Hydra. Obelia. The structure of the hydra. Hydroid polyps

They live in marine and rarely in fresh water bodies. Hydroids are the most simply organized coelenterates: a gastric cavity without septa, nervous system without ganglia, the gonads develop in the ectoderm. Often form colonies. Many in life cycle there is a change of generations: sexual (hydroid jellyfish) and asexual (polyps) (see. Coelenterates).

Hydra sp.(Fig. 1) - a single freshwater polyp. The length of the hydra's body is about 1 cm, its lower part - the sole - serves to attach to the substrate; on the opposite side there is a mouth opening, around which 6-12 tentacles are located.

Like all coelenterates, hydra cells are arranged in two layers. The outer layer is called ectoderm, the inner layer is called endoderm. Between these layers is the basal plate. In the ectoderm there are the following types cells: epithelial-muscular, stinging, nervous, intermediate (interstitial). Any other ectoderm cells can be formed from small undifferentiated interstitial cells, including germ cells during the reproductive period. At the base of the epithelial-muscle cells are muscle fibers located along the axis of the body. When they contract, the hydra's body shortens. Nerve cells are stellate in shape and located on the basement membrane. Connected by their long processes, they form a primitive nervous system of the diffuse type. The response to irritation is reflexive in nature.

rice. 1.
1 - mouth, 2 - sole, 3 - gastric cavity, 4 - ectoderm,
5 - endoderm, 6 - stinging cells, 7 - interstitial
cells, 8 - epithelial-muscular ectoderm cell,
9 - nerve cell, 10 - epithelial-muscular
endoderm cell, 11 - glandular cell.

The ectoderm contains three types of stinging cells: penetrants, volventes and glutinants. The penetrant cell is pear-shaped, has a sensitive hair - cnidocil, inside the cell there is a stinging capsule, which contains a spirally twisted stinging thread. The capsule cavity is filled with toxic liquid. At the end of the stinging thread there are three spines. Touching the cnidocil causes the release of a stinging thread. In this case, the spines are first pierced into the body of the victim, then the venom of the stinging capsule is injected through the thread channel. The poison has a painful and paralyzing effect.

The other two types of stinging cells perform the additional function of retaining prey. Volvents shoot trapping threads that entangle the victim's body. Glutinants release sticky threads. After the threads shoot out, the stinging cells die. New cells are formed from interstitial ones.

Hydra feeds on small animals: crustaceans, insect larvae, fish fry, etc. The prey, paralyzed and immobilized with the help of stinging cells, is sent to the gastric cavity. Digestion of food is cavity and intracellular, undigested residues are excreted through the mouth.

The gastric cavity is lined with endoderm cells: epithelial-muscular and glandular. At the base of the epithelial-muscular cells of the endoderm there are muscle fibers located in the transverse direction relative to the axis of the body; when they contract, the body of the hydra narrows. The area of ​​the epithelial-muscle cell facing the gastric cavity carries from 1 to 3 flagella and is capable of forming pseudopods to capture food particles. In addition to epithelial-muscular cells, there are glandular cells that secrete digestive enzymes into the intestinal cavity.

rice. 2.
1 - maternal individual,
2 - daughter individual (bud).

Hydra reproduces asexually (budding) and sexually. Asexual reproduction occurs in the spring-summer season. The buds are usually formed in the middle areas of the body (Fig. 2). After some time, young hydras separate from the mother’s body and begin to lead independent life.

Sexual reproduction occurs in autumn. During sexual reproduction, germ cells develop in the ectoderm. Sperm are formed in areas of the body close to the mouth, eggs - closer to the sole. Hydras can be either dioecious or hermaphroditic.

After fertilization, the zygote is covered with dense membranes, and an egg is formed. Hydra dies, and from the egg next spring A new hydra is developing. Direct development without larvae.

Hydra has high ability to regeneration. This animal is able to recover even from a small severed part of the body. Interstitial cells are responsible for regeneration processes. The vital activity and regeneration of hydra were first studied by R. Tremblay.

Obelia sp.- a colony of marine hydroid polyps (Fig. 3). The colony has the appearance of a bush and consists of individuals of two types: hydranthus and blastostyles. The ectoderm of the members of the colony secretes a skeletal organic shell - the periderm, which performs the functions of support and protection.

Most of the colony's individuals are hydrants. The structure of a hydrant resembles that of a hydra. Unlike hydra: 1) the mouth is located on the oral stalk, 2) the oral stalk is surrounded by many tentacles, 3) the gastric cavity continues in the common “stem” of the colony. Food captured by one polyp is distributed among members of one colony through the branched channels of the common digestive cavity.

rice. 3.
1 - colony of polyps, 2 - hydroid jellyfish,
3 - egg, 4 - planula,
5 - young polyp with a kidney.

The blastostyle has the form of a stalk and does not have a mouth or tentacles. Jellyfish bud from the blastostyle. Jellyfish break away from the blastostyle, float in the water column and grow. The shape of the hydroid jellyfish can be compared to the shape of an umbrella. Between the ectoderm and endoderm there is a gelatinous layer - mesoglea. On the concave side of the body, in the center, on the oral stalk there is a mouth. Numerous tentacles hang along the edge of the umbrella, serving for catching prey (small crustaceans, larvae of invertebrates and fish). The number of tentacles is a multiple of four. Food from the mouth enters the stomach; four straight radial canals extend from the stomach, encircling the edge of the jellyfish's umbrella. The method of movement of the jellyfish is “reactive”; this is facilitated by the fold of ectoderm along the edge of the umbrella, called the “sail”. The nervous system is of a diffuse type, but there are clusters of nerve cells along the edge of the umbrella.

Four gonads are formed in the ectoderm on the concave surface of the body under the radial canals. Sex cells form in the gonads.

From the fertilized egg, a parenchymal larva develops, corresponding to a similar sponge larva. The parenchymula then transforms into a two-layer planula larva. The planula, after swimming with the help of cilia, settles to the bottom and turns into a new polyp. This polyp forms a new colony by budding.

The life cycle of obelia is characterized by alternation of asexual and sexual generations. The asexual generation is represented by polyps, the sexual generation by jellyfish.

Description of other classes of the type Coelenterates.

To class hydroid include invertebrate aquatic cnidarians. In their life cycle, two forms are often present, replacing each other: polyp and jellyfish. Hydroids can gather in colonies, but solitary individuals are also not uncommon. Traces of hydroids are found even in Precambrian layers, but due to the extreme fragility of their bodies, the search is very difficult.

A bright representative of hydroids - freshwater hydra , single polyp. Its body has a sole, a stalk and long tentacles relative to the stalk. She moves like a rhythmic gymnast - with each step she makes a bridge and somersaults over her “head”. Hydra is widely used in laboratory experiments, its ability to regenerate and high activity of stem cells, providing " eternal youth"polyp, pushed German scientists to search and study the "immortality gene."

Hydra cell types

1. Epithelial-muscular cells form the outer covers, that is, they are the basis ectoderm. The function of these cells is to shorten the hydra's body or make it longer; for this they have muscle fibers.

2. Digestive-muscular cells are located in endoderm. They are adapted to phagocytosis, capture and mix food particles that enter the gastric cavity, for which each cell is equipped with several flagella. In general, flagella and pseudopods help food penetrate from the intestinal cavity into the cytoplasm of hydra cells. Thus, her digestion occurs in two ways: intracavitary (for this there is a set of enzymes) and intracellular.

3. Stinging cells located primarily on the tentacles. They are multifunctional. Firstly, the hydra defends itself with their help - a fish that wants to eat the hydra is burned with poison and throws it away. Secondly, the hydra paralyzes prey captured by its tentacles. The stinging cell contains a capsule with a poisonous stinging thread; on the outside there is a sensitive hair, which, after irritation, gives a signal to “shoot”. The life of a stinging cell is short-lived: after being “shot” by a thread, it dies.

4. Nerve cells, together with shoots similar to stars, lie in ectoderm, under a layer of epithelial-muscle cells. Their greatest concentration is at the sole and tentacles. With any impact, the hydra reacts, which is unconditioned reflex. The polyp also has such a property as irritability. Let us also remember that the “umbrella” of a jellyfish is bordered by a cluster of nerve cells, and the body contains ganglia.

5. Glandular cells release a sticky substance. They are located in endoderm and promote food digestion.

6. Intermediate cells- round, very small and undifferentiated - lie in ectoderm. These stem cells divide endlessly, are capable of transforming into any other, somatic (except epithelial-muscular) or reproductive cells, and ensure the regeneration of the hydra. There are hydras that do not have intermediate cells (hence, stinging, nerve and reproductive cells), capable of asexual reproduction.

7. Sex cells develop into ectoderm. The egg cell of the freshwater hydra is equipped with pseudopods, with which it captures neighboring cells along with their nutrients. Among the hydras there is hermaphroditism, when eggs and sperm are formed in the same individual, but at different times.

Other features of freshwater hydra

1. Respiratory system Hydras do not have, they breathe over the entire surface of the body.

2. Circulatory system not formed.

3. Hydras eat larvae of aquatic insects, various small invertebrates, and crustaceans (daphnia, cyclops). Undigested food remains, like other coelenterates, are removed back through the mouth.

4. Hydra is capable of regeneration, for which intermediate cells are responsible. Even when cut into fragments, the hydra completes the necessary organs and turns into several new individuals.

The first to see and describe the hydra was the naturalist A. Levenguk, who invented the microscope. This scientist was the most significant naturalist of the 17th-18th centuries.

While examining aquatic plants with his primitive microscope, Leeuwenhoek noticed a strange creature that had hands “in the form of horns.” The scientist even observed the budding of these creatures and saw their stinging cells.

The structure of freshwater hydra

Hydra belongs to the coelenterate animals. Its body is tube-shaped; in the front part there is a mouth opening, which is surrounded by a corolla consisting of 5-12 tentacles.

Under the tentacles, the hydra's body narrows and a neck is formed, which separates the body from the head. The back of the body is tapered into a stalk or stalk, with a sole at the end. When the hydra is well-fed, its body length does not exceed 8 millimeters, and if the hydra is hungry, the body is much longer.

Like all representatives of the coelenterates, the body of the hydra is formed by two layers of cells.

The outer layer consists of a variety of cells: some cells are used to kill prey, other cells have contractility, and others secrete mucus. And in the outer layer there are nerve cells, which form a network covering the body of the guides.

Hydra is one of the few representatives of the coelenterates that lives in fresh water, and most of these creatures live in the seas. The habitat of hydras is a variety of bodies of water: lakes, ponds, ditches, river backwaters. They settle on aquatic plants and the roots of duckweed, which covers the entire bottom of the reservoir with a carpet. If the water is clean and transparent, then hydras settle on the rocks near the shore, sometimes forming a velvet carpet. Hydras love light, so they prefer shallow places near the banks. These creatures can discern the direction of light and move towards its source. If hydras live in an aquarium, they always move to the illuminated part of it.

If you place aquatic plants in a vessel with water, you can see hydras crawling along their leaves and the walls of the vessel. There is an adhesive substance on the sole of the hydra, which helps it firmly attach to aquatic plants, stones and the walls of the aquarium; it is quite difficult to tear the hydra from its place. Occasionally, the hydra moves in search of food; this can be observed in aquariums, when a mark remains on the stack in the place where the hydra was sitting. In a few days, these creatures move no more than 2-3 centimeters. While moving, the hydra attaches itself to the glass with a tentacle, tears off the sole and drags it to a new place. When the sole is attached to the surface, the hydra levels out and rests on its tentacle again, taking a step forward.

This method of movement is similar to the movement of moth butterfly caterpillars, which are often called “land surveyors.” But the caterpillar pulls up back to the front and then moves the front again. And the hydra turns over its head every time it moves. This is how the hydra moves quite quickly, but there is another, slower way of moving - when the hydra slides on its sole. Some individuals can detach from the substrate and swim in the water. They straighten their tentacles and sink to the bottom. And the hydras rise upward with the help of a gas bubble that forms on the sole.

How do freshwater hydras feed?

Hydras are predatory creatures; they feed on ciliates, cyclops, small crustaceans - daphnia and other small living creatures. They sometimes eat larger prey, such as small worms or mosquito larvae. Hydras can even cause damage to fish ponds as they eat newly hatched fish.

How hydra hunts can be easily observed in an aquarium. She spreads her tentacles widely, which form a net, while she hangs with her tentacles down. If you observe a hydra, you will notice that its body, slowly swaying, describes a circle with its front part. A prey swimming by brushes against the tentacles, tries to free itself, but becomes silent as the stinging cells paralyze it. The hydra pulls the prey to its mouth and begins to eat.

If the hunt is successful, the hydra swells from the number of crustaceans eaten, and their eyes are visible through its body. Hydra can eat prey that is larger than itself. The hydra's mouth can open wide and its body can stretch significantly. Sometimes a part of the victim sticks out of the hydra’s mouth, which did not fit inside.

Reproduction of freshwater hydra

If there is enough food, hydras multiply quickly. Reproduction occurs by budding. The process of bud growth from a tiny tubercle to a fully formed individual takes several days. Often several buds form on the hydra’s body until the young individual separates from the mother hydra. Thus, asexual reproduction occurs in hydras.

In autumn, when the water temperature drops, hydras can also reproduce sexually. On the body of the hydra, gonads form in the form of swellings. In some swellings, male reproductive cells are formed, and in others, egg cells. Male reproductive cells float freely in water and penetrate into the body cavity of hydras, fertilizing immobile eggs. When eggs are formed, the hydra usually dies. At favorable conditions Young individuals emerge from the eggs.

Regeneration in freshwater hydra

Hydras exhibit an amazing ability to regenerate. If a hydra is cut in half, new tentacles will quickly grow in the lower part, and a sole will grow on the upper part.

In the 17th century, the Dutch scientist Tremblay conducted interesting experiments with hydras, as a result of which he was not only able to grow new hydras from pieces, but also to fuse different halves of hydras, obtain seven-headed polyps and turn their bodies inside out. When a seven-headed polyp similar to the hydra from Ancient Greece was obtained, these polyps began to be called hydra.

Differs more complex processes life activity compared to the first multicellular organisms - sponges. What structural features is this related to? Let's figure it out together.

What is hydra in mythology

Given biological species got its name because of its similarities with the mythological hero - the Lernaean Hydra. According to legend, it was a snake-like monster with poisonous breath. The hydra's body had several heads. No one was able to defeat her - in place of the cut-off head, several new ones immediately grew.

The Lernaean Hydra lived in Lake Lerna, where it guarded the entrance to the underground kingdom of Hades. And only Hercules was able to cut off her immortal head. Then he buried her in the ground and covered her with a heavy stone. This is the second labor of Hercules out of twelve.

Hydra: biology

A high ability to restore lost body parts or regenerate is also characteristic of freshwater hydra. This animal is a representative of the coelenterate phylum. So what is a solitary freshwater polyp that leads an exclusively attached lifestyle.

General characteristics of coelenterates

Like all coelenterates, hydra is an aquatic inhabitant. They prefer shallow puddles, lakes or rivers with little current, which allow them to attach to plants or bottom objects.

The classes of coelenterates are represented by hydroids, jellyfish and coral polyps. All their representatives are characterized by ray or radial symmetry. This structural feature is associated with in a sedentary manner life. In this case, an imaginary point can be placed in the center of the animal’s body, from which rays can be drawn in all directions.

All coelenterates are multicellular animals, but they do not form tissues. Their body is represented by two layers of specialized cells. Inside there is an intestinal cavity in which food is digested. Different classes of coelenterates differ in their lifestyle:

• Hydroids are attached to the substrate using the sole and are solitary.
• Coral polyps are also immobile, but form colonies containing hundreds of thousands of individuals.
• Jellyfish actively swim in the water column. At the same time, their bell contracts and the water is pushed out with force. This movement is called reactive.

Body structure

The body of the freshwater hydra has the shape of a stalk. Its base is called the sole. With its help, the animal attaches to underwater objects. At the opposite end of the body there is a mouth opening surrounded by tentacles. It leads into the intestinal cavity.

The walls of the hydra's body consist of two layers of cells. The outer one is called ectoderm. It consists of dermal-muscular, nerve, intermediate and stinging cells. The inner layer, or endoderm, is formed by their other types - digestive and glandular. Between the layers of the body there is a layer of intercellular substance, which looks like a plate.

Cell types and life processes

Since no tissues or organs are formed in the hydra's body, everything physiological processes carried out using specialized cells. Thus, epithelial-muscular ones provide movement. Yes, despite their fixed lifestyle, hydroids are capable of movement. In this case, the epithelial-muscle cells of one side of the body first contract, the animal “bends over”, stands on the tentacles and again falls on the sole. This movement is called walking.

Between the epithelial-muscular cells there are stellate-shaped nerve cells. With their help, the animal perceives irritations from environment and responds to them in a certain way. For example, if you touch the hydra with a needle, it shrinks.

The ectoderm also contains intermediate cells. They are capable of amazing transformations. If necessary, cells of any type are formed from them. They are the ones who determine high level regeneration of these animals. It is known that hydra can be completely restored from 1/200 of its part or mushy state.

Sex cells are also formed from intermediate cells. This happens with the onset of autumn. In this case, the eggs and sperm merge, forming a zygote, and the mother’s body dies. In the spring, young individuals develop from them. In the summer, by budding, a small tubercle is formed on its body, which increases in size, acquiring the features of an adult organism. As it grows, it splits off and begins to exist independently.

Digestive cells are located in the endoderm of coelenterates. They split nutrients. And enzymes are released into the intestinal cavity, under the influence of which food breaks down into pieces. Thus, hydra is characterized by two types of digestion. They are called intracellular and cavity.

Stinging cells

It is impossible to answer the question of what a hydra is if you do not get acquainted with the features. In nature, they are found only in coelenterate animals. With their help, protection, defeat and retention of prey are carried out. Therefore, most of them are located on the tentacles.

The stinging cell consists of a capsule with a spirally twisted thread. On the surface of this structure there is a sensitive hair. It is he who is touched by prey passing by. As a result, the thread unwinds and digs forcefully into the victim’s body, paralyzing him.

By type of nutrition, coelenterates, hydra in particular, are heterotrophic predators. They feed on small aquatic invertebrates. For example, daphnia, cyclops, oligochaetes, rotifers, fleas, mosquito larvae and fish fry.

The importance of coelenterates

The importance of hydra in nature lies primarily in the fact that it plays the role of a biological filter. It purifies water from suspended particles that it consumes as food. This is an important link in the food chains of fresh water bodies. Hydras feed on some cladocerans, turbellaria and fish whose size exceeds 4 cm. Hydra itself infects fry with the poison of stinging cells.

But scientists, when asked what a hydra is, will probably answer that it is a well-known object laboratory research. These coelenterates are used to study the features of regeneration processes, the physiology of lower multicellular organisms, and budding.

So, the freshwater hydra is a representative of the Hydroid class. This is a multicellular two-layer animal with radial symmetry, the body of which consists of several types of specialized cells.

The body shape of the hydra is tubular. The mouth opening of these animals is covered with tentacles. Hydras live in water, and with their stinging tentacles they kill and bring prey to their mouths.

   Type - Coelenterates
   Class - Hydroid
   Genus/Species - Hydra vulgaris, H.oligactis, etc.

   Basic data:
DIMENSIONS
Length: 6-15 mm.

REPRODUCTION
Vegetative: has a budding character. A bud appears on the body of the mother, from which the daughter gradually develops.
Sexual: Most species of hydra are dioecious. The gonads contain cells from which eggs develop. Sperm cells develop in the testis.

LIFESTYLE
Habits: live in fresh and brackish waters.
Food: plankton, fish fry, ciliates.
Lifespan: no data.

RELATED SPECIES
The phylum Coelenterata includes more than 9,000 species, some of them (15-20) live only in fresh waters.

   Freshwater hydras are one of the smallest predators. Despite this, they are able to provide themselves with food. Hydras have a tubular body shape. Using their soles, they attach themselves to underwater plants or rocks and move their tentacles in search of prey. Green hydras contain photosynthetic algae.

FOOD

   Hydra is a predatory animal that lives in water. It feeds on small organisms living in water, for example, ciliates, oligochaete worms, planktonic crustaceans, water fleas, insects and their larvae, and fish fry. A hydra that hunts attaches itself to an aquatic plant, branch or leaf and hangs on it. Her tentacles are very wide open. They constantly make circular searching movements. If one of them touches the victim, others rush towards it. Hydra paralyzes prey with sting cell venom. The hydra uses its tentacles to pull its paralyzed prey towards its mouth. She swallows small animals whole. If the prey is larger than the hydra, the predator opens its mouth wide and the walls of its body stretch. If such prey is so large that it does not fit into the gastric cavity, then the hydra swallows only part of it and, to the extent of digestion, pushes the victim deeper and deeper.

LIFESTYLE

   Hydras live alone. However, in places that are especially rich in food, several hydras hunt at once. This happens because the water current brings a lot of food to a certain place. Hydras of the Nuiga genus prefer fresh water. These animals were discovered by the researcher who invented the microscope, A. Leeuwenhoek (1632-1723). Another scientist, G. Tremblay, discovered that hydras easily restore lost body parts. A nondescript tubular body topped with tentacles that grow around the mouth opening and a sole at the end of the body are the main features appearance hydra. The gastric cavity of this animal is continuous. The tentacles are hollow. The body walls consist of two layers of cells. There are glandular cells located in the middle part of the hydra's body. Various types very similar to each other. They differ mainly in color (and, as a consequence, different colors talk about some structural feature). Bright green hydras have symbiotic algae living in their bodies. Hydras react to light and swim towards it. These animals are sedentary. They spend most of their lives in an attached state, waiting for prey. With the sole, like a suction cup, hydras are firmly attached to plants.

REPRODUCTION

   Hydras reproduce in two ways - sexual and vegetative. Vegetative propagation is represented by budding. When suitable external conditions Several buds develop on the hydra's body. At the very beginning, the bud looks like a small mound, later miniature tentacles appear at its outer end. The tentacles grow and stinging cells appear on them. Bottom part the body of the daughter individual becomes thinner, the hydra's mouth opens, the young individual branches off and begins an independent life. These animals reproduce by budding in the warm season. With the onset of autumn, hydras begin sexual reproduction. Sex cells are formed in the gonads. The gonad cracks and an egg emerges. Around the same time, sperm are formed in the testes of other hydras. They also leave the gonad and swim in the water. One of them fertilizes the egg. An embryo develops in the egg. Protected by a double shell, it overwinters at the bottom. In the spring, a fully formed hydra emerges from the egg.
  

DID YOU KNOW THAT...

• Hydra does not age, since every cell in its body is renewed after a few weeks. This animal lives only in the warm season. With the beginning of winter, all adult hydras die. Only their eggs, protected by a strong double shell - the embryotheca, can survive the winter.
• Hydras easily restore their lost limbs. The scientist G. Tremblay (1710-1784), as a result of his numerous experiments, obtained a seven-headed polyp, from which severed heads grew back. He looked like a mythical creature - the Lernaean Hydra, defeated by a hero ancient Greece- Hercules.
• During constant movements in the water, the hydra performs quite original acrobatic tricks.

  

CHARACTERISTIC FEATURES OF HYDRA

   Tentacles: the mouth opening is surrounded by a corolla with 5-12 tentacles with stinging cells. With their help, the animal paralyzes its prey and pulls it into its mouth. A hydra that hunts attaches itself to a hard surface and, spreading its tentacles widely, makes circular searching movements with them.
   Body: body shape is tubular. At the anterior end is a mouth opening surrounded by tentacles. The aboral pore is located in the middle of the sole. The hydra wall consists of two layers of cells. Digestive processes occur in the midsection of the body.
   Mouth opening: covered with a corolla of tentacles. With its tentacles, the hydra pulls the animal into its mouth and swallows it.
   Leg: The rear end of the hydra is narrowed - this is a leg that has a sole at the end.
   Gonads: are formed in the ectoderm and have the appearance of tubercles. Sex cells accumulate in them.
   Dome: length about 13 mm. This is for self-defense. The hydra rises and forms a dense dome.
   Bud: The vegetative propagation of hydra has the nature of budding. Several buds may appear on the body at the same time. The buds are growing quickly.

PLACES OF ACCOMMODATION
Freshwater hydras live in fresh and brackish waters. They inhabit rivers, lakes, swamps and other bodies of water. The most common species are the common and brown hydra.
SAVE
Each species of a genus living in a certain territory. These days they are not in danger of extinction.