What time of year does the freshwater hydra die. Hydra - class Hydrozoa: sense organs, nervous and digestive systems, reproduction. Hydra sexual reproduction

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

A bright representative of hydroid - 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 every 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, which provides "eternal youth" to the polyp, prompted German scientists to search for 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 body of the hydra or make it longer, for this they have a muscle fiber.

2. Digestive-muscular cells are located in endoderm. They are adapted to phagocytosis, capture and mix food particles that have entered the gastric cavity, for which each cell is equipped with several flagella. In general, flagella and pseudopods help food to penetrate from the intestinal cavity into the cytoplasm of hydra cells. Thus, her digestion goes 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 the prey captured by the tentacles. The stinging cell contains a capsule with a poisonous stinging thread, a sensitive hair is located outside, which, after irritation, gives a signal to “shoot”. The life of a stinging cell is fleeting: after a “shot” with a thread, it dies.

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

5. glandular cells secrete a sticky substance. They are located in endoderm and aid in the digestion of food.

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 for epithelial-muscular) or sex cells, and ensure the regeneration of hydra. There are hydras that do not have intermediate cells (hence, stinging, nervous and sexual), capable of asexual reproduction.

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

Other features of freshwater hydra

1. Hydras do not have a respiratory system; they breathe the entire surface of the body.

2. The circulatory system is not formed.

3. Hydra feed on larvae of aquatic insects, various small invertebrates, crustaceans (daphnia, cyclops). Undigested food residues, like other coelenterates, are removed back through the mouth opening.

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

Hydra is a typical representative of the Hydrozoa class. It has a cylindrical body shape, reaching a length of up to 1-2 cm. At one pole there is a mouth surrounded by tentacles, the number of which in different species varies from 6 to 12. At the opposite pole, the hydra has a sole that serves to attach the animal to the substrate.

sense organs

In the ectoderm, hydras have stinging or nettle cells that serve to protect or attack. In the inner part of the cell is a capsule with a spiral thread.

Outside this cell is a sensitive hair. If any small animal touches a hair, then the stinging thread rapidly shoots out and pierces the victim, who dies from the poison that has fallen on the thread. Usually many stinging cells are ejected simultaneously. Fish and other animals do not eat hydras.

Tentacles serve not only for touch, but also for capturing food - various small aquatic animals.

In the ectoderm and endoderm, hydras have epithelial-muscular cells. Thanks to the contraction of the muscle fibers of these cells, the hydra moves, “stepping” alternately either with tentacles or with the sole.

Nervous system

The nerve cells that form a network throughout the body are located in the mesoglea, and the processes of the cells extend outside and inside the body of the hydra. This type of structure of the nervous system is called diffuse. Especially a lot of nerve cells are located in the hydra around the mouth, on the tentacles and soles. Thus, the simplest coordination of functions already appears in the coelenterates.

Hydrozoans are irritable. When nerve cells are irritated by various stimuli (mechanical, chemical, etc.), the perceived irritation spreads to all cells. Due to the contraction of muscle fibers, the body of the hydra can be compressed into a ball.

Thus, for the first time in the organic world, coelenterates have reflexes. In animals of this type, the reflexes are still uniform. In more organized animals, they become more complex in the process of evolution.

Digestive system

All hydras are predators. Having captured, paralyzed and killed the prey with the help of stinging cells, the hydra pulls it with its tentacles to the mouth opening, which can stretch very strongly. Further, the food enters the gastric cavity, lined with glandular and epithelial-muscular cells of the endoderm.

Digestive juice is produced by glandular cells. It contains proteolytic enzymes that promote protein digestion. Food in the gastric cavity is digested by digestive juices and breaks down into small particles. In the cells of the endoderm, there are 2-5 flagella that mix food in the gastric cavity.

Pseudopodia of epithelial-muscular cells capture food particles and further intracellular digestion occurs. Undigested food remains are removed through the mouth. Thus, for the first time in hydroids, cavitary, or extracellular, digestion appears, which goes in parallel with more primitive intracellular digestion.

Organ regeneration

In the ectoderm, the hydra has intermediate cells, from which, when the body is damaged, nerve, epithelial-muscular and other cells are formed. This contributes to the rapid overgrowth of the wounded area and regeneration.

If a Hydra's tentacle is cut off, it will regenerate. Moreover, if the hydra is cut into several parts (even up to 200), each of them will restore the whole organism. On the example of hydra and other animals, scientists are studying the phenomenon of regeneration. The revealed patterns are necessary for the development of methods for treating wounds in humans and many vertebrate species.

Hydra breeding methods

All hydrozoans reproduce in two ways - asexual and sexual. Asexual reproduction is as follows. In the summer, approximately in the middle, the ectoderm and endoderm protrude from the body of the hydra. A tubercle, or kidney, is formed. Due to the multiplication of cells, the size of the kidney increases.

The gastric cavity of the daughter hydra communicates with the cavity of the mother. A new mouth and tentacles form at the free end of the kidney. At the base, the kidney is laced, the young hydra is separated from the mother and begins to lead an independent existence.

Sexual reproduction in hydrozoans under natural conditions is observed in autumn. Some types of hydras are dioecious, while others are hermaphroditic. In freshwater hydra, female and male sex glands, or gonads, are formed from the intermediate cells of the ectoderm, that is, these animals are hermaphrodites. The testicles develop closer to the oral part of the hydra, and the ovaries develop closer to the sole. If many motile spermatozoons are formed in the testes, then only one egg matures in the ovaries.

Hermaphroditic individuals

In all hermaphroditic forms of hydrozoans, spermatozoons mature earlier than eggs. Therefore, fertilization occurs crosswise, and consequently, self-fertilization cannot occur. Fertilization of eggs occurs in the mother individual even in autumn. After fertilization, the hydra, as a rule, die, and the eggs remain in a dormant state until spring, when new young hydra develop from them.

budding

Marine hydroid polyps can be solitary like hydras, but more often they live in colonies that have appeared due to the budding of a large number of polyps. Polyp colonies often consist of a huge number of individuals.

In marine hydroid polyps, in addition to asexual individuals, during reproduction by budding, sexual individuals, or jellyfish, are formed.

The naturalist A. Leeuwenhoek, who invented the microscope, was the first to be able to see and describe the hydra. This scientist was the most significant naturalist of the XVII-XVIII centuries.

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 refers to intestinal animals. Its body has a tubular shape, in front there is a mouth opening, which is surrounded by a corolla, consisting of 5-12 tentacles.

Under the tentacles, the body of the hydra narrows and a neck is obtained, which separates the body from the head. The back of the body is narrowed into a stalk or stalk, with a sole at the end. When the hydra is full, its body does not exceed 8 millimeters in length, and if the hydra is hungry, the body is much longer.

Like all representatives of the intestinal cavity, 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 defeat prey, other cells have contractility, and still others secrete mucus. And in the outer layer there are nerve cells that form a network that covers the body of the guides.

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

If aquatic plants are placed in a vessel with water, then you can see how hydras crawl along their leaves and walls of the vessel. On the sole of the hydra there is an adhesive substance that helps it to 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 trace remains on the stack in the place where the hydra sat. In a few days, these creatures move no more than 2-3 centimeters. During movement, the hydra is attached 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 off and rests on its tentacles again, taking a step forward.

This method of movement is similar to the movement of moth caterpillars, which are often called "surveyors". But the caterpillar pulls the rear to the front and then moves the front again. And the hydra flips over its head every time it moves. So the hydra moves fast enough, but there is another, slower way to move - when the hydra slides on its sole. Some individuals can detach from the substrate and swim in the water. They spread their tentacles and sink to the bottom. And hydras rise up with the help of a gas bubble that forms on the sole.

How do freshwater hydras eat?

Hydras are predatory creatures, they feed on ciliates, cyclops, small crustaceans - daphnia and other small living creatures. Sometimes they eat larger prey, such as small worms or mosquito larvae. Hydras can even wreak havoc on fish ponds as they feed on newly hatched fish.

How the hydra hunts can be easily traced in the aquarium. She spreads her tentacles widely, which form a web, while she hangs tentacles down. If you watch the hydra, you will notice that its body, slowly swaying, describes a circle with its front part. A passing victim catches on the tentacles, tries to free itself, but calms down as the stinging cells paralyze it. Hydra pulls prey to the mouth and begins to eat.

If the hunt is successful, the hydra swells from the number of crustaceans eaten, and their eyes appear through its body. Hydra can eat prey larger than itself. The mouth of the hydra is able to open wide, and the body is significantly stretched. Sometimes a part of the victim sticks out of the mouth of the hydra, which did not fit inside.

Reproduction of freshwater hydra

If there is enough food, hydras multiply rapidly. Reproduction occurs by budding. The process of kidney growth from a tiny tubercle to a mature individual takes several days. Often, several buds are formed on the body of the hydra, while the young individual has not separated 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, the sex glands are formed in the form of swellings. In some swellings, male sex cells are formed, and in others, egg cells. Male sex cells float freely in the water and penetrate into the hydra body cavity, fertilizing immobile eggs. When eggs are formed, the hydra usually dies. Under favorable conditions, young individuals emerge from the eggs.

Freshwater hydra regeneration

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

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

Hydra. Obelia. Hydra structure. hydroid polyps

They live in marine, rarely - in fresh water. Hydroid - the most simply organized coelenterates: the gastric cavity without partitions, the nervous system without ganglia, the gonads develop in the ectoderm. They often form colonies. Many in the life cycle have a change of generations: sexual (hydroid jellyfish) and asexual (polyps) (see. Coelenterates).

Hydra (Hydra sp.)(Fig. 1) - a single freshwater polyp. The body length of the hydra 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 there are 6-12 tentacles.

Like all coelenterates, hydra cells are arranged in two layers. The outer layer is called the ectoderm, the inner layer is called the endoderm. Between these layers is the basal lamina. In the ectoderm, the following types of cells are distinguished: epithelial-muscular, stinging, nervous, intermediate (interstitial). From small undifferentiated interstitial cells, any other cells of the ectoderm can form, including during the reproduction period and germ cells. At the base of the epithelial-muscle cells are muscle fibers located along the axis of the body. With their contraction, the body of the hydra is shortened. Nerve cells are stellate and located on the basement membrane. Connecting with their long processes, they form a primitive nervous system of a diffuse type. The response to irritation has a reflex character.

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

There are three types of stinging cells in the ectoderm: penetrants, volvents, and glutinants. The penetrant cell is pear-shaped, has a sensitive hair - knidocil, inside the cell there is a stinging capsule, in which there is a spirally twisted stinging thread. The cavity of the capsule is filled with a toxic liquid. There are three spines at the end of the stinging thread. Touching the cnidocil causes the ejection of the stinging thread. At the same time, spines are first pierced into the body of the victim, then the poison of the stinging capsule is injected through the thread channel. The poison has a painful and paralyzing effect.

Stinging cells of the other two types perform an additional function of holding prey. Volvents shoot trapping threads that entangle the victim's body. Glutinants throw out sticky threads. After the filaments are fired, the stinging cells die. New cells are formed from interstitial cells.

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 - abdominal and intracellular, undigested residues are excreted through the mouth opening.

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 with respect to the axis of the body; when they contract, the body of the hydra narrows. The section of the epithelial-muscular cell facing the gastric cavity carries from 1 to 3 flagella and is able to form 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 (kidney).

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

Sexual reproduction occurs in autumn. During sexual reproduction, germ cells develop in the ectoderm. Spermatozoa are formed in areas of the body near the mouth opening, eggs - closer to the sole. Hydra can be both dioecious and hermaphroditic.

After fertilization, the zygote is covered with dense membranes, an egg is formed. The hydra dies, and a new hydra develops from the egg the following spring. Development is direct without larvae.

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

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

Most of the individuals in the colony are hydrants. The structure of the hydrant resembles the structure of the 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 the members of one colony through the branched canals of the common digestive cavity.

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

Blastostyle looks like a stalk, has no mouth and tentacles. Jellyfish bud from the blastostyle. Jellyfish break away from the blastostyle, swim in the water column and grow. The shape of a hydroid jellyfish can be compared to the shape of an umbrella. Between the ectoderm and endoderm is a gelatinous layer - the mesoglea. On the concave side of the body, in the center, on the oral stalk is the mouth. Numerous tentacles hang along the edge of the umbrella, serving to catch 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 depart from the stomach, encircling the edge of the jellyfish umbrella. The way the jellyfish moves is “reactive”, this is facilitated by a fold of ectoderm along the edge of the umbrella, called the “sail”. The nervous system is diffuse type, but there are accumulations 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.

A parenchymula larva develops from a fertilized egg, corresponding to a similar sponge larva. The parenchymula then transforms into a two-layer planula larva. Planula, having floated 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 the alternation of asexual and sexual generations. The asexual generation is represented by polyps, the sexual generation is represented by jellyfish.

Description of other classes of type Coelenterates.

The body shape of 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 - Gidra vulgaris, H. oligactis and others.

   Basic data:
DIMENSIONS
Length: 6-15 mm.

BREEDING
Vegetative: has a budding character. A kidney appears on the body of the mother individual, from which the daughter individual gradually develops.
Sexual: most types of hydras have separate sexes. The gonads accumulate cells from which eggs develop. Sperm develop in the testis.

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

RELATED SPECIES
More than 9,000 species belong to the type of coelenterates, 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. With the help of the sole, 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 that live in the water, such as ciliates, small bristle worms, planktonic crustaceans, water fleas, insects and their larvae, as well as fish fry. A hunting hydra attaches itself to an aquatic plant, branch or leaf and hangs on them. Her tentacles are very wide open. They constantly make circular search movements. If one of them touches the victim, others rush to him. Hydra paralyzes prey with stinger cell venom. Hydra pulls paralyzed prey with tentacles to the mouth opening. She swallows small animals whole. If the prey is larger than the hydra, the predator opens its mouth wide, 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 genus Nuiga 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 of the external appearance of the hydra. The gastric cavity of this animal is continuous. The tentacles are hollow. The walls of the body are composed of two layers of cells. There are glandular cells located in the middle part of the hydra body. The various species are very similar to each other. They differ mainly in color (and, as a result, different colors speak of some structural feature). Hydras are bright green in color, symbiotic algae live in the body. Hydras react to light and swim towards it. These animals are immobile. They spend most of their lives attached, waiting for prey. With a sole, like a sucker, hydras are firmly attached to plants.

BREEDING

   Hydras reproduce in two ways - sexually and vegetatively. Vegetative propagation is represented by budding. Under suitable external conditions, several buds develop on the body of the hydra. At the very beginning, the bud looks like a small mound, later miniature tentacles appear on its outer end. The tentacles grow, stinging cells appear on them. The lower part of the body of the daughter individual becomes thinner, the mouth opening opens at the hydra, the young individual branches off and begins an independent life. These animals reproduce by budding during 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 comes out of it. At about the same time, spermatozoa are formed in the testes of other hydras. They also leave the gonad and swim in the water. One of them fertilizes the egg. The embryo develops in the egg. Under the protection of a double shell, it hibernates at the bottom. In the spring, a fully formed hydra emerges from the egg.
  

DO YOU KNOW WHAT...

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

  

CHARACTERISTIC FEATURES OF THE HYDRA

   Tentacles: the mouth opening is surrounded by a corolla with 5-12 tentacles with stellate cells. With their help, the animal paralyzes the prey and pulls it into the mouth. The hydra, which hunts, attaches itself to a hard surface, and, spreading its tentacles wide, makes circular search movements with them.
   Body: tubular body shape. At the front end is a mouth opening surrounded by tentacles. The aboral pore is located in the middle of the sole. The wall of the hydra consists of two layers of cells. Digestive processes take place in the middle part of the body.
   mouth opening: covered with a corolla of tentacles. With tentacles, the hydra pulls the animal into its mouth and swallows it.
   Leg: the back end of the hydra is narrowed - this is a leg that has a sole at the end.
   Gonads: are formed in the ectoderm and look like tubercles. They accumulate sex cells.
   Dome: length about 13 mm. This is for self defense. The hydra is charged and forms a dense dome.
   Bud: vegetative reproduction of hydra has the character of budding. Several kidneys can appear on the body at the same time. The kidneys are growing fast.

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