The variety of species of marine animals is so wide that not yet soon humanity will be able to study them in their entirety. However, even the long-discovered and well-known inhabitants of the waters can 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 with immortality.
General morphology
Medusa hydroid is a type of intestinal , a class of hydroid. These are the closest relatives of polyps, but they are more complicated. Probably, everyone is well aware of what jellyfish look like - transparent disks, 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 have a proboscis. Some individuals even have small pinkish tentacles at the edges.
The digestive system of these jellyfish is called gastrovascular. They have a stomach, from which four radial channels extend into the periphery of the body, flowing into a common annular channel.
Tentacles with stinging cells are also located on the edges of the umbrella body, they serve simultaneously as the organ of touch, and a tool for hunting. The skeleton is absent, but there are muscles due to which the jellyfish moves. In some subspecies, part of the tentacles are transformed into statoliths and statocysts - organs of balance. The method of movement depends on the type to which a particular hydroid (jellyfish) belongs. Their reproduction and structure will also be different.
The nervous system of hydromeduses is a network of cells that form two rings on the edge of an umbrella: the external is responsible for sensitivity, the internal for movement. Some have photosensitive eyes located at the base of the tentacles.
Types of Hydroid Jellyfish
Subclasses that have the same balance organs - statocysts are called trachilides. They move due to the expulsion of water from the umbrella. They also have a sail - an annular outgrowth on the inside, narrowing the exit from the body cavity. He adds jellyfish speed while moving.
Leptolides lack statocysts, or they are transformed into a special vesicle, inside which there can be one or more statoliths. They move in water far less reactive, because their umbrella can not be reduced often and intensively.
There are still jellyfish hydrocorals, but they are underdeveloped and look a little like ordinary jellyfish.
Chondrophores live in large colonies. Part of their polyps buds jellyfish, which then live on their own.
Siphonophore is a hydroid
(jellyfish), the structure of which is unusual and interesting. This is a whole colony, in it everyone fulfills his role for the functioning of the whole organism. Outwardly, it looks like this: on top of a large floating bubble in the shape of a boat. He has glands that produce gas, which helps to float up. If the siphonophore wants to go back deeper - it just relaxes its muscular organ closure. Under the bubble on the trunk are other jellyfish in the form of small swimming bells, followed by gastrosoids (or hunters), then gonophores, whose goal is to continue the genus.
Breeding
Medusa hydroid is male or female. Fertilization is more often external than inside the body of a female. The genital glands of jellyfish are located either in the ectoderm of the oral proboscis, or in the ectoderm of the umbrella under the radial channels.
Ripen germ cells are outside due to the formation of special breaks. Then they begin to fragment, forming a blastula, part of the cells of which are then drawn inward. The result is an endoderm. In the process of further development, a certain amount of its cells degenerates in order 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 off new polyps and small jellyfish. Then they already grow and develop as independent organisms. In some species, only jellyfish are formed from the planes.
The variation in egg fertilization depends on the type, species or subspecies of the hydroid (jellyfish). Physiology and reproduction, as well as structure, are different.
Where do they live
The vast majority of species live in the sea, they are much less common in freshwater bodies of water. You can meet them in Europe, America, Africa, Asia, Australia. They can appear in greenhouse aquariums, and in artificial reservoirs. Where the polyps come from and how hydroids spread in the world is not yet understood by science.
Siphonophores, chondrophores, hydrocorals, trachilides live exclusively in the sea. Only leptolid can be found in fresh water. But then there are much less dangerous representatives among them than among marine ones.
Each type of jellyfish occupies its own habitat, for example, a specific sea, lake or bay. It can expand only thanks to the movement of water, specially jellyfish do not capture new territories. Some people like cold more, others like warmth. They can live closer to the surface of the water or in depth. The latter are not peculiar to migration, but the former do this in order to search for food, by day going deeper into the water column, and again rising up at night.
Lifestyle
The first generation in the hydroid life cycle is a polyp. The second is a jellyfish hydroid with a transparent body. It is made by the strong development of mesogley. She is a student and contains water. It is because of it that the jellyfish can be difficult to notice in the water. Hydroids due to the variability of reproduction and the presence of different generations can actively spread in the environment.
Jellyfish consume zooplankton. Larvae of some species feed on eggs and fry of fish. But at the same time, they themselves are part of the food chain.
Hydroid (jellyfish), a way of life, in fact, is devoted to nutrition, usually grows very quickly, but, of course, does not reach such sizes as scyphoids. As a rule, the diameter of the hydroid umbrella does not exceed 30 cm. Their main competitors are planktonivorous fish.
Of course, they are predators, and they are quite dangerous for humans. All jellyfish have stinging cells that are used during hunting.
What is the difference between hydroids and scyphoids
According to morphological characteristics, this is the presence of a sail. Scyphoids do not have it. They, as a rule, are much larger and live exclusively in the seas and oceans. Arctic cyanide in diameter reaches 2 m, but at the same time the poison of its stinging cells can hardly cause severe harm to humans. To grow to a large size, the scyphoid helps more than the hydroids, the number of radial channels of the gastrovascular system. And some types of jellyfish are eaten by humans.
There is a difference in the type of movement - hydroids reduce the annular fold at the base of the umbrella, and the scyphoid - the entire bell. The latter have more tentacles and sense organs. Their structure is also different, since scyphoids have muscle and nerve tissue. They are always dioecious, they do not have vegetative propagation and colonies. This is a loner.
Scyphoid jellyfish are surprisingly beautiful - they can be of different colors, have fringe edges and a bizarre bell shape. It is these inhabitants of the waters who become the heroines of television programs about sea and ocean animals.
Jellyfish 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 by its death! She can trigger the regeneration mechanism as many times as she wants. It would seem that everything is very simple - having reached old age, the jellyfish again turns into a polyp and goes through all stages of growing up again. And so in a circle.
The nutricula lives in the Caribbean and has a very small size - the diameter of its umbrella is only 5 mm.
The fact that the jellyfish hydroid is immortal, it became known by chance. Scientist Fernando Boero from Italy studied hydroids and experimented with them. Several individuals of the turitopsis nutriculum were placed in the aquarium, but for some reason the experiment itself was postponed for such a long time that the water dried up. Having discovered this, Boero decided to study the dried remains, and realized that they did not die, but simply threw off the tentacles and became larvae. Thus, the jellyfish adapted to adverse environmental conditions and began to crouch in anticipation of better times. After placing the larvae in water, they turned into polyps, the life cycle started.
Dangerous representatives of hydroid jellyfish
The most beautiful view is called the Portuguese boat (siphonophore physalis) and is one of the most dangerous marine inhabitants. Its bell shimmers with different colors, as if attracting to itself, but it is not recommended to approach it. Physalia 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 bladder can be 15-20 cm. But the worst thing is the tentacles, which can go 30 meters deep. Physalia attacks its victim with poisonous stinging cells that leave severe burns. It is especially dangerous to meet with a Portuguese boat people who have weakened immunity have a tendency to allergic reactions.
On the whole, 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 possess stinging cells. For some, their poison will not turn out to be a problem, but for someone it will harm more seriously. It all depends on individual characteristics.