TYPE

The type of intestinal cavities includes lower multicellular animals, the body of which consists of two layers of cells and has radial symmetry. They live in marine and fresh waters. Among them there are free-floating (jellyfish), sessile (polyps), attached forms (hydra).

The body of the intestinal cavity is formed by two layers of cells - the ectoderm and endoderm, between which is the mesoglea (non-cellular layer). Animals of this type have the appearance of an open bag at one end. The hole serves as a mouth, which is surrounded by a corolla of tentacles. The mouth leads into a blindly closed digestive cavity (gastric cavity). Digestion of food occurs both inside this cavity and by individual cells of the endoderm - intracellularly. Undigested food remains are excreted through the mouth opening. In intestinal cavities, a diffuse-type nervous system first appears. It is represented by nerve cells randomly scattered in the ectoderm, which are in contact with their processes. Swimming jellyfish have a concentration nerve cells and a nerve ring is formed. Coelenterates reproduce both asexually and sexually. Many coelenterates are dioecious, but there are also hermaphrodites. The development of some coelenterates is direct, while others have a larval stage.

The type has three classes:

1. Hydroids

2. Jellyfish

3. Coral polyps

Hydroid class

His representative is freshwater hydra. The body of the hydra is up to 7 mm long, the tentacles are up to several cm.

The bulk of the large number of different types of hydra cells are integumentary muscle cells, forming integumentary tissue. Muscle tissue as such is absent, its role is also performed by skin-muscle cells.

In the ectoderm there are stinging cells, which are mainly located on the tentacles. With their help, the hydra defends itself, and also delays and paralyzes prey.

Nervous system- primitive, diffuse. Nerve cells (neurons) are evenly distributed in the mesoglea. Neurons are connected by strands, but do not form clusters. Sensitive and nerve cells provide the perception of irritation and its transmission to other cells.

There is no respiratory system, hydras breathe through the surface of the body. There is no circulatory system.

Glandular cells that secrete sticky substances are concentrated mainly in the ectoderm of the sole and tentacles. They also produce enzymes that aid in the digestion of food.

Hydra digestion occurs in the gastric cavity in two ways - intracavitary, with the help of enzymes and intracellular. Endoderm cells are capable of phagocytosis (capture of food particles from the gastric cavity). Part of the skin-muscle cells of the endoderm is equipped with flagella, which are in constant motion, which scoop particles up to the cells. They organize pseudopods, thereby capturing food. Undigested food remains are removed from the body through the mouth.

Between all these cells are small undifferentiated intermediate cells that can turn into any other types of cells if necessary, regeneration (the process of restoring lost or damaged parts of the body) is due to these cells.

Reproduction:

Asexual (vegetative). In summer, under favorable conditions, budding occurs.

· Sexual. In autumn, with the onset of adverse conditions. The sex glands form as tubercles in the ectoderm. In hermaphroditic forms, they are formed in different places. The testes develop closer to the oral pole, and the ovaries closer to the sole. Cross fertilization. A fertilized egg (zygote) is dressed in dense shells and falls to the bottom, where it hibernates. The following spring, a young hydra emerges from it.

class scyphoid

The scyphoid jellyfish class is found in all seas. There are species of jellyfish that have adapted to live in major rivers flowing into the sea. The body of the scyphomedusa has the form of a rounded umbrella or bell, on the lower concave side of which the oral stalk is placed. The mouth leads to a derivative of the dermis - the pharynx, which opens into the stomach. From the stomach, radial channels diverge to the ends of the body, forming the gastric system.

In connection with the free lifestyle of jellyfish, the structure of their nervous system and sensory organs becomes more complicated: clusters of nerve cells appear in the form of nodules - ganglia, balance organs - statocysts, light-sensitive eyes.

Scyphomedusa have stinging cells located on tentacles around the mouth. Their burns are very sensitive even to humans.

Reproduction:

Jellyfish are dioecious, male and female sex cells are formed in the endoderm. The fusion of germ cells in some forms occurs in the stomach, in others in the water. Jellyfish combine in the features of development both their own and hydroid signs.

Among the jellyfish there are giants - fisariya or Portuguese boat (from 3 or more m in diameter, tentacles up to 30 m).

Meaning:

・Used for food

Some jellyfish are deadly and poisonous to humans. So, for example, when bitten by a Cornerot, significant burns can occur. When bitten by a cross, the activity of all systems of the human body is disrupted. The first meeting with a cross is not dangerous, the second is fraught with consequences due to the development of anophyloxia. The sting of a tropical jellyfish is fatal.

Class coral polyps

All representatives of this class are inhabitants of the seas and oceans. They live mainly in warm waters. There are both solitary corals and colonial forms. Their sac-like body is attached to underwater objects (in solitary forms) or directly to the colony with the help of the sole. A characteristic feature of corals is the presence of a skeleton, which can be either calcareous or consist of a horn-like substance and is located either inside the body or outside (the sea anemone does not have a skeleton).

All coral polyps are divided into two groups: eight-ray and six-ray. The former always have eight tentacles (sea feathers, red and white corals). In six-rayed, the number of tentacles is always a multiple of six (anemones, stony corals, etc.).

Reproduction:

Coral polyps are dioecious animals, fertilization occurs in water. The larva develops from the zygote - planula. The planula is attached to various underwater objects, turns into a polyp, which already has a mouth and a corolla of tentacles. In colonial forms, budding occurs later, and the kidneys do not separate from the mother's organism. Polyp colonies are involved in the formation of reefs, atolls, coral islands.

Hydroids are a class of animals belonging to the type Cnidaria (belong to the Intestinal). Hydroids include more than 2.5 thousand species, including freshwater hydra. However, unlike hydra, most hydroids live in the seas and oceans and have two forms in their life cycle - a colonial polyp and a jellyfish. All hydroids have a larval stage from which a polyp develops.

Both the polyp and the jellyfish are predators, capturing prey with tentacles.

Hydroid polyps form colonies as a result of asexual reproduction by budding. Unlike solitary hydras, in marine representatives, daughter individuals do not separate from their mothers. Their intestinal cavities communicate with each other, this allows you to redistribute the food captured by one polyp throughout the colony.

Hydroid jellyfish are small in size (within 1 cm). They form on some polyps of the colony, break away from them and begin to swim.

The jellyfish looks like an inverted polyp. However, her body shape is not cylindrical, but similar to an umbrella or a bell, i.e., the shape of the body is more flattened. A jellyfish can swim by contracting the umbrella and ejecting water from it, but more often in hydroid jellyfish, they swim passively due to the current. At the bottom, the mouth opening is surrounded by tentacles. Unlike polyps, jellyfish have a more powerful layer of mesoglea (gelatinous substance between the ectoderm and endoderm).

With the help of jellyfish in hydroids, sexual reproduction occurs. Each jellyfish has sex glands from below. In some individuals, they contain eggs, in others, spermatozoa; i.e., hydroid jellyfish are dioecious animals. When the germ cells mature, they enter the water, where fertilization takes place. It happens that the eggs do not leave the jellyfish.

The resulting zygote turns into a larva covered with flagella (moss larva). Such a larva can actively swim. Having sunk to the bottom, it gives rise to a hydroid polyp.

Hydras do not have a medusa stage. Sex cells mature directly on the polyp. There is an opinion that in the process of evolution the medusa stage was reduced in them.

Medusa allows hydroids to settle in larger areas.

Unlike other coelenterates, hydroids do not have any partitions in the intestinal cavity. That is, they can be considered more primitive coelenterates.

• Subclass of hydroids (Hydroidea)

The body of a hydroid polyp is cylindrical or ovoid, in its tender part it is usually equipped with a leg, with which single polyps are attached to the soil, aquatic plants, mollusk shells, i.e. generally to any underwater objects.

In colonial forms, the stalk connects the polyp to the colony.

At the upper end of the body of the polyp, there is a mouth opening surrounded by tentacles, which can be arranged in regular corollas or without a strict order.

The number of tentacles may vary different types.
For example, a giant single hydroid branchiocerianthus polyp (Branchiocerianthus imperator), reaching more than 1 m in height, has up to 380 tentacles, while a small monobrachium (Monobrachium parasiticum) has only one. More often, each polyp is equipped with 10-30 tentacles, which can be simple or equipped with a pin-shaped thickening at the end.

In one species (Cladocoryne), the tentacles even branch.
There are also polyps that lack tentacles. These include freshwater microhydra (Microhydra). Polyps use their tentacles to capture food, and solitary polyps, such as freshwater hydra, use them when moving.

The internal structure of the hydroid polyp is very simple.
It has the appearance of a two-layer bag. Outside, the polyp is covered with a layer of ectoderm cells, and its intestinal (gastric) cavity is lined with endoderm.

Between the layers of ectoderm and endoderm in hydroid polyps is a thin layer of non-cellular substance - mesoglea. The ectoderm is formed by special epithelial-muscular cells. The body of such a cell has the appearance of a multifaceted prism, the cells are closely spaced, like a honeycomb.

The prismatic part performs an integumentary function.
At their inner end, the epithelial cells have a long outgrowth that extends up and down along the body of the polyp. Inside this process passes a thin muscle fiber. The same contractile processes extend from the cells of the endoderm, but they are located perpendicular to the processes of the ectodermal cells.
The combination of muscle fibers of many ectodermal and endodermal cells allows the polyp and its tentacles to stretch and contract.

Between the epithelial-muscular cells are stinging cells.
In the ectoderm there are also special nerve cells, equipped with long thin processes, which together form reticular nerve plexuses, somewhat denser at the ends of the tentacles and around the mouth.

In polyps that can reproduce sexually (for example, in hydra), germ cells also develop in the ectoderm, which accumulate in the lower or middle part of the body.

These cells are called sex glands or gonads. Finally, here, in the epithelium, there are intermediate or reserve cells, from which the epithelial-muscular, stinging, nerve and sex cells of hydroid polyps develop.

The ectoderm of many types of polyps secretes a thin shell from the outside - the theca, consisting of chitin.

This shell plays the role of the external skeleton in hydroid polyps, which serves as a support and protection.
In some species, the theca forms a cup around the polyps - a hydrotheca, into which they are drawn in in case of danger.

Endoderm consists of glandular and epithelial-muscular cells. Glandular cells produce digestive juice (enzymes) that aid in the digestion of food.

Small animals that have fallen into the gastric cavity of the polyp are digested under the influence of digestive juices and fall apart.

hydroid polyps. Structure. Metagenesis

Endoderm cells have 2-5 thin flagella, which wriggle all the time and move the contents of the gastric cavity. Food particles that are near the walls of the gastric cavity are captured by pseudopodia formed on the surface of epithelial-muscular cells. Further assimilation of food takes place already inside the cell, just as it happens in unicellular animals.

The products of digestion are transferred to the cells of the ectoderm, separated from the endoderm by a thin but dense layer of mesoglea, through direct contacts between the cells of the endoderm and exoderm, the outgrowths of which cross the mesoglea layer, tightly adjoining each other.
In colonies, the gastric cavities of individual polyps communicate with each other, forming a single cavity of the colony.

The lecture was added on 08/24/2012 at 05:17:45

Class Hydroids (Hydrozoa)

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. 1.

Hydra:
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 directed 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.

Class Hydroids (Hydrozoa)

Hydra budding:
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 next 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. Obelia life cycle:
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.

This class includes those living mainly in the seas and partly in fresh water. Individuals can be either in the form of polyps or in the form of jellyfish. In the school biology textbook for grade 7, representatives of two orders from the hydroid class are considered: the hydra polyp (Hydra order) and the cross jellyfish (Trachymedusa order). The central object of study is the hydra, the additional one is the cross.

Hydra

Hydras are represented in nature by several species. In our freshwater bodies, they keep on the underside of the leaves of pondweed, white lilies, water lilies, duckweed, etc.

freshwater hydra

Sexually, hydras can be dioecious (for example, brown and thin) or hermaphrodites (for example, ordinary and green). Depending on this, testes and eggs develop either on the same individual (hermaphrodites) or on different ones (male and female). The number of tentacles in different species varies from 6 to 12 or more. The tentacles of the green hydra are especially numerous.

For educational purposes, it is enough to acquaint students with structural and behavioral features common to all hydras, leaving aside special species characteristics. However, if it turns out to be green among other hydras, one should dwell on the symbiotic relationship of this species with zoochorella and recall a similar symbiosis in. In this case, we are dealing with one of the forms of the relationship between the animal and flora supporting the cycle of substances in nature. This phenomenon is widespread among animals and occurs in almost every type of invertebrate. It is necessary to explain to the students what the mutual benefit is here. On the one hand, symbiont algae (zoochorella and zooxanthellae) find shelter in the body of their hosts and assimilate the carbon dioxide and phosphorus compounds necessary for synthesis; on the other hand, host animals (in this case, hydras) receive oxygen from algae, get rid of unnecessary substances, and also digest part of the algae, receiving additional nutrition.

You can work with hydras both in summer and winter, keeping them in aquariums with sheer walls, in tea glasses or in bottles with a cut neck (so as to remove the curvature of the walls). In the vessel, the bottom can be covered with a layer of well-washed sand, and it is advisable to lower 2-3 branches of elodea into the water, on which hydras are attached. Do not place other animals with hydras (except for daphnia, cyclops and other food items). If hydras are kept clean, with room and good nutrition, they can live for about a year, make it possible to conduct long-term observations on them and set up a series of experiments.

Exploring hydras

To examine the hydras in a magnifying glass, they are transferred to a Petri dish or on a watch glass, and during microscopy - on a glass slide, placing pieces of glass hair tubes under the coverslip so as not to crush the object. When hydras attach themselves to the glass of the vessel or to the branches of plants, you should consider them appearance, mark parts of the body: mouth end with a corolla of tentacles, body, stalk (if any) and sole. You can count the number of tentacles and note their relative length, which varies depending on the satiety of the hydra. In the hungry, they stretch out strongly in search of food and become thinner. If you touch the body of the hydra with the end of a glass rod or thin wire, you can observe a defensive reaction. In response to a slight irritation, the hydra removes only individual disturbed tentacles, while maintaining the normal appearance of the rest of the body. This is a local reaction. But with strong stimulation, all tentacles shorten, and the body contracts, taking on a barrel shape. In this state, the hydra remains for quite a long time (you can invite students to time the duration of the reaction).

To show that the hydra's reactions to external stimuli are not stereotyped and can be individualized, it is enough to knock on the wall of the vessel and cause a slight shaking in it. Observation of the behavior of hydras will show that some of them will have a typical defensive reaction (the body and tentacles will shrink), others will only slightly shorten the tentacles, and still others will remain in the same state. Consequently, the threshold of irritation was not the same in different individuals. A hydra can become addicted to a certain stimulus, to which it will stop responding. So, for example, if you often repeat a prick with a needle, causing a contraction of the hydra's body, then after repeated use of this stimulus, it will stop responding to it.

In hydras, it is possible to develop a short-term connection between the direction of extension of the tentacles and the obstacle that restricts these movements. If the hydra is attached to the edge of the aquarium so that the extension of the tentacles can be carried out only in one direction, and kept in such conditions for some time, and then given the opportunity to act freely, then after the restriction is removed, it will extend the tentacles mainly to the side, which in the experiment was free. This behavior persists for about an hour after the obstacles are cleared. However, after 3-4 hours, this connection is destroyed, and the hydra again begins searching movements with its tentacles evenly in all directions. Consequently, in this case we are not dealing with a conditioned reflex, but only with its likeness.

Hydras well distinguish not only mechanical, but also chemical stimuli. They reject inedible substances and seize food objects that act on the sensitive cells of the tentacles precisely by chemical means. If, for example, a hydra is offered a small piece of filter paper, it will reject it as inedible, but if the paper is soaked in meat broth or moistened with saliva, the hydra will swallow it and begin to digest it (chemotaxis!).

Hydra nutrition

It is usually believed that hydras feed on small daphnia and cyclops. In fact, hydra food is quite diverse. They can ingest nematode roundworms, coretra larvae and some other insects, small snails, newt larvae, and juvenile fish. In addition, they gradually absorb algae and even silt.

Considering that hydras still prefer daphnia and are very reluctant to eat cyclops, an experiment should be set up to determine the relationship of hydra to these crustaceans. If you put an equal number of daphnia and cyclops in a glass of hydras, and then after a while count how many of them are left, it turns out that most of the daphnia will be eaten, and many of the cyclops will survive. Since hydras are more likely to eat daphnia, which in winter time difficult to harvest, then this food began to be replaced by more affordable and easily obtained, namely bloodworms. Moths can be kept all winter in an aquarium along with the silt captured in the fall. In addition to bloodworms, hydras are fed with pieces of meat and earthworms cut into pieces. However, they prefer bloodworms to everything else, and they eat earthworms worse than pieces of meat.

Organize hydra feeding various substances and to acquaint students with the feeding behavior of these coelenterates. As soon as the hydra's tentacles touch the prey, they grab a food piece and simultaneously shoot stinging cells. Then they bring the affected victim to the mouth opening, the mouth opens, and the food is drawn in. After that, the body of the hydra swells (if the swallowed prey was large), and the victim inside is gradually digested. Depending on the size and quality of the ingested food, it takes from 30 minutes to several hours to break down and assimilate it. The undigested particles are then thrown out through the mouth opening.

Hydra Cell Functions

Regarding nettle cells, it must be borne in mind that these are only one of the types of stinging cells that have a toxic substance. In general, on the tentacles of the hydra there are groups of stinging cells of three types, the biological significance of which is not the same. Firstly, some of her stinging cells do not serve for defense or attack, but are additional organs for attachment and movement. These are the so-called glutinants. They throw out special sticky threads with which hydras attach to the substrate when they move from place to place with the help of tentacles (by the method of walking or turning over). Secondly, there are stinging cells - volvents, which shoot a thread that wraps around the body of the victim, holding it near the tentacles. Finally, the actual nettle cells - penetrants - throw out a thread armed with a stylet that pierces the prey. The poison located in the capsule of the stinging cell penetrates through the thread channel into the wound of the victim (or enemy) and paralyzes its movements. With the combined action of many penetrants, the affected animal dies. According to the latest data, in hydra, some of the nettle cells react only to substances that enter the water from the body of animals harmful to it, and function as a defense weapon. Thus, hydras are able to distinguish food objects and enemies among the organisms around them; attack the former and defend against the latter. Consequently, her neuromotor responses act selectively.

By organizing long-term observations of the life of hydras in an aquarium, the teacher has the opportunity to introduce students to the various movements of these interesting animals. First of all, the so-called spontaneous movements (for no apparent reason) are striking, when the body of the hydra slowly sways, and the tentacles change their position. In a hungry hydra, search movements can be observed when its body is stretched into a thin tube, and the tentacles are greatly elongated and become like spider webs that wander from side to side, making circular movements. If there are planktonic organisms in the water, this eventually leads to the contact of one of the tentacles with the prey, and then a series of quick and energetic actions occur aimed at seizing, holding and killing the victim, pulling it to the mouth, etc. If the hydra is deprived of food , after an unsuccessful search for prey, it separates from the substrate and moves to another place.

The external structure of the hydra

The question arises: how does the hydra attach and detach from the surface on which it was located? Students should be told that the sole of the hydra has glandular cells in the ectoderm that secrete a sticky substance. In addition, there is a hole in the sole - the aboral pore, which is part of the attachment apparatus. This is a kind of suction cup that acts in conjunction with the adhesive and firmly presses the sole to the substrate. At the same time, the pore also promotes detachment, when a gas bubble is squeezed out of the body cavity by the pressure of water through it. Detachment of hydras by releasing a gas bubble through the aboral pore and subsequent floating to the surface can occur not only with insufficient nutrition, but also with an increase in population density. The detached hydras, after swimming for some time in the water column, descend to a new place.

Some researchers consider surfacing as a mechanism that controls the population, as a means of bringing the population to an optimal level. This fact can be used by the teacher in working with older students in the course of general biology.

It is interesting to note that some hydras, falling into the water column, sometimes use a surface tension film for attachment and thereby temporarily become part of the neuston, where they find food for themselves. In some cases, they put their foot out of the water, and then hang their soles on the film, and in other cases they are attached to the film widely. open mouth with tentacles spread out on the surface of the water. Of course, such behavior can only be noticed with long-term observations. When moving the hydra to another place without leaving the substrate, three ways of movement can be observed:

1. slip sole;
2. walking by pulling the body with the help of tentacles (like moth caterpillars);
3. flip over the head.

Hydras are light-loving organisms, as can be seen by observing their movement to the illuminated side of the vessel. Despite the absence of special photosensitive organs, hydras can distinguish the direction of light and strive for it. This is a positive phototaxis that they developed in the process of evolution as a useful feature that helps to find the place where food objects are concentrated. The planktonic crustaceans that the hydra feeds on are usually found in large clusters in areas of the reservoir with well-lit and sun-warmed water. However, not every light intensity causes a positive reaction in the hydra. Empirically, you can set the optimum lighting and make sure that a weak light has no effect, and a very strong one entails a negative reaction. Hydras, depending on the color of their body, prefer different rays of the solar spectrum. With regard to temperature, it is easy to show how the hydra extends its tentacles towards the heated water. Positive thermotaxis is explained by the same reason as the positive phototaxis noted above.

Hydra Regeneration

Hydras are characterized by a high degree of regeneration. At one time, Peebles established that the smallest part of the hydra's body capable of restoring the whole organism is 1/200. This, obviously, is the minimum at which the possibility of organizing the living body of the hydra in its entirety still remains. It is not difficult to acquaint students with the phenomena of regeneration. To do this, it is necessary to set up several experiments with a hydra cut into pieces and organize observations over the course of recovery processes. If you put the hydra on a glass slide and wait for it to stretch out its tentacles, at this moment it is convenient to cut off 1-2 tentacles for it. You can cut with thin dissecting scissors or the so-called spear. Then, after amputation of the tentacles, the hydra must be placed in a clean crystallizer, covered with glass and protected from direct sunlight. If the hydra is cut across into two parts, then the front part relatively quickly restores the back, which in this case turns out to be somewhat shorter than normal. The rear part slowly builds up the front end, but still forms tentacles, a mouth opening and becomes a full-fledged hydra. Regenerative processes go on in the hydra's body throughout its life, as tissue cells wear out and are continuously replaced by intermediate (reserve) cells.

Hydra breeding

Hydras reproduce by budding and sexually (these processes are described in a school textbook - biology grade 7). Some types of hydra overwinter in the egg stage, which in this case can be likened to an amoeba, euglena or ciliate cyst, since it endures the winter cold and remains viable until spring. To study the process of budding, it is necessary to plant a hydra that does not have kidneys in a separate vessel and provide it with enhanced nutrition. Invite students to keep records and observations with fixing the date of jigging, the time of the appearance of the first and subsequent buds, descriptions and sketches of the stages of development; note and record the time of separation of the young hydra from the mother's body. In addition to familiarizing students with the laws of asexual (vegetative) reproduction by budding, one should give a visual representation of the reproductive apparatus in hydras. To do this, in the second half of summer or autumn, several specimens of hydras must be removed from the reservoir and shown to students the location of the testicles and eggs. It is more convenient to deal with hermaphroditic species, in which eggs develop closer to the sole, and testes closer to the tentacles.

Medusa-cross

This small hydroid jellyfish belongs to the trachymedusa order. Large forms from this order live in the seas, and small ones live in fresh waters. But even among marine trachymedusas there are small-sized jellyfish - gonionema, or crosses. Their umbrella diameter varies from 1.5 to 4 cm. Within Russia, gonionems are common in the coastal zone of Vladivostok, in the Gulf of Olga, off the coast of the Tatar Strait, in the Amur Bay, off the southern part of Sakhalin and the Kuril Islands. Students need to know about them, since these jellyfish are the scourge of swimmers off the coast of the Far East.

The jellyfish got its name "cross" by the position in the form of a cross of dark yellow radial channels emerging from the brown stomach and clearly visible through a transparent greenish bell (umbrella). Up to 80 movable tentacles hang along the edge of the umbrella with groups of stinging filaments located in belts. Each tentacle has one sucker, with which the jellyfish is attached to the zoster and other underwater plants that form coastal thickets.

reproduction

The crossbreeder reproduces sexually. In the gonads located along the four radial canals, sexual products develop. Small polyps are formed from fertilized eggs, and these latter give rise to new jellyfish that lead a predatory lifestyle: they attack fish fry and small crustaceans, hitting them with the poison of highly toxic stinging cells.

Human danger

During heavy rains that desalinate sea water, jellyfish die, but in dry years they become numerous and pose a danger to swimmers. If a person touches the cross with his body, the latter attaches to the skin with a suction cup and sticks numerous threads of nematocysts into it. The poison, penetrating into the wounds, causes a burn, the consequences of which are extremely unpleasant and even dangerous to health. After a few minutes, the skin turns red and blistered. A person experiences weakness, palpitations, back pain, numbness of the limbs, difficulty breathing, sometimes dry cough, intestinal disorders and other ailments. The victim needs urgent medical assistance, after which recovery occurs in 3-5 days.

During the period of the mass appearance of crosses, swimming is not recommended. At this time, preventive measures are organized: mowing underwater thickets, fencing baths with fine mesh nets, and even a complete ban on swimming.

Of the freshwater trachymedusa, a small jellyfish kraspedakusta (up to 2 cm in diameter) deserves mention, which is found in reservoirs, rivers and lakes in some areas, including the Moscow region. The existence of freshwater jellyfish points to the fallacy of students' perception of jellyfish as exclusively marine animals.

general characteristics type intestinal.

Coelenterates - two-layer animals with radial symmetry.

Symmetry. In the body of the coelenterates there is a main axis, at one end of which there is a mouth opening. Several axes of symmetry pass through the main axis, along which the appendages and internal organs of the animal are located. This type of symmetry is called radial .

life forms. The main life forms of coelenterates are the polyp and the jellyfish.

Body polyp generally cylindrical, at one end there is a mouth opening surrounded by a different number of tentacles, and at the other - a sole. Polyps are usually sedentary or inactive. Polyps mostly form colonies.

Body jellyfish has the form of a regular umbrella or bell, on the lower, concave side of which there is a mouth opening. There are tentacles or lobes along the edge of the umbrella and sometimes around the mouth. Jellyfish lead, as a rule, a mobile lifestyle and do not form colonies.

Different types of coelenterates either exist in the form of only one of these life forms (jellyfish or polyp), or go through both stages throughout their life cycle.

Systematics. In the type of coelenterates, three classes are distinguished:

hydroid (hydra, obeli, polypodium, siphonophores);

Scyphoid (Aurelia jellyfish, cornerots, cyanides, sea wasps);

coral (black and red corals, acropores, fungi, sea anemones, alcyoniums).

There are 9000 in total modern species coelenterates.

Body dimensions coelenterates vary widely. Some types of polyps in adulthood do not exceed a few millimeters, while some sea anemones can reach 1 meter in diameter. In jellyfish, the diameter of the umbrella can be from 2 mm to 2 meters. In addition, the tentacles of some jellyfish can stretch up to 30 m.

Movement. polyps sedentary. They can bend the body, contract, move their tentacles. Hydras can "walk" like ground surveyor caterpillars (larvae of moths). Anemones can crawl slowly on their soles.

jellyfish actively move by contracting the umbrella. An important role is also played by sea currents that carry jellyfish over long distances.

Body structure. As already mentioned, coelenterates are two-layer animals. Their body wall consists of two cell layers - ectoderm (outdoor) and endoderm (internal). Between them is mesoglea - a layer of structureless gelatinous substance. the only cavity in the body of the coelenterates - intestinal, or gastral .

ectoderm represented by a single-layer flat, cubic or cylindrical epithelium . In addition to ordinary epithelial cells, the ectoderm includes epithelial-muscular cells whose base is elongated longitudinal direction contractile (muscle) fiber. In some corals, muscle fibers separate from the epithelium and lie under it or sink into the mesoglea layer, forming an independent muscular system. Between the epithelial cells are interstitial cells that give rise to various cellular elements of the ectoderm. A characteristic feature of the coelenterates is the presence in the ectoderm of the so-called tentacles. stinging cells . Each such cell contains a capsule into which a spirally folded long hollow process is inserted - a stinging thread. Outside the cell there is a sensitive hair, upon irritation of which the stinging thread sharply turns out, straightens and pierces the body of the prey or the enemy. At the same time, a poisonous secret is poured out of the capsule, causing paralysis of small animals, as well as a burning sensation in large ones.

Endoderm. The epithelium lining the gastric cavity consists of flagellated cells. Some of these cells are epithelial-muscular , however, the muscular processes are located in the transverse direction, forming together, layers of annular fibers. The cells of the ectodermal epithelium are able to form pseudopodia, with the help of which they capture food particles. There are also glandular cells.

Mesoglea. In polyps, the mesoglea is poorly developed (with the exception of corals), while in jellyfish this layer reaches a considerable thickness. The mesoglea contains a number of ectodermal cells that take part in the formation of the skeleton.

Skeletal formations. Only polyps have a skeleton. In hydroid polyps, the body is covered with a thin chitinous theca - a dense shell that performs a protective function. Most coral species have a calcareous skeleton, sometimes horny. The development of the skeleton can vary from individual spicules scattered in the mesoglea to powerful stone-like formations of various sizes and shapes (in madrepore corals). These skeletons are derived from the ectoderm.

The formation of the skeleton in corals is largely due to the presence of polyps in the body. symbiotic algae . Consider chemical reactions that occur during the formation of a calcareous skeleton. The starting materials - calcium ions and carbon dioxide - are found in sea ​​water in sufficient quantity.

Carbon dioxide, when dissolved in water, forms a very unstable carbonic acid:

H 2 O + CO 2 ↔ H 2 CO 3, which immediately dissociates into ions:

H 2 CO 3 ↔ H + + HCO 3 -.

When Ca and HCO 3 ions interact, calcium bicarbonate is formed:

Ca ++ + 2 HCO 3 - ↔ Ca (HCO 3) 2. This substance is soluble in water, but it is also not stable and easily turns into insoluble calcium carbonate:

Ca (HCO 3) 2 ↔ Ca CO 3 ↓ + H 2 O + CO 2.

With an excess of CO 2, this reaction shifts to the left and a soluble bicarbonate is formed. With a decrease in the concentration of CO 2, the reaction shifts to the right and lime precipitates.

Algae living in the body of polyps constantly remove carbon dioxide from the tissues of the intestinal cavities for the process of photosynthesis, constantly creating a reduced concentration of CO 2. Such conditions favor the formation of insoluble calcium carbonate and the construction of a powerful skeleton by polyps.

Digestive system and nutrition. The digestive system is represented by the gastric cavity. Most coelenterates are predators. Prey, killed or stunned by stinging cells, they bring with tentacles to the mouth opening and swallow.

In hydroid polyps, the gastric cavity looks like a simple bag, which communicates with the environment through the oral opening. Various small animals that enter the gastric cavity are most often absorbed by endoderm cells ( intracellular digestion). Larger prey can be digested by enzymes secreted by glandular cells. Undigested residues are ejected through the mouth opening.

In coral polyps, the gastric cavity is divided longitudinally by septa, which increases the area of ​​the endoderm. In addition, the ectodermal pharynx protrudes into the digestive cavity of corals.

As already mentioned, reef-building corals enter into a symbiotic relationship with a certain type of unicellular algae that settle in the endodermal layer. These plants, receiving carbon dioxide and metabolic products from the polyp, supply it with oxygen and a number of organic substances. Algae themselves are not digested by polyps. Under normal conditions, such a symbiosis makes it possible for polyps to do without the intake of organic substances from the environment for a long time.

At jellyfish the gastric cavity is generally formed by the stomach located in the central part of the umbrella, radial canals extending from the stomach and an annular canal running along the edge of the umbrella. Hydromedusas often have 4 radial canals, while scyphomedusas have 16 radial canals. The entire complex of canals forms the so-called gastrovascular system .

Nervous system. At polyps nervous system diffuse type . Separate nerve cells located at the base of the epithelium of the ectoderm and endoderm are connected by their processes into a nervous network. The mouth opening and the sole of the polyps are surrounded by a denser nervous network.

At jellyfish the nervous system is more concentrated than in polyps, which is associated with a mobile lifestyle.

At hydroid jellyfish accumulation of nerve cells is located on the edge of the umbrella. The cells themselves and their processes form a double nerve ring. The outer ring performs sensory functions, while the inner ring performs motor functions.

At scyphoid jellyfish the nerve ring is less pronounced, but at the base of the ropalia (marginal sensory bodies) there are clusters of nerve cells that can be called ganglia.

sense organs. Due to a sedentary lifestyle, polyps special no sense organs . There are only a few sensitive (tactile) cells, which are located mostly near the mouth opening.

At jellyfish there are also sensitive cells, but there are also special sense organs - vision, balance and smell.

Along the edge of the umbrella are located organs of vision - eyes , different in structure. In hydroid jellyfish, the eyes lie singly, while in scyphoid jellyfish, the eyes are on ropalia - sensitive marginal bodies. Moreover, one ropaliy can carry several eyes of varying degrees of complexity at once.

In connection with a mobile lifestyle, jellyfish have appeared organs of balance - statocysts. They are a bubble lined from the inside with sensitive cells. Inside the bubble is a calcareous body - statolith. Depending on the position of the jellyfish in space, the statolith irritates a certain section of the bubble wall. There are other types of structure of statocysts. In addition, statocysts are able to capture the vibrations of water, so they can also be called organs of hearing. In hydroid jellyfish, the balance organs are located along the edge of the umbrella in the amount of 4-80 in different species.

Scyphoid jellyfish also have olfactory pits - organs of chemical sense.

In scyphoids, all the senses are located on 8 ropalia - modified tentacles.

Breath. Gas exchange in coelenterates occurs by diffusion of oxygen and carbon dioxide. Large species (corals) have siphonoglyphs lined with ciliated epithelium on the pharynx. Cells equipped with cilia constantly carry out the flow of fresh water into the intestinal cavity of the animal. Many polyps, as already mentioned, have switched to symbiosis with algae, supplying the coelenterates with oxygen and releasing carbon dioxide.

Sex organs. At polyps there are no special sex organs. Sex cells are laid either in the ectoderm or in the endoderm. In the first case, the gametes exit through the rupture of the ectoderm, in the second, they first enter the gastric cavity, and then out through the mouth. Among the polyps there are hermaphrodites (hydras) and dioecious (corals).

At jellyfish , which are almost always separate sexes, there are sex glands.

At hydromedus they form in the ectoderm of the lower side of the umbrella under the radial canals, less often on the oral proboscis. The number of gonads corresponds to the number of radial canals. Gametes exit through ruptured glands.

At scyphoid jellyfish gonads of endodermal origin. They form in the pockets of the stomach. Gametes first enter the gastric cavity, and then into the environment.

Reproduction. Coelenterates reproduce both asexually and sexually.

asexual reproduction most often proceeds through budding . This path is characteristic of polyps, and is rare in jellyfish. In single polyps, a kidney appears on the body, which gradually forms tentacles and a mouth opening and then breaks away from the mother's body. In colonial hydroids and corals, the daughter individual does not separate from the mother, which leads to the formation of colonies.

Colonial hydroid polyps they are not capable of sexual reproduction, so they bud off and sexual individuals - jellyfish. Jellyfish are formed either on the axis of the colony, or on special outgrowths - blastostyles.

Another method of asexual reproduction is strobilation when the polyp at a certain stage begins to lace up in the transverse direction several times and a small jellyfish is formed from each part. Almost the entire body of the polyp is spent on the formation of jellyfish. This method is typical for scyphoid jellyfish.

Thus, there is a change of polypoid asexual and medusoid sexual generations. At the same time, the polypoid generation predominates in hydroids, and the medusoid generation in scyphoids. Corals do not have a medusoid generation.

In a number of hydroids, jellyfish do not break away from the colony, and in some, the jellyfish is reduced to the state of a "genital sac" - a sporosarca.

Very interesting siphonophores , which are a huge colony consisting of organisms of various structures. Each colony has a pneumatophore, an air bladder that supports the siphonophore on the surface of the water.

sexual reproduction characteristic of all jellyfish, all corals and some hydroid polyps. The sexual process involves haploid cells - gametes that copulate either in the environment or in the body of the coelenterate. The egg undergoes complete uniform crushing. Gastrulation of the blastula most often occurs by immigration, less often by invagination. In the future, a two-layer larva is formed - a planula, covered with cilia and leading a mobile lifestyle. For such sedentary animals as corals (which do not have a medusoid generation), the planula is the only settling stage. A polyp is always formed from the planula, later budding from itself either only polyps (corals), or polyps and jellyfish (hydroid), or only jellyfish (scyphoid). Thus, the development of the vast majority of coelenterates goes with metamorphosis. Sometimes a polyp is immediately formed from an egg (for example, in hydra).

Regeneration. Coelenterates have a high ability to regenerate. Experiments on the study of this phenomenon in hydra were staged as early as 1740 by Tremblay. It turned out that the animal can regenerate from 1/200 of a part.

Origin. Most likely, the ancestors of the coelenterates were free-floating organisms of the type parenchymella , which was described by I.I. Mechnikov. These hypothetical organisms were devoid of a skeleton and therefore could not be preserved as a fossil.

The oldest finds of coelenterates - coral skeletons - date back to the Cambrian period (about 600 million years ago). At the same time, not only individual prints were preserved, but also entire petrified reefs. A few imprints of jellyfish and hydroids are also known. In total, more than 20,000 species of fossil coelenterates are known.

Meaning. In nature, coelenterates, being predators and at the same time food for other animals, participate in complex food chains of marine biocenoses. Corals are of great geochemical importance, forming thick layers of calcareous rocks. Throughout their existence, corals have been involved in the formation of islands. Reefs are unique biocenoses, where a huge number of animal species live.

Practical significance modern coelenterates is small.

Corals (especially red and black) are used as decorations. They are mined in large quantities, mainly by artisanal methods. Coral collection is prohibited on large reefs.

Some jellyfish pose a serious danger to humans. In our seas, these include a small Far Eastern cross jellyfish that lives in thickets of marine plants and a large Black Sea cornerot, often found off the coast. The poison of the cross is sometimes fatal. The most dangerous jellyfish - the sea wasp - lives off the coast of Australia. Touching this animal causes severe pain and shock. Many people died when they met her.

In China and some other countries, specially prepared ropil jellyfish are eaten. There is a special trade there.

The variety of species of marine animals is so wide that humanity will not soon be able to study them in their entirety. However, even long-discovered and well-known inhabitants of the waters can surprise with hitherto unseen features. For example, it turned out that the most common hydroid (jellyfish) never dies of old age. It appears to be the only creature known on earth to possess immortality.

General morphology

Medusa hydroid belongs to the class of hydroids. These are the closest relatives of polyps, but they are more complicated. Probably everyone has a good idea of ​​what jellyfish look like - transparent discs, umbrellas or bells. They can have ring-shaped constrictions in the middle of the body or even be in the shape of a ball. Jellyfish don't have a mouth, but they do have an oral proboscis. Some individuals even have small pinkish tentacles on the edges.

The digestive system of these jellyfish is called gastrovascular. They have a stomach, from which four radial canals extend to the periphery of the body, flowing into a common annular canal.

Tentacles with stinging cells are also located at the edges of the umbrella body; they serve both as an organ of touch and as a hunting tool. The skeleton is missing, but there are muscles due to which the jellyfish moves. In some subspecies, some of the tentacles are transformed into statoliths and statocysts - balance organs. The method of movement depends on the type to which a particular hydroid (jellyfish) belongs. Their reproduction and structure will also differ.

The nervous system of hydrojellyfish is a network of cells that form two rings at the edge of the umbrella: the outer one is responsible for sensitivity, the inner one for movement. Some have light-sensitive eyes located at the base of the tentacles.

Types of hydroid jellyfish

Subclasses that have the same balance organs - statocysts, are called trachilids. They move by pushing water out of the umbrella. They also have a sail - an annular outgrowth on the inside, narrowing the exit from the body cavity. It adds speed to the jellyfish when moving.

Leptolids are devoid of statocysts, or they are transformed into a special vesicle, inside which there may be one or more statoliths. They move in the water far less reactively, because their umbrella cannot contract often and intensely.

There are also jellyfish hydrocorals, but they are underdeveloped and bear little resemblance to ordinary jellyfish.

Chondrophores live in large colonies. Some of their polyps are budded by jellyfish, which continue to live on their own.

Siphonophore - a hydroid which is unusual and interesting. This is a whole colony, in which everyone performs his role for the functioning of the whole organism. Outwardly, it looks like this: on top is a large floating bubble in the shape of a boat. It has glands that produce a gas that helps it float to the top. If the siphonophore wants to go back into the depths, it simply relaxes its muscular organ - the contactor. Under the bubble on the trunk are other jellyfish in the form of small swimming bells, followed by gastrozoids (or hunters), then gonophores, whose goal is to procreate.

reproduction

Medusa hydroid is either male or female. Fertilization often occurs externally rather than inside the body of the female. The sex glands of jellyfish are located either in the ectoderm of the oral proboscis, or in the ectoderm of the umbrella under the radial canals.

Mature sex cells are outside due to the formation of special gaps. Then they begin to split up, forming a blastula, some of the cells of which are then drawn inward. The result is endoderm. As it develops, some of its cells degenerate to form a cavity. It is at this stage that the fertilized egg becomes a planula larva, then settles to the bottom, where it turns into a hydropolyp. Interestingly, he begins to bud new polyps and small jellyfish. Then they grow and develop as independent organisms. In some species, only jellyfish are formed from planulae.

The variation of egg fertilization depends on which type, species or subspecies the hydroid (jellyfish) belongs to. Physiology and reproduction, like the structure, are different.

Where do they live

The vast majority of species live in the sea, they are much less common in freshwater reservoirs. You can meet them in Europe, America, Africa, Asia, Australia. They can appear in greenhouse aquariums, and in artificial reservoirs. Where polyps come from and how hydroids spread in the world is still unclear to science.

Siphonophores, chondrophores, hydrocorals, trachilids live exclusively in the sea. Only leptolid can be found in fresh water. But on the other hand, there are much fewer dangerous representatives among them than among the marine ones.

Each occupies its own habitat, for example, a particular sea, lake or bay. It can expand only due to the movement of waters, especially jellyfish do not capture new territories. Some people like cold more, others like warm. They can live closer to the surface of the water or at depth. The latter are not characterized by migration, while the former do this in order to search for food, going deeper into the water column during the day, and rising again at night.

Lifestyle

The first generation in the hydroid life cycle is the polyp. The second is a hydroid jellyfish with a transparent body. The strong development of the mesoglea makes it such. She is student and contains water. It is because of her that the jellyfish can be difficult to notice in the water. Due to the variability of reproduction and the presence of different generations, hydroids can actively spread in the environment.

Jellyfish eat zooplankton. The larvae of some species feed on fish eggs and fry. But at the same time, they themselves are part of the food chain.

Hydroid (jellyfish), a lifestyle essentially dedicated to nutrition, usually grows very quickly, but certainly does not reach the size of scyphoids. As a rule, the diameter of the hydroid umbrella does not exceed 30 cm. Their main competitors are plankton-eating fish.

Of course, they are predators, and there are quite dangerous for humans. All jellyfish have which are used during hunting.

What is the difference between hydroids and scyphoids

According to morphological features, this is the presence of a sail. Scyphoids do not have it. They are usually much larger and live exclusively in the seas and oceans. in diameter reaches 2 m, but at the same time, the poison of its stinging cells is hardly capable of causing severe harm to a person. The greater number of radial canals of the gastrovascular system helps scyphoids grow to large sizes than hydroids. And some species of such jellyfish are eaten by humans.

There is also a difference in the type of movement - hydroids shorten the annular fold at the base of the umbrella, and scyphoids - the entire bell. The latter have more tentacles and sensory organs. Their structure is also different, since scyphoids have muscle and nerve tissue. They are always dioecious, they do not have vegetative reproduction and colonies. These are singles.

Scyphoid jellyfish can be surprisingly beautiful - they can be of different colors, have fringes around the edges and a bizarre bell shape. It is these inhabitants of the waters who become the heroines of television programs about marine and ocean animals.

Medusa hydroid is immortal

Not so long ago, scientists discovered that the hydroid jellyfish turitopsis nutricula has an amazing ability to rejuvenate. This species never dies a natural death! She can trigger the regeneration mechanism as many times as she likes. It would seem that everything is very simple - having reached old age, the jellyfish again turns into a polyp and goes through all the stages of growing up again. And so in a circle.

Nutricula lives in the Caribbean and has a very small size - the diameter of its umbrella is only 5 mm.

The fact that the hydroid jellyfish is immortal, it became known by chance. Scientist Fernando Boero from Italy studied and experimented with hydroids. Several individuals of turitopsis nutricula were placed in an aquarium, but for some reason the experiment itself was postponed for such a long time that the water dried up. Boero, discovering this, decided to study the dried remains, and realized that they did not die, but simply shed their tentacles and became larvae. Thus, the jellyfish adapted to adverse environmental conditions and pupated in anticipation of better times. After placing the larvae in the water, they turned into polyps, the life cycle started.

Dangerous representatives of hydroid jellyfish

The most beautiful species is called (physalia siphonophora) and is one of the most dangerous marine life. Its bell shimmers with different colors, as if beckoning to itself, but it is not recommended to approach it. Physalia can be found on the coast of Australia, Indian and Pacific Oceans and even in the Mediterranean. Perhaps this is one of the largest types of hydroids - the length of the bubble can be 15-20 cm. But the worst thing is the tentacles that can go as deep as 30 m. Physalia attacks its prey with poisonous stinging cells that leave severe burns. It is especially dangerous to meet with a Portuguese boat for people who have a weakened immune system, there is a tendency to allergic reactions.

In general, hydroid jellyfish are harmless, unlike their scyphoid sisters. But in general it is better to avoid contact with any representatives of this species. All of them have stinging cells. For some, their poison will not turn into a problem, but for someone it will cause more serious harm. It all depends on individual characteristics.