Multicellular are characterized a body of many cells differentiated by form and function.

Feature- a complex individual development cycle, during which an adult organism is formed from a fertilized egg (in parthenogenesis, from an unfertilized one):

Radiant or two-layer(there are several planes of symmetry and a radial arrangement of organs around the main axis of the body. In the body of radiata there is one main axis of symmetry, around which the organs of animals are located in a radial order. The order of symmetry depends on the number of repeating organs. Several planes of symmetry can be drawn through the body of a radiate animal ( 2,4,6,8). In the process of ontogenesis, only two distinct layers of cells are formed: ectoderm and endoderm, while the third germ layer is in its infancy and is represented by a gelatinous substance - mesoglea.

Bilaterally symmetrical or three-layer(they have one plane of symmetry, on both sides of which various organs are located. In addition to the ectoderm and endoderm, these animals always have a third germ layer (mesoderm), due to which a significant part of the internal organs develop)

The most primitive multicellular organisms stand alone - lamellar And sponges.

Type Coelenterates.

Includes lower multicellular animals (more than 9 thousand species) that appeared in the Proterozoic era. Coelenterates lead an aquatic lifestyle (in the seas). Among them there are free-floating and bottom-attached forms.

Body:

cylindrical (in Hydra)

flattened in the direction of the main axis (jellyfish).

Characteristics:

the body wall is formed by two layers of cells: the ectoderm, which performs integumentary and motor functions, and the endoderm, the cells of which are equipped with flagella and perform a digestive function. Ectoderm and endoderm are separated by structureless mesoglea

radial symmetry

intestinal cavity

primary mouth surrounded by tentacles with stinging cells. Undigested food remains are removed through the mouth. Along with the cavity, intracellular digestion of food particles by the endoderm is preserved

In coelenterates, diffuse nervous system, consisting of scattered nerve cells forming a nervous network.

Breathing is carried out over the entire surface of the body.

Reproduction sexual and asexual. Gametes are released into water, fertilization is external. Dioecious, and hermaphrodites are also found. They live as individuals or form colonies.

Shapes:

sessile (hydroid, coral polyps)

free-swimming (jellyfish)

Basic aromorphoses that contributed to the emergence of coelenterates:

– 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 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 cell types, 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 in organic world nervous system.

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

In hydra, as in other coelenterates, digestion both lumen and intracellular. Hydras are predators that feed on small crustaceans and fish fry.

Breath And allocation in hydras it 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, since nerve and epithelial-muscle cells are most densely concentrated in them.

Reproduction:

budding

sexually(in autumn. Some intermediate cells of the ectoderm turn into germ cells. Fertilization occurs in water. In spring, new hydras appear. Among the coelenterates, hermaphrodites and dioecious animals are found).

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.

Unites jellyfish large sizes (Cornerot, 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 arise. 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. Except shared network 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 life cycle Jellyfish naturally alternate between sexual and asexual generations. 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.

Include single ( sea ​​anemones, brain sea anemones) or colonial forms ( red coral). 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.

Thematic assignments

A1. 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

A3. The cells from which all other hydra cells are formed are called

1) glandular

2) intermediate

3) stinging

4) epithelial-muscular

A4. The endoderm of Hydra contains cells

1) intermediate

2) sexual

3) glandular

4) nervous

A5. From a zygote, jellyfish first develop

1) planula

3) adult form

4) colony of polyps

A6. The nervous system is the most complex structure

2) brainiac

3) corner mouth

4) sea anemones

A7. The gonads of jellyfish develop into

1) ectoderm

2) stomach pockets

3) mesoglea

A8. Internal skeleton have

1) aurelia

3) sea anemones

4) corner mouth

A9. The nervous system of coelenterates consists of

1) single cells

2) individual nerve nodes

3) one nerve

4) interconnected nerve cells

B1. Select the cells found in the ectoderm of Hydra

1) glandular

2) intermediate

3) nervous

4) digestive

5) stinging

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 one another. 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 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 rarely solitary. The vast majority of them, starting life as a single polyp, then form, through budding, which does not reach the end, colonies consisting of hundreds and thousands of individuals. 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.

Coelenterates (jellyfish, corals, sea ​​anemones) - two-layer multicellular, possessing true tissue formations in the form of ecto- and endoderm. Between these layers is an unstructured jelly-like mesoglea.

Among the cells included in the tissue layers, forms such as stinging cells, ciliated cells, glycocytes, and interstitial cells are described. In the mesoglea are presented in small quantity wandering amoebocytes, which are also localized in the endoderm surrounding digestive tract. In addition to their digestive function, wandering amoebocytes are involved in transplant rejection.
Other cells that claim to be protective cellular elements are the motile interstitial cells of the ectoderm.

The diffuse type nervous system that first appeared consists of nerve cells evenly distributed in the gel, interconnected by processes and forming a nervous network.

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. In a small number of species, development is direct (hydra). The phylum Coelenterata unites three classes: Hydroid, Scyphoid and Coral polyps.

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.

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 parts of the body due to the reproduction and differentiation of nonspecific cells. This phenomenon is called regeneration.

Class Scyphoid

This class unites large jellyfish (representatives are 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.

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.

General characteristics of coelenterates

Organ system	Characteristic
Digestion	Intracellular and cavity (digestion of food occurs in the intestinal cavity - this is where the name of the type comes from).
Circulation	Absent
Breath	There are no specialized respiratory organs. Absorption of oxygen by the entire surface of the body
Selection	There are no specialized excretory organs. Selection carbon dioxide and unnecessary substances - through the outer layer of cells directly into the water, through the outer layer - into the intestinal cavity, then into the water.
Reproduction	There are two ways – asexual and sexual. Asexual - strobilation and budding (characteristic only of polyps). Reproductive - with the help of the genital organs - gonads. Fertilization is external. Formation of planktonic or crawling larvae.
Nervous	It is based on a nerve plexus (nervous plexus).
Sense organs	All have tactile sensitivity, jellyfish have light-perceiving “eyes” and balance organs.
Life cycle	Metagenesis is a natural alternation of asexual and sexual generations.



Coelenterates, like sponges, first appeared on earth more than 500 million years ago. They have multicellular organisms and the most in different forms. Coelenterates include sea anemones, jellyfish and corals.

General characteristics

The body of coelenterates has the shape of a sac with a hole, which is surrounded by tentacles. They can face up like polyps or down like jellyfish. Coelenterates and sponges have a radially symmetrical body, that is, body parts are located around a central axis.

Nutrition

The internal cavity in the body of coelenterates communicates with the surface through a single opening, which serves for the intake of food and the release of undigested residues. Around the hole are tentacles that capture, paralyze and pull prey inside.

Habitat

Coelenterates live in warm tropical seas; Some of them lead a sedentary lifestyle, others are free-swimming. Thus, hydroids can be both stationary (polyps) and floating (jellyfish); The scyphoid class consists only of jellyfish, and the class of coral polyps includes only motionless forms - polyps living separately or in colonies. Coelenterates are multicellular organisms characterized by a simple structure and radial symmetry. This structure is very convenient for animals that are not able to move freely: both food and enemies can appear from anywhere, so it is important to be prepared for attack or defense from any side.

The body of all coelenterates consists of one internal cavity, communicating with the surface through an opening - the mouth, the walls of which perform respiratory functions, serve for eating and removing processed products.

The mouth is surrounded by tentacles containing nettle, or stinging, cells. When a small animal touches one of them, a tubular fiber containing a poisonous liquid is thrown out. Hundreds of such threads dig into the victim, and the tentacles pull it, paralyzed, into the oral cavity. Thus, coelenterates are predators; their prey is small fish and crustaceans. Due to the specificity of their body structure, coelenterates are well camouflaged at the bottom and become a sudden trap for their victims.

The type of structure of coelenterates (there are two main types - polyps and jellyfish) can change during the development of the animal: the larva can be motionless, in the form of a polyp, and the adult can be mobile, like a jellyfish; and vice versa, the larva is mobile, and the adult animal has a stationary polyp form, like in corals.

The body walls of coelenterates consist of two rows of cells: one external, called ectoderm, and the other internal, called endoderm. Between two rows of cells there is a jelly-like layer with a large number water.

The ectoderm consists of elongated muscle cells, and the endoderm is round. The shooting motion characteristic of jellyfish is achieved by the activity of these two rows of cells, which stretch and contract. Such movements allow the jellyfish to move forward: compression pushes the water out from under the umbrella, and the jellyfish receives a jet push, like a rocket.

The remaining cells have transformed into nerve cells and envelop the surface of the body with a mesh, giving the jellyfish sensory organs.

Coelenterates are divided into three large classes: hydroid, scyphoid and coral polyps.

There are 2,700 hydroid species; They are small in size, reproduce only by budding and come in two forms - polyps and jellyfish. They live isolated, like hydras, or in colonies, like hydrants.

The scyphoid class includes jellyfish of bright colors with large umbrellas; they live only in isolation. There are about 250 species of scyphoids: the largest representative of this class is the Arctic cyanea, whose umbrella is more than 2 m in diameter.

Coral polyps are the class of coelenterates with the largest number of species - 6500 species. They are found only in the form of polyps, can be solitary, like sea anemones or sea anemones, but more often live in colonies, like corals and madrepores.

The most popular of the coral polyps, red coral, has been known since ancient times in China and Japan; in Europe it began to be widely used for making jewelry even before our era. For the inhabitants of Tibet in the 13th century BC, red coral was a bargaining chip. In addition, back in late XIX centuries, corals have been attributed various healing properties: Coral powder was considered a panacea for many diseases.

Species

Noble, or red, coral is found mainly in the Mediterranean Sea at a depth of 20 to 200 m in colonies 10-14 cm high. Other representatives of this species, living in the Sea of ​​Japan, reach 1 m in height and weigh about 40 kg.

For thousands of years, noble coral has been used to make small decorative items and jewelry. It is even found in burials of the 4th century BC.

The part of the coral visible to us is an external skeleton, very hard and fragile, formed by small polyps. They form branched colonies that resemble small trees, especially when they move their tentacles, similar to the corollas of flowers.

Type	Class	Subclass	Squad	Family	Genus	View
Coelenterates	hydroid					hydra
	scyphoid					jellyfish
	coral polyps	Alcyonaria, or eight-rayed corals				corals, horn corals
		cortical or six-rayed corals				madrepores, sea anemones

Hydra lives in fresh water. Due to its six thin tentacles, which are six times longer than the size of the hydra itself, it closely resembles algae. Looking at it, it is difficult to imagine that this innocent animal was identified in Greek mythology with a monstrous snake with nine heads that grew back every time they were cut off.

The structure of the jellyfish is interesting because this animal is 95% composed of water, and organic matter makes up only 5% total mass. If you throw a large jellyfish onto land, it will completely “melt”, and after a few hours there will be nothing left on the sand except a small wet spot.

Xenia is a very beautiful coral, like a tree, sparkling with its feathered tentacles.

The sea pen, unlike its coral relatives, has a soft and flexible external skeleton, which makes it look like an elegant goose feather. It emits a bright blue-green color, which is why it received the Latin name pennatula phosphorea, translated into Russian as “phosphorous”.

The verrucoso anemone is a medium-sized sea anemone (about 3 cm) with a characteristic knobby leg. In case of danger, she hides her tentacles in her mouth and becomes like a hard ball.

Gorgonaria unicella cavolinii is a very rare coral found in the Mediterranean Sea. It lives in large colonies, and its branched “crown” reaches 70 cm in length. Unfortunately, the beauty of this coral attracts the attention of poachers.

In the Mediterranean Sea you can find Caryophylla clava, an isolated madrepora with a thin transparent body.

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 (hydromedusa, scyphomedusa, 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 life form 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 type of coelenterates, there is a complication of structure digestive system. 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 - 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 nerve 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 ones (scyphoid, coral polyps) - in the endoderm, which ensures their better supply 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 are 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 fry fish 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 quantity polyps called hydrants that 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 trachymedusae there are very poisonous jellyfish crosswort (Gonionemus vertens), living in the Sea of ​​Japan and nearby 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 care. When crosses appear nearby settlements Swimming in the sea is prohibited and measures are being 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 top 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. Yes, y Portuguese man-of-war(Physalia) 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, scyphomedusae 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 threads. 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, coastal waters overflowing with jellyfish. They are hunted in China and Japan and used as food.

Scyphojellyfish are extremely varied in shape and size. The most large 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.

Coelenterates (cnidarians, cnidarians) are a very ancient group of primitive bilayer animals, numbering about 9,000 species. Their study is of great importance for understanding evolution; some species are of interest for medicine.

Cnidarians got their name from the Greek. knide - to burn. Another common name for this type of animal is coelenterata. Radially symmetrical, mostly marine animals, armed with tentacles and unique stinging cells (nematocytes - approx..

Coelenterates lead an exclusively aquatic lifestyle. They live in marine and fresh water bodies. Most species are characterized by radial-axial symmetry of the body. This type of symmetry is characteristic of animals leading a sedentary or sedentary lifestyle. In the simplest case, the body of coelenterates has the form of a sac, the opening of which is surrounded by a corolla of tentacles. The cavity of the sac is called the gastric cavity. Sessile forms - polyps - have this structure. Free-living forms have a more flattened body and are called jellyfish.

The division into polyps and jellyfish is not systematic, but purely morphological. Often, the same species of coelenterates at different stages of the life cycle can have the structure of either a polyp or a jellyfish. Using the example freshwater hydra the basic principles of the organization of coelenterates are visible.

Sea anemones. Photo: tigrecanela

A common feature for all representatives of the type is two-layered. Their body consists of ectoderm and endoderm, between which is mesoglea. In hydra it has the form of a non-cellular supporting plate, in jellyfish it is more developed. It is rich in water and takes on a gelatinous form, making up most of the body.
The cells of the body of coelenterates are differentiated. The ectoderm contains epithelial-muscle cells, interstitial, or intermediate, stinging, reproductive and nervous cells.

Epithelial muscle cells perform motor and protective functions. Stinging devices are the apparatus of attack and defense. They have a capsule, inside of which there is a stinging thread in the form of a spiral, which is thrown out when irritated. Interstitial are small undifferentiated cells; subsequently, all types of ectoderm cells are formed from them. The endoderm is divided into epithelial-muscle cells and glandular cells. The latter secrete enzymes and perform the function of digestion. There are also small amounts in the endoderm nerve cells. With their processes they communicate with each other, forming a diffuse nervous system.

Digestion of coelenterates occurs in the gastric cavity, therefore, it becomes cavitary. Undigested food remains are removed from the body through the mouth. However, intracellular digestion is also preserved, since endoderm cells are capable of phagocytosis - capturing food particles from the gastric cavity.

Coelenterates are characterized by asexual and sexual reproduction. Asexuality occurs by budding. IN summer period a kidney-shaped protrusion forms on the body of the polyp. The bud then separates and falls to the bottom of the pond, growing into a new individual. Sexual reproduction usually observed in autumn. There are dioecious and hermaphroditic species. The egg develops in the ectoderm closer to the sole, and the sperm develops near the mouth. Mature sperm enter the water and meet the egg. The fertilized egg is covered with a thick shell, the body of the hydra is destroyed, and the zygote sinks to the bottom and begins to divide again only in the presence of heat, in the spring, forming a new individual.

Many coelenterates are characterized by alternating generations. Polyps reproduce by budding and give rise to both polyps and jellyfish. Jellyfish reproduce sexually. From fertilized eggs, larvae are formed - planulae, covered with cilia. They attach to the substrate and give rise to a new generation of polyps.

Class Hydrozoa

Individual species of this class have 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. The Hydroid class unites about 4,000 species, living mainly in the seas and oceans, but there are several freshwater forms.

The subclass Hydroids (Hydroidea) is represented by adherent bottom colonies. 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 identical.

Order Leptolida.
The order is represented by polypoid and medusoid individuals. Colonies are covered with a chitinous skeleton. In some representatives of the order, for example (Thecaphora), a protective calyx is formed around the polyps - hydrotheca; others (Athecata) lack such a calyx. Representatives of this group are predominantly marine organisms, are very rare in fresh waters.

Order Hydrocorals (Hydrocorallia).
Representatives of this order have a calcareous trunk and branches of colonies, usually variegated in various colors - red, yellow, pink. Medusoid individuals in species of this order are underdeveloped and buried deep in the skeleton. Some scientists do not consider hydrocorals to be an independent order and classify them as a species of the Leptolid order. These are exclusively marine organisms and do not live in fresh waters.

Order Chondrophora, or Velellina.
Colonies of this order consist of a large floating polyp and polymorphic individuals attached to it, some of which bud jellyfish that break away from the colony. Exclusively marine organisms.

Order Trachylida.
They are also exclusively marine hydroids, jellyfish-shaped, with no polyps.

Hydra squad.
Solitary freshwater polyps, do not form jellyfish.

Subclass Siphonophora.
They are floating colonies, which include diversely arranged individuals of polypoid and medusoid origin. They live exclusively in the seas.

Class Scyphozoa

Individual individuals of this class look like either a small polyp or a large jellyfish, or the animal has characteristics of both generations. This class includes about 200 species. Exclusively marine organisms.

Order Coronomedusa (Coronata).
It is represented mainly by deep-sea jellyfish, the umbrella of which is divided by a constriction into a central disk and a crown. Large tentacles sit on special gelatinous outgrowths of the edge of the umbrella.

Order Discomedusae (Semeostomea).
The umbrella of these jellyfish is solid, disc-shaped, flattened, and usually bears numerous tentacles along the edge. There are radial canals, the corners of the mouth are elongated into long lobes. Polyps of this order lack a protective tube.

Order Root-mouthed jellyfish (Rhizostomea).
Jellyfish of this order have a solid umbrella with radial canals and no tentacles. The oral cavities are highly branched and form a network that serves to capture prey. Polyps without a protective tube.

Order Cubomedusae.
Box jellyfish have a solid umbrella, devoid of radial canals, the function of which is performed by the far protruding stomach pouches. The box jellyfish polyp buds off many daughters, each of which develops into a separate jellyfish. Some scientists consider box jellyfish as a separate class of Cubozoa.

Order Stauromedusae.
Peculiar bottom organisms that combine in their structure the characteristics of a jellyfish and a polyp.

Class Coral polyps (Anthozoa)

Colonial or solitary exclusively marine organisms. There is only a polypoid generation; jellyfish are not formed. The intestinal cavity is divided into chambers by radial partitions (septa). The tentacles are hollow. Reproductive products develop in the endoderm. The class includes about 5000 species.

Subclass Eight-rayed corals (Octocorallia).
Colonial forms, usually rooted to the ground. The polyp has eight tentacles with lateral projections; The intestinal cavity is divided by the same number of partitions. The skeleton is always internal, lying in the mesoglea.

Order Alcyonaria (Alcyonacea).
Most of them are soft corals, the skeleton is made of calcareous needles, they do not have an axial skeleton.

Order Horn corals (Gorgonacea).
Tree-like and whip-like colonies. The skeleton of Horn Corals consists of calcareous needles and an axial rod.

Order Sea feathers (Pennatulacea).
Non-branching colonies, often similar to a bird's feather and consisting of a long primary polyp and secondary polyps extending from it or fused at the bases. Skeleton of needles and axial rod. The base of the colony is embedded in the ground. Some species are able to move.

Order Sun corals (Helioporacea).
Massive or creeping colonies with a solid calcareous skeleton. The order is represented by two families (Helioporidae and Lithotelestidae), each of which contains one genus (Epiphaxum and Heliopora).

Blue coral. Photo: Jon Connell

The genus Epiphaxum is represented by three species, and the genus Heliopora is represented by a single species - blue coral (Heliopora coerulea).
Among the eight-rayed corals, only the blue coral forms a strong calcareous skeleton, which is sometimes used to make jewelry. The presence of iron salts in the skeleton gives these corals a characteristic bluish tint, which was the reason for the name of the species.

Subclass Six-rayed corals (Hexacorallia).
The species are colonial or solitary forms. Tentacles without lateral outgrowths; their number is usually equal to or a multiple of six, hence the name. The same number of radial partitions divides the chambers and the intestinal cavity.

Order of sea anemone (Actiniaria).
Solitary, locomotive, non-skeletal polyps that live on the seabed (there are several burrowing species).

Order Madreporia corals (Madreporaria or Scleractinia).
It is represented mainly by colonial, less often solitary (but immobile) corals with a thick external calcareous skeleton. It is these corals that form the basis of the famous coral reefs.

Order Cork corals (Zoantharia).
Colonial or solitary corals of fixed forms. Colonies are creeping. Skeleton of alien particles.

Antipataria squad.
Colonial corals with an axial skeleton made of horn-like substance. The surface of the colony is covered with small spines.

Order Ceriantharia.
Solitary non-skeletal polyps living in muddy soil. They build tubes from silt, holding it together with mucous secretions. The polyp is able to move inside the tube.

The importance of coelenterates is great. The calcareous skeletons of reef-forming coral polyps form reefs and atolls in tropical seas. Coral reefs and islands are a dangerous obstacle to navigation. Coral polyps play a beneficial role in cleansing sea ​​water from suspended organic particles. Huge layers of limestone were formed from the skeletons of coral polyps that died over many millennia. In many tropical coastal countries it is used in construction. The skeletons of some types of coral, such as red coral, are used to make various jewelry.

Jellyfish sensitively pick up sound vibrations that occur when water rubs against air, and swim away from the shore long before a storm approaches. Based on this property, bionics scientists created the “Jellyfish Ear” device, which allows one to determine the approach of a storm approximately 15 hours before its onset.

Some types of jellyfish provide refuge for fish fry and hermit crabs. Coelenterates have great value in the food chain of marine biocenoses.