Biology at the Lyceum. Characteristics and structure of coral polyps Marine polyps corals
Coral polyps or marine - living creatures that may not move at all, and if they move, then very little. They live at the very bottom of the sea in large groups, rarely alone and do not have a backbone.
You can find more precise definition What are polyps, biologists say - these are some forms of aquatic animals that have stopped at a certain stage of development. And at the next stage, a jellyfish is already obtained. Among this class, you can count about 6 thousand species, among them there are even those that do not have a skeleton, which consists only of protein.
If we translate literally from Latin the name of coral polyps, then we get such a funny name - an animal - a flower. It is this name that indicates the shape of the polyps themselves. All of them really resemble a flower, they can be of different diameters, sometimes they reach a diameter of about 60 cm, and the height may well be a meter. Coral polyps can be used as aquarium decorations, and they are also used by jewelers to make jewelry.
Coral grows about one centimeter per year if they grow in comfortable conditions. They grow on great depth because that's where we live a large number of plankton, they feed on them. And large polyps that live alone can eat small fish.
Polyps can reproduce in two ways: the first is the larva, which is obtained from the mating of jellyfish, it settles somewhere and begins to grow. The second is the division of polyps into parts, in other words, sterile reproduction. Jellyfish appear thanks to polyps.
There are certain types of polyps that cannot turn into a jellyfish. Such polyps create coral reefs, they have only a skeleton consisting of lime.
Since it was already mentioned earlier that some polyps do not have a skeleton, anemone belongs to them. She lives alone, can be of impressive size - about one and a half meters. They lead an exclusively sedentary lifestyle, while they can also coexist with some species of fish. Very large sea anemones can even feed on fish that have the average size. They may well move along the bottom due to the fact that they compress and unclench the sole, but very slowly.
In nature, there are not only polyps that do not turn into a jellyfish, since they do not have this stage, but there are also jellyfish that cannot become polyps.
Polyps are very important in the environment, they purify sea water from organic particles. Also, coral limestone can be used for construction, but not in all countries. It is coral polyps that take part in the formation of reefs.
The body of a coral polyp is usually cylindrical and is not subdivided into a trunk and a leg. In colonial forms of coral polyps, the base is immersed in the common body of the colony - the coenosark, and in single forms it turns into an attachment sole.
The tentacles of these organisms are always hollow, located in one or more closely spaced corollas.
There are two large groups coral polyps - eight-ray (Octocorallia) and six-ray (Hexacorallia).
The first group always has eight tentacles and they are equipped with small outgrowths at the edges - pinnules, the second group has more tentacles and, as a rule, a multiple of six.
The tentacles of six-pointed corals are almost always smooth, without pinnules. Top part polyp, between the tentacles, is called the oral disc. In its middle is a slit-like mouth opening. Internal structure coral polyps are much more complex than hydroid and scyphoid polyps. The mouth leads into a laterally compressed pharynx lined with ectoderm. Usually, a groove runs along one of the edges of the pharynx, carrying cells with very long eyelashes- siphonoglyph. Sometimes there are two siphonoglyphs, in such cases they are located on opposite narrow edges of the pharyngeal tube. Cilia constantly move and drive water into the intestinal cavity. The latter is divided by longitudinal partitions (septa) into chambers.
In the upper part of the body of the coral polyp (in the region of the pharynx), the septa are either complete (adhering one edge to the body wall and the other to the pharynx) or incomplete (not reaching the pharynx). The septa have holes through which all the chambers communicate with each other.
In the lower part of the coral polyp (below the pharynx), the septa adhere only to the body wall. Thereby central part gastric cavity - stomach - remains undivided. The free edges of the septa are thickened and are called mesenteric filaments. They play an important role in the digestion of food, as they contain many glandular cells that secrete digestive enzymes.
In corals with one siphonoglyph, two mesenteric filaments located on a pair of opposing septa are not thickened and bear cells with long, strong cilia. Being in constant motion, the cilia drive water out of the gastric cavity of the coral polyp. The joint work of two mesenteric filaments and a siphonoglyph (or two opposite siphonoglyphs, as in sea anemones) ensures a constant change of water in the gastric cavity. As a result, fresh, oxygen-rich water is constantly supplied there, and with it bacteria, planktonic organisms, and detritus particles that coral polyps feed on. With the reverse flow of water, carbon dioxide, metabolic products and undigested food residues are carried out.
The number of septa and chambers in coral polyps always coincides with the number of tentacles, the cavity of which is a continuation of the corresponding chambers of the gastric cavity. Thus, octagonal corals always have eight septa and chambers, and six-arm corals always have six.
Septa are laid gradually and always in pairs.
Like all coelenterates, corals are radially symmetrical. However, in their internal organization there are also features of bilateral symmetry (pharynx compressed from the sides and siphonoglyphs). through the longitudinal axis of the pharynx, only one plane of symmetry can be drawn, which divides the body of the coral polyp into two mirror halves. The chambers lying against the narrow edges of the pharyngeal tube differ from the rest by the location of the muscular ridges. These chambers and the septa that form them are called directional septa, which are used to conditionally determine the "dorsal" and "ventral" sides of the body of the coral polyp.
The muscle cells of coral polyps separate from the ectoderm and endoderm and pass into the mesoglea, forming a layer of longitudinal and transverse muscles in the body walls. In addition, in the mesoglea of each septum, on one side, there is a thin layer of transverse muscles, and on the other, a powerful roller of longitudinal muscles.
The mesoglea is represented in most of the six-rayed corals by a thin supporting plate. On the other hand, in octagonal corals, it reaches a significant development, especially in the trunk and branches of the colony. The gelatinous substance of the mesoglea is reinforced with collagen elements and filled with a huge number of skeletal calcareous needles - spicules, or sclerites.
Thus, the mesoglea constitutes a strong support for the coral colony. At the same time, it is involved in the transport of nutrients, as it is permeated with a dense network of endodermal channels connecting individual intestinal cavities of coral polyps into one cavity. The same channels play an important role in the rhythmic change of the active and passive state of the coral polyp colony.
The skeleton reaches significant development in many coral polyps. In octagonal corals, this is an internal, mesogleal skeleton, consisting of sclerites that develop in special cells - scleroblasts. Sometimes sclerites fuse with each other or unite with an organic horn-like substance, forming the skeleton of a coral colony. It may also consist of pure horny substance.
Among six-ray corals there are non-skeletal forms (anemones and periantharia). More often, however, there is a skeleton, and it can be either internal (in the form of a rod of a horn-like substance) or external (calcareous), but always of ectodermal origin.
But neither the calcareous nor the organic skeleton is able to maintain the constancy of the body shape of coral polyps. This is provided in a different way. All polyps have a peculiar hydroskeleton, which reaches its greatest perfection in coral polyps.
Due to the constant flow of water created by siphonoglyphs, gastric high blood pressure, without which the coral polyp would have the shape of an empty two-layer bag. The polyp expands under the pressure of the fluid that fills the gastric cavity. In this state, it can be very long and almost without energy expenditure. Meanwhile, in other animals such a tense state cannot be prolonged, since the muscles get tired, the animal must change the position of the body or move in space.
But one should not think that once straightened out, the coral polyp will retain its shape indefinitely. Periodically, it is disturbed by the contraction of any muscle group. Contraction of the circular muscles, for example, elongates the body of the polyp and makes it thinner, contraction of the longitudinal muscles of the tentacles leads to their bending, and so on.
In case of danger, all muscles contract at once, water from the gastric cavity is squeezed out and the polyp shrinks or is drawn into the colony.
Colonies of coral polyps, as a rule, are not polymorphic, but dimorphism is observed in some octagonal corals - two types of polyp structure.
All corals are characterized only by the polypoid state. They do not form jellyfish. The gonads develop in the endoderm of the septa of coral polyps.
Class Coral polyps (Anthozoa)
Coral polyps are marine colonial, rarely solitary polyps that develop without generational change. They mostly live in warm tropical seas, where the water temperature is not lower than 20 ° C, and at depths of no more than 20 m, in conditions of abundant plankton, which they feed on. In total, about 6 thousand species of coral polyps are known. Many of them have a calcareous skeleton and are reef-forming.
Coral polyps, despite the general similarity of the structure with hydroids, differ from the latter in the following features:
The sizes of coral polyps are larger and they have a highly developed mesoglea,
Most species are well developed skeleton(horny or calcareous). The skeleton may be external, formed by the ectoderm, or internal, formed in the mesoglea;
- touring cavity divided by septa into chambers. There is an ectodermal pharynx with flagellar grooves-siphonoglyphs that provide water flow in the gastric cavity;- gonads formed in the endoderm. Reproduction is asexual and sexual. development with metamorphosis. Larva - planula. There is no alternation of generations;
Available muscle cells, forming longitudinal and transverse muscles;
- nervous system forms a dense plexus on the oral disc;
The ray symmetry is broken and there is a transition to two-beam, or bilateral, symmetry.
Rice. 96. The structure of a six-rayed coral polyp (according to Pfurgsheller): 1 - tentacles, 2 - mouth, 3 - pharynx, 4 - septa, 5 - plantar plate, 6 - calyx, 7 - scleroseptae, 8 - polyp tissues
Rice. 97. Formation of the internal skeleton in eight-ray polyps (according to Hadorn): 1 - tentacles, 2 - skeletal needles at the base of the tentacles, 3 - stomach with septa, where eggs ripen, 4 - skeletal cords, 5 - mesoglea, gastric canal in the trunk of the colony, surrounded by a skeleton, 6 - the trunk of the colony
There are two subclasses of modern coral polyps: Octocorallia and Hexacorallia, between which there are significant differences in organization. Therefore, in characterizing the morphology and physiology of coral polyps, it is more convenient to give a comparative outline of the organization of Octocorallia and Hexacorallia.
Comparative morphophysiological characteristics of 6- and 8-ray coral polyps. The body of polyps is cylindrical. Single polyps are attached to the substrate with their soles, and colonial colonies to the body are attached to the coenosarca. On the oral pole of the polyp there is a mouth, always surrounded by hollow tentacles (Fig. 96). By the number of tentacles, it is easy to distinguish subclasses of coral polyps: 8-rayed ones always have eight tentacles and they are pinnate, with lateral outgrowths, while 6-rayed tentacles are smooth and their number is a multiple of six (Fig. 96, 97).
The gastric cavity is complex. The mouth leads into a unidirectionally flattened pharynx with a folded ectodermal lining. Octocorallia at one end of the pharyngeal fissure has siphonoglyph- groove lined with ciliated epithelium. Hexacorallia has two siphonoglyphs - in both corners of the pharyngeal fissure. Siphonoglyphs ensure the flow of water through the gastric cavity. The slit-like pharynx and the presence of 1-2 siphonoglyphs violate the radial symmetry of the polyps, and therefore, in 8-ray polyps, only one, and in 6-ray polyps, only two planes of symmetry can be drawn. The pharynx leads to the gastric cavity, which is subdivided
Rice. 98. Cross sections through the eight-beam and six-ray polyps(A - according to Hickson, B - according to Hyman): 1 - pharynx, 2 - pharyngeal cavity, 3 - siphonoglyph, 4 - ventral guiding chamber, 5 - septum, 6 - muscular roller of the septum, 7 - dorsal guiding chamber, 8 - internal chambers between septa of the first order, 9 - inner chambers between secondary septa, 10 - intermediate chambers, 11 - ectoderm, 12 - endoderm, mesogley blackened
radial partitions - septa. Septa are lateral folds of the endoderm, each fold respectively consisting of two layers of endoderm, between which there is a mesoglea with muscle cells. The septa adhere to the pharynx with a free edge, and do not close below the pharynx, forming the stomach. The edges of the septa are thickened, corrugated, seated with stinging and digestive cells, forming mesenteric filaments. Their free ends are called acontions. The prey that enters the stomach of the polyp is tightly wrapped with mesenteric filaments, killed and gradually digested under the influence of digestive enzymes. The presence of septa increases the digestive surface in polyps. The number of septa and their location are different in the two subclasses (Fig. 98).
Octocorallia has eight septa with muscular ridges. Pairs of septa extending from two corners of the flattened pharynx are called guiding chambers. The guiding chamber opposite the single siphonoglyph differs in that the muscular ridges in its septa are turned inward. This chamber is conditionally called "ventral". On the septa of the opposite "dorsal" chamber, the ridges face outwards from the chamber. Thus, the location of the muscular ridges in the septa of Octocorallia also breaks the radial symmetry.
Hexacoralha has many septa, at least 12, and their number is a multiple of six. The muscle ridges in the guiding chambers are turned outward and do not violate the two-beam symmetry determined by the shape of the pharynx and two
siphonoglyphs. Septa in 6-beam polyps form gradually. Initially, there are six pairs of first-order septa that adhere to the pharynx. Between the septa of each pair, the main chambers are formed, and between them - intermediate ones, in which additional pairs of second-order septa are formed, etc. (Fig. 98).
The nutrition of coral polyps is varied. Many feed on plankton or catch small animals with their tentacles. Large single polyps - Anemones (Actinia) are able to catch large animals: fish, shrimp. Well, in recent times it turned out that some species of coral polyps live due to symbiosis with unicellular algae that live in their mesoglea.
For coral polyps, leading mainly an attached lifestyle, the presence of a skeleton is characteristic, which is formed differently in different subclasses.
In 8-ray polyps, the skeleton is internal and is formed in the mesoglea, it can be horny or calcareous. Skeletal elements (Fig. 99) are formed in scleroblast cells. The skeletal needles may fuse with each other or be joined by the horny substance to form the skeleton of the colony. For example, in the noble coral (Corallium rubrum), the skeletal trunk of the colony is calcareous, purple in color. From above, the branch of the colony is covered with ectoderm. The internal skeleton is permeated with a network of endodermal channels connecting all members of the colony (Fig. 97).
In 6-beam polyps, the skeleton is external, secreted by the ectoderm, less often internal or absent. The growth of the outer skeleton around a young polyp comes from the area of the sole, where the plantar plate first appears, and calcareous septa - sclerosepts - form on it, and then a calyx is formed - the theca, which protects the entire polyp to the level of the tentacles. The skeleton is often overgrown with folds of skin from above and gives the impression of being internal.
There are polyps without a skeleton, such as sea anemones. In many 8-ray polyps, the skeleton is poorly developed and is replaced by a hydroskeleton - the turgor of the colony, provided by the filling of the gastric cavity with water.
Reproduction and development. Polyps can reproduce asexually: by budding, division in the transverse and longitudinal directions.
Before sexual reproduction, gonads mature on septa in the endoderm. Polyps are usually dioecious. Spermatozoa through ruptures in the wall of the gonads exit into the gastric cavity, and then out and penetrate through the mouth into the cavity of the female. Fertilized eggs develop for some time in the mesoglea of the septum. Planula larvae usually leave the parent polyp, and then settle on a solid substrate and turn into polyps (Fig. 100, 5). In many coral polyps, development proceeds without metamorphosis and the planula larva does not form.
Overview of subclasses and orders of coral polyps. In total, five subclasses of coral polyps are known, of which three subclasses are known only in the fossil state (Tabulata, Rugosa, Heliolitoidea). Two subclasses are represented modern forms(Octocorallia and Nexocoratha) (Fig. 101, 102).
Subclass Eight-pointed corals (Octocorallia)
Eight-pointed corals have eight tentacles, eight septa, and an internal skeleton. There is a violation of radial symmetry to bilateral due to the presence of one siphonoglyph and the location of muscular ridges in the septa (Fig. 98 A).
Detachment Alcyonaria (Alcyonaria)- the most numerous, including about 1300 species of marine polyps. Most of them are soft corals, without a developed skeleton, with separate spicules scattered in the mesoglea. They form colonies various forms: branched, lobed, spherical. Alcyonaria colonies - "hands" (Fig. 103) can serve as an example of soft corals. Only some species of the genus Tubipora, an organ, have a developed calcareous skeleton, which forms tubules in the mesoglea, welded together by transverse plates. Their skeleton is vaguely shaped like an organ, hence their name. Organs form large spherical colonies and participate in reef formation. Corals of the genus Versemia fruticosa are common in the White Sea. Alcyonaria often form dense thickets on rocky soils.
Order Horn corals (Gorgonacea) make up polyps with an internal horny skeleton. It is also a species-rich order (1200 species), found mainly in tropical areas, but some of them have adapted to living in polar regions. Fan-shaped colonies form polyps of the genus Gorgonia, called the fan of Venus.
Rice. 101. Eight-pointed corals (according to Dogel): A - Alcyonaria Gersemia, B - Pennatula sea pen, C - Leptogorgia horn coral
Among the gorgonians are commercial red corals (Corallium rubrum) and species close to it, mined in the Mediterranean, Red and other seas. Their organic skeleton is impregnated with lime and has various shades of red. Valuable jewelry is made from red coral.
Order Sea feathers (Pennatulacea). Sea feathers form colonies of a feather-like form: with a thick trunk, on which polyps are located on the sides in regular rows. The number of species is small (300). Some species are common in Arctic Ocean, and among them there are the largest colonies up to 2.5 m high (Umbrella encrinus). Pennatula colonies are capable of glowing. Sea feathers, unlike other coral polyps, do not adhere to the substrate. They anchor in the ground, and sometimes swim from place to place.
Subclass Six-pointed corals (Hexacorallia)
Six-pointed corals have many smooth tentacles, the number of which is a multiple of six. The gastrovascular cavity is divided by a complex system of septa, the number of which is also a multiple of six. Six-beam symmetry is broken to two-beam due to two siphonoglyphs and the slit-like shape of the pharynx. Often the skeleton is external, calcareous, rarely absent. There are five orders of six-ray corals.
Squad of anemones (Actinaria) includes mainly large forms of single polyps, devoid of a skeleton. Anemones are able to move slowly on the sole. These are active predators, sometimes even eating small fish. They are often brightly colored and are called sea anemones. Some anemones are in symbiosis with hermit crabs, which serve them for movement, and anemones with stinging properties protect hermits from enemies (Fig. 104).
Order of Ceriantharia (Ceriantharia)- solitary burrowing polyps with strong muscles and no skeleton.
Detachment of Zoantaria (Zoantharia)- solitary and colonial polyps with underdeveloped muscle cells.
Detachment Antipatharia (Antipatharia) form pinnate colonies with an axial horny skeleton. This includes commercial black coral, from the skeleton of which various artistic products are made: pipes, cane handles, knives.
Order Madrepore corals (Madreporaria)- the most extensive and includes more than 2500 species. This includes both solitary and colonial polyps. All madreporaceae are characterized by the presence of a powerful calcareous skeleton. This group of corals are the main reef builders. These include medulla (Leptoria) in the form of hemispheres with bizarre furrows, mushroom corals (Fungia), etc.
Coral reefs and their origin. Mass settlements of coral polyps with a calcareous skeleton form reefs. The reef consists mainly of madreporous polyps, but six-ray corals are also partially involved, as well as other animals with a skeleton: sponges, bryozoans, mollusks, etc.
Coral reefs are peculiar ecosystems characterized by a special composition of autotrophic and heterotrophic organisms that are interconnected food chains and other forms of interspecies relations. The population of coral reefs is so large and diverse that they are called marine "oases". These are reserves of marine fauna and flora, they deserve human protection.
Reef-building coral polyps are distributed only in the tropical regions of the World Ocean, as they need normal ocean salinity(not less than 35% ppm), high and constant water temperature (not less than 20°С). In addition, corals are sensitive to light and water saturation with oxygen and, therefore, are found in shallow water and usually do not go to a depth of more than 50 m. The dependence of the distribution of corals on light is determined by their symbiosis with unicellular algae - symbiodiniums, or zooxanthellae, inhabiting the cells of the endoderm of polyps. The mutual benefit of their coexistence is as follows. Algae receive protection from corals and carbon dioxide (respiratory products) for photosynthesis, as well as some deficient in sea water nitrogen and phosphorus compounds from polyp dissimilation products. Coral polyps, in turn, receive oxygen from algae, which is necessary for respiration, as well as for activating the processes of skeleton formation. In addition, polyps partially feed on algae, but not in the way that was previously thought - by digesting them in the cytoplasm, but through the direct use of photosynthesis products coming directly from algae cells. Symbiosis is also based on pace life cycles these types. Like all protozoa, zooxanthellae have a diurnal rhythm of reproduction, while corals exist for a long time. dying
algae are digested in the cytoplasm of the polyp. Thus, this system is based on waste-free process. At the same time, the dependence of coral polyps on zooxanthellae is especially great, without which they die.
Reefs are coastal, barrier and atolls - ring-shaped coral islands. For the first time, the hypothesis about the origin of coral reefs was proposed by Charles Darwin (1836). He applied the method of historical geology of secular land fluctuations to explain the formation of coral islands. In his opinion, all types of reefs were formed as a result of land subsidence (Fig. 105). If the island, surrounded by a coastal reef, gradually sinks, its shores recede from the reef, which completes itself to the surface of the ocean and turns into a barrier reef. When the island is completely submerged, a ring remains from the former barrier reef, i.e., a coral island is formed - an atoll, which is then gradually populated by plants and animals. There are many other hypotheses about the origin various types reefs, however, the hypothesis of Ch. Darwin remains the most reasoned and has stood the test of time. At present, this hypothesis is supplemented by new scientific data. It is assumed that the change in land level depends not only on its subsidence, but also on changes in ocean level during periods of glaciation or melting. ice caps at the poles. From the dying coral reefs, immersed in the ocean, sedimentary rocks arose - coral limestones. In the Paleozoic, these rocks were formed by subclasses of corals Rugosa and Tabulata, and starting from the Mesozoic, mainly by madrepore polyps.
Coral polyps are a class of marine invertebrates belonging to the intestinal type. These are colonial or rarely solitary polyps that live in the seas. Currently, two subclasses are distinguished: eight-ray and six-ray coral polyps. The first group includes colonial organisms with 8 feathery tentacles (red coral, sea pen, organ). Polyps of the second group, mostly solitary, have a number of tentacles that is a multiple of six (anemones, stony corals). In total, about six thousand species of coral polyps are known, distributed in the seas from high salinity in different climatic zones. Most coral polyps live in warm tropical seas with a water temperature of at least 20 degrees, at a depth of up to 20 m, provided there is an abundance of food - plankton.
The most primitive firms have been found in strata dating back to the Cambrian period. At first mesozoic era on Earth, subclasses of eight-ray and six-ray coral polyps appeared.
Hydroid coral polyps differ from other representatives of the class in a more complex structure, the presence of a pharyngeal tube located inside the body and ending in a mouth opening, the division of the body by radial septa into separate cavities, and a more perfect structure of the body as a whole. The vast majority of coral polyps form colonies, representatives rare species single.
These organisms have a typical cylindrical body shape. At the rear end of the body there is a flat round surface, the so-called "sole", with which polyps are attached to objects under water. On the cutting edge a mouth opening is distinguished with one or several rows of tentacles around the circumference. The mouth opening opens into a wide pharyngeal tube - a kind of stomach. The structure of the stomach wall is three-layer, similar in structure to the wall of the animal's body. Undigested food debris is expelled external environment through the mouth. The gastric cavity is multi-chamber due to its division into parts by radial partitions. During the day, polyps squeeze their tentacles, and at night they straighten and catch prey - various smallest animals of plankton. Single polyps large sizes they can also catch larger animals - shellfish, fish.
Some species of coral polyps have stinging organs in the form of filaments that perform a protective function, which, in case of danger, are thrown out through the mouth opening or through holes in the wall of the polyp's body. In the structure of the body wall of a coral polyp, three layers are distinguished - ectoderm, mesoderm and endoderm. The ectoderm covers the outside of the entire body of the individual and is the inner lining of the pharyngeal tube. The ectoderm consists of three layers: epithelial, nervous and muscular. Many representatives of this group of animals have a calcareous skeleton of ectodermal origin, giving rise to horny and calcareous deposits that form a polyp forest. The mesoderm is a gelatinous substance that fills the cavities of coral polyps and includes spindle-shaped or star-shaped cells and fibers. In the mesoderm, calcareous bodies may also be present, which sometimes join together to form a dense calcareous mass. The endoderm is divided into the same three layers as the ectoderm, but the structure of the layers of the ectoderm and endoderm is different. special bodies These organisms do not have feelings.
Reproduction of coral polyps is carried out both asexually and sexually. asexual reproduction occurs by budding. The development of germ cells occurs in the endoderm of the mesenteries. Young organisms leave the mother at the planula stage, floating in the water column. certain time, and then attached to the bottom during the transformation into an adult.
Extensive colonies of coral polyps are formed with incomplete budding. Corals in the seas are motionless and outwardly look like branches of plants. But each coral branch is nothing but accumulations of small animals - coral polyps. These clusters are called colonies. Coral "grows" with the birth of young polyps. If conditions environment favorable, coral growth is about 1 cm per year. With the growth of colonies of coral polyps in the tropics, barrier reefs, atolls (coral islands). The vast majority of coral polyps in the reefs are six-pointed corals. Due to their calcareous skeleton, they are widely used as a building material. The Mediterranean Sea is home to red and black octagonal corals whose skeletons are highly valued as ornaments.
Coral polyps are a class of marine invertebrates belonging to the intestinal type. These are colonial or rarely solitary polyps that live in the seas. Currently, two subclasses are distinguished: eight-ray and six-ray coral polyps. The first group includes colonial organisms with 8 feathery tentacles (red coral, sea pen, organ). Polyps of the second group, mostly solitary, have a number of tentacles that is a multiple of six (anemones, stony corals). In total, about six thousand species of coral polyps are known, distributed in seas with high salinity in different climatic zones. Most coral polyps live in warm tropical seas with a water temperature of at least 20 degrees, at a depth of up to 20 m, provided there is an abundance of food - plankton.
The most primitive firms of coral polyps have been found in beds dating back to the Cambrian period. Since the beginning of the Mesozoic era, subclasses of eight-ray and six-ray coral polyps have appeared on Earth.
Hydroid coral polyps differ from other representatives of the class in a more complex structure, the presence of a pharyngeal tube located inside the body and ending in a mouth opening, the division of the body by radial septa into separate cavities, and a more perfect structure of the body as a whole. The vast majority of coral polyps form colonies, representatives of rare species are solitary.
These organisms have a typical cylindrical body shape. At the rear end of the body there is a flat round surface, the so-called "sole", with which polyps are attached to objects under water. An oral opening with one or several rows of tentacles along the circumference stands out on the anterior margin. The mouth opening opens into a wide pharyngeal tube - a kind of stomach. The structure of the stomach wall is three-layer, similar in structure to the wall of the animal's body. Undigested food residues are removed outside into the external environment through the mouth. The gastric cavity is multi-chamber due to its division into parts by radial partitions. During the day, polyps squeeze their tentacles, and at night they straighten and catch prey - various smallest animals of plankton. Single polyps of large sizes can also catch larger animals - shellfish, fish.
Some species of coral polyps have stinging organs in the form of filaments that perform a protective function, which, in case of danger, are thrown out through the mouth opening or through holes in the wall of the polyp's body. In the structure of the body wall of the coral polyp, three layers are distinguished - ectoderm y, mesoderm y and endoderm y. Ectoderm a covers the outside of the entire body of the individual and is the inner lining of the pharyngeal tube. Ectoderm a consists of three layers: epithelial, nervous and muscular. Many representatives of this group of animals have a calcareous skeleton of ectodermal origin, giving rise to horny and calcareous deposits that form a polyp forest. Mesoderm a is a gelatinous substance that fills the cavities of coral polyps and includes spindle-shaped or star-shaped cells and fibers. In the mesoderm, calcareous bodies may also be present, which sometimes join together to form a dense calcareous mass. Endoderm a divided into the same three layers as the ectoderm a , but the structure of the ectoderm layers s and endoderm are different. These organisms do not have special sense organs.
Reproduction of coral polyps is carried out both asexually and sexually. Asexual reproduction occurs by budding. The development of germ cells occurs in the endoderm of the mesenteries. Young organisms leave the mother at the planula stage, floating in the water column for a certain time, and then attaching to the bottom during the transformation into an adult.
Extensive colonies of coral polyps are formed with incomplete budding. Corals in the seas are motionless and outwardly look like branches of plants. But each coral branch is nothing but accumulations of small animals - coral polyps. These clusters are called colonies. Coral "grows" with the birth of young polyps. If environmental conditions are favorable, coral growth is about 1 cm per year. With the growth of colonies of coral polyps in the tropics, barrier reefs, atolls (coral islands) are formed. The vast majority of coral polyps in the reefs are six-pointed corals. Due to their calcareous skeleton, they are widely used as a building material. The Mediterranean Sea is home to red and black octagonal corals whose skeletons are highly valued as ornaments.Coral reefs are a valuable ocean resource because of their beauty, variety of forms, and indispensability in their ecosystem. The sea, as it is also called, is perhaps the most massive and vivid expression of life in the aquatic environment.
They provide shelter for many marine life, serve as a food source for a myriad of organisms, shape the seafloor topography, and form island land masses. For a person, coral reefs are important not only as beautiful ones worth admiring during a vacation, but they also protect the coastline from large ocean waves, their skeletons form important Construction Materials- sand and limestone.
Coral ecosystems are called the pharmacy of the 21st century. On the basis of useful compounds that were found in this biocenosis, many medical preparations: antibacterial, tonic, digestive, cardiac, cosmetic, as well as medicines for treatment viral infections, asthma, skin cancer, arthritis.
The class of coral polyps includes more than 6 thousand main species. These marine invertebrates may be solitary or form colonies. They also differ in size, in the presence or absence of a skeleton, its shape and composition (calcareous or proteinaceous). Reef structures are capable of forming coral polyps of the Madreporidae order.
"Stone gardens" form not only these miniature animal organisms. Most coral polyps have mutually beneficial relationship with unicellular algae zooxanthellae that live inside the cells of an invertebrate. It is believed that these autotrophic protozoa are also involved in the construction of the coral skeleton. Other calcareous algae also play an important role in reef formation, they perform several functions: they create a reef frame, cement various damage and supply loose material. Some other animal organisms are also of importance for reef building, namely representatives of individual families of mollusks, polychaetes and sponges.
The mechanism of nutrition of polyps is interesting. About 90% organic matter, which form the microscopic zooxanthellae in algae is transferred to the host tissue. The second type of food is external. Coral polyps can capture and absorb previously stunned prey - microscopic zooplankton and small fish.
Coral polyps can reproduce in two ways: sexually and asexually. Isolation of male and female gametes also occurs in two ways. During the first, which is called "spawning into the ether", spermatozoa and eggs are simultaneously thrown into the water column in huge numbers. Above coral reef a protein "cloud" is formed, which attracts many predators that feed on plankton. Gradually, the larvae of polyps, planula, are carried by ocean currents. In the second method of sexual reproduction, only male free-swimming corals enter the water before meeting with a female coral.
These creatures are multifaceted: they can bud in several ways, divide transversely, and spread in broken fragments.
Coral reefs - unique phenomenon nature, beautiful and unique, but, unfortunately, very fragile. "Stone gardens" are extremely sensitive to changes in lighting, temperature, salinity and water pollution.
Human activity is one of the most serious threats to the existence of coral colonies, which in last years discolor and die at an accelerated rate. Only joint actions by many countries of the world can stop or at least slow down this process. Recently, marine protected areas have been created, in which, with the cooperation of authorities and scientists, fish catches are being reduced, and special measures are being taken to conserve reefs. There are also world organizations that are making efforts to solve this issue, they are developing ways to artificially form reefs and accelerate the growth of coral polyps.