Life forms of coral polyps. Characteristics and structure of coral polyps
The body of a coral polyp is usually cylindrical in shape and is not divided into a trunk and a leg. In colonial forms of coral polyps, the base is immersed in the common body of the colony - the coenosarc, and in solitary forms it turns into an attachment sole.
The tentacles of these organisms are always hollow, arranged in one or several closely spaced corollas.
There are two large groups of coral polyps - eight-rayed (Octocorallia) and six-rayed (Hexacorallia).
The first group always has eight tentacles and they are equipped with small outgrowths at the edges - pinnules; in the second group the number of tentacles is larger and, as a rule, a multiple of six.
The tentacles of six-rayed corals are almost always smooth and without quilts. The upper part of the polyp, between the tentacles, is called the oral disc. In its middle there is a slit-like mouth opening. The internal structure of coral polyps is much more complex than that of hydroid and scyphoid polyps. The mouth leads into a laterally compressed pharynx lined with ectoderm. Usually along one of the edges of the pharynx there runs a groove carrying cells with very long eyelashes - a siphonoglyph. Sometimes there are two siphonoglyphs, in such cases they are located on opposite narrow edges of the pharyngeal tube. The cilia continuously move and drive water into the intestinal cavity. The latter is divided into chambers by longitudinal partitions (septa).
In the upper part of the body of a coral polyp (in the pharynx area), the septa are complete (adhering with one edge to the body wall, the other to the pharynx) or incomplete (not reaching the pharynx). The septa have openings through which all the chambers communicate with each other.
In the lower part of the coral polyp (below the pharynx), the septa grow only to the body wall. As a result, the central part of the gastric cavity - the 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 a single siphonoglyph, the 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 opposing siphonoglyphs, as in sea anemones), ensures a constant change of water in the gastric cavity. As a result, fresh, oxygen-rich water constantly flows there, and along 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, eight-rayed corals always have eight septa and chambers, while six-rayed corals always have six.
Septa are laid gradually and always in pairs.
Like all coelenterates, corals are radially symmetrical. However, their internal organization also contains features of bilateral symmetry (laterally compressed pharynx and siphonoglyphs). Only one plane of symmetry can be drawn through the longitudinal axis of the pharynx, 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 others in the location of the muscular ridges. These chambers and the septa that form them are called guide chambers, by which the “dorsal” and “ventral” sides of the body of a coral polyp are conventionally determined.
The muscle cells of coral polyps separate from the ecto- and endoderm and pass into the mesoglea, forming a layer of longitudinal and transverse muscles in the walls of the body. 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 ridge of longitudinal muscles.
The mesoglea is represented in most six-rayed corals by a thin supporting plate. But in eight-rayed corals it reaches significant development, especially in the trunk and branches of the colony. The gelatinous substance of the mesoglea is strengthened by collagen elements and filled with a huge number of skeletal calcareous needles - spicules, or sclerites.
Thus, the mesoglea forms a strong support for the coral colony. At the same time, it is involved in the transport of nutrients, as it is penetrated by a dense network of endodermal canals connecting the individual intestinal cavities of coral polyps into one cavity. These same channels play an important role in the rhythmic change between the active and passive states of a colony of coral polyps.
The skeleton reaches significant development in many coral polyps. In eight-rayed corals, this is the internal, mesogleal skeleton, consisting of sclerites, which develop in special cells - scleroblasts. Sometimes the sclerites merge with each other or are united by an organic horn-like substance, forming the skeleton of a coral colony. It may also consist of pure horny substance.
Among the six-rayed 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 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 achieved in a different way. All polyps have a kind of hydroskeleton, which reaches the greatest perfection in coral polyps.
Thanks to the constant flow of water created by the siphonoglyphs, increased pressure arises in the gastric cavity, without which the coral polyp would have the shape of an empty two-layer sac. The polyp expands under the pressure of the fluid filling the gastric cavity. It can remain in this state for a very long time and with almost no energy expenditure. Meanwhile, in other animals such a tense state cannot last long, 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 expanded, the coral polyp will retain its shape indefinitely. Periodically, it is disrupted by the contraction of any muscle group. Compression of the circular muscles, for example, lengthens the body of the polyp and makes it thinner, contraction of the longitudinal muscles of the tentacles leads to their bending, etc.
In case of danger, all muscles contract at once, water from the gastric cavity is squeezed out and the polyp is compressed or pulled into the colony.
Colonies of coral polyps, as a rule, are not polymorphic, but some eight-rayed corals exhibit dimorphism - 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.
Coral polyps
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Brain Coral Diploria labyrinthiformis |
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Anthozoa Ehrenberg, 1831 |
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Corals live in the sea; they are motionless and resemble plant branches in appearance. However, these are not plants: each coral branch is a cluster of tiny animals, coral polyps. Such clusters are called colonies. Each polyp forms a protective calcareous shell around itself. When a new polyp is born, it attaches to the previous one and begins to build a new shell - this is how the coral “grows”. Coral “growth” is about 1 cm per year in favorable conditions. Large concentrations of corals form so-called coral reefs. Coral polyps live in warm tropical seas, where the water temperature is not lower than 20 ° C, and at depths of no more than 20 meters, in conditions of abundant plankton, which they feed on. Usually during the day the polyps shrink, and at night they stretch out and straighten their tentacles, with the help of which they catch various small animals. Large single polyps are capable of catching relatively large animals: fish, shrimp. Some species of coral polyps live due to symbiosis with autotrophic protozoa (single-celled algae) that live in their mesoglea. There are muscle cells that form longitudinal and transverse muscles. There is a nervous system that forms a dense plexus on the oral disc.
Taxonomy
There are two subclasses of modern coral polyps (eight-rayed and six-rayed), within which the following orders are distinguished:
- eight-rayed ( Octocorallia)
- Stolonifera
- soft corals ( Alcyonaria)
- horn corals ( Gorgonaria)
- sea feathers ( Pennatularia)
- six-rayed ( Hexacorallia)
- ceriantharia ( Ceriantharia)
- madrepore corals ( Scleractinia)
- sea anemones ( Actiniaria)
- zoantaria ( Zoanthidea)
- Corallimorpharia
- black corals ( Antipatharia).
Notes
see also
Links
- // - information about six-rayed corals
- // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). - St. Petersburg. , 1890-1907.
Wikimedia Foundation. 2010.
- Marilyn Manson
- Coral reefs
See what “Coral polyps” are in other dictionaries:
CORAL POLYPS- (Anthozoa), class marine. cnidarians. Colonial, less often single polyps; jellyfish do not form. Many have a calcareous or horny skeleton. Dept. individuals are usually cylindrical. forms, with their base fused with the colony or (single, capable of slowly... ... Biological encyclopedic dictionary
CORAL POLYPS- a class of marine invertebrates such as cnidarians. Many have a calcareous skeleton. Some colonial coral polyps (eg, madrepore corals) form coral reefs and islands. OK. 6000 modern species, widely distributed... Big Encyclopedic Dictionary
coral polyps- a class of marine invertebrates such as cnidarians. Many have a calcareous skeleton. Some colonial coral polyps (such as madrepore corals) form coral reefs and islands. There are about 6,000 modern species, widely distributed. *... encyclopedic Dictionary
coral polyps- koraliniai polipai statusas T sritis ekologija ir aplinkotyra apibrėžtis Duobagyvių (Coelenterata) tipo bestuburių gyvūnų klasė (Anthozoa), kurią sudaro coral polyps6000 rūšių. Sėslūs kolojininiai gyvūnai. Įvairaus dydžio (nuo kelių mm iki 1 … Ekologijos terminų aiškinamasis žodynas
Coral polyps- corals (Anthozoa) constitute the class of the phylum Coelenterates. They differ from hydroid polyps (see Hydromedusa) mainly by the existence of a pharyngeal tube protruding into the body and ending in an opening, and by the division of the internal cavity... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
Coral polyps- (Anthozoa) class of invertebrate animals such as coelenterates. Colonial or, less commonly, solitary marine organisms. The body of an individual is built according to the radial type of symmetry. The polyp is usually cylindrical; its foundation is either... Great Soviet Encyclopedia
There are amazing forms of corals. Some of them resemble underwater flowers. Each “twig” of such a flower consists of many individual polyps.
Class -Row - Alcionaria, Gorgonaria, Madreporaria, etc.
Basic data:
DIMENSIONS
Diameter: individual polyps up to 2 cm, colonies on average reach 3 m.
REPRODUCTION
They reproduce asexually through fission and budding. Colonies also produce sperm and eggs. Fertilized eggs hatch into larvae.
LIFESTYLE
Habits: lead an attached lifestyle on the seabed; there are individual individuals and columns.
Food: living plankton. Madrepore corals feed on waste products of algae that live in their bodies.
RELATED SPECIES
The class of coral polyps includes more than 6,500 species of madrepore corals, sea feathers, gorgonians, sea anemones and many other animals. Jellyfish are not their close relatives.
Coral polyps are unique underwater architects. In the shallow waters of tropical seas, they form entire fabulous forests and clearings, which are an ideal place for the existence of many marine animals.
FOOD
Coral polyps are active at night. They feed on plankton and organic particles in the water. Corals catch prey using paralyzing stinging cells, the stinging fibers of which are studded with small hooks. Many coral polyps live in symbiosis with unicellular algae. Algae receive from the coral carbon dioxide and nitrogen and phosphorus compounds necessary for photosynthesis. Corals use both the main and by-products of photosynthesis - organic matter and oxygen. There is a continuous exchange of phosphorus between the owner and the cohabitant.
REPRODUCTION
A coral colony grows as a result of budding, that is, asexual reproduction, when a small shoot appears on an old individual, which turns into a new young individual. Buds appear on tissues that connect individuals in a colony, or that grow on the base of the mother polyp. During sexual reproduction in the first phase of the month after the full moon, corals release billions of eggs and sperm into the water. All polyps of the same species release their reproductive cells into the water at the same time. Fertilized eggs develop into small larvae that become part of the zooplankton.LIFESTYLE
Coral polyp colonies are a large number of individual polyps firmly attached to each other, which together form branches, horns or other complex shapes. Individual polyps have the shape of a short cylinder with an opening at the upper end, surrounded by a corolla of tentacles. Special channels connect several layers of cells and transmit digested food to other members of the colony. Coral polyps can be divided into two groups. The first is formed by polyps that build a calcareous skeleton; they are called madrepore corals. The second group includes polyps with feathery tentacles, such as gorgonians, sea feathers and sea anemones. Coral polyps strengthen their massive skeleton with a special layer formed by the sole. Thanks to such a strong base, in case of danger, the polyp can instantly pull the body into the calcareous skeleton. Other types of coral are like large fans, they can bend and sway with sea currents because their skeleton is created by individual calcareous rods that are embedded in a jelly-like substance. HABITAT
Most often, coral polyps are found in shallow, warm seas. Typically, the water temperature here does not drop below -16 C. For madrepore corals, the most optimal temperature is within 23 C. If the temperature changes significantly, the corals may die. Some types of coral polyps require sunlight to reach them. Madrepore corals find ideal conditions at depths of up to 45 m, soft and mobile alcyonari are found up to a depth of 100 m. Madrepore corals do not settle near river mouths because they do not survive in fresh, running water. “Hunting” coral polyps willingly settle in the area of sea currents. Thin but elastic gorgonians perfectly tolerate light waves of water (their columns are elastic and bend), while hard but fragile madrepore corals break under the influence of water or waves. DID YOU KNOW THAT...
- Corals “fight” among themselves for territory. Coral polyps shoot out stinging fibers from their neighbors or grow so that they block their light.
- Noble coral is mined in large quantities in the Mediterranean Sea. Jewelry is made from it.
- Red coral is colored in various shades of red - from light pink to dark red. The most expensive coral is the rare black coral.
TWO NORTH ATLANTIC CORAL
Alcyonarians: This is a coral that lives alone. It looks like an anemone, so it is easy to confuse it with it. The animal reaches 25 mm in diameter, its transparent tentacles grow in a corolla around the slit-like mouth opening.Gorgonians: lives in the Atlantic Ocean, in waters warmed by the Gulf Stream. Colonies of this polyp form a horny, lime-soaked skeleton.
PLACES OF ACCOMMODATION
They are found in all tropical and subtropical seas, as well as in some temperate zones. Reefs form on the warmer eastern parts of continents.
PRESERVATION
Corals are very fragile animals, so they are often destroyed by the anchors of ships that drag along the bottom.
TYPE Coelenterate
The type of coelenterates includes lower multicellular animals, the body of which consists of two layers of cells and has radial symmetry. They live in marine and fresh water bodies. Among them there are free-swimming (jellyfish), sessile (polyps), and attached forms (hydra).
The body of coelenterates is formed by two layers of cells - ectoderm and endoderm, between which there is mesoglea (non-cellular layer). Animals of this type have the appearance of an open sac at one end. The hole serves as a mouth, which is surrounded by a corolla of tentacles. The mouth leads into the 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. In coelenterates, a diffuse type nervous system appears for the first time. It is represented by nerve cells randomly scattered in the ectoderm, which touch with their processes. In swimming jellyfish, a concentration of nerve cells occurs and a nerve ring is formed. Reproduction of coelenterates is carried out both asexually and sexually. Many coelenterates are dioecious, but hermaphrodites are also found. The development of some coelenterates is direct, while in others it is with a larval stage.
There are three classes in the type:
1. Hydroid
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 the integumentary tissue. There is no muscle tissue as such; its role is also played by skin-muscle cells.
The ectoderm contains stinging cells, which are mainly located on the tentacles. With their help, the hydra defends itself and also detains and paralyzes prey.
The nervous system is primitive, diffuse. Nerve cells (neurons) are evenly distributed in the mesoglea. Neurons are connected by strands, but do not form clusters. Sensory 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 secreting adhesive substances are concentrated mainly in the ectoderm of the sole and tentacles. They also synthesize enzymes that help digest food.
Digestion in hydra occurs in the gastric cavity in two ways - intracavitary, with the help of enzymes, and intracellular. Endoderm cells are capable of phagocytosis (capturing food particles from the gastric cavity). Some of the skin-muscle cells of the endoderm are equipped with flagella that are in constant motion, which rake particles towards the cells. They organize pseudopods, thereby capturing food. Undigested food remains are removed from the body through the mouth.
Between all these cells there are small undifferentiated intermediate cells that can, if necessary, turn into any other types of cells; regeneration (the process of restoring lost or damaged parts of the body) occurs due to these cells.
Reproduction:
· Asexual (vegetative). In summer, under favorable conditions, budding occurs.
· Sexual. In autumn, with the onset of unfavorable conditions. The gonads form as tubercles in the ectoderm. In hermaphrodite forms they are formed in different places. The testes develop closer to the oral pole, and the ovaries closer to the sole. Cross fertilization. The fertilized egg (zygote) is covered with dense membranes and falls to the bottom, where it overwinters. The following spring, a young hydra emerges from it.
Class scyphoid
The class of scyphoid jellyfish is found in all seas. There are species of jellyfish that have adapted to live in large rivers flowing into the sea. The body of scyphojellyfish has the shape of a rounded umbrella or bell, on the lower concave side of which an oral stalk is placed. The mouth leads to a derivative of the dermis - the pharynx, which opens into the stomach. Radial canals diverge from the stomach to the ends of the body, forming the gastric system.
Due to the free lifestyle of jellyfish, the structure of their nervous system and sensory organs becomes more complex: clusters of nerve cells appear in the form of nodules - ganglia, balance organs - statocysts, and light-sensitive eyes.
Scyphojellyfish have stinging cells located on the tentacles around the mouth. Their burns are very sensitive even for humans.
Reproduction:
Jellyfish are dioecious; male and female reproductive cells are formed in the endoderm. The fusion of germ cells in some forms occurs in the stomach, in others in water. Jellyfish combine their own and hydroid characteristics in their developmental features.
Among the jellyfish there are giants - Physaria or Portuguese man-of-war (from 3 m or more in diameter, tentacles up to 30 m).
Meaning:
· Consumed as food
· Some jellyfish are deadly and poisonous to humans. For example, when bitten by a cornet, significant burns can occur. When bitten by a cross, the activity of all systems of the human body is disrupted. The first encounter with a cross is not dangerous, the second is fraught with consequences due to the development of anophiloxia. A tropical jellyfish sting 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, with the help of the sole, is attached to underwater objects (in solitary forms) or directly to the colony. 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 anemone has no skeleton).
All coral polyps are divided into two groups: eight-rayed and six-rayed. The former always have eight tentacles (sea feathers, red and white corals). In six-rayed species, the number of tentacles is always a multiple of six (anemones, madrepore corals, etc.).
Reproduction:
Coral polyps are dioecious animals; fertilization occurs in water. From the zygote a larva develops - a planula. The planula attaches to various underwater objects and turns into a polyp, which already has a mouth and a corolla of tentacles. In colonial forms, budding subsequently occurs, and the buds are not separated from the mother’s body. Colonies of polyps participate in the formation of reefs, atolls, and coral islands.
These are exclusively marine, mostly heat-loving organisms. There are both solitary and colonial forms (the latter more often). There is no jellyfish form in the development cycle.
Compared to hydroid polyps, they are more complex. An individual coral polyp of a colony resembles a hydra in appearance, but is usually located in the calyx of its exoskeleton. The complication of their organization is the presence of a pharynx, dividing the intestinal cavity into chambers using vertical partitions, which increases the surface area for secretion and absorption of food.
There is a separation of the muscular and epithelial parts of the epithelial-muscle cell and the formation of differentiated muscle tissue.
The nervous system is of a diffuse type, but with a greater concentration of nerve cells at the mouth opening than in Hydra.
Coral polyps reproduce both asexually and sexually. The gonads develop in the endoderm of the intestinal septa.
The fertilized egg begins to fragment. First, it divides in two, then each of the resulting cells, in turn, also divides, and so on. As a result, a large number of small cells are formed, arranged in one layer and looking like a small hollow ball. Following this, some of the cells are immersed inside, resulting in a two-layer embryo. The endoderm is subsequently formed from its inner layer, and the ectoderm of the future polyp is formed from the outer layer. The ectoderm is covered with numerous small cilia, with the help of which the embryo gains the ability to swim; from this moment it turns into a larva called planula. The planula is unable to feed or reproduce. It swims in the water column for some time, then sits on the bottom and attaches itself to it with its front end. Soon after this, a mouth opening breaks through at the posterior end (now upper) end of the planula and a corolla of tentacles is formed. This is how the first polyp appears. In colonial forms, this polyp soon buds on itself other polyps, which in turn follow, etc. a colony appears. Once the colony reaches a certain stage of development, the polyps that make it up begin to reproduce also sexually, forming eggs. This completes the cycle.
Among solitary soft coral polyps, widely known sea anemones, which are called sea flowers for their varied colors.
Colonial forms are numerous and varied (spherical, tree-like, etc.). Their skeleton is made of calcium carbonate. Calcareous skeletons of colonial forms form reefs and oceanic islands - atolls. Organic red skeletonnoble coral used for making jewelry.
Control questions:
What structural features are characteristic of coelenterates (using the example of Hydra)?
How does hydra feed?
What types of reproduction does hydra have?
What common features and differences do representatives of the classes Scyphoid and Coral polyps have?
How do Scyphoids reproduce?
