Hydroid (jellyfish): structure, reproduction, physiology

The variety of species of marine animals is sowidely, that humanity will not soon be able to study them in its entirety. However, even long-established and famous inhabitants of the water are able to surprise with hitherto unprecedented features. For example, it turned out that the most common hydroid (jellyfish) never dies of old age. It seems that this is the only creature known on earth, possessing immortality.

General morphology

Medusa hydroid refers to the type of coelenterates,class of hydroids. These are the closest relatives of polyps, but they are more complicated. Probably everyone is well aware of how jellyfish look - transparent discs, umbrellas or bells. They can have annular constrictions in the middle of the body or even be in the shape of a ball. Jellyfish do not have a mouth, but there is a mouth proboscis. Some individuals have even small pinkish tentacles on the edges.

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

Tentacles with stinging cells are locatedalso on the edges of the umbrella body, they serve simultaneously as an organ of touch, and an instrument for hunting. The skeleton is absent, but there are muscles through which the jellyfish moves. In some subspecies a part of tentacles is transformed into statoliths and statocysts - organs of equilibrium. The mode of motion depends on the type to which the particular hydroid belongs (jellyfish). Reproduction and construction of them will also be different.

The nervous system of hydromedusa is aa network of cells that form two rings on the edge of the umbrella: the outer ring is responsible for the sensitivity, the inner one is responsible for the movement. Some have light-sensitive eyes located on the basis of tentacles.

Types of Hydroid Jellyfish

Subclasses having the same organs of equilibrium -statocysts, are called trachylides. They move by pushing water out of the umbrella. They also have a sail - a ring-shaped growth on the inside, a narrowing exit from the body cavity. It adds jellyfish speed when driving.

The leptolids are devoid of statocysts, or theyare transformed into a special vial, within which there can be one or several statoliths. They move in the water is not so reactive, because their umbrella can not shrink often and intensively.

There are also meduzoidnye hydrocorals, but they are underdeveloped and little like ordinary jellyfish.

Chondrophors live in large colonies. A part of their polyps exudes jellyfish, which further live independently.

Siphonophora is a hydroid (jellyfish), the structure of whichunusual and interesting. This is a whole colony, in it everyone performs his role for the functioning of the whole organism. Outwardly it looks like this: above is a large floating bubble in the shape of a boat. He has glands that produce gas, which helps to float upward. If the siphonophora wants to go back deeper - it just relaxes its muscular organ a contactor. Under the bubble on the trunk are other jellyfish in the form of small swimming bells, followed by gastrozoids (or hunters), then gonofors, whose goal is the continuation of the genus.

Reproduction

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

Ripe germ cells are outsidebecause of the formation of special ruptures. Then they begin to crumble, forming a blastula, some of the cells of which are then drawn inward. The result is an endoderm. In the process of further development, some of its cells degenerate to form a cavity. It is at this stage that the fertilized egg becomes a larval-planulum, then settles on the bottom, where it turns into a hydro-polyp. It is interesting that he begins to bud new polyps and small jellyfish. Further they already grow and develop as independent organisms. In some species, only jellyfish are formed from planulas.

The variation in the fertilization of the egg depends on which type, species or species belongs to the hydroid (jellyfish). 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 frequent 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, while science is not clear.

Siphonophores, chondrophores, hydrocorals, trachylideslive exclusively in the sea. Only leptolide can be found in fresh water. But there are also fewer dangerous representatives among them, than among sea ones.

Each species of jellyfish occupies its habitat,for example, some specific sea, lake or bay. It can expand only due to the movement of water, especially jellyfish do not seize new territories. Some like cold more, others - warmth. They can live closer to the surface of the water or at a depth. The latter are not peculiar to migration, and the first do so in order to find food, moving deeper into the water during the day, and rising again at night.

Lifestyle

The first generation in the life cycle of hydroids -it's a polyp. The second is the hydroid of a jellyfish with a transparent body. Such is the strong development of mesogloe. It is gelatinous and contains water. It is because of it that the jellyfish is difficult to notice in the water. Hydroids due to the variation in reproduction and the presence of different generations can actively spread in the environment.

Jellyfish consume zooplankton food. Larvae of some species feed on eggs and fish fry. But at the same time they themselves are part of the food chain.

The hydroid (jellyfish), the way of life, in fact, is dedicated tonutrition, usually grows very quickly, but, of course, does not reach such sizes as scythoids. As a rule, the diameter of the umbrella of the hydroid does not exceed 30 cm. Their main competitors are plankton-eating fish.

Of course, they are predators, and they are quite dangerous for humans. All jellyfish have stinging cells that are used during hunting.

The difference between hydroids from the Scyphoids

According to morphological features, this is the presence of a sail. Scythians do not have it. They are, as a rule, much larger and live exclusively in the seas and oceans. Arctic cyanide in diameter reaches 2 m, but the poison of its stinging cells is unlikely to cause severe harm to humans. To grow to larger sizes, scyphoids are helped by more than the hydroids, the number of radial canals of the gastrovascular system. And some species of such jellyfish are used for human consumption.

There is a difference in the type of movement - hydroidscut the ring fold at the base of the umbrella, and the scythoids - the entire bell. The latter have more tentacles and sensory organs. Their structure is also different, since the scyphoids have muscular and neural tissue. They are always dioecious, they do not have vegetative reproduction and colonies. It's a loner.

Scythian jellyfish are surprisingly beautiful -they can be of different colors, have fringes and a bizarre shape of the bell at the edges. It is these inhabitants of the water that become the heroines of telecasts about marine and ocean animals.

Medusa hydroid is immortal

Not so long ago, scientists found that the hydroidjellyfish turethopsis nutricula has an amazing ability to rejuvenate. This species never dies of its death! It can start the regeneration mechanism as many times as necessary. It would seem that everything is very simple - after reaching old age, the jellyfish again turns into a polyp and passes through all the stages of growing up again. And so on a circle.

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

The fact that the jellyfish hydroid is immortal, has becomeis known by chance. Scientist Fernando Boero from Italy studied hydroids and conducted experiments with them. Several individuals of turiotysis nutricula were placed in the aquarium, but the experience itself for some reason was postponed for such a long period that the water dried. Bauer, having discovered this, decided to study the dried up remains, and realized that they had not died, but simply dropped the tentacles and became larvae. Thus, the jellyfish has adapted to unfavorable environmental conditions and has cluttered up 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 view is called Portugueseboat (siphonophoros of the fisalia) and is one of the most dangerous sea inhabitants. His bell is poured with different colors, as if luring to himself, but it is not recommended to approach it. The fisalia can be found on the coast of Australia, the 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 is the tentacles, which can go to a depth of 30 m. Fisalia attacks its victim with poisonous stinging cells that leave severe burns. Especially dangerous to meet with the Portuguese ship to people who have weakened immunity, there is a tendency to allergic reactions.

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