there is a 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.