Stinging animals. Type Coelenterates, or Cnidarians

(Greek cnidos - thread)

The phylum cnidarians, or cnidarians, include numerous diverse animals, among which the most famous are hydra, jellyfish and corals. They are planktonic or benthic, immobile, predominantly attached lifestyle,

settling in colonies or alone. These are exclusively aquatic, often marine, less often brackish or freshwater organisms. Benthic forms live at all depths, right down to the abyssal. The body shape is different. The embryo develops two layers of cells: ectoderm and endoderm. Due to the ectoderm, the adult individual develops an epidermal layer consisting of muscle, nerve, stinging, skeletal-forming and other cells. Due to the endoderm, the inner gastric layer is formed, consisting mainly of various digestive cells. In an adult animal, between the epidermal and gastric layers, a structureless gelatinous layer is formed - mesoglea, formed due to cellular secretions and the introduction of various cells of ecto- and endodermal origin. In the adult state, cnidarians are represented by two life forms: polyps and jellyfish. Jellyfish have the shape of an umbrella, bell or mushroom, and single polyps are most often sac-shaped (Fig. 107). Colonies of polyps of various shapes; they are, as a rule, polymorphic, since they consist of individuals of different structures that perform different functions. Polyps are bottom organisms, mostly attached, in rare cases they can lead a planktonic lifestyle, for example siphonophores, or move along the bottom, for example hydra and

Rice. 107. Longitudinal and cross sections of a hydroid polyp (a, b), a scyphoid jellyfish (c, d) and a coral polyp (e, f) g - pharynx, gs - gastric (inner) layer, m - mesoglea, p - digestive cavity, r - mouth, s - skeleton, sch - tentacles, es - epidermal (outer) layer

anemones. Many polyps have a skeleton: mineral (calcareous) or organic (chitinous and protein), less often agglutinated. Jellyfish are planktonic organisms; as an exception, sessile bottom forms are found.

Cnidarians have five functional systems: digestive, muscular, nervous, reproductive, and skeletal. Systems such as excretory, circulatory and others are absent. The digestive cavity itself first appears in the evolution of the animal kingdom in cnidarians, therefore for a long time this type was called Coelenterata (Greek koilos - full; enteron - intestine, entrails) - coelenterata. The digestive cavity is saccular, folded or non-folded. A single oral opening leads into it, which serves as both oral and anal. The mouth opening of polyps and jellyfish is surrounded by tentacles, the number of which can reach 100; they form one or more cycles. Tentacles - with a large number of stinging capsules, each of them has a spirally coiled thread inside with a point at the end. When defending or attacking, the thread unfolds with lightning speed and, penetrating like a harpoon into the victim’s body, paralyzes it. With the help of tentacles, food is transferred to the mouth.

The type of cnidarians is divided into three classes: Hydrozoa, Scyphozoa and Anthozoa, which differ from each other in many characteristics, but primarily in the structure of the digestive system and reproductive characteristics.

Cnidarians reproduce sexually and asexually. In the first case, after the formation of reproductive products and fertilization, the process of fragmentation of the egg begins and a two-layer planktonic larva, the planula, appears. Then the planula settles to the bottom and the polyp begins to grow. Asexual reproduction occurs in two main ways: fission and budding. During division, regeneration (restoration) of the missing parts occurs, resulting in the appearance of new individuals. During budding, outgrowths appear in various parts of the animal - buds, the further growth of which leads to the formation of a new individual. The result of asexual reproduction is the formation of polyp colonies. The emergence of jellyfish is also associated with asexual reproduction.

Cnidarians include hydra, jellyfish and sea anemones. Largest part Such organisms live in seas and oceans, but hydras are also found in freshwater bodies. Corals and sea anemones inhabit mainly warm seas.

The smallest are some hydras, the size of which is about 1 mm, while the largest can be called the hairy jellyfish Cyane, the length of its tentacles can reach 40 meters, and the diameter of the body exceeds 2 meters.

The body of any cnidarian contains a single large cavity, at one end of which there is a mouth opening surrounded by tentacles. The body cavity is surrounded by a wall consisting of 2 layers of cells and a gelatinous substance between them. The inner cell layer forms the tissue involved in the digestion of food. The outer layer of cells contains muscle fibers, so organisms can respond with movement to external stimuli. From nerve cells a network, the simplest nervous system, is formed. In the outer layer of the body and tentacles there are special stinging cells. Using part of such a cage, which resembles a harpoon, the animal injects poison into the body of the victim or enemy. All cnidarians are carnivorous and feed by drawing prey to their mouths with their tentacles.

Forms of existence

Animals have 2 forms of existence: polyps and jellyfish. The body shape of the polyp (hydra, sea anemone and coral) resembles a vase. The polyp's mouth opens upward, and with the other end it is attached to the bottom of the reservoir or to other surfaces. And the body of a jellyfish resembles an umbrella or an inverted bowl. The jellyfish's mouth opens downwards and it drifts freely in the water. Some cnidarians, for example, long-eared aurelia, at the adult stage they are jellyfish, and at the larval stage they are polyps. This type of aquatic animal leads a different lifestyle.

Lifestyle

Anemones are immobile animals; they live at the bottom of a reservoir, fixed in one place. They live separately and, thanks to their brightly colored tentacles, resemble a plant rather than an animal. The wide, dome-shaped body of jellyfish is well suited for swimming in water. Jellyfish move by swinging on the waves or using the current, alternately contracting and relaxing their body: the water pushed out from under the dome-shaped body pushes the animal forward. Some of them are extremely poisonous and their touch can be fatal even to humans. Hydroids are attached to plants, stones, etc. The location is changed extremely slowly: on the surface they are alternately attached first with the sole and then with the tentacles, i.e. they move as if tumbling.

Like some of the animals listed above, corals also live fixed in one place. Most of their species form a hard calcareous skeleton around the lower part of the polyp. Corals live in large colonies in which calcareous skeletons are united. And they, in turn, anchor new corals, thanks to which colonies can reach impressive sizes. Despite the fact that colonies grow only a couple of centimeters per year, over several thousand years they can form coral islands of various shapes.

If the water is contaminated or if there is too much high temperature The algae that live in symbiosis with corals die, which leads to the death of the corals, leaving only a lifeless white skeleton of the colorful colonies.

Update: Previously, coelenterates and cnidarians were synonymous names for this type of animal. But now the coelenterates are called a supertype, which includes the type of cnidarians and the type of ctenophores. So far I have corrected only the title of the article, but soon I will completely redo it, but for now you will encounter coelenterates in the text as a synonym for cnidarians. Be patient.

Among the cnidarians there are creatures that resemble flowers, bushes, trees several meters high, cauliflower and even grass lawns. The ancient Romans and Greeks believed that corals are sea flowers that immediately petrify in the air (see Ovid “Metamorphoses”). But many modern Jews, residents of Eilat, even after repeated visits to the Underwater Observatory, do not believe that these are animals. These are such stiff-necked people.

Cnidaria allocated to separate type animals, including about 9000 species. The phylum is divided into three classes: hydroids ( Hydrozoa , about 3000 species), scyphoid jellyfish ( Scyphozoa , 200 species) and coral polyps ( Anthozoa , 6000 species). In each of the classes there are sessile plant-like animals, and there are also active swimmers/crawlers.

For zoologists, coelenterates are notable for the fact that they have real tissues for the first time in the evolution of the animal world. This group got its name because the body of the coelenterates has the appearance of a bag, open at one end. Digestion occurs in the cavity of the bag, and the hole serves as both an entrance (that is, the mouth, in our understanding) and an exit (through it, undigested food remains are removed). If the animal is attached to the substrate and the mouth is at the top, then it is called a “polyp”.

Free-swimming coelenterates whose mouths point downwards are called jellyfish. The division into jellyfish and polyps is not systematic, but purely morphological - the same species of coelenterates at different stages of the life cycle can successively look like either a polyp or a jellyfish.

Coelenterates are radially symmetrical creatures, which makes them look like flowers. These animals are two-layered; they have only two layers of cells - outer and inner. Between them there is a non-cellular substance, sometimes in the form of a thin layer, sometimes, for example, in large jellyfish, this is a thick gelatinous layer. One more characteristic feature coelenterates - presence stinging cells .

The most simply structured coelenterates are hydroids, hydroid polyps and hydromedusae. Colonies of hydroid polyps are usually small and can be seen in aquariums rather than swimming underwater.
Many hydroids look like openwork twigs.

Hydroids usually reproduce asexually, by budding. Some kidneys develop differently than usual. It is not new polyps that form from them, but jellyfish. Usually small (maximum several centimeters) jellyfish, unlike polyps, form reproductive cells. Actively swimming jellyfish release mature reproductive cells into the water. The larva that develops from a fertilized egg also moves in the plankton for some time, and then sinks to the bottom and forms a new colony. Thus, in life cycle hydroids alternate two generations - benthic polyps, reproducing by budding, and planktonic jellyfish, “responsible” for sexual reproduction. The meaning of this phenomenon is simple - planktonic jellyfish, unlike attached polyps, allow the species to spread and capture new substrates.

There are also hydroids that form mixed colonies, consisting of polyps and jellyfish that have not completely budded. Moreover, these colonies can be not only attached, but also free-floating. Planktonic colonial hydroids are classified into a separate subclass siphonophore, which some zoologists consider to be a class of their own.

The most dangerous jellyfish and corals for humans also belong to the class of hydroids. Contact with a small Far Eastern cross jellyfish ( Gonionemus vertens ) can cost the bather his life.

This group also includes false fire corals (Millepora ), which can seriously injure the skin if touched. Often, after burns, long-term non-healing ulcers form on the skin. Unlike physalia and crosswort, fire corals can be found off the coast of Eilat.

The second class of coelenterate type is scyphoid jellyfish ( Scyphozoa ).
In scyphoid jellyfish, the body has the shape of an umbrella with long tentacles suspended from below. Most people associate the word “jellyfish” with this group. Scyphojellyfish are much larger than hydromedusae: umbrella diameter arctic jellyfish Cyanea capillata reaches 2 m. The body of jellyfish is always transparent and very tender, gelatinous. When the umbrella contracts, jellyfish swim quite quickly. Jellyfish usually stay on the surface, although an expedition on the Challenger vessel caught a jellyfish from a depth of 2000 meters.

There is information on the website about the life and reproduction of a typical scyphoid jellyfish, since its mass appearance off the Eilat coast caused panic.

But even among scyphojellyfish there are some that can be mistaken for plants. In our shallow waters you can find rather strange whitish-greenish formations that resemble cauliflower. This is a scyphomedusa, which in Latin is called Cassiopea andromeda , named after the legendary mother and daughter from Greek myths, but in Hebrew and English they call it that way - “ cauliflower" There are more English name upside down jellyfish - upside down jellyfish. In its normal state, Cassiopeia lies in the sand, well, if not “upside down,” then, in any case, “upside down,” and catches plankton with its short thick tentacles. This jellyfish has learned to grow symbiotic algae in its body.

Finally, the third class of coelenterates is coral polyps ( Anthozoa ). This is the largest group of coelenterates. Among its representatives greatest number plant-like forms. I would like to draw your attention to the fact that those corals that we see in the waters of the Gulf of Eilat are hard colonial reef-forming corals (their scientific name is madrepore corals, the most famous, but not the only representatives coral polyps. These also include sea ​​anemones, soft corals, sea feathers, sea fans, sea fingers, jewelry corals (black and red) and many other interesting animals. Coral polyps are both solitary and colonial animals. Only some of them develop a calcareous or horny skeleton. These animals do not have a change of generations, and they do not form jellyfish. In addition to microscopic larvae, short time Living in plankton, the entire life of coral polyps passes on the bottom, to which most of them are firmly attached, although some, for example, sea anemones, can crawl.
Corals A separate article is devoted to them, they are very important for the sea and for Eilat.

In soft corals, individual polyps do not have a calcareous skeleton, and their colonies of various shapes and colors sway on reefs, piles, and stones, like bushes in the wind. In the water column, these colonies have no weight, so even without a supporting skeleton they reach large sizes.

Type Coelenterata, or Cnidarians, are the most ancient and lowly organized organisms of true multicellular animals. Cnidarians got their name from the Greek. knide - to burn. Another common name for this type of animal is coelenterata. Radially symmetrical, mostly marine animals, armed with tentacles and unique stinging cells (nematocytes), with which they capture and kill prey.

The body wall consists of two layers surrounding the gastrovascular cavity: the outer (epidermis) of ectodermal origin and the inner (gastrodermis) of endodermal origin. These layers are separated by gelatinous connective tissue– mesoglea. The gastrovascular cavity serves to digest food and circulate water throughout the body.

In cnidarians, real nerve cells and a diffuse type nervous system (in the form of a network) appeared for the first time. Polymorphism is characteristic, i.e. the presence within the same species that differ sharply in appearance forms One typical shape– a sessile polyp attached to the substrate and similar to a cylinder, at the free end of which there is a mouth surrounded by tentacles; another form is a free-swimming jellyfish, resembling an inverted bowl or umbrella with tentacles hanging from the edges. Polyps form jellyfish by budding. They, in turn, reproduce sexually: the fertilized egg develops into a larva, which gives rise to a polyp. Thus, in the life cycle of many cnidarians there is an alternation of sexual and asexual generations. Species that do not have a medusoid form reproduce sexually or by budding. They can be dioecious or hermaphroditic.

Their body consists of two layers of cells - the outer one, which forms the ectoderm, and the inner one, which is called the endoderm. Between these layers there is a developed non-cellular layer - mesoglea.

The function of support in coelenterates is performed by the mesoglea. In polyps it looks like a thin supporting plate.

In the coelenterates, the most primitive among multicellular type nervous system. In the ectoderm, nerve cells that perceive irritation are located relatively evenly. Irritation is transmitted through the contacting processes of nerve cells to the contractile fibers of epithelial muscle cells and then the response follows - contraction of the hydra body.

Coelenterate animals are characterized by radial symmetry and a two-layer body structure.
Most coelenterates have radial or radial symmetry. Coral polyps show deviations towards biradial or even bilateral (bilateral) symmetry.

Coelenterates are characterized by two life forms: sessile saccular polyp (coral polyps) and floating disc jellyfish. The polyp has the following structure. The part of the body with which the body attaches to objects is called the sole. On the upper part of the body there is a mouth surrounded by tentacles. All coelenterates are characterized by the presence of special stinging cells, which are designed to protect against enemies, as well as attack. This has not been found in other animals.

The stinging cells contain capsules with paralyzing poison. It enters the victim’s body through a special channel located in the stinging filament of these cells. When a sensitive hair is irritated, the stinging thread straightens with force and pierces the victim. After the shot, the stinging cell dies, and a new one is formed from the intermediate cell.

In addition to stinging cells, coelenterates also have other specialized cells: skin-muscle, glandular, reproductive, and nerve cells.

The digestive system of coelenterates is very primitive. The mouth leads into the intestinal or gastric cavity.

Digestion of food at the first stage occurs under the action of enzymes in the gastric cavity. This is extracellular or cavity digestion. Small food particles into which food breaks down are captured by endoderm cells, i.e. inner layer of cells, and are digested intracellularly.

Coelenterates reproduce both asexually and sexually.

The simple cnidarians include the hydra, which reaches 2.5–3 cm in length and leads a solitary lifestyle. Many form extensive colonies. Approximately 10,000 species have been described, grouped into three classes.

The type of coelenterates unites about 9,000 species - inhabitants of the seas and oceans and about 20 species of inhabitants fresh water. The type of coelenterates includes three classes:
Hydrozoa Scyphozoa Coral polyps Anthozoa

The importance of coelenterates is great. The calcareous skeletons of reef-forming coral polyps form reefs and atolls in tropical seas. Coral reefs and the islands are a dangerous obstacle to navigation. Coral polyps play a beneficial role in cleansing sea ​​water from suspended organic particles. Huge layers of limestone were formed from the skeletons of coral polyps that died over many millennia. In many tropical coastal countries it is used in construction. The skeletons of some types of coral, such as red coral, are used to make various jewelry.

Jellyfish sensitively pick up sound vibrations that occur when water rubs against air, and swim away from the shore long before a storm approaches. Based on this property, bionics scientists created the Jellyfish Ear device, which allows one to determine the approach of a storm approximately 15 hours before its onset.

Some types of jellyfish provide refuge for fish fry and hermit crabs. Coelenterates have great value in the food chain of marine biocenoses.

Lower multicellular organisms.

True multicellular organisms (Eumetazoa).

All multicellular organisms are divided into two unequal groups - lower multicellular two-layered (radial) and higher three-layered (bilaterally symmetrical). The lower ones include cnidarians and crested ones. To the highest - annelids, arthropods, molluscs, bryozoans, brachnopods, echinoderms, hemichordates, chordates.

Supersection true multicellular organisms (Eumetazoa).

True multicellular organisms have stable cell differentiation, they have tissues and organs, and in the embryonic stage two or leaves are formed. Depending on the number of germ layers and the type of symmetry, two divisions are distinguished among true multicellular organisms: radially symmetrical or two-layered and bilaterally symmetrical or three-layered. Two-layer ones are at a lower level than three-layer ones.

Section rabbi-symmetrical (Radiath) (double-layer).

Radially symmetrical consist of 2 layers - ecto- and endoderm. Their body has an axis of symmetry. The emergence of radial symmetry is due to the attached or free-swimming lifestyle. Among the two-layered ones, there are 2 types: cnidarians and ctenophores. The latter are not found in fossil form. Therefore, we will consider only cnidarians.

Among the cnidarians, the most famous are jellyfish and corals. All of them are marine animals living in normal sea basins at all depths down to the abyssal. All cnidarians have specialized stinging capsules - stinging capsules, which consist of a cavity with a poisonous one. Liquid and a thread coiled in it, which is thrown out like a harpoon, wounds and paralyzes the enemy. Thus, cnidarians are active predators. At the embryonic stage there are 2 layers - ectoderm and endoderm. Due to the ectoderm, the adult organism develops an epidermal layer consisting of muscle, first stinging, and skeletal-forming cells. Due to the endoderm, the inner gastric layer is formed, consisting of digestive cells. The gastric cavity opens outward through the oral opening. Through it, food gets inside. Through it, the final products of digestion are also removed. The mouth opening is surrounded by tentacles with stinging cells. In cnidarians, alternation of sexual and asexual reproduction is observed, i.e. the same species has two forms of existence: medusoid and polypoid. During sexual intercourse, free-swimming solitary forms arise—the medusoid generation.

Class Yastrododa (gastropods, gastropods).

Gastropods are solitary animals , having, with a few exceptions, an asymmetric body and a spiral-turret-shaped shell. Gastropods are the most numerous class of mollusks. About 85,000 belong to it modern species and about 15,000 fossils. Such diversity of gastropods is due to the fact that they adapted in the process of evolution to diverse living conditions. They are most widely represented in the neritic region. Individual forms are found in all zones of the sea, including the abyssal zone. Among them there are also freshwater ones. They usually crawl along the bottom, some swim or cling to rocks. They feed on plants; silt, other animals. This is the only mollusk that has adapted to life on land.

Gastropods have a well-separated head with sensory organs, legs and a torso. Gastropods do not have bilateral symmetry. For chopping and grinding food in the mouth, there is a rainbow, which is a grater equipped with a number of teeth.

The soft body of the animal occupies the entire shell. A powerful leg is sucked out of the mouth of the shell, the shape of which depends on the lifestyle. In crawling forms, its underside is flat. There is a cap on the leg that closes the opening of the shell when the leg is pulled in.

The vast majority of gastropods have shells that are preserved in fossil form. It consists of calcite and aragonite and usually has a three-layer structure. The outer layer is chitinous, often colored, the middle layer is prismatic or porcelain-shaped, and the inner layer is pearlescent. The shape of the shell is different: cap-shaped, flat-spiral, tile-shaped.

... with each other using thin connecting tubes. The septa are short and spiny.

5. p.Heliolites (O3-D2). The colonies are branched, consisting of cylindrical corallites, separated from each other by connective tissue. The corallites do not touch each other.

Geological significance. Tabulates are used for the stratigraphic Paleozoic, with different genera characteristic of different intervals.

Subclass Rugosa (four-rayed corals).

Rugosas are an extinct group of organisms. They have solitary and colonial forms. All of them had a calcareous skeleton. Massive colonies consisted of prismatic corallites, bushy ones - of cylindrical ones. Single ones were of the most varied shapes - conical, cylindrical, pyramidal. The base of single corals is horn-shaped and curved, which is due to the lateral attachment of the larva. Single corals reached up to 10 cm in height. In the internal cavity of the corallite, the skeletal elements are represented by septa, bottoms, bubbles, and columns. The septa are lamellar, long and short, and needle-shaped. At the first stage individual development 6 septa are formed, but in subsequent ones only 4 develop, which is where the name comes from - 4 rays (Tetarcorallia). The bottoms are varied: from flat to irregularly curved. Along the periphery of the coral, vesicular tissue - dessepiments - develops, and in the axial part (especially in the S-R) - a column. On the outer surface there is a wrinkled cover in the form of vertical ribs reaching the cup in which the polyp was placed, which is why they are also called rugoses.

As the coral grew, it moved upward and built a bottom - a horizontal plate. Colonies arise as a result of budding. In addition to the central or axial budding, lateral budding is also known in Rugosa, in which case branched colonies are formed (p. Neomphyma).

Rugosas lived mainly in the upper sublittoral zone of normal marine basins of the tropics and subtropics. They participated in the formation of coral limestones and reef structures. The most ancient rugoses appeared in O, which were solitary forms with spinous septals and without bottoms. Evolution proceeded as the skeletal elements became more complex - septa lengthened, vesicular tissue developed, and a column appeared.

Rugoses are used in the stratigraphy of the entire Pz and in the reconstruction of paleographic settings. Based on the growth lines of the epitheca and its wrinkles, one can calculate the number of days per year in past geological conditions. It turned out that in E the year consisted of 420-425 days. Existed with O-R.

Representatives:

1.p.Lambeophyllum (0) – small, conical coral, single-zone.

2.p.Streptelasma (O-S) – Conical or cylindrical coral with septa different lengths. The outer surface is ribbed. The septa are thick, adjacent to each other, forming a rim at the periphery.

3.p.Amplexus (C-P) – single coral with short septa.

4.p.Caninia (C-P) is a cylindrical coral, solitary with a thick wrinkled epitheca. In the center there is a column formed by a vortex long years in the center of the coral.

5.p.Cystiphyllum (S) – a single cylindrical coral. The entire cavity of the coral is filled with bubble tissue. Septa and epitheca are absent.

6.p.Calceola (D2) – single cap coral, rounded triangular in shape. The underside is flattened, the surface is covered with transverse ribs. The septa are short and very thick.

7.p.Fasciphyllum(D1-D2) – a massive colony consisting of prismatic corallites, closely adjacent to each other. The surface is covered with thin longitudinal ribs.

8.p.Lonsdaleia (C) – massive colony consisting of prismatic corallites. The septa are short and do not reach the wall. A column is developed in the center.

9.p.lythostrotion (C) – single cylindrical coral.

10.p.Dibunophyllum (C) – conical or cylindrical coral, thick septa at an early stage, a column that disappears with age. Fixed benthos.

11.p.Gshelia (C) – conical or cylindrical coral, thick septa at an early stage and a column that disappears with age. Fixed benthos.

12.p.Fryplasma (S2-D2) is a single cylindrical coral. The septa are short. The surface is covered with wrinkled epitheca.

13.p.Neomphyma (S2-D1) – a branched colony consisting of small cylindrical corallites. The septa are thin and short.

14.Bothrophyllum (C) – a single conical coral, two-zone, i.e. there are septa, bottoms, and bubbles.

15Heliophyllum (D) is a single coral with clearly defined longitudinal ribs (wrinkles).

Subclass Hexacorallia (six-rayed - scleratinia).

These are modern and fossil, solitary and colonial forms. Around the mouth opening there are tentacles, the number of which is a multiple of 6. Most have a calcareous skeleton, but non-skeletal forms are also found. So modern sea anemones do not have a skeleton. Corallites occur as solitary forms or form colonies of massive bushy type. Sometimes corallites merge to form an irregular myander-shaped polypnyak. Single ones have a conical, cylindrical shape up to 10 cm high, and up to 30 cm in diameter. Colonies reach 3 m in diameter and up to 1 m in height. The entire internal cavity of the corallite is filled with septa, bottoms, bubbles and columns. In the uppermost part - the calyx - there is a polyp, separated from the rest by a bottom, which separates the upper living part of the corallite from the lower - non-living part. On the outside, single forms have a wrinkled cover - an epitheca, which does not reach the upper edge of the corallite. This is due to the fact that the body of the polyp extends beyond the internal cavity of the corallite and glows in its lateral surface. As a result, a marginal zone of septa is formed, rising above the epitheca.

1.p.Montlivaultio (T-K) - single coral, conical in shape with a wrinkled epitheca. All septa rise above the epitheca, which do not reach the upper end of the coral.

2.p.Cyclolites (I-P2) – a single hemispherical coral with a flattened underside. The rugose epitheca is developed at the base of the coral and on the sides.

3.p.Fungia(P-Q) – coral of a discoidal or hemispherical shape, round in cross section. The epitheca is missing. The septa are numerous and very closely spaced.

4.p.Stylina(T-K2) – massive or branched colony, consisting of rounded coralites. The septs extend beyond the coralites.

5.p.Acropora(P-Q) – branched colony, consisting of small tubular corallites. One of the main reef-building corals in modern seas.

6.p.Fhamnasteria(F2-K) – a massive or branched colony with poorly demarcated corallites without walls. The contour of the corallites is created by the raised edges of the septa.

7.p.Leptoria(K2-Q) - massive colony. The septa are constructed from several systems of fan-shaped trabeculae.

8.9.10. Mendroid pomtnyay.

Geological significance of Cnidaria. All cnidarians serve as salinity indicators marine environment, all of them are rock-forming, play an important role in stratigraphy, especially for I-K when correlating far distant areas. But the main significance is reef formation. Reefs are still being formed. It has long been noted that reefs appear on sunken ships. The first inhabitants of such ready-made substrates are sponges and corals. Covering vast areas of reefs with living cover, they need huge amounts of oxygen, because... I release a lot of carbon dioxide and could suffocate. But then algae came to their aid, which in the form of tiny lumps are placed in the cells of reef-forming corals. Algae receive a convenient habitat and nitrogenous substances from the waste products of the polyps, and the polyps receive the necessary oxygen.