Coelenterates have. Type Coelenterates: general characteristics

And coral polyps belong to type of coelenterates. They are also called stinging– for stinging cells located in the tentacles and other parts of the body. Animals use stinging cells to catch, immobilize and kill victims; the burns of some are very painful for people, and several species of coelenterates are even capable of fishing for humans. The name coelenterates reflects the threefold structure of their body - they resemble an empty bag, the inside of which is occupied by the digestive cavity. Most of these creatures live in the sea and only a few species have adapted to life in fresh water. There are no land coelenterates.

The digestive cavity of jellyfish and other coelenterates has a single opening - this is both the mouth and the outlet for undigested residues. It is usually surrounded by long and thin tentacles, the number of which can exceed a hundred. On the outside, their surface is strewn with stinging cells.
If we look at a jellyfish from below, we will see swaying tentacles, or oral lobes, that immobilize the prey and pull it towards the mouth.
Purple-striped jellyfish are quite difficult to spot in the murky sea waters where they drift like ghosts.

Most coelenterates have a soft, transparent, quivering body containing a large sac-like digestive cavity. The body of an animal is formed by two layers of cells and a jelly-like substance between them. Some species, such as corals, build strong cup-shaped protective shells around themselves. Jellyfish have a particularly thick layer of jelly-like substance.
BODY SHAPE. In the group of coelenterates, there are two main life forms: jellyfish and polyp. Some coelenterates spend their entire lives in one form. For example, hydra and sea anemones always live in the form of polyps. But many coelenterates begin life as a polyp and then turn into jellyfish - or vice versa.

POLYP. A typical polyp has a soft, cylindrical shape. The elongated lower part of the body serves to attach the animal to stones, algae and other objects. At the top of the polyp there is a mouth surrounded by a ring of hunting stinging tentacles directed upward. Sea anemones and corals spend their entire lives in the form of polyps; they do not have the jellyfish stage.

JELLYFISH. The typical one resembles a polyp turned upside down. Her body looks like an umbrella or a bell, from behind the edge of which tentacles pointing downwards peek out. The mouth is located in the center on the underside of the body. Usually the jellyfish swims in the water column, and the polyp sits and slowly crawls at the bottom. Jellyfish spend all or most of their lives drifting in the oceans.

PALE OR BRIGHT. Some jellyfish, sea anemones and corals are pale or milky in color, especially in cold waters. At the same time, tropical species are often colored in bright shades of pink, red, yellow and orange.
At low tide, sea anemones appear as dull patches of jelly on the exposed rocky seabed. But with the onset of tide, they spread their soft tentacles, similar to the corollas of flowers. For this they are called “sea anemones”. But of course sea anemones are animals. Like all coelenterates, sea anemones look harmless, but in fact they are merciless predators.

Coelenterates:
- about 10,000 species
- mainly marine inhabitants, there are several freshwater species
- have a round body shape
- mouth surrounded by tentacles
- most are soft-bodied, but some (corals) form strong, hard protective shells or skeletons
- the stinging cells of some representatives contain poison dangerous to humans

The type is divided into three classes:
1. Hydroid
– about 3500 species
– marine and freshwater (hydra)
– in the life cycle the stages of polyp and jellyfish usually alternate; there are colonial forms.

2. Coral polyps (including sea anemones)
– about 6000 species
– only sea
– live only in the form of polyps

3. Scyphoid (jellyfish)

Type coelenterate classes cells meaning biology body sponges characteristics structure life symmetry representatives of the system signs of jellyfish general characteristics hydroid groups

Latin name Coelenterata

To type coelenterates These include lower multicellular animals, which, however, are superior to sponges in a number of ways. They are predominantly marine animals, and only a few of them live in fresh waters. The phylum Coelenterata includes about 9,000 species. The body of coelenterates is formed by two layers of cells: the outer - ectoderm and the inner - endoderm. Between the ectoderm and endoderm there is a structureless substance, which in some forms (hydra, marine hydroid polyps) forms a thin basement membrane, and in others (hydromedusa, scyphomedusa, coral polyps) is represented by gelatinous mesoglea.

Coelenterates

General characteristics of coelenterates

The phylum coelenterates include lower multicellular animals, which, however, are superior to sponges in a number of ways. They are predominantly marine animals, and only a few of them live in fresh waters. Type of coelenterates includes about 9000 species. The body of coelenterates is formed by two layers of cells: the outer - ectoderm and the inner - endoderm. Between the ectoderm and endoderm there is a structureless substance, which in some forms ( hydra, marine hydroid polyps) forms a thin basement membrane, and in others (hydromedusae, scyphomedusae, coral polyps) it is represented by gelatinous mesoglea.

Most coelenterates have radial, or radial, symmetry, but in more highly organized coral polyps, deviations towards two-radial and even bilateral, or bilateral, symmetry are observed.

Coelenterates are characterized by two life forms: a sessile sac-like polyp and a floating disc-shaped jellyfish. Both life forms can alternate in the life cycle of the same species, i.e., a generation of polyps that reproduce asexually gives rise to a generation of floating jellyfish that form sexual products (marine hydroid polyps, scyphoid ones). Thus, most coelenterates are characterized by alternation of generations - metagenesis. However, some groups of coelenterates do not have a medusoid generation (hydra, coral polyps) or have lost the life form of a polyp (some species of hydroids and scyphoids).

All coelenterates are characterized by the presence of special stinging cells that serve as a means of defense and attack, which are not found in other types of animals.

The digestive system of coelenterates is very primitive. The mouth is the only opening leading to the blindly closed gastric cavity. Unlike sponges, digestion of food in coelenterates occurs under the action of enzymes in the gastric cavity. Small food particles into which food breaks down are captured by endoderm cells and digested intracellularly. Thus, in addition to extracellular, or cavity, digestion, primitive intracellular digestion of food takes place. Excretion occurs through the mouth. In polyps, the gastric cavity is sac-shaped, and in jellyfish, due to the powerful development of the mesoglea, it breaks up into a system of canals (radial and annular), which is called gastrovascular. The latter ensures the digestion of food and the distribution of nutrients throughout the animal’s body. In addition, the gastrovascular system takes part in gas exchange.

Within the phylum of coelenterates, a complication of the structure of the digestive system is observed. In more primitive hydroids and scyphoids, the entire gastric cavity is formed by endoderm. They have the so-called gastric type of structure: the ectoderm and endoderm converge along the edges of the mouth opening, which resembles the stage of the embryo - the gastrula. In more highly organized coral polyps, the anterior part of the intestine - the ectodermic pharynx - is formed for the first time. An increase in the surface of the gastric cavity can also be considered a progressive feature, which is achieved in polyps by the formation of septa, or septa, and in jellyfish - by the complication of the gastrovascular system.

Coelenterates are at the tissue level of organization, that is, they have real, albeit poorly differentiated, tissues. In more primitive hydroids, the ectoderm and endoderm are formed predominantly by epithelial-muscle cells. In this case, the ectoderm combines integumentary and motor functions, and the endoderm combines digestive and motor functions. Within the type, partial release of independent muscle tissue occurs.

For the first time, a diffuse type nervous system appears, consisting of scattered nerve cells, processes in contact with each other and forming a nervous network, or plexus. In swimming jellyfish, concentration of nerve cell bodies and the formation of organs of vision and balance are observed.

Coelenterates reproduce both asexually and sexually. In a number of species, incomplete asexual reproduction leads to the formation of large colonies. Many coelenterates are dioecious, but hermaphrodites are also found. Reproductive products develop in more primitive forms (hydroid) in the ectoderm, and in more highly organized forms (scyphoid, coral polyps) in the endoderm, which ensures their better supply of nutrients. Mature reproductive products are usually released into water, fertilization is external. Development with a free-swimming larva covered with cilia - planula - or direct.

Classification of coelenterates

The type of coelenterates combines 3 classes: 1. Hydroid (Hydrozoa); 2. Scyphoid (Scyphozoa); 3. Coral polyps (Anthozoa).

Class Hydrozoa

General characteristics of hydroids

Hydroids represent a large group, including about 2800 species of the most primitively organized coelenterates. The primitiveness of their organization is expressed primarily in the simplicity of the structure of the digestive system. In polypoid forms, the gastric cavity is sac-like and has no partitions. The pharynx is missing. Both cell layers - ectoderm and endoderm - converge along the edge of the oral opening (gastric type of structure). The tissues are poorly differentiated: the ectoderm and endoderm are formed mainly by epithelial-muscular cells, as a result of which the functions of the integumentary and muscle tissues are combined.

Reproductive products are formed in the ectoderm. The nervous system is very primitive, diffuse in nature. Nerve cells - neurons - form nerve networks and plexuses.

Hydroids can exist in the form of a single sessile polyp or a single floating jellyfish, but most hydroids (marine hydroid polyps) have a regular alternation of generations: an attached polypoid, reproducing asexually, and a free-swimming medusoid, reproducing sexually. The life cycle of hydroids can be greatly modified due to the loss or modification of one of the stages (medusoid or polypoid). Development proceeds with the stage of a free-swimming planula larva; in forms that have invaded fresh waters, the larval stage is absent.

Hydroids are overwhelmingly marine animals, often colonial; only a few species live in fresh water.

The class Hydrozoa is divided into two subclasses: 1. Hydroids ( Hydroidea) and 2. Siphonophores ( Siphonophora).

Subclass Hydroids ( Hydroidea)

Hydroids are represented by both single polyps and jellyfish, and colonies of polyps that grow on the seabed. The subclass of hydroids includes several orders, the most important of which are the following: 1. Hydras (Hydrida); 2. Marine hydroid polyps (Leptolida); 3. Trachylids, or Trachymedusae (Trachylida).

Hydras Hydrida

Hydra- Appearance: Single freshwater polyp. The body length is about 1 cm, attached to the substrate using the sole, on the opposite side there is a mouth, around which 6-12 tentacles are located. Habitat: everywhere in water bodies of the temperate zone.

Lifestyle: lives at shallow depths. Attaches to various underwater objects. Diet: predator, feeds on ciliates, oligochaete worms, planktonic crustaceans, small fish fry. Prey is paralyzed by stinging cells. Reproduction: in the spring-summer season - asexually (budding) and in the fall - sexually. Features: has a high ability to regenerate. Able to recover even from a small severed part of the body. Hydra is a convenient model object for biological research.

Order Marine hydroid polyps Leptolida

Some marine hydroid polyps are solitary, like hydra, but the vast majority are colonial. Colonies grow by budding large numbers of polyps, called hydrants, which do not separate from the colony. Colonies often form trunks creeping along the substrate, from which branches bearing hydrants extend. Polyp colonies can consist of a very large number of individuals. Marine hydroid polyps differ from freshwater hydras in that, in addition to polyps, or hydrants - asexual individuals, they also form special sexual individuals - jellyfish - by budding.

ORDER TRACHILIDAS, OR TRACHYMEDUSA TRACHYLIDA

Trachylids differ from marine hydroid polyps in the absence of polypoid generation in most species. They usually only have jellyfish that reproduce sexually.

Trachyjellyfish are almost exclusively marine animals. However, several freshwater forms are also known. The trachyjellyfish Craspedacusta sowerbii is common in freshwater bodies of North and South America. It appears sporadically in the pools of botanical gardens and in the aquariums of hobbyists in many countries around the world; in Russia it was found in artificial reservoirs near Tula, in the Don River, in Georgia in a reservoir near Tbilisi, in reservoirs of Bukhara, and is also found in the aquariums of fish farmers in Moscow and St. Petersburg. The life cycle of Craspedacusta is very complex. It has, in addition to the medusoid stage, two generations of polyps.

Among the trachymedusas there is a very poisonous cross jellyfish (Gonionemus vertens), which lives in the Sea of ​​Japan and near the Kuril Islands. Crossfish breed in shallow water in thickets of sea grass - zostera. Sometimes they appear in masses. The edge of the umbrella of this jellyfish is armed with 80 tentacles, equipped with numerous batteries of stinging cells and suckers. A burn to the cruciate causes general weakness, a drop in cardiac activity and respiratory failure. In this case, the victim may die if he is not provided with medical assistance. When cross jellyfish appear near populated areas, swimming in the sea is prohibited and measures are taken to destroy these dangerous jellyfish.

Subclass Siphonophora Siphonophora

Siphonophores are a very peculiar group of colonial marine hydroids, characterized by particularly strong polymorphism of the individuals that make up the colony.

Siphonophores lead a floating lifestyle, and stay either at the very surface of the water or close to the surface. They are common in warm seas. Their colonies sometimes reach very large sizes. The largest siphonophores are 2-3 m long, and the smallest are 1-2 cm.

The entire diversity of siphonophore structure can be reduced to two main types. In some, the basis of the colony is a more or less long hollow trunk, the wall of which consists, like all hydroids, of ectoderm, endoderm and mesoglea. On the trunk, along its entire length, individuals of the colony are located, which are connected to each other by a common gastrovascular cavity, which also passes through the trunk. In other siphonophores the trunk is greatly shortened, and individuals are placed on its lower, very widened part.

The apex of the colony in many siphonophores is a special bubble called a pneumatophore. The upper part of the bladder contains a cavity filled with gas, and in the lower part there are glandular cells that secrete gas. In some species of siphonophores, the cavity of the pneumatophore opens outward into a pore, which can close. When the colony is kept at the surface of the water, the pore is closed and the pneumatophore is filled with gas, due to which the density of the colony decreases. If the pneumatophore contracts and gas escapes through the opening pore, the colony sinks deeper into the water. Some siphonophores are constantly located near the surface. Their pneumatophore reaches large sizes and its cavity is divided by mesoglea partitions; the pore is absent. The upper part of the pneumatophore is equipped with an S-shaped curved ridge and protrudes above the surface of the water. Such siphonophores move, driven by the wind, along the surface of the sea. Thus, in the Portuguese man-of-war (Physalia), the pneumatophore reaches a length of 20-30 cm. It is brightly colored and floats on the surface of the water.

Under the pneumatophore, and if there is none, at the very top of the colony, many siphonophores have individuals called swimming bells or nectophores in greater or lesser numbers. These jellyfish-like individuals are capable, like jellyfish, of rhythmic contractions of the umbrella, but, unlike them, they lack a mouth and proboscis. The above-mentioned Physalia and some other siphonophores, passively transported by wind and currents, do not have swimming bells.

Below the swimming bells are other individuals of the colony, and they sit on the trunk of the colony in groups repeating along the length of the trunk. These groups of individuals are called cormidia.

In its most complete form, each cormidium consists of the following individuals: a feeding individual, or gastrozoid, a lasso, a cystozoid, a tentacle, an operculum, and a sexual individual, or gonozoid.

Gastrozoids are polyps without tentacles, but with a mouth leading into the gastric cavity, which communicates with the cavity of the colony trunk and continues into the cavity of other mouthless individuals.

Near the gastrozoid there is usually a lasso - a more or less long, often branched tentacle, seated with many stinging cells. In the Portuguese man-of-war, the extended lasso reaches 20 m in length and is lined with a large number of stinging cells. The lassos play a protective role and at the same time serve as hunting tentacles. Physalia burns are very sensitive and can be dangerous to humans.

Cystozoids differ from gastrozoids by the absence of a mouth. With a cystozoid, an unbranched tentacle is usually located. The meaning of cystozoids is not entirely clear. It is assumed that they perform an excretory function, and the tentacle has a sensitive function.
The cap is a flat plate covering the cormidium from above.

Sexual individuals - gonozoids - are usually built according to the type of medusoids and gonophores of hydroid polyps. Gonozoids are always dioecious, but among siphonophores there are both species whose colonies form gonozoids of only one sex (either male or female), and species that include hermaphroditic colonies, in which gonozoids of both sexes are located on one colony.

Thus, pronounced polymorphism is observed in siphonophores. There are a significant number of individuals adapted to perform various functions. Such a peculiar structure of siphonophores led to disagreements among zoologists on the question of whether siphonophores should be considered individual individuals or polymorphic colonies. It is now generally accepted that long-term integration of polymorphic colonies of siphonophores led to the formation of independent organisms. Individual zooids of siphonophores finally lost the ability to lead an independent lifestyle and actually turned into organs of this whole organism.

Class Scyphoid

Scyphozoa

Scyphoid - A group of marine coelenterates specialized for a swimming lifestyle. Most of their life cycle takes place in the form of swimming jellyfish. The polyp phase in the life cycle is short-lived or absent. The general structural plan of scyphomedusae coincides with that of hydromedusae. But scyphojellyfish have significant distinctive features. As a rule, scyphojellyfish are larger than hydromedusae, with a highly developed mesoglea. They do not have a sail and move by contracting the walls of the umbrella. Unlike hydroids, scyphojellyfish have a more developed nervous system with separate ganglia, and more complex sensory organs that form complexes - rhopalia. Gonads are formed in the endoderm. The gastrovascular system is complex: with branching and non-branching channels. The stomach is divided into chambers with gastric filaments. There is an ectodermal pharynx.

The number of species of scyphojellyfish is small, only about 200. However, their numbers in the seas can be very high. Thus, in the South China Sea, during the period of tropical rains, when a lot of organic matter is carried into the sea and many planktonic organisms develop, the coastal waters are overflowing with jellyfish. They are hunted in China and Japan and used as food.

Scyphojellyfish are extremely varied in shape and size. The largest jellyfish, Cyanea arctica, lives in the polar seas and reaches 2 m in diameter, and its tentacles hang down 20-30 m. It is a brightly colored jellyfish with strong stinging properties. The most widespread jellyfish is Aurelia aurita, large specimens of which reach 40 cm in diameter. This species has non-stinging properties. This is a flattened jellyfish with a completely transparent body, and only pink or purple horseshoe-shaped gonads stand out in color.

This order is small; its representatives usually have a tetrahedral high umbrella with four rhopalia and four simple or branched tentacles. They feed on various planktonic invertebrates, sometimes young fish. Box jellyfish are found in the shallow waters of warm seas. Some species common off the coast of Australia and Indonesia ( Chiropsalmus), can cause severe and sometimes fatal burns to humans.

Class Coral polyps ( Anthozoa)

Latin name Anthozoa- class of marine cnidarians.

Coral polyps- Colonial, less often single polyps; jellyfish do not form. Many have a calcareous or horny skeleton. Dept. individuals are usually cylindrical. forms, with their base fused with the colony or (single, capable of slowly crawling) have a sole that attaches them to the ground. At the opposite end of the body there is an oral disc with a crown of tentacles and a mouth in the center. The gastric cavity is divided by radial septa (mesenteries) into the chamber; the ectodermal pharynx descends from the mouth into it.

Reproduction is sexual and asexual. Reproductive products develop in the endoderm of the mesentery. The offspring usually leaves the mother's body at the planula stage, floats for some time, then attaches to the bottom and turns into an adult polyp. Asexual reproduction is by budding. Single non-skeletal sea anemones (anemones) can divide longitudinally. Colonies (often large) are formed as a result of incomplete budding. Several subclasses, modern and fossils, including living 6-rayed and 8-rayed corals, as well as extinct Rugosa, Tabulata, Heliolitoidea. About 6,000 modern ones. species, in the seas of Russia - about 150 species.

Marine, less often freshwater animals that lead an attached lifestyle or swim in water. Attached forms are called polyps, floating - jellyfish.

Double layer animals, their body consists of two cellular layers: outer - ectoderm and internal - endoderm. Endoderm forms intestinal, or gastric cavity. The gastric cavity communicates with the environment through an opening that functions as oral And anal. Between the ectoderm and endoderm is mesoglea. In polyps, the mesoglea forms a supporting plate, while in jellyfish it forms a thick gelatinous layer.

Ectoderm cells perform protective and motor functions. The ectoderm contains special stinging cells that serve for defense and attack. Endoderm cells line the gastric cavity and perform mainly a digestive function. Digestion intracellular And cavity.

Breathing occurs through the entire surface of the body.

Nervous system absent-minded, or diffuse, type. Available tactile sensitivity, and in jellyfish, due to their swimming lifestyle, they are light-perceiving "eyes" And balance organs.

Coelenterates have radial, or radial, symmetry.

Asexual reproduction budding. Genital organs presented gonads. Fertilization is external. Some representatives are characterized by alternating asexual (polyp) and sexual (jellyfish) generations in the life cycle.

The type of coelenterates includes the following classes: Hydrozoans, Scyphoid jellyfish, Coral polyps.

Class Hydrozoa

Freshwater hydra

A BRIEF DESCRIPTION OF

Habitat	Freshwater bilayer animals. Lead an attached lifestyle
Appearance	Saccular up to 1.5 cm. Radial symmetry. The mouth at the anterior end of the body is surrounded by tentacles, the sole is the posterior end of the body, for attachment
Body cover	Ectoderm - outer layer, endoderm - inner layer, mesoglea - middle layer
Body cavity	There is no body cavity. There is only an intestinal cavity
Digestive system	Blindly closed intestinal cavity. Mouth opening for food intake and for expelling undigested food debris. Digestion intracavitary and intracellular
excretorysystem	Ectoderm cells
Nervous system	Star-type nerve cells. Diffuse nervous system
Sense organs	Not developed
Respiratory system	None. Breathing through the entire surface of the body
Reproduction	Asexual - by budding. Hermaphrodites. Cross fertilization.

GENERAL CHARACTERISTICS

This class includes small forms of coelenterates. Polyps And jellyfish belonging to this class are called hydroid.

Structure . The body of the hydra is oblong double layer bag, attached by the base, or sole, to the substrate (Fig. 1). Outer layer - ectoderm, inner layer - endoderm. There is space between the layers - mesoglea.

At the free end of the body there is oral cone, surrounded by a rim of 6-12 tentacles. Located on the oral cone mouth, employee and anus. The entire body surface is covered ectoderm, consisting mainly of cylindrical or cuboidal epithelial cells. Their base is extended upward and downward, along the longitudinal axis of the body, into a long process. The cytoplasm of the process differentiates as contractile fibers, in connection with this the process plays muscular role. The cylindrical parts of the cells form single layer epithelium. Thus, the cells perform a double function - cover And motor and are called epithelial-muscular. With the simultaneous contraction of all muscular processes, the body of the hydra is shortened. Between the epithelial-muscle cells there are small intermediate cells who participate in the formation stinging And germ cells, and also in the process regeneration- restoration of lost body parts or organs. Directly under the epithelium are located star-shaped nerve cells. Connected by their processes, nerve cells form the nervous system absent-minded, or diffuse, type. Of particular importance in the ectoderm are stinging cells, or capsules, serving for attack and defense.

Endoderm lines the whole gastric, or digestive cavity. The basis of endoderm cells is epithelial-muscular digestive cells. The muscular processes of these cells, unlike ectodermal ones, are located transversely with respect to the longitudinal axis of the body. When they contract, the hydra's body narrows and becomes thinner. Endodermal cells include glandular cells, secreting digestive enzymes into the gastric cavity, and cells with phagocytic activity. The latter are capable of capturing food particles using the movement of 1-3 flagella and the formation of pseudopodia. Thus, the hydra combines two types of digestion: intracellular And cavitary.

Rice. 1.The structure of freshwater hydra: a - longitudinal section; b - cross section; c - two-layer body; d - epithelial muscle cell; d - tentacle with discarded stinging threads; f, g - stinging cells; 1 - tentacles; 2 - testis; 3 - sperm; 4 - gastric cavity; 5 - budding young hydra; 6 - support plate; 7 - endoderm; 8 - ectoderm; 9 - egg at different stages of development; 10 - stinging cells; 11 - mouth opening; 12 - sole

Mesoglea presented in the form of a thin structureless plate - basement membrane.

Asexual reproduction. Approximately at the level of the middle of the hydra's body there is a so-called budding belt, where it is formed from time to time bud, from which a new individual is subsequently formed. After the formation of the mouth and tentacles, the bud at the base is unlaced, falls to the bottom and begins to exist independently. This method of asexual reproduction is called budding.

Sexual reproduction . As cold weather approaches, hydras begin to reproduce sexually. Intermediate cells of the ectoderm can transform directly into eggs or by multiple division - in spermatozoa. Intermediate cells that form eggs located closer to the base of the hydra, and those that form spermatozoa - to the mouth opening. The eggs are fertilized in the mother's body in the fall and are surrounded by a dense shell, then the mother dies, and the eggs remain dormant until spring. In the spring, a new individual develops from them. Hydras dioecious, but they meet and hermaphroditic kinds.

Marine hydroid polyps

Most marine hydroid polyps form colonies. Colonies most often take the form of a tree or shrub. The trunk branches, the branches form separate colonies - hydrants. The gastric cavities of all hydrants communicate with each other, thus food captured by one hydrant is distributed throughout the colony. In marine hydroid polyps, the ectodermal epithelium forms a special membrane - flowing, which gives the entire colony greater stability.

Marine hydroid polyps reproduce only asexually- budding. Sexual reproduction carry out sexual individuals- jellyfish, which are formed on a polyp by budding and transition to a free-swimming lifestyle. Jellyfish have the same structure as polyps, although

there are also differences (Fig. 2, 3). The body of jellyfish is characterized strong development of mesoglea which contains a large amount of water. The nervous system is also much more complex. In jellyfish, along the edge of the umbrella, a solid nerve ring. There are sense organs: eyes And statocysts (equilibrium organs). Jellyfish dioecious. Sex glands located on the underside of the umbrella between the ectoderm and mesoglea. Fertilization and development of eggs occurs in the external environment. Eggs develop into larvae parenchymula, then the second larva - planula, which floats freely for some time, then sinks to the bottom and gives rise to a polyp. A new colony subsequently forms from the polyp, and the cycle repeats. Thus, the life of hydroid polyps consists of two generations. One generation- polyps, lead a sedentary lifestyle and reproduce asexually. Second generation - jellyfish, lead a free-swimming lifestyle and reproduce sexually. That is, in hydroid polyps it occurs alternation of generations.

Rice. 2.The structure of a hydroid polyp (A) and a hydroid jellyfish (B), inverted with the mouth opening upward: 1 - mouth; 2 - tentacles; 3 - gastric cavity; 4 - mesoglea; 5 - radial channel; 6 - sail

Rice. 3Scheme of the structure of a hydroid jellyfish: 1 - mouth; 2 - oral stalk with gonad (3); 4 - radial channels; 5 - ring channel; 6 - tentacles; 7 - eyes; 8 - sail

Class Scyphoid jellyfish

This class includes jellyfish, living only in the seas. They are larger than hydroid jellyfish, and their structure is more complex (Fig. 4). The mouth ends in a pharynx, and the gastric cavity is divided into chambers. The annular canal, running along the edge of the body, unites the canals extending from the stomach, forming gastrovascular system. Clumps of nerve cells appear in the form ganglia. Sex cells are formed in gonads- gonads located in the endoderm. Development proceeds with alternation of generations (Fig. 5).

Rice. 4.Scheme of the structure of a scyphoid jellyfish: 1 - oral lobes; 2 - mouth opening; 3 - tentacles; 4 - ring channel; 5 - radial channel; 6 - gonad; 7 - gastric threads; 8 - stomach; 9 - ectoderm; 10 - mesoglea; 11 - endoderm

Rice. 5.Development of scyphoid jellyfish: 1 - egg; 2 - planula; 3 - scyphistoma; 4 - budding scyphistoma; 5 - strobilation; 6 - ether; 7 - adult jellyfish

Class Coral polyps

Coral polyps have only one life form - polyp. They do not have alternation of generations. Marine, solitary, mostly colonial animals. Coral polyps differ from other classes by the presence of a hard calcareous skeleton, as well as muscle fibers in the ectoderm and endoderm, which allow them to change the shape of the body.

Origin. Coelenterates descended from some of the first primitive multicellular animals, the body of which consisted of two types of cells - motor cells with flagella and digestive cells capable of forming pseudopods. The ancestors of the coelenterates themselves descended from the most ancient colonial single-celled animals.

Meaning. Marine coelenterates are an important link in the food chains of many animals. The tentacles and bells of some jellyfish, such as polar jellyfish, serve as a refuge for fish fry. Coral polyps are biological water filters. Reefs and islands formed by corals are dangerous obstacles for navigation. Over many millennia, coral skeletons formed huge deposits of limestone. Noble corals, such as red coral, are used to make various jewelry. In Japan and China, the gelatinous mass of jellyfish, such as Aurelia and Rhopilema, is eaten. Some jellyfish are dangerous to humans: the poison of the Far Eastern jellyfish, the cross jellyfish, causes blisters to appear on the skin and numbness in the hands.

Interesting things on the site:

Coelenterate or radial- this group multicellular invertebrate animals. Main characteristics of coelenterates is radial symmetry and a two-layer body structure.

COELENTERATES

The body walls of coelenterates consist of ectoderm (outer layer) and endoderm (inner layer), which are separated by a layer of mesoglea - a structureless mass.

Ectoderm consists of skin-muscle cells that perform the function of integumentary tissue and the motor apparatus, as well as special stinging cells, which the animal uses to defeat prey and protect itself from predators.

Stinging cells are capable of releasing poisonous threads at high speed, which paralyze prey and cause burns.

Inner layer ( endoderm), in addition to those listed above, has glandular digestive cells. Inside the body of coelenterates there is gastric or intestinal cavity.

Coelenterates contact the external environment only through the mouth opening. Around it there are tentacles that capture prey and send it into the mouth, and then remove the undigested food. In this case, food is digested inside the glandular cells, as well as in the cavity. Coelenterates feed plankton and larger aquatic animals.

Coelenterates live alone and can also lead a colonial lifestyle.

Most often, this species of animal is dioecious, that is, hermaphrodites can occur.

Reproduction of coelenterates occurs both sexually and asexually.

Some species alternate between two generations: polyps and jellyfish. Polyps lead a sedentary lifestyle and live in bodies of water. Jellyfish They also live in water and can move. Each generation reproduces the other during reproduction.

Additional materials on the topic: Coelenterates.

Type Coelenterates. General characteristics. Diversity of coelenterates

Basic terms and concepts tested in the examination paper: bilayer animals, hydroid, glandular cells, ectoderm cells, endoderm cells, coral polyps, jellyfish, nerve cells, stinging cells, scyphoid cells, development cycle of coelenterates.

Coelenterates- one of the oldest groups of multicellular animals, numbering 9,000 thousand.

species. These animals lead an aquatic lifestyle and are common in all seas and freshwater bodies. Descended from colonial protozoa - flagellates.

Coelenterates lead a free or sedentary lifestyle. The phylum Coelenterata is divided into three classes: Hydroid, Scyphoid and Coral polyps.

The most important general characteristic of coelenterates is their two-layer body structure.

It consists of ectoderm And endoderm , between which there is a non-cellular structure - mesoglea .

These animals got their name because they have intestinal cavity in which food is digested.

Basic aromorphoses, which contributed to the emergence of coelenterates, are the following:

– the emergence of multicellularity as a result of specialization and association;

– cells interacting with each other;

– the appearance of a two-layer structure;

– the occurrence of cavity digestion;

– the appearance of body parts differentiated by function; the appearance of radial or radial symmetry.

Hydroid class. Representative - freshwater hydra.

Hydra is a polyp about 1 cm in size.

Lives in freshwater bodies. It is attached to the substrate by the sole. The front end of the body forms a mouth surrounded by tentacles. Outer layer of the body - ectoderm consists of several types of cells differentiated by their functions:

– epithelial-muscular, ensuring the movement of the animal;

– intermediate, giving rise to all cells;

– stinging insects that perform a protective function;

– sexual, ensuring the process of reproduction;

– nerves, united into a single network and forming the first nervous system in the organic world.

Endoderm consists of: epithelial-muscular, digestive cells and glandular cells that secrete digestive juice.

Hydra, like other coelenterates, has both intracellular and intracellular digestion.

Hydras are predators that feed on small crustaceans and fish fry. Breathing and excretion in hydras is carried out over the entire surface of the body.

Irritability manifests itself in the form of motor reflexes. The tentacles react most clearly to irritation, because Nerve and epithelial-muscle cells are most densely concentrated in them.

Reproduction occurs budding And sexually .

The sexual process occurs in the fall. Some intermediate cells ectoderms turn into germ cells. Fertilization occurs in water. In the spring, new hydras appear.

Among the coelenterates there are hermaphrodites and dioecious animals.

Many coelenterates are characterized by alternating generations. For example, jellyfish are formed from polyps. Larvae develop from fertilized jellyfish eggs - planulae. The larvae develop into polyps again.

Hydras are able to restore lost body parts due to the reproduction and differentiation of nonspecific cells.

This phenomenon is called regeneration .

Class Scyphoid. Combines large jellyfish. Representatives: Kornerot, Aurelia, Cyanea.

Jellyfish live in the seas. The body resembles an umbrella in shape and consists mainly of gelatinous mesoglea, covered on the outside with a layer of ectoderm, and on the inside with a layer of endoderm.

Along the edges of the umbrella there are tentacles surrounding the mouth, located on the underside. The mouth leads into the gastric cavity, from which radial canals extend. The channels are connected to each other by a ring channel. As a result, gastric system .

The nervous system of jellyfish is more complex than that of hydras. In addition to the general network of nerve cells, along the edge of the umbrella there are clusters of nerve ganglia, forming a continuous nerve ring and special balance organs - statocysts .

Some jellyfish develop light-sensitive eyes and sensory and pigment cells corresponding to the retina of higher animals.

In the life cycle of jellyfish, sexual and asexual generations naturally alternate. They are dioecious. The gonads are located in the endoderm under the radial canals or on the oral stalk. Reproductive products exit through the mouth into the sea. A free-living larva develops from the zygote. planula .

The planula turns into a small polyp in the spring. Polyps form groups similar to colonies. Gradually they disperse and turn into adult jellyfish.

Class Coral polyps. Includes solitary (anemones, brain sea anemones) or colonial forms (red coral).

General characteristics of coelenterates, lifestyle, structure, role in nature

They have a calcareous or silicon skeleton formed by needle-shaped crystals. They live in tropical seas. Clusters of coral polyps form coral reefs. They reproduce asexually and sexually. Coral polyps do not have a jellyfish stage of development.

EXAMPLES OF TASKS

Part A

One of the major aromorphoses in coelenterates was the emergence

1) stinging cells

2) multicellularity

3) intracellular digestion

4) budding abilities

A2. Polyp is the name

1) type of animal

2) class of animals

3) animal subkingdoms

4) stages of animal development

The cells from which all other hydra cells are formed are called

1) glandular 3) stinging

2) intermediate 4) epithelial-muscular

A4. The endoderm of Hydra contains cells

1) intermediate 3) glandular

2) sexual 4) nervous

A5. From a zygote, jellyfish first develop

1) planula 3) adult form

2) polyp 4) colony of polyps

The nervous system is the most complex structure

1) hydra 3) cornerrota

2) brain sea anemone 4) sea anemone

A7. The gonads of jellyfish develop into

1) ectoderm 3) mesoglea

2) stomach pockets 4) throat

A8. Has an internal skeleton

1) aurelia 3) sea anemone

2) hydra 4) cornerrota

A9. The nervous system of coelenterates consists of

1) single cells

2) individual nerve nodes

3) one nerve

4) interconnected nerve cells

Part B

Select the cells found in the ectoderm of Hydra

1) glandular 4) digestive

2) intermediate 5) stinging

3) nervous 6) sexual

General characteristics, variety of types

The type of coelenterates has about 9 thousand species. They originated from colonial protozoa - flagellates and are distributed in all seas and freshwater bodies. The type of coelenterates is divided into three classes: hydroid, scyphoid and coral polyps.

The main aromorphoses that contributed to the appearance of coelenterates:

• the emergence of multicellularity as a result of specialization and association of interacting cells;
• the appearance of a two-layer structure;
• the occurrence of cavity digestion;
• the appearance of body parts differentiated by function;
• the appearance of radial symmetry.

Coelenterates lead an aquatic, free-living or sedentary lifestyle. These are two-layer animals, in ontogenesis they form two germ layers - ecto- and endoderm, between which there is mesoglea - the supporting plate. Their internal cavity is called the gastric cavity. Here food is digested, the remains of which are removed through the mouth, surrounded by tentacles (in hydras).

Hydroid class

A representative of this class is the freshwater hydra.

Hydra is a polyp about 1 cm in size. It lives in freshwater bodies, attaching itself to the substrate with its sole. The front end of the animal's body forms a mouth surrounded by tentacles. The body of the hydra is covered with ectoderm, consisting of several types of cells:

• epithelial-muscular;
• intermediate;
• stinging;
• sexual;
• nervous.

Hydra endoderm consists of epithelial-muscular, digestive cells and glandular cells.

Left - Diagram of the location of nerve cells in the body of the hydra. (according to Hesse). On the right - Stinging cells: A - in a resting state, B - with the stinging thread thrown out (according to Kuhn): 1 - nucleus; 2 - stinging capsule; 3 - cnidocil; 4 - stinging thread with spines; 5 - spikes

Important features of coelenterates:

1. the presence of stinging cells in the outer layer. They develop from intermediate ones and consist of a stinging capsule filled with liquid and a stinging thread placed in the capsule. Stinging cells serve as weapons of attack and defense;
2. cavity digestion with preservation of intracellular digestion.

Hydras are predators that feed on small crustaceans and fish fry.

Breathing and excretion are carried out over the entire surface of their body.

Irritability manifests itself in the form of motor reflexes. The tentacles react most clearly to irritation, since nerve and epithelial-muscle cells are densely concentrated in them.

Hydras reproduce by budding and sexually. The sexual process occurs in the fall. Some intermediate cells of the ectoderm turn into germ cells. Fertilization occurs in water. In the spring, new hydras appear. Among the coelenterates there are hermaphrodites and dioecious animals.

Many coelenterates are characterized by alternating generations. For example, jellyfish are formed from polyps, larvae - planulae - develop from fertilized jellyfish eggs, and polyps develop from the larvae again.

Hydras are able to restore lost body parts due to the reproduction and differentiation of nonspecific cells. This phenomenon is called regeneration.

Class Scyphoid

This class unites large jellyfish (representatives - cornerot, aurelia, cyanea).

Jellyfish live in the seas. In their life cycle, sexual and asexual generations naturally alternate. The body is shaped like an umbrella and consists mainly of gelatinous mesoglea, covered on the outside with one layer of ectoderm, and on the inside with a layer of endoderm. Along the edges of the umbrella there are tentacles surrounding the mouth, located on the underside. The mouth leads into the gastric cavity, from which radial canals extend, which are connected to each other by a ring canal. As a result, the gastric system is formed.

The nervous system of jellyfish is more complex than that of hydras.

Rice. 34. Development of scyphomedusa: 1 - egg; 2 - planula; 3 - single polyp; 4 - budding polyp; 5 - dividing polyp; 6 - young jellyfish; 7 - adult jellyfish

In addition to the general network of nerve cells, along the edge of the umbrella there are clusters of nerve ganglia, forming a continuous nerve ring and special balance organs - statocysts. Some jellyfish develop light-sensitive eyes, sensory and pigment cells corresponding to the retina of higher animals.

Jellyfish are dioecious. Their gonads are located under the radial canals or on the oral stalk. Reproductive products exit through the mouth into the sea. From the zygote, a free-living larva develops - a planula, which in the spring turns into a small polyp.

Class Coral polyps

Includes solitary (anemone) or colonial forms (red coral). They have a calcareous or silicon skeleton formed by needle-shaped crystals, live in tropical seas, reproduce asexually and sexually (there is no jellyfish stage of development). Clusters of coral polyps form coral reefs.