Phylum Cnidaria. Stinging V-Q

Cnidarians or cnidarians (Cnidaria)- a type of aquatic animal that includes jellyfish, corals, sea ​​anemones and hydra. The body structure of cnidarians is quite simple and consists of a gastrovascular cavity with one opening through which food and oxygen pass, and waste products are eliminated. Cnidarians are radially symmetrical and have tentacles that surround the mouth.

The body of cnidarians consists of an outer layer or epidermis, an inner layer or gastrodermis, and a middle layer or mesoglea (a jelly-like substance).

Cnidarians have organs and possess a primitive nervous system known as a neural network. Life cycle Cnidarians come in two main forms: a swimming form (jellyfish) and a sessile form (polyps).

Jellyfish have an umbrella-shaped body (called a bell), tentacles that hang from the edge of the bell, a mouth opening located at the bottom of the bell, and a gastrovascular cavity.

Polyps are a sessile form of cnidarians that attach to the seafloor and often form large colonies. The structure of the polyps consists of a basal disc attached to the substrate, a cylindrical body stalk, inside of which there is a gastrovascular cavity, an oral opening located in the upper part of the polyp and numerous tentacles located around the mouth.

Most coelenterates are carnivores and feed on small crustaceans. The prey becomes entangled in the tentacles, and then the stinging cells release poison and paralyze the victim. After which, the tentacles push the prey through the mouth into the gastrovascular cavity, where it is digested.

Classification

Cnidarians are divided into the following taxonomic groups:

• Box jellyfish (Cubozoa);
• Scyphoid (Scyphozoa);
• Coral polyps (Anthozoa);
• Hydroid (Hydrozoa).

(Greek сnidos- thread)

Cnidarians or coelenterates ( Coelenterata), these are exclusively aquatic animals (marine and freshwater), which include hydroid and coral polyps, jellyfish, etc. The sac-like body of cnidarians has a gastric cavity, which is divided by partitions into chambers and has one opening that serves as both an introductory - oral and excretory - anal. The mouth opening is surrounded by tentacles carrying stinging capsules, each of which has a coiled thread containing a poisonous liquid inside. When defending or attacking, the thread straightens with lightning speed, paralyzes the victim and pushes it into the throat with tentacles. Except digestive system cnidarians have muscular, nervous, and skeletal systems; reproduce by budding or division. The phylum is divided into three classes: hydroid (V-Q), scyphoid (V-Q), coral polyps V-Q. Let's look at the class of coral polyps below.

(a nthos- flower, zoa– animal), i.e. Animals that look like flowers were colorful in life.

Exclusively marine organisms , stenohaline, attached and sessile benthos, extinct and modern, calcareous skeleton. The individual organism is called a coral polyp, and its skeleton is corallite.

There are 6 subclasses, extinct among them: Tabulatoidea, Tetracoralla, Heliolitoidea and the Chaetetoidea group (Table 6).

Subclass Tabulatoidea. Tabulatoidea C 2 -P(lat. tabula- board; Greek oides-type, form)

These are exclusively colonial animals, kept motionless lifestyle. The colonies are massive (the walls of one corallite fit tightly to another), branched, chain-like. In cross-section, corallites can be round, elliptical, polygonal, reaching up to 10 mm in diameter, and the entire colony up to 1.5 m. In the internal cavity of the corallites there are horizontal partitions - bottoms, ceilings (taboules) and vertical (septa) - small, spiky .

Subclass Tetracoralla. 4-ray; Rugosa. Rugosa O-P(Greek tetra- four; corallion– coral or lat. ruga- wrinkled)

Paleozoic solitary and colonial animals with a calcareous skeleton. The shape of single corals is horn-shaped, cylindrical, prismatic. The length was no more than 25 cm and the diameter was 6 cm. The massive colonies consisted of prismatic corallites, up to 4 cm in diameter, and the colonies themselves were up to 1.5 m. The skeleton consisted of bottoms, septa, bubble-like formations, and columns.

The septa were formed naturally. First, one septa was formed, which split into one short and one long on the opposite edge. Then four side ones appeared. In four of the six sectors received, new septs were established.

The cross-section of single corals is round, polygonal, or quadrangular. Some forms have caps (genus Calceola). Solitary four-rayed corals have a well-developed integumentary wrinkled layer - epitheca. Its presence determined the second name of the subclass - rugosa.

Subclass Heliolitoidea. Heliolithoidea O 2 -D 2(Greek helios- Sun; lites–distorted from lithos- stone)

Heliolithoids are colonial animals. The shapes of the colonies are varied, the corallites are cylindrical, with twelve or six septa, reminiscent of the sun.

Group Chaetetoidea. Chaetetoidea O-N(Greek chaite– hair)

Chaetetoideans are the subject of constant debate. Most often, chaetetoids are classified in the phylum Cnidaria, class Anthozoa. Some researchers consider chaethetoids among bryozoans, algae or sponges.

Chaetetoids are colonial animals. The colonies are massive, represented by thin, calcareous, hair-like (0.15-1 mm) tubes (corallites). The cross sections of the tubes are round.

Class Anthozoa. Coral polyps V-Q

Table 6

Subclass	Genus	Characteristics of the genus
Tabulatoidea.Tabulates C 2 -P	Michelinia C	Massive bun-shaped colony. The corallites are large (up to 8 mm), prismatic in shape, and the tabulae are vesicular.
Favosites S-D	The colony is disc-shaped, hemispherical in shape. The corallites are polygonal, honeycomb-shaped, tightly adjacent to each other, the tabulae are flat and horizontal.
Halysites O2-S	Chain colony. Corallites are oval, small in cross section (1-2 mm), tabulae are concave.
Syringopora O3-C	The colony is bushy, of isolated cylindrical corallites. Corallites are connected by thin horizontal tubes. Tabulae are funnel-shaped.
Tetracoralla. Quadruple; Rugosa O-P	Caninia C-P 1	A single coral, cylindrical or horn-shaped, with a wrinkled epitheca. The long thin septa do not extend from the very edge and do not reach the center. Attached benthos.
Triplasma altaicus D 1	Single coral, short thick septa located along the edge. Attached benthos.
Lithostrotion C 1	Colonial coral. The colony is massive, hemispherical. Short septa alternate with long ones that reach the column in the center. Free-lying benthos.
Heliolitoidea O 2 -D 2	Heliolites D 1-2	Colonies of various shapes consist of round and prismatic corallites with 12 septa.
Chaetetoidea O-N	Chaetetes D-P (C)	The colony is massive, hemispherical. Hair-like corallites fit tightly to each other. Attached benthos.

Lifestyle and living conditions. Tabulates and tetracorals are inhabitants of warm, shallow seas, mainly in the upper part of the sublittoral zone. Participated in reef formation. Corals are very fastidious animals - they do not tolerate desalination of water, or when there are a lot of suspended particles of silt in the water, so they settled far from the shore.

Geological distribution. Tabulata appeared in the Cambrian, and tetracorals and heliolithoids appeared in the Ordovician. Great diversity was achieved in the middle of the Paleozoic. They die out at the end of the Paleozoic era.

Geological significance. Tabulates, tetracorals and heliolithoids are of great biostratigraphic importance for Paleozoic deposits, since these groups, which are completely extinct, are the leading forms.

Corals, as stenobiont animals, are used in the reconstruction of paleogeographic sedimentation conditions. Using the growth lines of the epitheca rugosa, one can calculate the number of days per year in past geological eras. In this case, corals act as a “geological clock”.

The role of corals in rock formation is also enormous. The reef structures of the corals became coral limestones, which are traps for oil and gas.

(Greek cnidos - thread)

The phylum cnidarians, or cnidarians, include numerous diverse animals, among which the most famous are hydra, jellyfish and corals. They lead a planktonic or benthic, stationary, 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) d - 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 nonfolded. 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 is formed, the simplest nervous system. 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.