Cells are unique to cnidarians. Cnidaria are multicellular animals. Hydrozoa. systematic position. Features of the structure and reproduction. Meaning
22. General characteristics of cnidating animals. Classification. Polyp and jellyfish as two forms of animal existence.
Type Cnidaria - Cnidaria
Class Hydrozoa - hydrozoa
Order Anthoathecatae
Suborder Capitata
Genus Hydra - hydra
H. oligastis species - freshwater hydra
Order Leptothecatae
Genus Obelia - obelia
Bilayer animals. Between the epidermis and gastrodermis is mesoglea, either in the form of a basal plate or in the form of a gelatinous substance. The mesoglea is similar in structure to the mesochyls of sponges. Mesoglea - gelatinous extracellular matrix - lies between two epithelial layers. The main function is supporting; plays an important role in locomotion (swimming jellyfish), ensures the stability of conditions and the supply of nutrients to the muscles, nerves, germ cells. Symmetry is radial, some representatives have elements of bilateral symmetry. Two forms of existence are known: a polyp and a jellyfish. Both life forms can alternate in the life cycle of the same species. It is possible to suppress one of them. This phenomenon is called hypomorphosis. The presence of cnidocytes is characteristic. The digestive system is the gastric or gastrovascular cavity. Digestion is abdominal and intracellular. Undigested food debris is expelled through the mouth. Functions of the gastric cavity: digestive, circulatory, adsorption, sometimes serves as a hydroskeleton and a brood chamber for developing embryos. There are real, albeit poorly differentiated, tissues. The nervous system is of a diffuse type. It consists of sensory neurons located superficially, motor neurons (motor neurons), intercalary neurons. Neurons are connected to each other by processes that pass through the mesoglea and form two networks. One network lies at the base of the epidermis, and the other at the base of the gastrodermis. The sense organs (eyes, statocysts) are developed in jellyfish. Excretory organs are absent. Breathing is carried out by the entire surface of the body. Animals are dioecious and hermaphrodites. Reproduction is sexual and asexual. Larva - planula. Many representatives form colonies, which may consist of polyps, jellyfish, or both.
23. Hydrozoa. systematic position. Features of the structure and reproduction. Meaning
Class Hydrozoa: (on the example of hydra) Either polyps or jellyfish are represented in the life cycle, but often generations of jellyfish and polyps alternate. The body is elongated, attached to the substrate by the sole, which ends the stalk.
At the opposite end - the mouth or oral pole - there is a mouth cone (hypostome) surrounded by tentacles. The number of tentacles varies. The epidermis and gastrodermis are separated by a basement membrane. The gastric cavity continues into the tentacles.
The epidermis consists of several types of cells: epithelial-muscular, interstitial (intermediate, reserve), cnidia.
Interstitial cells (found only in hydroids) are formed in the endoderm of the embryo, and later migrate to all tissues of an adult animal. Glandular cells, gametes and cnidocytes develop from reserve cells. Gastrodermis consists of epithelial-muscular cells and glandular cells. Epithelial-muscular cells with flagella, they are able to form pseudopodia, with the help of which the hydra captures food. Glandular cells secrete digestive enzymes into the gastric cavity.
Hydras are dioecious or hermaphrodites. Fertilization takes place in the body. Female sex cells are located closer to the sole of the animal, male ones are formed closer to the mouth. Hydra sexual reproduction occurs with the approach of cold weather. Fertilized eggs are surrounded by a shell, remain dormant until spring. The hydra is dying. Hydra reproduce asexually by budding.
Kingdom Animalia
Subkingdom Eumetazoa - True multicellular
Section Radiata (= Diploblastica
Phylum Cnidaria - Cnidaria
Class Hydrozoa - Hydroids
Lower multicellular.
True multicellular (Eumetazoa).
All multicellular organisms are divided into two unequal groups - lower multicellular two-layer (radial) and higher three-layer (bilaterally symmetrical). The lower ones include cnidarians and crested ones. To the highest - annelids, arthropods, mollusks, bryozoans, brachnopods, echinoderms, hemichordates, chordates.
Supersection true multicellular (Eumetazoa).
Real multicellular organisms have stable cell differentiation, they have tissues and organs, and in the embryonic stage 2 or leaves are laid. Depending on the number of germ layers and the type of symmetry, two sections are distinguished among true multicellular organisms: radially symmetrical or two-layered and bilaterally symmetrical or three-layered. Two-layer are at a lower level than three-layer.
Section rabially symmetrical (Radiath) (two-layer).
Radially symmetrical ones 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-floating way of life. Among the two-layer, 2 types are distinguished: cnidarians and ctenophores. The latter is not found in the fossil state. Therefore, we will consider only cnidarians.
Among cnidarians, jellyfish and corals are the most famous. All of them are marine animals living in normal sea basins at all depths up to the abyssal. All cnidarians have specialized stinging capsules - stinging capsules, which consist of a cavity with a poisonous one. Liquid and coiled in it, which is thrown out like a harpoon, injures and paralyzes the enemy. Thus, cnidarians are active predators. At the embryonic stage, there are 2 layers - ectoderm and endoderm. Due to the ectoderm in an adult organism, an epidermal layer arises, consisting of muscle, first stinging, skeletal-forming cells. Due to the endoderm, an inner gastric layer is formed, consisting of digestive cells. The gastric cavity opens outward through the mouth. Through it, food enters. Through it, the end 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-floating single forms appear - the medusoid generation.
Class Yastrododa (gastropods, gastropods).
Gastropods are solitary animals , having, with a few exceptions, an asymmetric body and a spiral-turreted shell. Gastropods are the most numerous class of mollusks. About 85,000 modern species and about 15,000 fossils belong to it. Such a variety of gastropods is due to the fact that they have adapted in the process of evolution to various conditions of existence. They are most widely represented in the nerite region. Separate forms are found in all zones of the sea up to the abyssal. Some of them are freshwater. They usually crawl along the bottom, some swim or stick 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, a leg, and a trunk. Gastropods are not bilaterally symmetrical. For grinding and grinding food in the mouth, there is a rainbow, which is a grater equipped with a number of cloves.
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. Crawling forms have a flat underside. The leg has a lid that closes the shell opening when the leg is retracted inward.
The vast majority of gastropods have a shell, which is preserved in the fossil state. It consists of calcite and aragonite and usually has a three-layer structure. The outer layer is chitinous, often colored, the middle one is prismatic or porcelain-like, the inner one is mother-of-pearl. The shape of the shell is different: cap-shaped, flat-spiral, tiled.
… between each other with the help of thin connecting tubes. The septa are short, spike-shaped.
5. p.Heliolites (O3-D2). Colonies branched, consisting of cylindrical corallites separated from each other by connective tissue. Corallites do not touch each other.
Geological significance. Tabulates are used for the stratigraphic Paleozoic, and different genera are characteristic of different intervals.
Subclass Rugosa (four-beam corals).
Rugoses 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 colonies consisted of cylindrical ones. Single ones were of the most diverse shapes - conical, cylindrical, pyramidal. The base of solitary 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 inner cavity of the corallite, skeletal elements are represented by septa, bottoms, bubbles, and columns. The septa are lamellar, long and short, and needle-shaped. At the first stage of individual development, 6 septa are laid, but in the subsequent ones only 4 develop, from which the name comes - 4 ray (Tetarcorallia). The bottoms are varied: from flat to irregularly curved. Bubbly tissue develops along the periphery of the coral—dessepiments, and a column develops in the axial part (especially in the C-R). On the outer surface there is a wrinkled cover in the form of vertical ribs reaching the cup in which the polyp was placed, from which they are also called rugoses.
As the coral grew, it moved up and built the bottom - a horizontal plate. Colonies are formed by budding. In addition to the central or axial, lateral budding is also known in rugose, then branched colonies are formed (p.Neomphyma).
Rugoses lived mainly in the upper sublittoral of the 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 single forms with spiked septals and no bottoms. The evolution proceeded as the skeletal elements became more complex - the septa were lengthened, the vesicular tissue developed, and the column appeared.
Rugoses are used in the stratigraphy of the entire Pz and in the reconstruction of paleographic settings. According to the growth lines of the epithecus and its wrinkles, one can calculate the number of days in a year in past geological settings. 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 of different lengths. The outer surface is ribbed. The septa are thick, adjacent to each other, forming a rim on the periphery.
3.p.Amplexus (C-P) is a solitary coral with short septa.
4.p.Caninia (C-P) is a cylindrical coral, solitary with a thick wrinkled epithecus. In the center is a column formed by the swirl of long years in the center of the coral.
5.p.Cystiphyllum (S) is a single cylindrical coral. The entire cavity of the coral is filled with bubble tissue. Septa and epithecus are absent.
6.p.Calceola (D2) – solitary cap coral, round-triangular shape. The underside is flattened, the surface is covered with transverse ribs. The septa are short and very thick.
7.p.Fasciphyllum(D1-D2) is a massive colony consisting of prismatic corallites, closely adjacent to each other. The surface is covered with thin longitudinal ribs.
8.p.Lonsdaleia (C) is a massive colony of prismatic corallites. The septa are short and do not reach the wall. A column is developed in the center.
9.p.lythostrotion (C) is a single cylindrical coral.
10.p.Dibunophyllum (C) - conical or cylindrical coral, thick septa at an early stage, there is a column that disappears with age. immobile benthos.
11.p.Gshelia (C) - conical or cylindrical coral, thick septa at an early stage, there is a column that disappears with age. immobile benthos.
12.p.Fryplasma (S2-D2) is a single cylindrical coral. The septa are short. The surface is covered with wrinkled epithecus.
13.p.Neomphyma (S2-D1) is a branched colony consisting of small cylindrical corallites. The septa are thin and short.
14. Bothrophyllum (C) is a single cone-shaped coral, two-zoned, i.e. there are septa, bottoms, blisters.
15Heliophyllum (D) is a solitary coral with distinct longitudinal ribs (wrinkles).
Subclass Hexacorallia (six-beam - scleratinia).
These are modern and fossil, solitary and colonial forms. Around the mouth opening 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 anemones do not have a skeleton. Corallites occur as single forms or form massive bushy colonies. Sometimes corallites, merging, form an irregular meander-like polyp forest. Solitary 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 - a polyp is placed, separated from the rest by a bottom that separates the upper residential part of the corallite from the lower - non-residential one. From the outside, single forms have a wrinkled cover - an epitheca that 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 shines on its lateral surface. As a result, a marginal zone of septa is formed, which rises above the epithecus.
1.p.Montlivaultio (T-K) - solitary conical coral with wrinkled epithecus. All septa rise above the epithecus, which do not reach the upper end of the coral.
2.p.Cyclolites (I-P2) is a solitary hemispherical coral with a flattened underside. A wrinkled epithecus is developed at the base of the coral and along the sides.
3.p.Fungia(P-Q) is a discoidal or hemispherical coral, rounded in cross section. The epithecus is missing. The septa are numerous, very closely spaced.
4.p.Stylina(T-K2) is a massive or branched colony consisting of rounded coralites. The septa extend beyond the coralites.
5.p.Acropora(P-Q) is a branched colony consisting of small tubular corallites. One of the main reef-building corals in modern seas.
6.p.Fhamnasteria(F2-K) is a massive or branched colony with poorly demarcated wallless corallites. The outline of the corallites is created by the raised edges of the septa.
7.p.Leptoria(K2-Q) - massive colony. The septa are built from several systems of fan-shaped trabeculae.
8.9.10. Mendroid puffballs.
Geological significance of Cnidaria. All cnidarians serve as indicators of the salinity of the marine environment, all of them are rock-forming, play an important role in stratigraphy, especially for I-K in the correlation of remote areas. But the main value is reef formation. Reefs are still being formed. It has long been noticed that reefs appear on sunken ships. The first inhabitants of such ready-made substrates are sponges and corals. Covering vast expanses of reefs with living cover, they need a huge amount of oxygen, because. I give off 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 comfortable habitat and nitrogenous substances from the waste products of polyps, and polyps receive the necessary oxygen.
Type Intestinal, or Cnidaria. General characteristics of the type
Systematic position of the type
Remark 1
Type Intestinal (Coelenterata) belongs to the sub-kingdom of Animals, its representatives are eumetazoans, or true higher multicellular animals.
Representatives of the Supersection Eumetazoi have a number of common features:
- differentiation of tissues, organs;
- the presence of nerve cells;
- clearly manifested integrity and integration of individuals;
- pronounced bilateral (Section Bilateral) or radial (Section Radiant) symmetry.
Type Intestinal are included in the Section Radiant. They, as representatives of this section, are characterized by:
- beam symmetry;
- two-layer structure;
- the presence of a gastric (intestinal) cavity;
- diffuse nervous system.
Type Celiac includes polyps and jellyfish that have stinging cells, so this type is also called Cnidaria.
This type includes three classes:
- Hydroids (Hydrozoa);
- Scyphozoa (Scyphozoa);
- Coral polyps (Anthozoa).
Features of the external and internal structure
Remark 2
The body of the Coelenterates has a central heteropolar axis, around which morphological structures are located in a certain order. This axis penetrates the oral (oral) and aboral poles of the body.
In relation to the heteropolar axis, the body parts of the coelenterates and individual structures are oriented symmetrically:
- radially;
- asymmetrically, or biradially;
- bilaterally.
Through the body of the coelenterates, 2, 4, 6, 8, etc. can be passed. planes of symmetry. Representatives of the type, as a rule, lead a fixed or sedentary lifestyle. In the process of ontogenesis, two germ layers are formed. From the ectoderm (outer leaf) integuments are subsequently formed, and the endoderm (inner leaf) lines the intestinal cavity.
The tissues and organs of the coelenterates are formed by the epidermis and gastrodermis and the mesoglea between them - the intercellular matrix. The epidermis exhibits a high degree of differentiation of cells, tissues, and organs.
Type specific features:
- four-beam symmetry - tetramerism;
- development with metamorphosis, the presence of a two-layer planula larva is characteristic;
- stinging cells that perform the functions of attack and defense;
- the main part of the nervous system is the diffuse plexus.
Direct development is rare. The body of all coelenterates is a bag consisting of two layers with a gastric cavity. The cavity of the sac is lined with endoderm, where food is digested. The function of the mouth is performed by the opening of the “bag”, undigested food residues are also removed through it. The simplest representatives of the coelenterates in structure can be compared with a typical gastrula. This group of animals has a high ability to regenerate.
Morpho-ecological forms of coelenterates
There are two morpho-ecological forms of Coelenterates:
- polyp (benthic attached form);
- jellyfish (planktonic form).
Type Coelenterates is characterized by the presence of floating forms of animals with tentacles. Colonies are sometimes formed from medusoid and polypoid individuals. Often you can find a symbiosis of Cnidaria and unicellular algae. For most representatives of the type, a life cycle with alternating sexual and asexual reproduction is characteristic, the so-called metagenesis between a jellyfish and a polyp. As a rule, a jellyfish is formed from a polyp as a result of:
- formation of special transverse constrictions;
- metamorphosis;
- strobilation (terminal department);
- lateral budding.
The formation of a polyp occurs as a result of sexual reproduction of the jellyfish through the stage of planula formation.
The phylum Cnidaria has about 9,000 species, united in several classes, among which the most extensive are the Hydrozoa, Scyphozoa and Anthozoa.
The vast majority of cnidarians are marine animals, although there are species that have mastered fresh and brackish waters. These are radially symmetrical animals with an oral-aboral main axis of symmetry and a relatively simple body plan. The body wall is formed by two epithelial layers - the outer, or epidermis, and the inner, gastrodermis. The latter lines the gastrovascular cavity - celepterone, which also performs a digestive function and ensures the circulation of substances throughout the body of the animal. The gastrovascular cavity communicates with the external environment through an opening that simultaneously performs the functions of both the oral opening and the anus.
The composition of the epithelial layers includes a variety of cellular elements. In the epidermal layer there are epithelial-muscular, sensory, nervous, glandular and stinging cells - nematocytes, as well as undifferentiated multipotent interstitial cells (i-cells). The gastrodermis contains epithelial-muscular and glandular cells. Between the epithelial layers is an extracellular matrix - mesoglea, the degree of development of which varies greatly in different species. In the mesoglea, type IV collagen, fibronectin, heparan-sulfate-proteoglycan, laminin, etc., characteristic of basement membranes, are distinguished. In the mesoglea, Scyphozoa has a self-sustaining population of amoebocytes.
Cnidaria are characterized by two types of organization - polypoid and medusoid. In many species, for example, those belonging to the metagenetic Hydrozoa or the Scyphozoa, there is a regular alternation of these forms, or metagenesis. In this case, sexual reproduction is associated with the medusoid generation, while asexual reproduction is characteristic of the polypoid generation. The medusoid phase may be reduced or completely absent (for example, in representatives of the order Hydrida). The medusa stage is also absent in corals, in which both sexual and asexual reproduction is provided by polyps. However, there are forms represented only by jellyfish. Thus, in the life cycle of animals from the order Trachylida there is no polypoid phase.
Polyps often form colonies with a common gastrovascular cavity. There are different types of polyps, or zooids, in a Hydrozoa colony. Most of them are represented by gastprozooids, or feeding polyps; in some species, dashpilozooids are formed, which, due to the abundance cnidocytes(from Greek - nettle) protective function. Reproduction is carried out by gonozooids, or medusoid buds, which produce gametes. Medusoids either separate from the colony and turn into jellyfish, or remain in the colony as gonophores.
Sex cells are formed from interstitial cells. As shown by studies performed on hydras, among i-cells there is a special population committed as a line of germ cells. In the process of oogenesis, phagocytosis and cell fusion play an important role in supplying the oocyte with nutrients. Representatives of this type are characterized by temporary gonads, although in Scyphozoa permanent gonads are formed.
Fertilization in cnidarians is usually external. Nevertheless, in all classes of cnidarians there are species with internal fertilization, up to the peculiar copulation described in the anemone Sagartia. In the latter case, the pedal discs of the parent individuals form a common chamber into which the gametes are released and in which the fertilized eggs develop to the larval stage.
The first two divisions of crushing are meridional, and the third is equatorial. It is noteworthy that the furrows of cleavage divisions are not circular, but cutting: they begin at one pole of the fertilized egg and gradually spread to the opposite, where the connection between blastomeres is observed for a relatively long time.
Cnidaria are distinguished by a wide variety of types of crushing. With complete and uniform crushing, the radial nature of the location of blastomeres is often observed. In some species, however, the connection between blastomeres is weak, so that they can change their position relative to other cells. If the blastomeres rotate, then figures may appear that resemble spiral fragmentation in appearance, i.e., pseudospirality occurs. In other cases, the crushing embryo loses the definiteness of its geometric forms (anarchic type of crushing). With uneven crushing, the arrangement is disordered and its pattern is changeable. In eggs rich in yolk, cytotomy may be delayed. In some species, the central mass of the yolk does not divide at all. In this case, crushing becomes superficial.
The variety of cleavage forms also affects the structure of the blastula. Several types of blastula have been described in cnidarians: a hollow coeloblastula formed by a single row of cells that surround an extensive blastocoel; dense sterroblastula, also formed by one row of cells, but without a blastocoel, morula, and, finally, periblastula, which is characterized by the location of the outer layer of cells on the surface of the yolk mass. Cells of the coeloblastula are equipped with flagella, which ensure its movement.
At the next stage of development, gastrulation occurs, during which two main layers of the body are formed in cnidarians: the outer layer, or ectoderm, and internal - endoderm.
In cnidarians, a variety of cellular mechanisms for the formation of body layers have been described. Widespread ingression(from lat. ingressus - entry, entry), or immigration of cells. During ingression, some cells of the coeloblastula wall lose flagella, acquire amoeboid mobility and move into the blastula cavity, filling it completely. A distinction is made between unipolar ingression, which occurs in the region of the embryo, where the oral opening is subsequently laid, and multipolar ingression, in which invasion occurs over the entire surface of the embryo.
The colonization of the blastula cavity by individual cells can also occur as a result of oriented cell divisions in the blastula wall. This process is called delamination(from lat. de - separation, lamina - plate, layer). Cells that enter the blastula cavity after division form the endoderm. The immersion of the cells of the blastula wall can also occur as part of the epithelial layer. This type of epithelial morphogenesis is called invagination, or invagination (from lat. invaginatio - invagination).
The formation of the ectoderm and endoderm in the morula occurs as a result of cell rearrangement. The cells occupying the inner region of the embryo give rise to the endoderm, while the cells of the outer layer give rise to the ectoderm. This separation of layers is called morula, or secondary delamination.
Finally, in many species it is described epiboly(from Greek - vestment, cover), or fouling of large macromeres with fissile micromeres. Mixed types of reservoir isolation are also widely represented.
As a result of the gastrulation process, a usually radially symmetrical two-layered larva arises. planula(from Greek - wandering). The outer ectodermal layer of the planula is formed by ciliary cells. Between the ectoderm and endoderm, there is a thin layer of extracellular matrix - mesoglea. At the planula stage, differentiation of cell layers occurs. So, epithelial-muscular, glandular and sensory cells appear in the composition of the ectodermal epithelium. Interstitial cells and their derivatives, including stinging cells, are located between the epithelial cells. The place of formation of interstitial cells is the endoderm, where they are committed. In the endodermal epithelium, digestive and glandular cells are formed. The planula is elongated and slightly expanded at the anterior end, which is the successor to the vegetative region of the crushing embryo. Usually, planulas are lecithotrophic and the nutrition necessary for their life in the form of yolk grains stored during oogenesis is located in their cells. In some Anthozoa, planktotrophic planulae are described, in which, after the completion of invagination, a mouth opening forms in place of the blastopore.
The transformation of a larva into an adult form is called metamorphosis. During this process, the larva is attached to the substrate by the front end or side surface. Usually, the body of the planula is flattened in the longitudinal direction and turns into a disk, on which a polyp grows, connected to the disk by a stalk. This primary hydrant, the ancestor of the colony, develops tentacles and a mouth opening. In other cases, the planula turns into a hydrorhiza - a filamentous body spread over the substrate, on the surface of which polyps form. Colonial forms result from the budding of primary hydrants.
Sometimes the formation of polyp structures begins very early, even at the stage of a floating larva. In these cases, the larva is compressed along the anterior-posterior axis. In this case, the anterior (future aboral) region flattens, and the posterior (future oral) takes the form of a cone, at the top of which a hole is formed with a surrounding rim of tentacles. A stalk is formed at the aboral pole. Emerging free polyp, or actinula(from Greek - beam) soon settles and attaches to the substrate.
In cnidarians, asexual reproduction is widespread, which can occur in both polyps and jellyfish. As a result of asexual reproduction of the primary polyp, colonial forms arise. With asexual reproduction of hydroid jellyfish, the population of animals capable of sexual reproduction sharply increases.
In Scyphozoa, a single polyp formed after settling is called a scyphistoma, a characteristic feature of which are septa - vertical folds of the endoderm that divide the gastric cavity of the polyp into four pockets. Scyphozoa polyps reproduce asexually by budding and strobilation. Strobilation begins in the oral area of the polyp and spreads aborally. It consists in the sequential formation of disc-shaped elements by transverse divisions of the body. A polyp in the strobilation phase is called strobila(from lat. strobilus - bump). Disks separated from the strobila form ethers, or jellyfish larvae. The formation of the ether involves a radical restructuring associated with the loss of the provisional organs of the scyphistoma and the development of the organs of the emerging jellyfish.
In some Scyphozoa, polyp budding produces podocysts that can remain dormant for a long time. The podocysts then transform into motile larvae. Something similar takes place in Hydrozoa. For example, in representatives of the Leptolid order, fructulation(from lat. frustulum - a piece) - a peculiar form of asexual reproduction by fragmentation, during which planu-shaped frustula larvae arise.
Thus, in representatives of different classes of cnidarians, asexual reproduction occurring at the polypoid or medusoid phase of the life cycle can lead to the formation of a mobile larva characteristic of sexual reproduction. This phenomenon, apparently, can be regarded as evidence of the existence of relatively autonomous modular developmental subroutines that can be initiated both during sexual and asexual reproduction. Verification of this assumption requires a special study.
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