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✪ Freshwater hydra

✪ Freshwater polyp Hydra. Online preparation for the Unified State Exam in Biology.

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The body of the hydra is cylindrical; at the anterior end of the body (on the perioral cone) there is a mouth surrounded by a corolla of 5-12 tentacles. In some species, the body is divided into a trunk and a stalk. At the rear end of the body (stalk) there is a sole, with its help the hydra moves and attaches to something. Hydra has radial (uniaxial-heteropole) symmetry. The axis of symmetry connects two poles - the oral, on which the mouth is located, and the aboral, on which the sole is located. Through the axis of symmetry, several planes of symmetry can be drawn, dividing the body into two mirror-symmetrical halves.

The body of the hydra is a bag with a wall of two layers of cells (ectoderm and endoderm), between which there is a thin layer of intercellular substance (mesoglea). The body cavity of the hydra - the gastric cavity - forms outgrowths extending inside the tentacles. Although it is usually believed that the hydra has only one opening leading into the gastric cavity (oral), in fact there is a narrow aboral pore on the sole of the hydra. Through it, fluid can be released from the intestinal cavity, as well as a gas bubble. In this case, the hydra, together with the bubble, detaches from the substrate and floats up, holding itself upside down in the water column. In this way, it can spread throughout the reservoir. As for the mouth opening, in a non-feeding hydra it is virtually absent - the ectoderm cells of the oral cone close and form tight junctions, the same as in other parts of the body. Therefore, when feeding, the hydra has to “break through” its mouth anew each time.

Cellular composition of the body

Epithelial muscle cells

Epithelial-muscular cells of the ectoderm and endoderm form the bulk of the hydra's body. Hydra has about 20,000 epithelial-muscle cells.

Ectoderm cells have cylindrical epithelial parts and form a single-layer integumentary epithelium. Adjacent to the mesoglea are contractile processes of these cells, forming the longitudinal muscles of the hydra.

Epithelial-muscular cells of the endoderm are directed by epithelial parts into the intestinal cavity and carry 2-5 flagella, which mix food. These cells can form pseudopods, with the help of which they capture food particles. Digestive vacuoles form in the cells.

Epithelial-muscle cells of the ectoderm and endoderm are two independent cell lines. In the upper third of the hydra's body, they divide mitotically, and their descendants gradually move either towards the hypostome and tentacles, or towards the sole. As they move, cell differentiation occurs: for example, ectoderm cells on the tentacles give rise to stinging battery cells, and on the sole - glandular cells that secrete mucus.

Glandular cells of the endoderm

The glandular cells of the endoderm secrete digestive enzymes into the intestinal cavity that break down food. These cells are formed from interstitial cells. Hydra has about 5,000 glandular cells.

Interstitial cells

Between the epithelial-muscle cells are groups of small, round cells called intermediate or interstitial cells (i-cells). Hydra has about 15,000 of them. These are undifferentiated cells. They can transform into other types of cells in the hydra body, except for epithelial-muscular ones. Intermediate cells have all the properties of multipotent stem cells. It has been proven that each intermediate cell is potentially capable of producing both reproductive and somatic cells. Stem intermediate cells do not migrate, but their differentiating descendant cells are capable of rapid migration.

Nerve cells and nervous system

Nerve cells form a primitive diffuse nervous system in the ectoderm - a diffuse nerve plexus (diffuse plexus). The endoderm contains individual nerve cells. In total, hydra has about 5,000 neurons. Hydra has thickenings of the diffuse plexus on the sole, around the mouth and on the tentacles. According to new data, hydra has a perioral nerve ring, similar to the nerve ring located on the edge of the umbrella of hydromedusas.

Hydra does not have a clear division into sensory, intercalary and motor neurons. The same cell can perceive irritation and transmit a signal to epithelial muscle cells. However, there are two main types nerve cells- sensitive and ganglionic. The bodies of sensitive cells are located across the epithelial layer; they have a stationary flagellum surrounded by a collar of microvilli that sticks out into the external environment and is able to perceive irritation. Ganglion cells are located at the base of epithelial-muscular cells; their processes do not extend into the external environment. According to morphology, most hydra neurons are bipolar or multipolar.

Hydra's nervous system contains both electrical and chemical synapses. Of the neurotransmitters found in hydra, dopamine, serotonin, norepinephrine, gamma-aminobutyric acid, glutamate, glycine and many neuropeptides (vasopressin, substance P, etc.).

Hydra is the most primitive animal in whose nerve cells light-sensitive opsin proteins are found. Analysis of the Hydra opsin gene suggests that Hydra and human opsins share a common origin.

Stinging cells

Stinging cells are formed from intermediate cells only in the torso area. First, the intermediate cell divides 3-5 times, forming a cluster (nest) of stinging cell precursors (cnidoblasts) connected by cytoplasmic bridges. Then differentiation begins, during which the bridges disappear. Differentiating cnidocytes migrate into the tentacles. Stinging cells are the most numerous of all cell types; there are about 55,000 of them in Hydra.

The stinging cell has a stinging capsule filled with a poisonous substance. A stinging thread is screwed inside the capsule. There is a sensitive hair on the surface of the cell; when it is irritated, the thread is thrown out and hits the victim. After the thread is fired, the cells die, and new ones are formed from the intermediate cells.

Hydra has four types of stinging cells - stenoteles (penetrants), desmonemas (volventes), holotrichs isorhiza (large glutinants) and atriches isorhiza (small glutinants). When hunting, volvents are fired first. Their spiral stinging threads entangle the outgrowths of the victim’s body and ensure its retention. Under the influence of the victim's jerks and the vibration they cause, more high threshold irritation penetrants. The spines present at the base of their stinging threads are anchored in the body of the prey, and poison is injected into its body through the hollow stinging thread.

A large number of stinging cells are located on the tentacles, where they form stinging batteries. Usually the battery consists of one large epithelial-muscular cell in which the stinging cells are immersed. In the center of the battery there is a large penetrant, around it there are smaller volvents and glutinants. Cnidocytes are connected by desmosomes to the muscle fibers of the epithelial muscle cell. Large glutinants (their stinging thread has spines, but, like volventas, does not have a hole at the top) are apparently mainly used for protection. Small glutinants are used only when the hydra moves to firmly attach its tentacles to the substrate. Their firing is blocked by extracts from the tissues of Hydra victims.

The firing of Hydra penetrants was studied using ultra-high-speed filming. It turned out that the entire firing process takes about 3 ms. In its initial phase (before the spines are everted), its speed reaches 2 m/s, and the acceleration is about 40,000 (data from 1984); apparently this is one of the fastest cellular processes known in nature. The first visible change (less than 10 μs after stimulation) was an increase in the volume of the stinging capsule by approximately 10%, then the volume decreased to almost 50% of the original. Later it turned out that both the speed and acceleration when firing nematocysts were greatly underestimated; according to 2006 data, in the early phase of firing (throwing out spikes), the speed of this process is 9-18 m/s, and the acceleration ranges from 1,000,000 to 5,400,000 g. This allows a nematocyst weighing about 1 ng to develop a pressure of about 7 hPa at the tips of the spines (whose diameter is about 15 nm), which is comparable to the pressure of a bullet on a target and allows it to pierce the fairly thick cuticle of victims.

Sex cells and gametogenesis

Like all animals, hydras are characterized by oogamy. Most hydras are dioecious, but there are hermaphroditic lines of hydras. Both eggs and sperm are formed from i-cells. It is believed that these are special subpopulations of i-cells that can be distinguished by cellular markers and which are present in small numbers in hydras and during the period asexual reproduction.

Breathing and elimination

Respiration and excretion of metabolic products occurs through the entire surface of the animal’s body. Probably, vacuoles, which are present in hydra cells, play some role in the secretion. The main function of vacuoles is probably osmoregulatory; they remove excess water, which constantly enters the hydra cells through osmosis.

Irritability and reflexes

Hydras have a reticulate nervous system. Availability nervous system allows the hydra to carry out simple reflexes. Hydra reacts to mechanical irritation, temperature, lighting, the presence of chemicals in water and a number of other environmental factors.

Nutrition and Digestion

Hydra feeds on small invertebrates - daphnia and other cladocerans, cyclops, as well as naidid oligochaetes. There is evidence of hydra consuming rotifers and trematode cercariae. Prey is captured by the tentacles using stinging cells, the venom of which quickly paralyzes small victims. By coordinated movements of the tentacles, the prey is brought to the mouth, and then, with the help of body contractions, the hydra is “put on” the victim. Digestion begins in the intestinal cavity (cavitary digestion) and ends inside the digestive vacuoles of the epithelial-muscle cells of the endoderm (intracellular digestion). Undigested food remains are expelled through the mouth.
Since hydra does not have a transport system, and the mesoglea (the layer of intercellular substance between the ectoderm and endoderm) is quite dense, the problem of transporting nutrients to the ectoderm cells arises. This problem is solved by the formation of cell outgrowths of both layers, which cross the mesoglea and connect through gap junctions. Small particles can pass through them organic molecules(monosaccharides, amino acids), which provides nutrition to ectoderm cells.

Reproduction and development

Under favorable conditions, hydra reproduces asexually. A bud forms on the animal’s body (usually in the lower third of the body), it grows, then tentacles form and a mouth breaks through. A young hydra buds from the mother's body (in this case, the mother and daughter polyps attach with tentacles to the substrate and pull into different sides) and leads an independent lifestyle. In autumn, hydra begins to reproduce sexually. On the body, in the ectoderm, gonads are formed - sex glands, and in them, germ cells develop from intermediate cells. When hydra gonads form, a medusoid nodule is formed. This suggests that the hydra gonads are greatly simplified sporifers, final stage in the series of transformation of the lost medusoid generation into an organ. Most species of hydra are dioecious; hermaphroditism is less common. Hydra eggs grow rapidly by phagocytosis of surrounding cells. Mature eggs reach a diameter of 0.5-1 mm. Fertilization occurs in the body of the hydra: through a special hole in the gonad, the sperm penetrates the egg and merges with it. The zygote undergoes complete uniform fragmentation, resulting in the formation of a coeloblastula. Then, as a result of mixed delamination (a combination of immigration and delamination), gastrulation occurs. A dense protective shell (embryotheca) with spine-like outgrowths is formed around the embryo. At the gastrula stage, the embryos enter suspended animation. Adult hydras die, and the embryos sink to the bottom and overwinter. In the spring, development continues; in the parenchyma of the endoderm, an intestinal cavity is formed by divergence of cells, then the rudiments of tentacles are formed, and a young hydra emerges from under the shell. Thus, unlike most marine hydroids, hydra does not have free-swimming larvae and its development is direct.

Growth and regeneration

Cell migration and renewal

Normally, in an adult hydra, cells of all three cell lines divide intensively in the middle part of the body and migrate to the sole, hypostome and tips of the tentacles. Cell death and desquamation occurs there. Thus, all cells of the hydra's body are constantly renewed. With normal nutrition, the “excess” of dividing cells moves to the kidneys, which usually form in the lower third of the body.

Regenerative ability

Hydra has a very high regeneration ability. When cut crosswise into several parts, each part restores the “head” and “leg”, maintaining the original polarity - the mouth and tentacles develop on the side that was closer to the oral end of the body, and the stalk and sole develop on the aboral side of the fragment. The whole organism can be restored from individual small pieces of the body (less than 1/200 of the volume), from pieces of tentacles, and also from a suspension of cells. At the same time, the regeneration process itself is not accompanied by increased cell division and represents typical example morphallaxis.

Hydra can regenerate from a suspension of cells obtained by maceration (for example, by rubbing hydra through mill gas). Experiments have shown that to restore the head end, the formation of an aggregate of approximately 300 epithelial-muscle cells is sufficient. It has been shown that regeneration normal body possible from cells of one layer (only ectoderm or only endoderm).

Fragments of the cut body of the hydra retain information about the orientation of the body axis of the organism in the structure of the actin cytoskeleton: during regeneration, the axis is restored, the fibers direct cell division. Changes in the structure of the actin skeleton can lead to disturbances in regeneration (the formation of several body axes).

Experiments on studying regeneration and regeneration models

Local species

In the reservoirs of Russia and Ukraine, the following types of hydra are most often found (at present, many zoologists distinguish, in addition to the genus Hydra 2 more types - Pelmatohydra And Chlorohydra):

long-stemmed hydra ( Hydra (Pelmatohydra) oligactis, synonym - Hydra fusca) - large, with a bunch of very long thread-like tentacles, 2-5 times the length of its body. These hydras are capable of very intensive budding: on one maternal individual you can sometimes find up to 10-20 polyps that have not yet budded.
Hydra vulgaris ( Hydra vulgaris, synonym - Hydra grisea) - Tentacles in a relaxed state significantly exceed the length of the body - approximately twice longer than body, and the body itself narrows closer to the sole;
hydra subtle ( Hydra circumcincta, synonym - Hydra attenuata) - the body of this hydra looks like a thin tube of uniform thickness. The tentacles in a relaxed state do not exceed the length of the body, and if they do, it is very small. Polyps are small, occasionally reaching 15 mm. The width of the Holotrich isorhiz capsules exceeds half their length. Prefers to live closer to the bottom. Almost always attached to the side of objects that faces the bottom of the reservoir.
green hydra ( ) with short but numerous tentacles, grassy green in color.
Hydra oxycnida - tentacles in a relaxed state do not exceed the length of the body, and if they exceed, then very slightly. The polyps are large, reaching 28 mm. The width of the Holotrich isorhiz capsules does not exceed half their length.

Symbionts

The so-called “green” hydras Hydra (Chlorohydra) viridissima Endosymbiotic algae of the genus live in endoderm cells Chlorella- zoochlorella. In the light, such hydras can long time(more than four months) go without food, while hydras artificially deprived of symbionts die after two months without feeding. Zoochlorella penetrate the eggs and are transmitted transovarially to the offspring. Other types of hydras in laboratory conditions Sometimes it is possible to infect with zoochlorella, but a stable symbiosis does not arise.

It was with observations of green hydras that A. Tremblay began his research.

Hydras can be attacked by fish fry, for which the stinging cell burns are apparently quite sensitive: having grabbed a hydra, the fry usually spits it out and refuses further attempts to eat it.

The cladoceran crustacean from the family Hydoridae is adapted to feed on the tissues of hydras. Anchistropus emarginatus.

Turbellaria microstoma can also feed on hydra tissues, which are able to use undigested young stinging cells of hydras as protective cells - kleptocnidia.

History of discovery and study

Apparently, the hydra was first described by Antonio van Leeuwenhoek. Studied in detail the nutrition, movement and asexual reproduction, as well as the regeneration of Hydra

Scientific classification

Kingdom: Animals

Sub-kingdom: Eumetazoans

Type: Stinging

Class: Hydroid

Squad: Hydroids

Family: Hydridae

Genus: Hydra

Latin name Hydra Linnaeus , 1758

Building plan

The body of the hydra is cylindrical; at the anterior end of the body, on a perioral cone, there is a mouth surrounded by a corolla of 5-12 tentacles. In some species, the body is divided into a trunk and a stalk. At the rear end of the body (stalk) there is a sole, with its help the hydra moves and attaches. Hydra has radial (uniaxial-heteropole) symmetry. The axis of symmetry connects two poles - the oral, on which the mouth is located, and the aboral, on which the sole is located. Through the axis of symmetry, several planes of symmetry can be drawn, dividing the body into two mirror-symmetrical halves.

The body of the hydra is a bag with a wall of two layers of cells (ectoderm and endoderm), between which there is a thin layer of intercellular substance (mesoglea). The body cavity of the hydra - the gastric cavity - forms outgrowths that extend inside the tentacles. Although it is usually believed that the hydra has only one opening leading into the gastric cavity (oral), in fact, there is a narrow anal pore on the sole of the hydra. A gas bubble may be released through it. In this case, the hydra detaches from the substrate and floats up, holding itself upside down in the water column. In this way, it can spread throughout the reservoir. As for the mouth opening, in a non-feeding hydra it is virtually absent - the ectoderm cells of the mouth cone close and form tight junctions, the same as in other parts of the body . Therefore, when feeding, the hydra has to “break through” its mouth anew each time.

Cellular composition of the ectoderm

Epithelial muscle cells ectoderm form the bulk of the cells of this tissue. The cells have a cylindrical shape of epithelial parts and form a single-layer integumentary epithelium. Adjacent to the mesoglea are contractile processes of these cells, forming the longitudinal muscles of the hydra.

Between the epithelial-muscle cells are groups of small, round cells called intermediate or interstitial cells (i-cells). These are undifferentiated cells. They can transform into other types of cells in the hydra body, except for epithelial-muscular ones. Intermediate cells have all the properties of multipotent stem cells. Proven. that each intermediate cell is potentially capable of giving rise to both germ and somatic cells. Stem intermediate cells do not migrate, but their differentiating descendant cells are capable of rapid migration.

Nervous system

Nerve cells form a primitive diffuse nervous system in the ectoderm - a diffuse nerve plexus (diffuse plexus). The endoderm contains individual nerve cells. Hydra has thickenings of the diffuse plexus on the sole, around the mouth and on the tentacles. According to new data, hydra has a perioral nerve ring, similar to the nerve ring located on the edge of the umbrella of hydromedusas.
Hydra does not have a clear division into sensory, intercalary and motor neurons. The same cell can perceive irritation and transmit a signal to epithelial muscle cells. However, there are two main types of nerve cells - sensory and ganglion cells. The bodies of sensitive cells are located across the epithelial layer; they have a stationary flagellum, surrounded by a collar of microvilli, which protrudes into the external environment and is able to perceive irritation. Ganglion cells are located at the base of the epithelial-muscular cells; their processes do not extend into the external environment. According to morphology, most hydra neurons are bipolar or multipolar.
The nervous system of the hydra contains both electrical and chemical synapses .

Stinging cells

Hydra has four types of stinging cells - stenoteles (penetrants), desmonemas (volventes), holotrichs isorhiza (large glutinants) and atriches isorhiza (small glutinants). When hunting, volvents are fired first. Their spiral stinging threads entangle the outgrowths of the victim’s body and ensure its retention. Under the influence of the victim's jerks and the vibration they cause, penetrants with a higher threshold of irritation are triggered. The spines present at the base of their stinging threads are anchored in the body of the prey. and poison is injected into her body through a hollow stinging thread.

A large number of stinging cells are found on the tentacles, where they form stinging batteries. Usually the battery consists of one large epithelial-muscular cell in which the stinging cells are immersed. In the center of the battery there is a large penetrant, around it there are smaller volvents and glutinants. Cnidocytes connected desmosomes with muscle fibers of the epithelial muscle cell. Large glutinants (their stinging thread has spines, but, like volventas, does not have a hole at the top) are apparently mainly used for protection. Small glutinants are used only when the hydra moves to firmly attach its tentacles to the substrate. Their firing is blocked by extracts from the tissues of Hydra victims.

Cellular composition of the endoderm

Epithelial muscle cells are directed into the intestinal cavity and bear flagella that mix food. These cells can form pseudopods, with the help of which they capture food particles. Digestive vacuoles form in the cells. The glandular cells of the endoderm secrete digestive enzymes into the intestinal cavity that break down food.

Respiration and excretion of metabolic products occurs through the entire surface of the animal’s body. The presence of a nervous system allows the hydra to carry out simple reflexes. Hydra reacts to mechanical irritation, temperature, the presence of chemicals in water and a number of other environmental factors

Nutrition and Digestion

Hydra feeds on small invertebrates - daphnia and other cladocerans, cyclops, as well as naidid oligochaetes. There is data on consumption by hydras rotifers And cercariae trematodes. Prey is captured by the tentacles using stinging cells, the venom of which quickly paralyzes small victims. By coordinated movements of the tentacles, the prey is brought to the mouth, and then, with the help of body contractions, the hydra is “put on” the victim. Digestion begins in the intestinal cavity (cavitary digestion) and ends inside the digestive vacuoles of the epithelial-muscle cells of the endoderm (intracellular digestion). Undigested food remains are expelled through the mouth.
Since hydra does not have a transport system, and the mesoglea (the layer of intercellular substance between the ectoderm and endoderm) is quite dense, the problem of transporting nutrients to the ectoderm cells arises. This problem is solved by the formation of outgrowths of cells of both layers, which cross the mesoglea and connect through gap contacts. Small organic molecules (monosaccharides, amino acids) can pass through them, which provides nutrition to the ectoderm cells.

Reproduction and development

Under favorable conditions, hydra reproduces asexually. A bud forms on the animal’s body (usually in the lower third of the body), it grows, then tentacles form and a mouth breaks through. The young hydra buds from the mother's body (in this case, the mother and daughter polyps are attached with tentacles to the substrate and pull in different directions) and leads an independent lifestyle. In autumn, hydra begins to reproduce sexually. On the body, in the ectoderm, gonads are laid - sex glands, and in them, germ cells develop from intermediate cells. When the gonads form, hydras are formed medusoid nodule. This suggests that the hydra gonads are highly simplified sporosaki, the last stage in the series of transformation of the lost medusoid generation into an organ. Most species of hydra are dioecious, less common hermaphroditism. Hydra eggs grow rapidly by phagocytosis of surrounding cells. Mature eggs reach a diameter of 0.5-1 mm Fertilization occurs in the body of the hydra: through a special hole in the gonad, the sperm penetrates the egg and merges with it. Zygote undergoes complete uniform splitting up, which results in the formation coeloblastula. Then, as a result of mixed delamination(combination immigration and delamination) is carried out gastrulation. A dense protective shell (embryotheca) with spine-like outgrowths is formed around the embryo. At the gastrula stage, the embryos enter anabiosis. Adult hydras die, and the embryos sink to the bottom and overwinter. In the spring, development continues, in the parenchyma of the endoderm, an intestinal cavity is formed by divergence of cells, then the rudiments of tentacles are formed, and a young hydra emerges from under the shell. Thus, unlike most marine hydroids, hydra does not have free-swimming larvae and its development is direct.

Growth and regeneration
Cell migration and renewal

Normally, in an adult hydra, cells of all three cell lines divide intensively in the middle part of the body and migrate to the sole. hypostome and tips of tentacles. Cell death and desquamation occurs there. Thus, all cells of the hydra's body are constantly renewed. With normal nutrition, the “excess” of dividing cells moves to the kidneys, which usually form in the lower third of the body

Regenerative ability

Hydra has a very high ability to regeneration. When cut crosswise into several parts, each part restores the “head” and “leg”, maintaining the original polarity - the mouth and tentacles develop on the side that was closer to the oral end of the body, and the stalk and sole develop on the aboral side of the fragment. The whole organism can be restored from individual small pieces of the body (less than 1/100 of the volume), from pieces of tentacles, and also from a suspension of cells. At the same time, the regeneration process itself is not accompanied by increased cell division and is a typical example morphallaxis .

Hydra can regenerate from a suspension of cells obtained by maceration (for example, by rubbing hydra through mill gas). Experiments have shown that to restore the head end, the formation of an aggregate of approximately 300 epithelial-muscle cells is sufficient. It has been shown that regeneration of a normal organism is possible from cells of one layer (only ectoderm or only endoderm).

Lifespan

Still at the end 19th century a hypothesis was put forward about theoretical immortality hydra, which they tried to scientifically prove or disprove throughout XX century. IN 1997 hypothesis was proven experimentally by Daniel Martinez . Experiment continued about four years old and showed a lack mortality among the three groups of hydras due to aging. It is believed that the immortality of hydras is directly related to their high regenerative ability.

Local species

Long-stemmed hydra (Hydra (Pelmatohydra) oligactis) is large, with a bunch of very long thread-like tentacles, 2-5 times the length of its body;

Common hydra (Hydra vulgaris) - the tentacles are approximately twice as long as the body, and the body itself, like the previous species, narrows closer to the sole;

Thin hydra (Hydra attennata) - the body of this hydra has the appearance of a thin tube of uniform thickness, and the tentacles are only slightly longer than the body;

Green hydra (Hydra (Chlorohydra) viridissima) with short but numerous tentacles, grassy green color.

Green hydras

Symbionts

In the so-called “green” hydra Hydra (Chlorohydra) viridissima, endosymbiotic algae of the genus live in the endoderm cells Chlorella - zoochlorella. In the light, such hydras can go without food for a long time (more than four months), while hydras artificially deprived of symbionts die without feeding after two months. Zoochlorella penetrate eggs and are transmitted to offspring transovarian. Other types of hydras can sometimes be infected with zoochlorella in laboratory conditions, but a stable symbiosis does not arise.

Hydras can be attacked by fish fry, for which the stinging cell burns are apparently quite sensitive: having grabbed a hydra, the fry usually spits it out and refuses further attempts to eat it.

Hydras are adapted to feeding on tissues. cladocera from the chydorid family Anchistropus emarginatus.

Hydras can also feed on tissues turbellaria microstomulae, which are able to use undigested young stinging cells of hydras as protective cells - kleptocnid .

History of discovery and study

Apparently, he described the hydra for the first time Antonio van Leeuwenhoek. Studied in detail the nutrition, movement and asexual reproduction, as well as the regeneration of Hydra Abraham Tremblay, who described the results of his experiments and observations in the book “Memoirs on the history of a genus of freshwater polyps with hands in the shape of horns” (the first edition was published on French in 1744). Tremblay's discovery gained great fame; his experiments were discussed in secular salons and at the French royal court. These experiments refuted the then prevailing belief that the absence of asexual reproduction and developed regeneration in animals is one of their most important differences from plants. It is believed that the study of hydra regeneration (the experiments of A. Tremblay) marked the beginning of experimental zoology. Scientific name of the genus according to the rules zoological nomenclature appropriated Carl Linnaeus .

Literature and Sources

N.Yu. Zotova. The history of Hydra from Anton Leeuwenhoek to the present day.

Stepanyants S. D., Kuznetsova V. G., Anokhin B. A. Hydra: from Abraham Tremblay to the present day

Non-profit initiative of the laboratory of the University of Kiel for the production and use of transgenic hydras

Ru.wikipedia.org

On the reaction of freshwater hydra to exogenous biologically active (hormonal) compounds

CM. Nikitina, I.A. Vakolyuk (Kaliningrad State University)

The functioning of hormones as the most important regulators and integrators of metabolism and a variety of functions in the body is impossible without the existence of systems for specific signal reception and its transformation into the final beneficial effect, that is, without a hormone-competent system. In other words, the presence of a reaction at the organismal level to exogenous compounds is impossible without the presence of cytoreception to these compounds and, accordingly, without the existence in these animals of endogenous compounds related to those with which we act. This does not contradict the concept of universal blocks, when the basic molecular structures in functional systems living organisms are found in almost a complete set already at the earliest stages of evolution, which are only accessible to study, are represented by a limited number of molecules and carry out the same elementary functions not only in representatives of one kingdom, for example in different groups mammals or even different types, but also in representatives of various kingdoms, including multicellular and unicellular organisms, higher eukaryotes and prokaryotes.

However, it should be noted that data on the composition and functions of compounds that act as hormones in vertebrates in representatives of taxa of a fairly low phylogenetic level are just beginning to appear. Of the groups of animals of a low phylogenetic level, hydra, as a representative of the coelenterates, is the most primitive organism with a real nervous system. Neurons differ morphologically, chemically, and probably functionally. Each of them contains neurosecretory granules. A significant diversity of neuronal phenotypes in Hydra has been established. In the hypostome there are orderly groups of 6-11 synaptically connected cells, which can be considered as evidence of the presence of primitive nerve ganglia in hydras. In addition to providing behavioral reactions, the hydra nervous system serves as an endocrine regulatory system, providing control of metabolism, reproduction, and development. In hydras, there is differentiation of nerve cells according to the composition of the neuropeptides they contain). It is assumed that the molecules of oxytocin, vasopressin, sex steroids and glucocorticoids are universal. They are also found in representatives of the coelenterates. Head and plantar activators (and inhibitors) are isolated from methanol extracts of the body of hydra. The head activator, isolated from sea anemones, is similar in composition and properties to the neuropeptide found in the hypothalamus and intestines of cows, rats, pigs, humans and in the blood of the latter. In addition, it has been shown that in both invertebrates and vertebrates, cyclic nucleotides are involved in ensuring the response of cells to neurohormones, that is, the mechanism of action of these substances in two phylogenetically different lines is the same.

Purpose this study Taking into account the above, we chose to study the complex effect of exogenous biologically active (hormonal) compounds on freshwater hydra.

Material and research methods

Animals for the experiment were collected in June-July 1985-1992. at a hospital (channel of the Nemonin River, village of Matrosovo, Polesie district). Adaptation to keeping in laboratory conditions - 10-14 days. Volume of material: type - Coelenterata; class - Hydrozoa; species - Hydra oligactis Pallas; quantity - 840. The number of animals is reflected at the beginning of the experiment and the increase in number is not taken into account.

The work used water-soluble hormonal compounds of the oxytocin series, the anterior lobe of the pituitary gland with an initial activity of 1 ml (ip) (hyfotocin - 5 units, pituitrin - 5 units, mammophysin - 3 units, prefisone - 25 units, gonadotropin - 75 units) and a steroid - prednisolone - 30 mg , which in vertebrates provide three-tier endocrine regulation, including the hypothalamic-pituitary complex and epithelial glands.

In preliminary experiments, drug concentrations from 0.00002 to 20 ml ip/l of the animal housing environment were used.

There were three study groups:

1st - determination of the “+” or “-” reaction in all concentrations accepted by us;

2nd - determination of the range of concentrations that ensure work in a chronic mode of varying duration;

3rd - chronic experiment.

The experiment took into account the budding activity of Hydra. The obtained data were subjected to standard statistical processing.

Research results

When determining the "" reaction of hydras in a wide range of concentrations of compounds, three were selected (0.1 ml IP/L medium, 0.02 ml IP/L medium and 0.004 ml IP/L medium).

In the control group of hydras, budding remained at the level of 0.0-0.4 buds/hydra (Pa) for five days. In the environment of the minimum concentration of prefisone, the increase was 2.2 individuals/hydra, pituitrin - 1.9 individuals/hydra (the significance of the differences with the control is extremely high - with a significance level of 0.01). At medium concentrations, hyfotocin, mammophysin and prefisone performed well (1.8-1.9 individuals/hydra). Prednisolone in minimal, and especially in average concentration, caused an increase in the number of 1.1-1.3 individuals/hydra, which significantly exceeds the control.

In the following experiment, only optimal concentrations of hormonal compounds were used. The duration of the experiment was 9 days. At the beginning of the experiment, the control and experimental groups were not reliably distinguished by the Pa value. After nine days of the experiment, the Pa values were significantly different in the experimental groups and the control with a significance level of 0.05 (Table 1).

Table 1

The influence of hormonal drugs on hydra budding (Ra) and the likelihood of the significance of their differences (p)

Environment RaChange1 day9 daysRa1 day9 daysControl1,20,81,50,90,30,1-Gonadotropin2,11,25,10,33,00,80,710,95Prefisone1,10,74,92,03,81,30,130,97Hyphotocin1,80 ,86,12,24,31,40,580,99Pituitrin0,80,54,52,03,71,50,470,98Mammophysin1,10,35,32,04,21,70,150,99Prednisolone1,50,47,12,25,61 ,80,430,99

As can be seen from the table, highest value Ra was obtained when animals were kept in prednisolone. All peptide preparations give approximately similar Pa values (average 3.80.5). However, there is also variation here. The best effect (4.31.4) is achieved when animals are kept in an environment with a purified extract of the neurohypophysis - hyphotocin. Close to it in terms of impact is mammophysin. In the experimental groups with pituitrin and prefisone, the Ra values are 3.71.5 and 3.81.3, respectively. The least effect is achieved by influencing hydra with gonadotropin. Unreliable differences in Ra occur by the end of the first day after placing hydras in solutions of hormonal drugs. Over the course of nine days of the experiment, Ra in the control did not change. Starting from the third day, Ra in all experimental groups significantly exceeds Ra in the control. It should be noted that there was a gradual significant increase in this indicator in the experimental groups by the ninth day.

To assess the statistical reliability of the effects, the values of the F criterion (ratio of mean squares) obtained for each of the two factors separately (A - factor of duration of detention; B - factor of influence) and for their interaction (A + B), and the tabulated values of the criterion were compared for two significance levels P=0.05 and P=0.01 (Table 2).

table 2

Results of analysis of variance of the effect of hormonal drugs and duration of maintenance on the intensity of asexual reproduction of Hydra oligactis

Fact-Factual in groupsTable RtorsPituitrinMammophysinGifotocinGonadotropinPrefisonePrednisolone0.050.01A3.441.402.272.173.621.301.922.50B8.374.048.094.738.2612.704.007.08A+B1.12 0.960.560.371.071.031.922.50 As can be seen from the table, F fact for the impact factor at a significance level of 0.05 in all experimental groups is greater than F table, and at a significance level of 0.01, this pattern is observed in the groups with pituitrin, hyfotocin, prefisone and prednisolone, and the degree of effect in the group with prednisolone is the highest, much greater than in the groups with pituitrin, hyfotocin and prefisone, which have a similar effect strength (Fact values very close). The influence of the interaction of factors A and B in all experimental groups has not been proven.

For factor A, Ffact is less than Ftable (at both significance levels) in the groups with mammophysin and prednisolone. In the groups with hyfotocin and gonadotropin, Fact is greater than Ftable at P = 0.05, that is, the influence of this factor cannot be considered conclusively proven, in contrast to the experimental groups with pituitrin and prefisone, where Fact is greater than Ftable both at P = 0.01 and at P=0.05.

All hormonal drugs, in addition to gonadotropin, to varying degrees, delay the onset of asexual reproduction. However, this turns out to be statistically significant only in the group with prefisone (P = 0.01). The hormonal drugs used in the experiment do not reliably affect the duration of development of a single kidney, they change the mutual influence of the first and second kidneys: pituitrin, mammophysin, prefisone, gonadotropin - in the presence of only the formed head section of the developing kidneys; pituitrin, gonadotropin and prednisolone - in the presence of at least one formed plantar section of the developing kidneys.

Thus, the sensitivity of hydras to wide range hormonal compounds of vertebrates and assume that exogenous hormonal compounds are included (as synergists or antagonists) in the endocrine regulatory cycle inherent in the hydra itself.

Bibliography

1. Pertseva M.N. Intermolecular fundamentals

Hydras are a special genus of sessile coelenterates, which in their appearance and way of life resemble plants, but still they belong to the animal kingdom. The nervous system of the hydra is designed in such a way as to provide the creature with the ability to extract sufficient quantity food.

It is not easy to figure out what type of nervous system the hydra has, since this structure is quite simple and is found not only in these creatures, but also in some species of jellyfish and other primitive animals. Hydras are relatively small animal organisms, reaching sizes from 2 to 20 mm.

The cells that form the nervous system are shaped like stars, which are connected by rays to each other, forming a neural network. The nervous system is located under the skin-muscle cells. Organ of central perception electrical impulses Hydras do not have any symptoms caused by external or internal stimuli. The maximum number of neurons is approximately 5000 pcs. and they are all connected to each other.

The nervous system of the hydra is called diffuse plexus, since there is a scattered and heterogeneous plexus. Condensation of the diffuse plexus is observed in the area of the sole, oral cavity and tentacles. Recent studies have shown that in the area of the mouth there is a nerve ring, which has a similar structure to the nerve ring located along the edge of the hydromedusa umbrella.

The nervous system of the hydra is extremely primitive, therefore the cells that form it do not have a clear division into motor, intercalary and sensory. At the same time, it must be taken into account that a certain division of cells in the nervous system of this creature still exists. There are 2 main types of nerve cells - ganglion and sensory.

The structure of these 2 types of cells has fundamental differences. Sensitive cells are located across the epithelial layer and have 1 immobile flagellum dotted with microscopic villi. This flagellum extends into the external environment and conducts stimuli acting from the outside. Ganglion-type cells are located at the very base of the epithelial-muscular layer, so their processes cannot perceive stimuli acting from the outside, but they are actively involved in muscle contraction when required.

In my own way morphological composition the vast majority of hydra nerve cells are bipolar, which provides them with better conductivity and the ability to adequately respond to stimuli affecting the body of this organism from the external environment.

Despite the primitive structure of the hydra nervous system, conductivity is still ensured not only by electrical, but also chemical reactions. Chemical neurotransmitters in an organism such as hydra include serotonin, dopamine, gamma amino acid, norepinephrine, glutamate, glycine, and in addition sick amount different types neuropeptides.

All these chemical substances are more characteristic of complex animal organisms, but a small part of them is also present in protozoa. Despite the fact that the hydra does not have a central nervous system, it is still capable of perceiving light stimuli. Relatively recently, even organisms such as jellyfish were considered completely incapable of distinguishing between light and dark, but later special cells were discovered that allow these creatures, drifting across the ocean, to distinguish between light and dark and choose the direction of movement. This is extremely effective, because in the more superficial layers of water there live a larger number of small crustaceans and other organisms that jellyfish feed on.

Hydra has a similar mechanism for recognizing light and darkness. A special sensitive protein, also known as opsin, helps hydras recognize light. Carrying out genetic analysis This protein, extracted from the body of hydra, revealed a number of similarities with a similar protein found in humans. A similar study showed that the opsin protein in humans and hydra has a common origin.

The hydra's nervous system is quite efficient and provides this creature with Better conditions for survival. With minimal contact with the hydra's body, the excitement that originates at one point of its body quickly spreads to others. Considering that the nerve impulse instantly spreads throughout the hydra’s body, a rapid contraction of the musculocutaneous system is observed, which is why the entire body of the creature quickly shortens. Such a response to an existing stimulus from the outside is considered an unconditioned reflex.

Nerve cells, like other tissues of the hydra body, have a significant ability to regenerate. When the hydra is divided into several parts, each of these halves can later become an independent organism and regrow the lost parts.

Despite the fact that hydras, as a rule, remain in one place for a long time, if necessary, this creature can move slowly to find more comfortable spot to hunt your prey. The peculiarities of the hydra's movement are also largely determined by the structure of the nervous system of this creature.

From this article you will learn everything about the structure of freshwater hydra, its lifestyle, nutrition, and reproduction.

External structure of the hydra

Polyp (meaning "many-legged") hydra is a tiny translucent creature that lives in clear clear waters slow-flowing rivers, lakes, ponds. This coelenterate animal leads a sedentary or sedentary lifestyle. The external structure of freshwater hydra is very simple. The body has an almost regular cylindrical shape. At one of its ends there is a mouth, which is surrounded by a crown of many long thin tentacles (from five to twelve). At the other end of the body there is a sole, with the help of which the animal is able to attach to various objects under water. The body length of freshwater hydra is up to 7 mm, but the tentacles can greatly stretch and reach a length of several centimeters.

Radiation symmetry

Let's take a closer look external structure hydra. The table will help you remember their purpose.

The body of the hydra, like many other animals leading an attached lifestyle, is characterized by What is it? If you imagine a hydra and draw an imaginary axis along its body, then the animal’s tentacles will diverge from the axis in all directions, like the rays of the sun.

The structure of the hydra's body is dictated by its lifestyle. It attaches itself to an underwater object with its sole, hangs down and begins to sway, exploring the surrounding space with the help of tentacles. The animal is hunting. Since the hydra lies in wait for prey, which can appear from any direction, the symmetrical radial arrangement of the tentacles is optimal.

Intestinal cavity

Let's look at the internal structure of the hydra in more detail. The hydra's body looks like an oblong sac. Its walls consist of two layers of cells, between which there is an intercellular substance (mesoglea). Thus, there is an intestinal (gastric) cavity inside the body. Food enters it through the mouth opening. It is interesting that the hydra, which is in this moment does not eat, there is practically no mouth. The ectoderm cells close and grow together in the same way as on the rest of the body surface. Therefore, every time before eating, the hydra has to break through its mouth again.

The structure of the freshwater hydra allows it to change its place of residence. There is a narrow opening on the sole of the animal - the aboral pore. Through it, liquid and a small bubble of gas can be released from the intestinal cavity. With the help of this mechanism, the hydra is able to detach from the substrate and float to the surface of the water. In this simple way, with the help of currents, it spreads throughout the reservoir.

Ectoderm

The internal structure of the hydra is represented by ectoderm and endoderm. The ectoderm is called the body-forming hydra. If you look at an animal under a microscope, you can see that the ectoderm includes several types of cells: stinging, intermediate and epithelial-muscular.

The most numerous group is skin-muscle cells. They touch each other with their sides and form the surface of the animal’s body. Each such cell has a base - a contractile muscle fiber. This mechanism provides the ability to move.

When all fibers contract, the animal’s body contracts, lengthens, and bends. And if the contraction occurs on only one side of the body, then the hydra bends. Thanks to this work of cells, the animal can move in two ways - “tumbling” and “stepping”.

Also in the outer layer are star-shaped nerve cells. They have long shoots, with the help of which they come into contact with each other, forming a single network - a nerve plexus that entwines the entire body of the hydra. Nerve cells also connect with skin and muscle cells.

Between the epithelial-muscle cells there are groups of small, round-shaped intermediate cells with large nuclei and a small amount of cytoplasm. If the hydra's body is damaged, the intermediate cells begin to grow and divide. They can turn into any

Stinging cells

The structure of hydra cells is very interesting; the stinging (nettle) cells with which the entire body of the animal, especially the tentacles, are strewn deserve special mention. have complex structure. In addition to the nucleus and cytoplasm, the cell contains a bubble-shaped stinging chamber, inside which there is a thin stinging thread rolled into a tube.

A sensitive hair emerges from the cell. If prey or an enemy touches this hair, the stinging thread sharply straightens and is thrown out. The sharp tip pierces the victim’s body, and poison flows through the channel running inside the thread, which can kill a small animal.

Typically, many stinging cells are triggered. The hydra grabs prey with its tentacles, pulls it to its mouth and swallows it. The poison secreted by the stinging cells also serves for protection. Larger predators do not touch the painfully stinging hydras. The venom of the hydra is similar in effect to the poison of nettles.

Stinging cells can also be divided into several types. Some threads inject poison, others wrap around the victim, and others stick to it. After triggering, the stinging cell dies, and a new one is formed from the intermediate one.

Endoderm

The structure of hydra also implies the presence of such a structure as the inner layer of cells, endoderm. These cells also have muscle contractile fibers. Their main purpose is to digest food. Endoderm cells secrete digestive juices directly into the intestinal cavity. Under its influence, the prey is split into particles. Some endoderm cells have long flagella that are constantly in motion. Their role is to pull food particles towards the cells, which in turn release pseudopods and capture food.

Digestion continues inside the cell and is therefore called intracellular. Food is processed in vacuoles, and undigested remains are thrown out through the mouth. Breathing and excretion occurs through the entire surface of the body. Let us consider once again the cellular structure of the hydra. The table will help you do this clearly.

Reflexes

The structure of the hydra is such that it is able to sense temperature changes, chemical composition water, as well as touch and other irritants. The nerve cells of an animal are capable of being excited. For example, if you touch it with the tip of a needle, the signal from the nerve cells that sensed the touch will be transmitted to the rest, and from the nerve cells to the epithelial-muscular cells. The skin-muscle cells will react and contract, the hydra will shrink into a ball.

Such a reaction is bright. It is a complex phenomenon consisting of successive stages - perception of the stimulus, transfer of excitation and response. The structure of the hydra is very simple, therefore the reflexes are monotonous.

Regeneration

The cellular structure of the hydra allows this tiny animal to regenerate. As mentioned above, intermediate cells located on the surface of the body can transform into any other type.

With any damage to the body, the intermediate cells begin to divide, grow very quickly and replace the missing parts. The wound is healing. The regenerative abilities of the hydra are so high that if you cut it in half, one part will grow new tentacles and a mouth, and the other will grow a stem and sole.

Asexual reproduction

Hydra can reproduce both asexually and sexually. Under favorable conditions in summer time appears on the animal's body small bump, the wall protrudes. Over time, the tubercle grows and stretches. Tentacles appear at its end and a mouth breaks through.

Thus, a young hydra appears, connected to the mother’s body by a stalk. This process is called budding because it is similar to the development of a new shoot in plants. When a young hydra is ready to live on its own, it buds off. The daughter and mother organisms attach to the substrate with tentacles and stretch in different directions until they separate.

Sexual reproduction

When it starts to get colder and unfavorable conditions are created, the turn of sexual reproduction begins. In the fall, hydras begin to form sex cells, male and female, from the intermediate ones, that is, egg cells and sperm. The egg cells of hydras are similar to amoebas. They are large and strewn with pseudopods. Sperm are similar to the simplest flagellates; they are able to swim with the help of a flagellum and leave the body of the hydra.

After the sperm penetrates the egg cell, their nuclei fuse and fertilization occurs. The pseudopods of the fertilized egg retract, it becomes rounded, and the shell becomes thicker. An egg is formed.

All hydras die in the fall, with the onset of cold weather. The mother's body disintegrates, but the egg remains alive and overwinters. In the spring it begins to actively divide, the cells are arranged in two layers. With the onset of warm weather, the small hydra breaks through the shell of the egg and begins an independent life.