Type Coelenterates. Appearance, movement and nutrition of freshwater hydra
Both asexual and sexual reproduction are characteristic.
Asexual reproduction by budding
In summer, a small tubercle appears on the hydra’s body - a protrusion of the wall of its body. This tubercle grows and stretches out. Tentacles appear at its end, and a mouth breaks out between them. This is how the young hydra develops, which at first remains connected to the mother with the help of a stalk. Outwardly, all this resembles the development of a plant shoot from a bud (hence the name of this phenomenon - budding). When the little hydra grows up, it separates from the mother’s body and begins to live independently. In Hydra, asexual reproduction predominates (Fig. 35).
Sexual reproduction
By autumn, with the onset of unfavorable conditions, the hydras die, but before that, germ cells develop in their body (Fig. 36): female - eggs, male - sperm. Hydra is a bisexual animal (hermaphrodite). Germ cells contain only half the set of chromosomes compared to somatic cells, which form all the tissues of the body.
IN life cycle organisms, sexually reproducing, there must be a stage, in which only half the set of chromosomes remains during division. Otherwise, the number of their chromosomes would double in each generation. This division is called meiosis.
After fertilization, the hydra egg is rounded, a thick shell is released on its surface - an egg is formed.
At the end of autumn, the hydra dies, but the egg remains alive and falls to the bottom. In the spring, the fertilized egg begins to divide, the resulting cells are arranged in two layers. From them a small hydra develops, which, with the onset of warm weather, comes out through a rupture in the egg shell.
Thus, the multicellular animal hydra at the beginning of its life consists of one cell - a fertilized egg.
On this page, material on the topics:
Hydra reproduction regeneration briefly
Biology essay on the topic of reproduction of hydras.
Brief essay on the topic of plant propagation
How does hydra reproduce by cross fertilization?
Hydra reproduction presentation
Questions about this material:
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 that form a network covering the body of the guide.
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 track pulls the back end towards the front and then moves the front end again. And the hydra turns over its head every time it moves. So the hydra moves quite quickly, but there is another, more slow way movement - 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 past is touched by 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 growth of a bud 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 a hydra was obtained from Ancient Greece, these polyps came to be called hydra.
Movement. Hydra can move from place to place. This movement occurs in different ways: either the hydra, bending in an arc, is sucked by the tentacles and partly glandular cells, surrounding the mouth, to the substrate and then pulls up the sole, or the hydra “tumbles,” as it were, attaching itself alternately with the sole and with the tentacles.
Nutrition. The stinging capsules entangle the prey with their threads and paralyze it. The prey processed in this way is captured by the tentacles and directed into the mouth opening. Hydras can “overpower” very large prey that exceeds them in size, for example evenfish fry. The extensibility of their mouth and entire body is great. They are very voracious - one hydra can swallow short term up to half a dozen daphnia. Swallowed food enters the gastric cavity. Digestion in hydras is apparently combined - intra- and extracellular. Food particles are drawn in by endoderm cells with the help of pseudodopodium inside and are digested there. As a result of digestion, endoderm cells accumulate nutrients, grains of excretory products also appear there, released from time to time in small portions into the gastric cavity. Excretion products, as well as undigested parts of food, are thrown out through the mouth
I - individual with male gonads; II—individual with female gonads
Reproduction. Hydras reproduce asexually and sexually. Etc; Through asexual reproduction, buds are formed on the hydra, which gradually detach from the mother’s body. Budding of hydras under favorable nutritional conditions can occur very intensively; observations show that in 12 days the number of hydras can increase 8 times. During summer period Hydras usually reproduce by budding, but with the onset of autumn it begins sexual reproduction, and hydras can be both hermaphroditic and dioecious (stalked hydra).
Reproductive products are formed in the ectoderm from interstitial cells. In these places, the ectoderm swells in the form of tubercles, in which either numerous spermatozoa or one amoeboid egg are formed. After fertilization, which occurs on the body of the hydra, the egg cell is covered with a membrane. Such a shell-covered egg overwinters, and in the spring a young hydra emerges from it. There is no larval stage of hydras.
More interesting articles
Asexual reproduction freshwater hydra
Budding hydra looks surreal. In the summer, under favorable conditions, a tubercle appears on the animal’s body, from which, as in a science-fiction film, a new hydra gradually grows: tentacles appear, a mouth opening is cut between them, a stalk lengthens... Having gained strength, having grown sufficiently, the “bud” separates from parental body and goes into adulthood.
Hydra sexual reproduction
1. Begins in the fall, under unfavorable environmental conditions. Soon the hydras will die, but before that they will have time to throw the zygotes into the reservoir.
2. gonads, gonads, are located in ectoderm, look like small tubercles.
3. In hydra-hermaphrodites, the gonads are located in different places: testes at the oral end, ovaries at the sole.
4. Fertilization cross, sperm penetrate the eggs through a micro-hole in the gonad. Fertilized egg ( zygote) fragments, occurs gastrulation, the embryo acquires a dense shell and, in a state of suspended animation, sinks to the bottom of the reservoir for wintering. The mother dies, but in the spring it will be replaced by a young hydra. There is no larval stage in freshwater hydra (although it is found in other hydroids), therefore, here we are observing direct postembryonic development.
Marine hydroids
The hydroid class includes six orders, and the species diversity here is quite high. For example, unlike single freshwater hydra, Obelia polyp lives in sea water and creates colonies.
Obelia hydroid polyp. Key Features
1. A colony of obelia looks like branching shrubs.
2. The intestinal cavities of obelia are united.
3. Has two life forms, alternation of generations - asexual generation(polyp) is replaced sexual(jellyfish).
4. Asexual reproduction by budding method it grows on the branches of the colony. Once the obelia reaches a certain age, gonozoid branches are formed on which jellyfish will appear.
5. At this stage, small jellyfish up to one centimeter in diameter, with developed mesoglea. It is they who, breaking away from the “parent”, contribute to the settlement of the colony. Essentially, a jellyfish is a polyp swimming with its mouth down.
Life cycle of obelia
1. A colony of polyps buds and grows without stopping.
2. Jellyfish, formed on the branches of the colony, dioecious.
3. gonads they are located on the oral stalk or on the underside of the umbrella.
4. External fertilization occurs in the aquatic environment, where gonads emerge from the body of the jellyfish.
5. A rounded one is formed from the zygote planula larva, equipped with flagella, which, after swimming in the water, sinks to the bottom.
6. On the ground it turns into polyp, which in turn buds and forms a young colony.
One of the typical representatives of the order of coelenterates is freshwater hydra. These creatures live in clean waters and attach to plants or soil. They were first seen by the Dutch inventor of the microscope and famous naturalist A. Leeuwenhoek. The scientist even managed to witness the budding of a hydra and examine its cells. Later, Carl Linnaeus gave the genus a scientific name, referring to the ancient Greek myths about the Lernaean Hydra.
Hydras live in clean bodies of water and attach to plants or soil. Structural features
This aquatic inhabitant is distinguished by its miniature size. On average, the body length is from 1 mm to 2 cm, but it can be a little more. The creature has a cylindrical body. In front there is a mouth with tentacles around (their number can reach up to twelve pieces). At the back there is a sole, with the help of which the animal moves and attaches to something.
There is a narrow pore on the sole through which liquid and gas bubbles from the intestinal cavity pass. Together with the bubble, the creature detaches from the selected support and floats up. At the same time, his head is located in the thick of the water. Hydra has a simple structure, its body consists of two layers. Oddly enough, when the creature is hungry, its body looks longer.
Hydras are one of the few coelenterates that live in fresh water. Most of these creatures inhabit the sea area . Freshwater species may have the following habitats:
- ponds;
- lakes;
- river factories;
- ditches.
If the water is clear and clean, these creatures prefer to be close to the shore, creating a kind of carpet. Another reason why animals prefer shallow areas is the love of light. Freshwater creatures are very good at distinguishing the direction of light and moving closer to its source. If you put them in an aquarium, they will definitely swim to the most illuminated part.
Interestingly, unicellular algae (zoochlorella) may be present in the endodermis of this creature. This is reflected in the appearance of the animal - it acquires a light green color.
Nutrition process
This miniature creature is a real predator. It is very interesting to find out what freshwater hydra eats. The water is home to many small animals: cyclops, ciliates, and crustaceans. They serve as food for this creature. Sometimes it can eat larger prey, such as small worms or mosquito larvae. In addition, these coelenterates cause great damage to fish ponds, because caviar becomes one of the things that hydra feeds on.
In the aquarium you can watch in all its glory how this animal hunts. The hydra hangs with its tentacles down and at the same time arranges them in the form of a network. Her torso sways slightly and describes a circle. Prey swimming nearby touches the tentacles and tries to escape, but suddenly stops moving. The stinging cells paralyze her. Then the coelenterate creature pulls it to its mouth and eats it.
If the animal has eaten well, it swells. This creature can devour victims, which exceeds it in size. Its mouth can open very wide, sometimes part of the prey’s body can be clearly seen from it. After such a spectacle, there is no doubt that the freshwater hydra is a predator in its feeding method.
Reproduction method
If the creature has enough food, reproduction occurs very quickly by budding. In a few days, a tiny bud grows into a fully formed individual. Often several such buds appear on the hydra’s body, which are then separated from the mother’s body. This process is called asexual reproduction.
In autumn, when the water becomes colder, freshwater creatures can reproduce sexually. This process works as follows:
- Gonads appear on the body of the individual. Some of them form male cells, and in others - eggs.
- Male reproductive cells move in water and enter the body cavity of hydras, fertilizing the eggs.
- When eggs are formed, the hydra most often dies, and new individuals are born from the eggs.
On average, the body length of a hydra is from 1 mm to 2 cm, but it can be a little more.
Nervous system and breathing
In one of the layers of the body of this creature there is a scattered nervous system, and in the other - a small amount nerve cells. In total, there are 5 thousand neurons in the animal’s body. The animal has nerve plexuses near the mouth, on the sole and on the tentacles.
Hydra does not divide neurons into groups. The cells perceive irritation and send a signal to the muscles. IN nervous system individuals have electrical and chemical synapses, as well as opsin proteins. Speaking about what the hydra breathes, it is worth mentioning that the process of excretion and respiration occurs over the surface of the entire body.
Regeneration and growth
Cells freshwater polyp are in the process of constant updating. In the middle of the body they divide, and then move to the tentacles and sole, where they die. If there are too many dividing cells, they move to the lower region of the body.
This animal has an amazing ability to regenerate. If you cut his torso crosswise, each part will be restored to its previous form.
The cells of a freshwater polyp are in the process of constant renewal. Lifespan
In the 19th century there was a lot of talk about the immortality of animals. Some researchers tried to prove this hypothesis, while others wanted to refute it. In 1917, after a four-year experiment, the theory was proven by D. Martinez, as a result of which the hydra officially became an ever-living creature.
Immortality is associated with an incredible ability to regenerate. The death of animals in winter is associated with unfavorable factors and lack of food.
Freshwater hydras are fascinating creatures. Four species of these animals are found throughout Russia and they are all similar to each other. The most common are ordinary and stalked hydras. When you go for a swim in the river, you can find a whole carpet of these green creatures on its bank.
