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 to possess immortality.
General morphology
Medusa hydroid belongs to the type of coelenterates, 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 may have ring-shaped constrictions in the middle of the body or even be in the form 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 channel.
Tentacles with stinging cells are also located on the edges of the umbrella body, they serve both as an organ of touch and a tool for hunting. 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 on 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 gives the jellyfish movement speed.
Leptolids are deprived of statocysts, or they are transformed into a special vial, inside of which there can be one or more statoliths. They are far less reactive in the water, as their umbrella can't 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.
Siphonophora is a hydroid (jellyfish) whose structure 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 deeper, 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 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 already grow and develop as independent organisms. In some species, only jellyfish form from planula.
Variation of egg fertilization depends on what type, species or subspecies the hydroid (jellyfish) belongs to. Physiology and reproduction, like structure, are different.
Where do they live
The vast majority of species live in the sea, they are much less common in freshwater. 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 species of jellyfish 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 prefer cold, others 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 it 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 are part of the food chain themselves.
Hydroid (jellyfish), a lifestyle essentially devoted to nutrition, usually grows very quickly, but certainly does not reach the size of scyphoids. As a rule, the diameter of a hydroid umbrella does not exceed 30 cm. Their main competitors are planktivorous fish.
Of course, they are predators, and there are quite dangerous ones for humans. All jellyfish have stinging cells that 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. The Arctic cyanide reaches 2 m in diameter, 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. They are loners.
Scyphoid jellyfish aresurprisingly 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 on 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 hydroid jellyfish is immortal, it became known by accident. 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 the Portuguese man-of-war (siphonophore physalia) and is one of the most dangerous marine life. His bell shimmers with different colors, as ifluring to him, but it is not recommended to approach him. 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 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 weakened immunity, have 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.
