The Scyphoid class includes jellyfish that inhabit the seas and oceans (they live only in salt water), which are able to move freely among the expanses of water (with the exception of the sessile jellyfish, which leads a sedentary lifestyle).
general characteristics
Scyphoid jellyfish live everywhere; they have adapted to life in cold and warm waters. There are about 200 species. They are transported over considerable distances with the current, but can also move independently. Thus, with the help of active contractions of the dome and the release of water from it, the jellyfish can develop greater speed. This method of movement was called reactive.
The jellyfish has the shape of an umbrella or a longitudinally elongated dome. There are quite large species. Some representatives of the scyphoid class reach 2 m in diameter (Cyanea arctica). Many tentacles extend from the edges of the bell, which can grow up to 15m in length. They contain stinging cells that contain toxic substances necessary for protection and hunting.
Structural features
In the middle of the inner concave part of the umbrella there is a mouth, the corners of which turn into oral lobes (necessary for capturing food). In rootostomes, they grow together and form a filtering apparatus for absorbing small plankton.
Scyphoids are endowed with a stomach with 4 pocket-like protrusions, and a system of radial tubules, through which nutrients from the intestinal cavity are distributed throughout the body. Undigested food particles are sent back to the stomach and eliminated through the mouth.
The body of jellyfish consists of two layers of epithelial cells: ectoderm and endoderm, between them is mesoglea - jelly-like tissue. It consists of 98% water, so jellyfish quickly die under the scorching sun. Jellyfish have enormous regenerative abilities; if you cut it into 2 parts, each will grow into a full-fledged individual.
Since scyphoid jellyfish have switched to an active way of life, their nervous system has become more developed. At the edges of the umbrella there are clusters of nerve cells; nearby there are also sensory organs that perceive light stimuli and help maintain balance.
Life cycle and reproduction
Scyphoid in its life cycle pass through two phases: sexual (jellyfish) and asexual (polyp).
All representatives are dioecious organisms. The germ cells originate from the endoderm and mature in the pouches of the gastric cavity.
The gametes exit through the mouth and end up in the water. During the process of fusion of germ cells and further maturation, a jellyfish larva, a planula, emerges from the egg. It sinks to depth, attaches to the bottom and enters the asexual phase.
A single polyp (scyphostoma) leads a benthic life and begins to reproduce through lateral budding. After a certain time, the scyphistoma turns into a strobila, then the tentacles begin to shorten, and transverse constrictions form on the body. This is how a division called strobilation begins. Thus, the strobila gives life to young organisms - ethers. The ethers are then converted into adults.
Lifestyle
Scyphoid jellyfish do not live in schools and do not transmit signals to each other, even when at close range. Life expectancy is about 2-3 years, sometimes it happens that a jellyfish lives only a couple of months. They are also often eaten by fish and turtles.
All jellyfish are predatory animals. They consume plankton and small fish, which are immobilized by poisonous cells. Stinging cells release poison not only during hunting, but also to all organisms passing by. Therefore, jellyfish are dangerous for people in the water. If you accidentally catch the tentacles of a jellyfish, it will burn your skin with its poison.
The most common representatives of the class of scyphoid jellyfish are Aurelia, Cyanea, which inhabits the Arctic seas, and Cornerot, which is devoid of tentacles and lives in the waters of the Black Sea.
Meaning in nature and human life
Scyphoid jellyfish are part of the food chain of the world's oceans.
In Chinese and Japanese cuisine, dishes with rhopilema or aurelia are often found. Jellyfish meat is considered a delicacy.
Cornerot is the largest jellyfish in the Black Sea with a dome diameter of about 40 cm. Thus, it serves as a shelter for fish fry and protects against predators and unfavorable conditions environment. Sometimes, when the fry grow up, they begin to bite off small pieces of the jellyfish, or may eat it altogether.
Scyphoid jellyfish filter water, clearing it of contaminants.
For humans, the dangerous poison of jellyfish, which causes skin burns, sometimes provokes a painful shock and a person, being at depth, can no longer surface on his own. It is not safe to touch a jellyfish even when it is dead. Develops when touched allergic reaction, disruption of the nervous and cardiovascular systems, convulsive attacks occur.
general characteristics Type Coelenterates.
Coelenterates are two-layered animals with radial symmetry.
Symmetry. The body of coelenterates has a main axis, at one end of which there is a mouth opening. Several axes of symmetry pass through the main axis, along which the appendages and internal organs of the animal are located. This type of symmetry is called radial .
Life forms. The main life forms of coelenterates are polyp and jellyfish.
Body polyp V general case cylindrical, at one end there is a mouth opening, surrounded different number tentacles, and on the other - the sole. Polyps are usually sedentary or inactive. Polyps mostly form colonies.
Body jellyfish has the appearance of a regular umbrella or bell, on the lower, concave side of which there is a mouth opening. There are tentacles or lobes along the edge of the umbrella and sometimes around the mouth. Jellyfish, as a rule, lead an active lifestyle and do not form colonies.
Different species of coelenterates either exist as only one of these life forms (jellyfish or polyp), or go through both stages throughout their life cycle.
Taxonomy. In the phylum Coelenterata there are three classes:
Hydroid (hydra, obels, polypodium, siphonophores);
Scyphoid (jellyfish aurelia, cornerota, cyanea, sea wasps);
Coral (black and red corals, acropora, fungi, sea anemones, alcyoniums).
There are 9000 in total modern species coelenterates.
Body measurements coelenterates vary widely. Some types of polyps in adulthood do not exceed a few millimeters, while some sea anemones can reach 1 meter in diameter. In jellyfish, the diameter of the umbrella can be from 2 mm to 2 meters. In addition, the tentacles of some jellyfish can stretch up to 30 m.
Movement. Polyps sedentary. They can bend their body, contract, and move their tentacles. Hydras can “walk” like moth caterpillars (the larvae of moths). Sea anemones can crawl slowly on their soles.
Jellyfish actively move by contracting the umbrella. Sea currents also play an important role, transporting jellyfish over long distances.
Body structure. As already mentioned, coelenterates are two-layered animals. Their body wall consists of two cell layers - ectoderm (external) and endoderm (internal). Between them is mesoglea - a layer of structureless gelatinous substance. The only one cavity in the body of coelenterates - intestinal, or gastric .
Ectoderm presented as a single-layer flat, cubic or cylindrical epithelium . In addition to ordinary epithelial cells, the ectoderm includes epithelial-muscular cells whose base is elongated longitudinal direction contractile (muscle) fiber. In some corals, muscle fibers are separated from the epithelium and lie underneath it or are immersed in the mesoglea layer, forming an independent muscular system. Between epithelial cells there are interstitial cells that give rise to various cellular elements of the ectoderm. A characteristic feature of coelenterates is the presence of so-called tentacles in the ectoderm stinging cells . Each such cell contains a capsule into which a spirally coiled long hollow process is inserted - a stinging filament. Outside the cell there is a sensitive hair, when irritated, the stinging thread sharply turns out, straightens and pierces the body of the prey or enemy. At the same time, a poisonous secretion is poured out of the capsule, causing paralysis in small animals, as well as a burning sensation in large ones.
Endoderm. The epithelium lining the gastric cavity consists of flagellar cells. Some of these cells are epithelial-muscular , however, the muscular processes are located in the transverse direction, collectively forming layers of annular fibers. Ectodermal epithelial cells are capable of forming pseudopodia, with the help of which they capture food particles. There are also glandular cells.
Mesoglea. In polyps, the mesoglea is poorly developed (with the exception of corals), but in jellyfish this layer reaches a significant thickness. The mesoglea contains a number of ectodermal cells that take part in the formation of the skeleton.
Skeletal formations. Only polyps have a skeleton. In hydroid polyps, the body is covered with a thin chitinous theca - a dense membrane that performs a protective function. Most types of corals have a calcareous skeleton, sometimes a horny one. Skeletal development can vary from individual spicules scattered in the mesoglea to powerful stone-like structures of various sizes and shapes (in madrepore corals). These skeletons are a derivative of ectoderm.
The formation of the skeleton in corals is largely due to the presence of polyps in the body symbiotic algae . Let us consider the chemical reactions that occur during the formation of the calcareous skeleton. The starting substances – calcium ions and carbon dioxide – are contained in sea water in sufficient quantities.
Carbon dioxide, dissolving in water, forms very unstable carbonic acid:
H 2 O + CO 2 ↔ H 2 CO 3, which immediately dissociates into ions:
H 2 CO 3 ↔ H + + HCO 3 - .
When Ca ions interact with HCO 3, calcium bicarbonate is formed:
Ca ++ + 2 HCO 3 - ↔ Ca (HCO 3) 2. This substance is soluble in water, but it is not strong and easily turns into insoluble calcium carbonate:
Ca (HCO 3) 2 ↔ Ca CO 3 ↓ + H 2 O + CO 2.
With an excess of CO 2, this reaction shifts to the left and soluble bicarbonate is formed. As the CO 2 concentration decreases, the reaction shifts to the right and a lime precipitate precipitates.
Algae living in the body of polyps constantly remove carbon dioxide from the tissues of coelenterates for the process of photosynthesis, constantly creating a reduced concentration of CO 2. Such conditions favor the formation of insoluble calcium carbonate and the construction of a powerful skeleton by polyps.
Digestive system and nutrition. The digestive system is represented by the gastric cavity. Most coelenterates are predators. They bring prey killed or stunned by stinging cells with their tentacles to the mouth opening and swallow it.
In hydroid polyps, the gastric cavity has the form of a simple sac, which communicates with the environment through the oral opening. Various small animals entering the gastric cavity are most often absorbed by endoderm cells ( intracellular digestion). Larger prey can be digested by enzymes secreted by glandular cells. Undigested remains are expelled through the mouth.
In coral polyps, the gastric cavity is divided longitudinally by septa, which increases the area of the endoderm. In addition, the ectodermal pharynx protrudes into the digestive cavity of corals.
As already mentioned, reef-building corals enter into a symbiotic relationship with a certain type of single-celled algae that settle in the endodermal layer. These plants, receiving carbon dioxide and metabolic products from the polyp, supply it with oxygen and a number of organic substances. The algae themselves are not digested by the polyps. IN normal conditions This symbiosis allows polyps to survive for a long time without the intake of organic substances from the environment.
U jellyfish The gastric cavity is generally formed by the stomach, located in the central part of the umbrella, radial canals extending from the stomach and an annular canal running along the edge of the umbrella. There are most often 4 radial canals in hydromedusae, and 16 in scyphomedusae. The entire complex of canals forms the so-called gastrovascular system .
Nervous system. U polyps nervous system diffuse type . Individual nerve cells located at the base of the epithelium of the ectoderm and endoderm are connected by their processes into a nervous network. The mouth opening and the base of the polyps are surrounded by a denser nerve network.
U jellyfish the nervous system is more concentrated than that of polyps, which is associated with a mobile lifestyle.
U hydroid jellyfish clusters of nerve cells are located along the edge of the umbrella. The cells themselves and their processes form a double nerve ring. The outer ring performs sensory functions, and the inner ring performs motor functions.
U scyphoid jellyfish the nerve ring is less pronounced, but at the base of the rhopalia (marginal sensory bodies) there are clusters of nerve cells that can be called ganglia.
Sense organs. Due to a sedentary lifestyle, polyps special no sense organs . There are only individual sensitive (tactile) cells, which are mostly located near the mouth opening.
U jellyfish There are also sensory cells, but there are also special sense organs - vision, balance and smell.
Along the edge of the umbrella there are organs of vision - eyes , different in structure. In hydroid jellyfish, the eyes lie alone, while in scyphoid jellyfish, the eyes are located on rhopalia - sensitive marginal bodies. Moreover, one ropalia can bear several eyes of varying degrees of complexity at once.
Due to their active lifestyle, jellyfish have developed balance organs - statocysts. They are a vesicle lined from the inside with sensitive cells. Inside the bubble there is a calcareous body - a statolith. Depending on the position of the jellyfish in space, the statolite irritates a certain area of the vesicle wall. There are other types of statocyst structure. In addition, statocysts are able to detect vibrations in water, so they can also be called organs of hearing. In hydroid jellyfish, the balance organs are located along the edge of the umbrella in the amount of 4-80 different types.
Scyphoid jellyfish also have olfactory pits are chemical sense organs.
In scyphoids, all sense organs are located on 8 rhopalia - modified tentacles.
Breath. Gas exchange in coelenterates occurs through the diffusion of oxygen and carbon dioxide. In large species (corals), the pharynx has siphonoglyphs lined with ciliated epithelium. Cells equipped with cilia constantly supply fresh water to the intestinal cavity of the animal. Many polyps, as already mentioned, have switched to symbiosis with algae, which supply the coelenterates with oxygen and relieve them of carbon dioxide.
Genital organs. U polyps There are no special genital organs. Sex cells are formed either in the ectoderm or in the endoderm. In the first case, the gametes exit through a break in the ectoderm, in the second, they first enter the gastric cavity, and then out through the mouth. Among the polyps there are hermaphrodites (hydra) and dioecious (corals).
U jellyfish , which are almost always dioecious, have gonads.
U hydromedusa they are formed in the ectoderm of the lower side of the umbrella under the radial canals, less often on the oral proboscis. The number of gonads corresponds to the number of radial canals. Gametes are released through the ruptures of the glands.
U scyphoid jellyfish gonads of endodermal origin. They form in the pockets of the stomach. Gametes first enter the gastric cavity and then into the environment.
Reproduction. Coelenterates reproduce both asexually and sexually.
Asexual reproduction most often occurs through budding . This path is typical for polyps, but is rare in jellyfish. In single polyps, a bud appears on the body, which gradually forms tentacles and a mouth opening and then breaks away from the mother’s body. In colonial hydroids and corals, the daughter individual does not separate from the mother, which leads to the formation of colonies.
Colonial hydroid polyps are not capable of sexual reproduction, so they also bud off sexual individuals - jellyfish. Jellyfish are formed either on the axis of the colony or on special outgrowths - blastostyles.
Another method of asexual reproduction is strobilation , when the polyp at a certain stage begins to lace in the transverse direction several times and a small jellyfish is formed from each part. Almost the entire body of the polyp is spent on the formation of jellyfish. This method is typical for scyphoid jellyfish.
Thus, there is a change between the polypoid asexual and medusoid sexual generations. At the same time, the polypoid generation predominates in hydroids, while the medusoid generation predominates in scyphoids. Corals do not have a medusoid generation.
In a number of hydroids, jellyfish do not separate from the colony, and in some, the jellyfish is reduced to the state of a “genital sac” - a sporosarca.
Very interesting siphonophores , representing a huge colony consisting of organisms of various structures. Each colony has a pneumatophore - a bubble of air that supports the siphonophore on the surface of the water.
Sexual reproduction characteristic of all jellyfish, all corals and some hydroid polyps. The sexual process involves haploid cells - gametes, which copulate either in environment, or in the body of a coelenterate. The egg undergoes complete uniform crushing. Gastrulation of the blastula most often occurs by immigration, less often by intussusception. Subsequently, a two-layer larva is formed - a planula, covered with cilia and leading an active lifestyle. For sedentary animals such as corals (which do not have a medusoid generation), the planula is the only dispersal stage. A polyp is always formed from the planula, which subsequently buds off either only polyps (corals), or polyps and jellyfish (hydroids), or only jellyfish (scyphoids). Thus, the development of the vast majority of coelenterates occurs with metamorphosis. Sometimes a polyp immediately forms from an egg (for example, in hydra).
Regeneration. Coelenterates have a high ability to regenerate. Experiments to study this phenomenon in hydra were carried out back in 1740 by Tremblay. It turned out that the animal can regenerate from 1/200 of the part.
Origin. Most likely, the ancestors of coelenterates were free-swimming organisms like parenchymella , which was described by I.I. Mechnikov. These hypothetical organisms lacked skeletons and therefore could not have been preserved as fossils.
The oldest finds of coelenterates - coral skeletons - date back to the Cambrian period (about 600 million years ago). At the same time, not only individual prints were preserved, but also entire fossilized reefs. A few prints of jellyfish and hydroids are also known. In total, more than 20,000 species of fossil coelenterates are known.
Meaning. In nature, coelenterates, being predators and at the same time food for other animals, participate in complex food chains of marine biocenoses. Corals are of great geochemical importance, forming thick layers of calcareous rocks. Throughout their existence, corals take part in the formation of islands. Reefs are unique biocenoses where a huge number of animal species live.
Practical significance modern coelenterates is small.
Corals (especially red and black) are used as jewelry. They are mined in large quantities mainly by artisanal methods. On large reefs, collecting corals is prohibited.
Some jellyfish pose a serious danger to humans. In our seas, these include the small Far Eastern cross jellyfish, which lives in thickets of marine plants, and the large Black Sea cornet, often found off the coast. The poison of the cross is sometimes fatal. The most dangerous jellyfish, the sea wasp, lives off the coast of Australia. Touching this animal causes severe pain and shock. Many people died when meeting her.
In China and some other countries, specially prepared rhopile jellyfish are eaten. There is a special craft there.
Since ancient times, people have known strange shapeless sea animals, to which they gave the name “jellyfish” by analogy with the mythological ancient Greek goddess Medusa the Gorgon. The hair of this goddess was a moving tuft of snakes. The ancient Greeks found similarities between the evil goddess and sea jellyfish with poisonous tentacles.
The habitat of jellyfish is all the salty seas of the World Ocean. There is only one known freshwater species of these sea creatures. Each species occupies a habitat limited to one body of water and will never be found in another sea or ocean. Jellyfish are either cold-water or heat-loving; deep-sea and those that stay near the surface.
However, such species swim near the surface only at night, and during the day they dive into the depths in search of food. The horizontal movement of jellyfish is passive in nature - they are simply carried by the current, sometimes over long distances. Due to their primitiveness, jellyfish do not contact each other in any way; they are solitary animals. Large concentrations of jellyfish are explained by the fact that the current brings them to places rich in food.
Due to the highly developed colorless mesoglea, the body of the “flower cap” jellyfish (Olindias formosa) looks almost transparent Types of jellyfish
More than 200 species of jellyfish are known in nature. Despite the primitiveness of the structure, they are very diverse. Their sizes range from 1 to 200 cm in diameter. The largest jellyfish is lion's mane(cyanea). Some of its specimens can weigh up to 1 ton and have tentacles up to 35 m long.
Jellyfish are shaped like a disk, an umbrella, or a dome. Most jellyfish have a transparent body, sometimes with bluish, milky, or yellowish tints. But not all species are so inconspicuous; among them there are truly beautiful ones, bright colors: red, pink, yellow, purple, speckled and striped. There are no green jellyfish in nature.
Species such as Equorea, Pelagia nocturna, and Rathkea can glow in the dark, causing a phenomenon called bioluminescence. Deep sea jellyfish emit red light, floating near the surface - blue. There is a special type of jellyfish (staurojellyfish) that hardly move. They are attached to the ground with a long leg.
The structure of jellyfish
The internal structure and physiology of jellyfish are uniform and primitive. They have one main hallmark– radial symmetry of organs, the number of which is always a multiple of 4. For example, a jellyfish umbrella can have 8 blades. The body of a jellyfish does not have a skeleton; it consists of 98% water. When thrown ashore, the jellyfish is unable to move and dries up instantly. Its consistency is similar to jelly, which is why the British called it “jelly fish.”
Body tissues have only two layers, which are connected to each other by an adhesive substance and perform different functions. The cells of the outer layer (ectoderm) are “responsible” for movement, reproduction, and are analogues of skin and nerve endings. The cells of the inner layer (endoderm) only digest food.
The outer part of the body of jellyfish is smooth, mostly convex, the inner (lower) shape resembles a bag. The mouth is located at the bottom of the dome. It is located in the middle and is very different in structure among different types of jellyfish. The umbrella is surrounded by hunting tentacles, which, depending on the species, can be either thick and short or thin, thread-like, and long.
What do jellyfish eat?
Jellyfish are predators; they consume only animal food (crustaceans, fry, small fish, caviar). They are blind and have no senses. Jellyfish hunt passively, catching with their tentacles the edibles that the current brings. The hunting tentacles kill the prey. This is done different ways.
This is the largest jellyfish in the world - the cyanea, or lion's mane (Cyanea capillata), its long tentacles can reach 35 m in length! Some types of jellyfish inject poison into the prey, others glue the prey to the tentacles, and others have sticky threads in which it becomes entangled. The tentacles push the paralyzed victim towards the mouth, through which undigested remains are then expelled. Interestingly, jellyfish living in the depths attract prey with their bright glow.
How do jellyfish reproduce?
Jellyfish have vegetative (asexual) and sexual reproduction. Externally, males are no different from females. Sperm and eggs are released through the mouth into the water, where fertilization occurs. After this, the larva (planula) develops. The larvae are not able to feed, they settle to the bottom and a polyp is formed from them. This polyp can reproduce by budding. Gradually, the upper parts of the polyp separate and float away; these are actually young jellyfish that will grow and develop.
Some species of jellyfish do not have a polyp stage. Young individuals are immediately formed from the planula. There are also species in which polyps are formed in the gonads, from which small jellyfish are born. Each egg cell in jellyfish produces several individuals.
Vitality of jellyfish
Although jellyfish do not live long - from several months to 2-3 years, their numbers are restored very quickly even after various disasters. Their reproduction rate is very high. Jellyfish quickly restore lost body parts. Even if they are cut in half, two new individuals are formed from the halves.
Interestingly, if such an operation is performed in at different ages jellyfish, then an individual of the corresponding developmental stage grows from the tissues. If you divide the larva, then two larvae will grow, and from the adult parts - jellyfish of the appropriate age.
Jellyfish swimming upside down Jellyfish and people
Some types of jellyfish pose a danger to humans. They can be roughly divided into two groups. Some cause allergies, while the venom of others affects the nervous system and can cause serious problems in the functioning of the muscles and heart, and in some cases, death.
To avoid putting yourself in danger, you should avoid touching jellyfish, both living and dead. In case of a burn, you should wash the injured area with water, or better yet, a vinegar solution. If the pain does not subside and there are complications, you should immediately call a doctor.
The nervous system of jellyfish is much more complex than that of polyps. In jellyfish, in addition to the common subcutaneous nerve plexus, along the edge of the umbrella there is an accumulation of ganglion cells, which, together with the processes, form a continuous nerve ring. It innervates the muscle fibers of the sail, as well as special sensory organs located along the edge of the umbrella. In some jellyfish these organs look like eyes, while in others they look like statocytes, which are not only organs of balance, but also devices that stimulate contractile movements of the edges of the umbrella: if you cut out all the statocytes from a jellyfish, it will stop moving. The simplicity of the nervous system of these animals gives them a great advantage in life - they can regenerate both individual lost parts of the body and the entire body from one tenth of it. The disadvantage is that they do not have a structured nervous system, which only perceives information about changes in the environment, but does not provide the ability to quickly and correctly respond to these changes.
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“Nervous system” - The olfactory lobes are small. Due to their terrestrial existence, the nervous system of reptiles becomes even more complex. The cortex covers the entire forebrain. The nervous system of fish is represented by the head and spinal cord. Nerve cell. The improvement of the nervous system also affected the development of sensory organs. The nervous system of amphibians is characterized by a more complex structure.
“Human nervous system” - Human behavior depends on the characteristics of the nervous system. Functions of the nervous system: To form an idea of the structure of the nerve cell and the features of the human nervous system. CENTRAL NERVOUS SYSTEM (brain). Diseases of the nervous system: Diseases of the nervous system. In the nervous system there are:
“Baltic jellyfish” - For more than half a century, ammunition filled with deadly poison lies on the bottom of the Baltic. Would we be able to survive in such a sea if we were jellyfish...? Posing a mortal threat. And the order is familiar to everyone... Was it possible to avoid death? The eared jellyfish lives in the waters of the Baltic Sea. What is left after people rest?!
“Autonomic nervous system” - To study the state of health of the nervous system of students of the Municipal Educational Institution “Secondary School No. 5”. The object of the study is students of school No. 5. Hygiene of mental work Proper nutrition Daily routine Contraindicated use alcoholic drinks. Performs its functions through two systems that coordinate the work of different organs - sympathetic and parasympathetic.
“Higher nervous activity of a person” - It is thanks to the mental component that human behavior is so diverse and unique. Methods of physiology of VNI. Studying the living conditions of an animal can be good welcome, revealing. Subject of physiology of higher nervous activity. In the process of evolution, conditioned reflexes begin to dominate behavior.
Rice. 34. Different types of sponges: a - badyaga; b - glass sponges
neem are dormant winter buds. For example,
and pr (and the water sponge badyaga reproduces in summer by normal budding
n sexually. But by autumn, in the mesoglea of badyagi, amebocytes form
Globular gemmules. In winter, the body of the badyagi dies and disintegrates. The gemmules remain at the bottom and overwinter. In the spring, the cell mass contained inside the cell mass crawls out, attaches to the substrate and grows into a new sponge. Gemmules also perform the function of dispersing I RMGIIN, since during the spring flood they are transported by currents.
When water bodies dry up, gemmules can be carried by the wind. 11solous reproduction of sponges occurs through the formation in meso-
I ngg it amebocytes of eggs and sperm. Spermine is carried into the lower part of the canaliculi and with the water of the paragastric cavity - into the external irradiation through the mouth (osculum). With the flow of water, sperm enters the body of the first egg and, having mature eggs, penetrates the mesoglea and is drained by them, i.e. Fertilization in sponges is cross-fertilization.
II in the maternal organism, a larva develops from the zygote, covered with cilia; The larva comes out, actively swims, and moves.” flowing water over considerable distances, then descends to the MMO. attaches to the substrate and turns into a sponge.
The most diverse and numerous sponges are from tropical and subtropical seas. Sponges are found at shallow depths, preferring a rocky bottom. They often cohabit with other organisms, entering into symbiotic relationships of various types with them. In sponge colonies you can find annelids, crustaceans, echinoderms and other animals. Sponges often settle on mobile animals (crabs, gastropods). Single-celled green algae often live inside the cells of freshwater sponges as symbionts, which provide the sponges with oxygen and can also serve as food for the sponges. About 20 species of freshwater sponges are found in Russia, most of which live in Lake Baikal. The most typical species in our rivers is the badyaga (Spongilla lacustris).
Boring sponges (genus Cliona) settle on calcareous substrates - mollusk shells, coral colonies, limestones. Drilling sponges live in the holes they make by dissolving lime with a special secretion; Only body outgrowths with apertures protrude outward.
The practical importance of sponges mainly comes down to the biological filtration of water from suspended mineral and organic substances. Despite small sizes(from a few millimeters to 1.5 m), sponges pass a huge amount of water through themselves: one badyaga sponge measuring 5-7 cm filters about 3 liters of water per day.
Sponges have many signs of primitive organization: they lack real differentiated tissues and organs, cellular elements are characterized by high plasticity, etc. Sponges are capable of regeneration: when individual parts of the body are removed, they are restored. If a crushed sponge is sifted through a sieve, the resulting mass of individual cells and their groups is capable of restoring the entire organism. The cells of the pulp actively move and gather together, subsequently a small sponge is formed from this accumulation of cells. This process of forming an organism from a collection of cells is called somatic embryogenesis.
Sponges are ancient organisms. The separation of sponges from the trunk of multicellular organisms occurred a very long time ago. There is an opinion that sponges could have evolved from colonial collared flagellates, independently of other multicellular organisms. No less justified is the hypothesis that multicellular organisms originated from a common trunk, from which sponges were one of the first to separate. The second hypothesis seems more reasonable, since the larvae of sponges are similar to the larvae of planulae of coelenterates.
TYPE COELENTERATA (Coelenterata)
General characteristics. The phylum unites more than 10 thousand species of primitive multicellular animals that lead an exclusively aquatic lifestyle and live mainly in the seas. Some of them lead a free-swimming lifestyle, others are sessile and attached to the bottom.
Coelenterates are characterized by radial symmetry, which is associated with their lifestyle. In sessile forms, one pole of the body usually serves for attachment to the substrate, and the other has a mouth. Many organs develop in the same way, resulting in radial symmetry. Coelenterates are two-layer animals: they develop only two germ layers - ectoderm and endoderm. Between these leaves there is a primary body cavity filled with mesoglea, which in some representatives has the form of a plate, while in others it is a large mass of gelatinous substance.
IN simple case The body of coelenterates has the appearance of a sac open at one end, in the intestinal (gastric) cavity of which, lined with endoderm cells, food is digested. The hole serves as a mouth for coelenterates; it is surrounded by a crown of tentacles that help capture food particles. The anus is absent, and undigested food remains are thrown out through the mouth. Thus, we can conclude that simply arranged coelenterates are reduced to a typical gastrula. The sessile forms that are closest to this structural scheme are polyps, which are widespread among coelenterates. Free-living forms have a flattened body; these are jellyfish that actively and passively move with currents aquatic environment. The body of jellyfish has the appearance of a transparent gelatinous umbrella. The mouth, located in the middle of the lower side of the dome and surrounded by preoral lobes, leads into the colic cavity, from which radial canals extend. Ocean jellyfish reach two meters in diameter.
The division of coelenterates into polyps and jellyfish is purely morphological, since sometimes the same species of coelenterates at different stages of the life cycle can have the structure of either a jellyfish or a polyp. Jellyfish are usually solitary, free-living animals, while polyps are mostly colonial forms. Starting life as a single organism, the polyp, through incomplete budding, forms colonies numbering thousands of individuals.
Coelenterates are characterized by the presence of stinging cells that serve for obtaining food and protection.
Coelenterates reproduce asexually (by budding) and by the buttocks. In many forms, an alternation of generations is observed: the asexual generation of polyps is replaced by the sexual generation of jellyfish.
Structure and vital functions. Veils coelenterates are formed by single-layer epithelium of ectodermal origin. The epithelium contains highly specialized cellular elements. Thisepithelial-muscularcells containing myofibrils, which ensure shortening of the polyp body. Sensitive cells that function as receptors that receive signals from the external environment are scattered throughout the entire surface of the body and especially densely on the tentacles and around the mouth. Characteristic of the integument of coelenterates are stinging cells, mainly located
Rice. 35. Stinging cells of Hydra olidactis:
a - at rest; b - with discarded thread
on the tentacles (Fig. 35). Inside each such cell there is a capsule with a spirally twisted hollow thread. If you touch the sensitive hair of the cell, the stinging thread is turned inside out and thrown out. A thread armed with spines is pierced into the body of the victim and held in the wound, while introducing into it a poisonous secretion that paralyzes small prey. In large animals this secretion causes burns. Stinging cells are disposable weapons. In place of the damaged cells, new ones are formed, since in the integument of coelenterates there are special cells that can turn into stinging, reproductive, sensitive and others.
The nervous system of polyps is represented by a diffuse-type nerve plexus formed by stellate nerve cells connected
with their shoots. Nerve plexus lies under the surface epithelium. In free-living jellyfish, the nervous system is more complex: it is a nerve ring located along the edge of the dome and clusters of nerve cells around the eyes and statocysts.
The sense organs are primitive and better developed in jellyfish (statocysts and eyes). Sensitive cells are present in the integument of the body, especially on the tentacles and around the mouth.
Musculature. In polyps, the body shape changes as a result of the action of epithelial muscle cells having myofibrils. In jellyfish, movement is ensured by special muscle fibers located in the mesoglea along the edges of the dome. In coral polyps, longitudinal and transverse muscle fibers are located in the septa of the intestinal cavity.
Digestive organs. In hydras and related forms, the mouth opening opens directly into the intestinal (gastric) cavity. In most species, the mouth leads into the ectodermal pharynx and then into the intestine. In coral polyps, radially located longitudinal partitions protrude into the intestinal cavity to increase the absorption surface. In jellyfish, radial canals extend from the intestinal cavity into the interior of the dome, flowing into the annular canal. The intestinal cavity of jellyfish continues into the cavity of the tentacles.
The intestinal cavity of coelenterates is lined with single-layer endodermal epithelium, the cells of which have flagella that serve to move food particles. There are special glandular cells. Some epithelial cells form pseudopodia that capture food particles. Simultaneously with intracellular digestion in coelenterates, cavity digestion partially occurs.
in the intestinal cavity with the help of digestive enzymes produced by the glandular cells of the intestinal epithelium. Hydroid polyps have two phases of food digestion. First, they swallow a large lump of food or a whole animal, which begins to be digested in the gastric cavity. Then small particles of semi-digested food enter the epithelial-muscular digestive cells, where intracellular digestion occurs. Undigested residues are thrown out through the mouth.
Coelenterates lack respiratory organs, and gas exchange occurs through the integument of the body.
Excretory system. Metabolic products (water, carbon dioxide, urea, uric acid, ammonia, etc.) are released through the epithelial layer of ectoderm and endoderm.
Reproduction. Most coelenterates are dioecious animals, but there are also hermaphrodites. In hydroids, reproductive products are formed in the ectoderm; in other representatives, their formation occurs in the endoderm. Fertilization in some species is external (in water), while in others it is internal, in the body of the female, where sperm penetrate. Development usually occurs with the planula larva stage covered with cilia, allowing the planula to swim. U freshwater hydras development is direct.
The phylum Coelenterates are divided into three classes: Hydrozoa, Scyphozoa and Anthozoa.
CLASS HYDROID (Hydrozoa)
The lowest class of coelenterates, consisting of approximately 4 thousand species. Hydroids are represented by a variety of solitary and colonial forms, inhabiting mainly seas and oceans. There are also freshwater representatives. Unlike scyphoid jellyfish and coral polyps, polyps and jellyfish that belong to the class Hydrozoa are called hydroids. Hydroids have no pharynx, and the walls of the intestinal cavity do not have longitudinal partitions. Reproductive products are formed in the ectoderm.
The most typical for fresh waters are different kinds hydras (Hydra), leading a solitary polyp lifestyle (Fig. 36). These are small animals 1-2 cm high with an expanded base on which they are held on the substrate. The mouth opening is surrounded by a corolla of 6-12 tentacles, and the wider body passes into the stem. Mesoglea has the appearance of a thin supporting plate in which nerve, epithelial-muscular and intermediate cells are scattered. From the latter, if necessary, reproductive, stinging and other cells are formed. The nervous system of the hydra is diffuse, although there are small clusters of nerve cells around the mouth and on the sole. Epithelial muscle cells can form pseudopodia and are therefore capable of phagocytosis.
Rice. 36. Freshwater hydra Hydra olidactis:
A - general form; b - longitudinal section; 7 - body; 2 - sole; 3 - tentacles; 4 - mouth; 5- kidneys; 6 - intestinal cavity; 7- endoderm; 8- ectoderm; 9- supporting plate - mesoglea; 10 - testes; 11 - egg formation
Hydras live in fresh water bodies with stagnant or slow-moving water. Hydras can move slowly by sliding the sole along the substrate or by “tumbling” through the head end. They feed on small crustaceans, ciliates, rotifers and other planktonic animals, capturing prey with tentacles armed with stinging cells.
Hydroids reproduce by budding and sexually. Approximately in the middle of the hydra's body there is a budding belt. Daughter organisms bud off and begin independent life throughout the summer. In autumn, hydras reproduce sexually. Special bulges appear on the surface of the body: several testes or one or two ovaries, each of which produces only one egg. Hydras are dioecious, but some are hermaphrodites. In the latter case, the testes on the hydra's body are formed above the ovaries. Sperm cells enter the water and penetrate the egg of another individual. Cross-fertilization in hermaphroditic forms is achieved at different times maturation of sperm and eggs. First, the development of the zygote occurs in the ovary, then the embryo becomes covered with membranes, falls to the bottom and overwinters. In this state, the embryo can tolerate freezing and drying out of the reservoir. In the spring, a hydra grows from an overwintered embryo. Thus, in freshwater hydras, development is direct.
Hydras are capable of regeneration, even from a part of the body the entire organism is restored.
Among the inhabitants sea waters the vast majority of hydroids are colonial forms with a complex life cycle (Fig. 37). Colonies are formed by repeated incomplete budding. The result is a complex of individuals sitting on a common trunk and its side branches. Therefore, the colony usually resembles brown growths of moss or a bush, on the branches of which individual individuals of the colony sit - hydrants, similar in structure to a hydra. The intestinal cavities of all hydrants communicate with each other, that is, food and colonies can be distributed throughout the colony, which ensures its survival. For stability and strength, due to the secretions of the ectodermal epithelium, the polyps form an organic shell - the theca, which covers not only the general trunk, but also individual hydrants.
Reproduction of hydroid polyps includes alternation of an asexual generation, leading an attached lifestyle, and a sexual generation - free-swimming hydroid jellyfish (hydromedusas). In the hydrants themselves, colonies do not form gonads. Periodically, special buds form on the branches of a colony of hydroid polyps,
a b
Rice. 37. Hydroid Obelia:
I colony (slightly enlarged); b - a separate branch of the colony (somewhat schematically, part of a special colony is shown in section); 1 - hydrant in straightened position; 2 - contracted hydrant; 3 - theca; 4- kidney; 5- blastostyle with developing jellyfish; 6 - hydrotheque; 7- gonoteca (the area of the theca covering the blastostyle)
giving rise to sexual individuals - small hydroid jellyfish. These jellyfish break away from the mother colony and swim freely. Hydroid jellyfish grow and sex cells develop in them. Jellyfish are dioecious. Hydroid jellyfish are much more complex than hydroid polyps; jellyfish have a nerve ring, statocysts, eyes, etc. Jellyfish lead a predatory lifestyle, capturing and killing small animals with their tentacles, swallowing and digesting them in the stomach. After maturation, the sex cells enter the water and copulate.
After copulation of the gametes, planula larvae are formed, which swim freely in the water with the help of numerous cilia. After some time, the planulae sink to the bottom, attach to the substrate and turn into stationary polyps, which give rise to new colonies.
CLASS Scyphoid Jellyfish (Scyphozoa)
The class, numbering about 200 species, is represented by large and small sea jellyfish. Most of their life cycle takes place in the form of swimming jellyfish (a few forms are attached); the polyp phase is short-lived or may be absent. The body of scyphoid jellyfish has the shape of an umbrella, dome, etc. (Fig. 38). The structure of the nervous, muscular and digestive systems at
Rice. 38. Scyphoid jellyfish:
a - cornet jellyfish; b - diagram of the structure of aurelia; 7 - mouth; 2 - ropalia; 3 - oral lobes; 4-ring channel; 5 - radial channels; b-tentacles; 7 sex glands
Rice. 39. Scheme of development of the scyphoid jellyfish Aurelia (Aurelia aurita):
/ - planula larva; 2 - scyphistoma polyp; 3,4 - stages of scyphistoma budding; 5 - separation of ether larvae from scyphistoma; 6- young ethereal jellyfish; 7-adult jellyfish
these jellyfish are more complex. The mesoglea of the dome contains muscle fibers that provide compression of the dome. Scyphoid jellyfish differ not only large sizes body, but also the absence of a special sail (a thin muscular membrane that narrows the edge of the bell), which plays an important role in the movement of hydroid jellyfish. The intestinal cavity has radial folds and radial canals flowing into the annular canal. The central part of the digestive apparatus is the stomach, from which the big number branched tubules that perform transport functions nutrients in the body of jellyfish.
The preoral lobes have numerous tactile and stinging cells. Along the edge of the umbrella there are clusters of nerve cells - ganglia. The sense organs are concentrated in shortened tentacles - rhopalia. Inside the rhopalia there is a statocyst, and on the sides there are two ocelli that perform photosensitive functions. The tentacles have olfactory pits - chemical sense organs.
Most jellyfish are dioecious. Reproductive products are formed in the endoderm: the gonads are located in the walls of the stomach. Sex cells exit through the mouth into the water, where copulation of male and female female gametes. From fertilized eggs, microscopic larvae - planulae - develop. They swim with the help of cilia, then sink to the bottom, attach to the substrate and turn into small single goblet-shaped polyps - scyphistomas. As the scyphistoma grows, transverse constrictions appear on its body, dividing the polyp into a number of discs - jellyfish (ethers). Each ether detaches from the scyphistoma, grows, and develops into a free-swimming adult jellyfish. Thus, the development of scyphoid jellyfish is not direct, but occurs through the stages of planula and scyphistoma (Fig. 39).
CLASS CORAL POLYPS (Anthozoa)
The class includes one of oldest groups marine animals - polyps, which are superior to hydroid polyps not only in size, but also have a more complex structure. These are single or mostly colonial polyps, one of the features of which is the absence of a jellyfish stage in the life cycle (Fig. 40), that is, they do not have alternation of generations. This is the largest class of coelenterates, including more than 6 thousand species that live in warm tropical seas with water temperatures of at least 20 ° C at depths of up to 50 m.
The mouth opening of coral polyps is surrounded by a corolla of tentacles, the number of which in some polyps is eight (eight-rayed corals), in others - six (six-rayed corals).
Food particles through the mouth first enter the laterally flattened ectodermal pharynx, and from there into the well-developed intestinal cavity with partitions (septa). The number of partitions can be either eight or six, or a multiple of six - according to the number of tentacles. In the pharynx there are cells with long cilia that continuously drive water into the gastric cavity of the polyp, from where the water is discharged out. This ensures a constant change of water. The septa are formed by mesoglea lined with endoderm (Fig. 41). In the lower part of the polyp, the septa are attached only to the body wall, resulting in central part The gastric cavity (stomach) remains undivided.
Rice. 40. Red Coral Colony Branch:
/ - polyps; 2 - branch bark; 3 - axial skeleton