Flatworms: structural features, types and general characteristics. Type Flatworms

7. Type of flatworms

1. Fill out a summary table in your notebooks while studying representatives of all types of worms

2. Is the statement true: “Parasitic worms have cilia as adults”?

3. Find in the text of the paragraph a description of the skin-muscular sac. Explain why it was called that.

4. Remember the internal structure of coelenterates. Compare the internal structure of coelenterates and flatworms. Note what complications occurred.

Flatworms do not have an internal cavity, and the internal organs, united in systems, are located inside the skin-muscular sac.

5. Write down the definitions of concepts:

Intermediate host - an organism in which worm larvae develop and reside for some time.

suction cups, hooks, proboscis

Worms produce many eggs to survive. Many eggs die either without finding an intermediate host, or after entering the body of an unusual animal.

8. List the characteristics that correspond to each class of flatworms

Answer:
A - 1, 7, 9, 6
B - 2, 3, 8, 11
B - 2, 4, 5, 8, 10

Worms are a fairly common species on earth. Roundworms differ from flatworms both in appearance and in the construction of internal vital systems. However, there are not only differences between these species. Worms of these classes do not have a circulatory or excretory system in the traditional sense, but life cycle theirs is the same. Adults become dangerous.

The differences between roundworms and flatworms are not significant, but the harm to human health is significant.

General information on comparing flatworms and roundworms

Flat individuals have a flattened (often ribbon-like) body. They are also distinguished by the presence of 3 muscle layers:

• annular;
• diagonal;
• longitudinal.

Roundworms

• Cylindrical thin body, consisting of the so-called outer cuticle, under which there is an epithelial layer and muscles running along it.
• Liquid fills the body (hydroskeleton).
• The structure of the digestive system is simple. This is a tube with oral and excretory openings. It is divided conditionally into 3 parts - front, middle and back.
• The nervous system is represented by the peripharyngeal ganglion (similar to the brain). Nerve trunks branch off from the ganglion. Roundworms have a sense of touch and taste.

The main differences between roundworms within a species are their habitat. It should be noted that, unlike flat ones, round ones are bisexual. Males and females are usually distinguishable. This type has more than 15 thousand species living almost everywhere. Some can be seen under a microscope, but others are giants in comparison.

Flatworms

• ciliary;
• tape;
• flukes.

The structure of flatworms is somewhat different from roundworms. Namely:

Flat representatives, with rare exceptions, are unisexual. Their reproduction system is quite complex. In addition to the present symbiosis of male and female genital organs, this includes additional appendages and formations that fully ensure the process of fertilization and development of the embryo, by providing it with all the necessary substances.

What is the difference?

What common?

Any worms that enter the human body pose a danger to him, especially if they are not noticed in time and adequate treatment is not applied. Helminths can cause many diseases, including: ulcers, colitis, intestinal obstruction, cysts, damage to the central nervous system, meningitis. Among the most dangerous species- flukes, - paragonims and schistosomes, echinococci, roundworms, hookworms, trichinella.

The causative agent of opisthorchiasis: what it looks like, structure, habitat

The first case of opisthorchis was recorded in 1884, when a helminth previously unknown to science was found in a cat in northern Italy. S. Rivolta called the helminth the cat fluke.

7 years after the first case, the cat fluke was found in the human body in Russian Siberia. In 1891, professor and pathologist K.N. Vinogradov conducted research on the liver and discovered a leaf-shaped worm in it, which he gave the name Siberian fluke. Further research showed that the Siberian fluke is nothing more than the cat fluke that was caught earlier. Subsequently, the helminth was given the name opisthorchiasis, and the disease began to be called opisthorchiasis.

The structure and appearance of the helminth

Unlike other representatives of its class, opisthorchis is much smaller in size. This is what the helminth looks like: the body of the cat fluke is shaped like an oblong flat leaf or lancet, its length rarely exceeds 18 millimeters, and its width varies from 1.5 to 2 millimeters.

There are two suckers on the body of the helminth, one abdominal sucker and the other oral, with the help of which opisthorchis attaches to the mucous membranes of the damaging organs and sucks out nutrients. The oral sucker of the helminth serves as the beginning of its digestive tract. At the rear end of the body there is a special channel through which the processed waste products of the worm are released.

The reproductive system of the causative agent of opisthorchiasis is based on the hermaphroditic principle. The helminth has two pairs of genital organs. Opisthorchis reproduces by releasing eggs. One individual of the worm in the body of its final host is capable of producing 900-1000 eggs daily.

Opisthorchis eggs are pale yellow in color, have a double-contour delicate shell, on one pole of the eggs there is a special cap, and the other pole is slightly thickened. The sizes of helminth eggs vary from 0.011 to 0.019 in width and from 0.023 to 0.034 in length.

Habitat and endemic areas

The habitat of opisthorchis eggs is freshwater bodies of water; in such conditions they are able to maintain their vital activity for one year. It should be noted that opisthorchises develop with the participation of three carriers - one definitive host and two intermediate ones.

Considering that the helminth develops in freshwater bodies, special endemic foci are identified where the likelihood of infection with opisthorchiasis is high. Such endemic foci include:

1. Yamalo-Nenets Aut. Okrug, Khanty-Mansiysk Autonomous District district, regions of Siberia, Altai Republic. Endemic foci in Russia are also confined to the basins of the Irtysh, Ob, Volga, Northern Dvina, Kama, Don, Dnieper, and Biryusa.
2. Ukraine and Kazakhstan.
3. Italy, France, Holland.
4. India, Thailand, and other countries in Southeast Asia where fishing predominates.
5. Canada and Northern regions of the USA.

Development of the causative agent of opisthorchiasis

The causative agent of opisthorchiasis belongs to biohelminths, which means that a change of hosts is necessary for its successful life. In this case, as mentioned above, the trematode has one final and two intermediate hosts; in their organisms it goes through a full life cycle.

The opisthorchis cycle begins in the body of the final host, which is a person, as well as some mammals (cats, dogs, pigs, foxes and others). Sexually mature individuals lay eggs, and together with the feces of the owner they are released into environment, in the presence of favorable conditions, they continue their development.

Once in bodies of water, opisthorchis eggs settle at the bottom, where they are eaten by freshwater mollusks. In their organisms, the larvae of opisthorchis, miracidia, emerge from the eggs. Miracidia have special cilia; when they penetrate the intestinal wall of a mollusk, they lose them and turn into a maternal sporocyst. The sporocyst gives rise to redia, which in turn transform into cercariae. Caudate cercariae leave the body of the mollusk through the integument or mouth opening and begin hunting for the second intermediate host.

The second intermediate host of the causative agent of opisthorchiasis is fish of the carp family. The fish swallows them through the mouth, and cercariae can also enter its body through the lateral lines and integument. In the organisms of carp fish, cercariae are localized in the muscles and subcutaneous tissue, turning into metacercariae. Metacercarial larvae are slightly oval in shape, measuring 0.34 mm in length and 0.24 mm in width. Metacercariae develop in the fish's body for one and a half months, during which time they become invasive to humans.

How does infection of the final host occur? The causative agent of opisthorchiasis enters the human (animal) body when eating raw or insufficiently thermally processed fish. In the human body, metacercariae reach sexual maturity within 10-14 days. The main centers of impact are the liver, its ducts, gallbladder and pancreas. Characteristic symptoms appear two to three weeks after the onset of invasion.

Opisthorchiasis occurs in two stages, this is due to the characteristics of the life cycle of the helminth. This implies the difference in the clinical picture for the period of invasion and more late period. Entering the human body at the metacercaria stage, the helminth develops until the stage of puberty, and then during for long years lives in its usual places of localization.

On early stages The causative agent of opisthorchiasis provokes the development of an allergic reaction, which is very pronounced. This reaction of the human body is due to the fact that the helminth secretes enzymes and metabolic products that have a toxic effect.

• Inflammatory processes occur in the lymphatic system, and the same phenomena are observed in the spleen.
• Purulent-inflammatory reactions can be detected in the mucous membranes of the gastrointestinal tract and respiratory system.
• There is a disruption of blood microcirculation in the internal organs; first of all, the part of the circulatory system located in the liver suffers.
• Hypoxic signs develop and gas exchange is disrupted.
• Dystrophic changes are observed in the liver, heart and other organs.

The rate of development of pathological changes in the human body directly depends on the intensity of the invasion.

The chronic stage of opisthorchiasis is characterized by mechanical, allergic and neuro-reflex harmful effects of the helminth. There is a secondary influence of the microbial flora, as well as the influence of the decay products of one’s own cells and tissues, most of all the cells of the gallbladder. Without timely diagnosis and treatment, the development of chronic cholangitis, pericholangitis, hepatitis, and cirrhosis is likely.

The neuro-reflex effect is fraught with disturbances in the tone of the gallbladder and bile ducts, secretory dysfunction, and impaired motor function of the stomach and intestines.

Symptoms of opisthorchiasis, as a rule, include the clinical picture of a disease such as chronic gastroduodenitis. The feature is related to pathological change functions of the pancreas and adrenal glands, as well as with the development of inflammatory processes in the mucous membranes of organs. The causative agent of opisthorchiasis also provokes hormonal instability.

Treatment of opisthorchiasis should be immediate and mandatory; advanced cases of the disease lead to the development of liver cancer. Prevention of opisthorchiasis involves proper and sufficient processing of freshwater fish before eating it.

source

Tapeworms (cestodes)

The most ancient traces of cestodes were found in the remains of sharks living 270 million years ago.

Human infection

People can become infected with several types of tapeworms in different ways. When eating undercooked meat: pork (pork tapeworm), beef (ox tapeworm) and fish (wide tapeworm). Or when living and eating in conditions of poor hygiene - dwarf and rat tapeworms, echinococcus.

Treatment

Currently, the main drugs used to treat tapeworms are Praziquantel and Albendazole. Praziquantel – effective remedy, which is preferable to the older Niclosamide. Cestodoses can also be treated with certain types of antibiotics. After a course of medications, doctors can give patients enemas to completely remove worms from the intestines.

Structure

Basic common elements body of the cestode. Others may differ (the presence of a corolla with hooks, types of suction cups may be slit-like, etc.)

Larvae, in contrast, show a wide range of habitat preferences and can be found in almost any organ of both vertebrate and invertebrate hosts. Although most larval species show preference for a specific organ.

The absence of a gastrointestinal tract noticeably separates cestodes from nematodes and trematodes. The outer tegument (special epithelium) of the body serves not only as protective coating, but also as a metabolically active layer through which nutrients are absorbed, along with secretions and wastes transported from the body. To facilitate this process, the entire surface of the body is covered with microscopic wrinkles or ridges, which greatly increase the surface area available for the absorption of nutrients.

The worms do not need to move around inside the host's body, so they do not have any musculoskeletal organs or external setae.

They also do not have a circulatory or respiratory system.

The excretory and nervous systems of cestodes are similar to those of other representatives of flatworms.

Proglottid

The body of helminths of this class consists of a chain of segments (proglottids), which can be immature and mature, the latter of which are located at the end of the body and contain a fully formed uterus filled with eggs.

The totality of all proglottids (from two to several thousand) is called strobila. It is thin and resembles a strip of tape. This is where the common name “tape” comes from.

New segments grow from the neck, containing independent digestive and reproductive systems. By the time the segment reaches the end of the worm's tail, only the reproductive organs remain. In fact, such segments are already just sacs with eggs. The segment then detaches from the body, carrying the tapeworm eggs from the definitive host outside along with the feces.

Thus, each cestode consists of a series of segments having a full set of reproductive organs in a progressive degree of sexual maturity, which bud from the body from the tail.

Scolex

Life cycle

The life cycle of cestodes includes an intermediate and a definitive host (with the exception of the Dwarf tapeworm, which can develop in the same organism). It consists of several stages.

At the first stage, sexually mature individuals of tapeworms are in the body of the final host (vertebrates and humans), reproduce and produce eggs, which are subsequently released into the environment along with feces.

At the second stage (depending on the type of cestodes), a larva (embryo) is formed in the eggs on land or in water.

At the third stage, the larvae enter the body of the intermediate host (vertebrate and invertebrate animals), where they form fins. Finna is a spherical bladder (less often worm-shaped) filled with liquid, inside of which there is one or more heads. Depending on the number of heads, as well as the presence of daughter bubbles inside, 5 forms of Finn are distinguished:

• cysticercus;
• cysticercoid;
• tsenur;
• echinococcus;
• plerocercoid.

At the fourth stage, the Finns enter the body of the final host, their shell falls off, and segments begin to grow from the heads attached to the intestinal walls. Thus, at this stage, the growth and development of adults occurs.

The most common representatives

Pork and bovine tapeworms (tapeworms)

Infections caused by the ingestion of larvae of representatives of the genus Tapei, in humans or animals, are called taeniasis. The presence of an adult worm in the body (taeniasis and teniahrynchiasis) rarely causes symptoms other than minor intestinal disturbances (diarrhea, constipation or stomach upset).

Bovine tapeworm does not cause human cysticercosis.

Dwarf tapeworm

The dwarf tapeworm (Hymenolepis nana) is the smallest member of the tapeworm genus that infects humans. This cestode belongs to big family, known as Hymenolepis. Diagnostic features of this family: the scolex contains 24-30 hooks; the adult has from one to three large testes and a sac-like uterus.

The dwarf tapeworm is cosmopolitan, i.e. widespread throughout the world. The infection most often occurs in children, although adults can also be infected (and develop the disease hymenolepiasis). The disease may not cause any symptoms even with significant infestation. However, some cases of anxiety, irritability, lack of appetite, abdominal pain and diarrhea have been reported with hymenolepiasis.

The life cycle of Hymenolepis nana does not necessarily require an intermediate host; complete development occurs within the intestines of a single host (the “direct” life cycle). It can also use insects as an intermediate host.

Wide tapeworm

As a rule, they have a scolex, which is characterized by two shallow elongated bothria (slits), one located dorsally (on the back) and the other ventrally (on the ventral side). The proglottids are smoothed dorsoventrally, i.e. from the dorsal to the ventral.

Diphyllobothriasis (a disease caused by broad tapeworm) occurs as a result of eating raw, poorly cooked or pickled fish. Symptoms may be absent or minimal (intestinal obstruction, diarrhea and abdominal pain are sometimes observed). The most serious symptom is the occurrence of pernicious anemia. This is due to vitamin B12 deficiency, caused by overabsorption of this vitamin by adult worms (occurs only in a small percentage of cases).

Flatworms, which belong to the group of bilaterally symmetrical ones, are studied by the science of biology. Flatworms (Platyhelminthes) are not the only representatives of this group; more than 90% of animals belong to it, including annelids and roundworms, arthropods, mollusks, etc.

The species of flatworms are diverse and distributed throughout the world. There are about 25 thousand of them.

Scientific classification of flatworms

Flatworms are classified in the kingdom Bilateral (symmetrical on both sides) Due to some disputes that arose when trying to divide flatworms into different groups, scientists classify them as a paraphyletic group. It includes representatives of a small part of the descendants of the same ancestors.

The structure of the internal organs of a flatworm

The body of flatworms is elongated and flattened, without a cavity inside. That is, its entire space is filled with cells. Inside there are layers of muscles that, together with the shell of the worm, form a skin-muscular sac.

Internal organ systems are present:

• The digestive system is represented by the mouth and the cecum (without exit) intestine. Nutrients enter through the mouth, and can be absorbed through the entire surface of the body.
• The nervous system consists of cerebral ganglia and nerve columns. Some classes of flatworms have primitive organs of balance and vision.
• The excretory system consists of special tubules, but most often excretion occurs over the entire surface of the body.
• The reproductive system is represented by both female (ovaries) and male (testes) genital organs. Flatworms are hermaphrodites.

Differences between flatworms and roundworms

Roundworms differ from flatworms in that when cross section the body has them round shape. Roundworms are also commonly called nematodes. Possessing a bilaterally symmetrical body structure, they have developed muscles. But the main difference from flatworms is that roundworms have an internal body cavity, while flatworms do not.

Diversity of classes of flatworms

The table “Flatworms” clearly shows the division of the species into classes, which modern science totals seven.

Eyelash worms

They are predators, eating small invertebrates, arthropods and even large mollusks. They swallow small prey whole or tear off pieces from it with strong sucking movements.

The body of worms is capable of regenerating itself. A bright representative is a planaria in which even a small part of the body grows back into a full-fledged individual.

Flatworms in home aquariums

Helminths can be a big problem for those who keep fish in aquariums.

The habitat of flatworms is mainly aquatic. Being flukes, flatworms can attach themselves via an attachment disk to the surface of the gills and skin of aquarium fish.

Adult worms lay eggs, from which larvae hatch and live on the skin of fish. Gradually they crawl onto the gills, where they grow, reaching sexual maturity.

Some types of flatworms end up in a home aquarium with soil and live food. Their larvae can be found on the surface of algae, on the skin of new fish introduced into the aquarium.

• Pseudophyllidea (wide tapeworm). Infection with it can occur if raw, poorly salted fish is present in the diet. The tapeworm can live in the human small intestine for decades, reaching a length of up to 20 m.
• Aeniarhynchus saginatus ( bovine tapeworm). The habitat of flatworms is the intestines of humans and cattle. By sticking to its walls, the helminth grows up to 10 m. The larvae can be found in other internal organs, in hard to reach places(brain, muscles, liver), so it is often impossible to completely get rid of them. The patient may have a fatal outcome. Infection occurs when helminth eggs enter the stomach with insufficiently thermally processed food, or from dirty hands.
• Echinococcus (Echinococcus) is often found in dogs and cats, from them passing into the body to humans. Despite its small size - only 5 mm - the ability of its larvae to form fins that paralyze internal organs is deadly. The larvae are able to penetrate the respiratory, bone, and urinary systems. Echinococcus flatworms are often found in the brain, liver and other internal organs. A person can easily become infected with larvae excreted in a dog’s feces, which spread to the fur, and from there to all household items and food.
• The liver fluke is the culprit of cholecystitis, hepatic colic, disruption of the stomach and intestines, and allergies. The habitat of flatworms is mainly the liver of humans and warm-blooded animals, and the bile ducts. The body length of the fluke does not exceed 3 cm. The peculiarity is that not only mature individuals, but also their larvae are capable of reproduction.

Prevention of helminth infection

Preventive measures for helminth eggs and larvae entering the human body are as follows:

• It is necessary to wash your hands thoroughly with soap before each meal and after visiting public places, toilet, street, communication with pets.
• Wash raw vegetables and fruits warm water with soap.
• Do not eat raw meat and fish.
• Heat food products, especially meat and fish, for a long time.
• Pay attention to the timely prevention of helminthic infestations in domestic animals.
• Regularly, at least once a year, have your stool tested for worm eggs.

§ 1 Habitats and external structure of flatworms

Type Flatworms have about 15 thousand species of animals. Flatworms are found in all habitats: aquatic, soil, land-air and organic. Their body sizes vary from half a millimeter to 15 meters. However, despite such diversity of species, all representatives of this type have a number of common characteristics.

All representatives of Flatworms are multicellular animals and have bilateral body symmetry. Let's remember what symmetry is. Symmetry in biology is the regular arrangement of identical parts of the body relative to the center, which is called the axis of symmetry. Bilateral symmetry means that one side of an animal's body is a mirror image of the other side.

Important feature external structure Representatives of this type of animal also have a flattened top and bottom body shape. On the outside, the body of flatworms is covered with only one layer of epithelium, under which there are 3 layers of muscles. The combination of skin and muscles of worms is usually called the skin-muscle sac.

§ 2 Internal structure of flatworms

Talking about internal structure this type of animal, it must be remembered that the circulatory and respiratory system none. They are characterized by aerobic or anaerobic respiration. Oxygen enters the body through the entire surface of the body.

The digestive system of flatworms consists of a mouth, pharynx and a highly branched intestine. However, the hindgut and anus are absent, so undigested food remains are eliminated through the mouth.

The work of the excretory system is aimed at removing excess water and some metabolic products from the body. In Flatworms, it is represented by a whole network of branched tubules, which are located along the entire body, uniting into 1 or 2 excretory canals; they open at the posterior end of the body.

A pair of suprapharyngeal nerve ganglia and longitudinal nerve trunks, connected by cords, form the nervous system. Among the sense organs, Flatworms have light-sensitive eyes, special balance organs, and tactile cells.

Most species of Flatworms are hermaphrodites. Hermaphrodites are animals whose bodies contain both male and female reproductive organs. Despite this, 2 individuals participate in the fertilization process.

§ 3 Taxonomy of Flatworms

The phylum Flatworms are divided into 3 main Classes, namely: Class Ciliated worms, Class Flukes and Class Tapeworms.

The class Ciliated worms includes about 3.5 thousand species of animals. Most ciliated worms are free-living, i.e. they live in any habitat, with the exception of organisms. Their skin is covered with cilia, which give this Class its name. Due to muscle contraction, the cilia move, thereby moving the body in space. The most famous representatives of the Class Ciliated worms are: Planaria milky, Planaria black and Many-eyed.

List of used literature:

1. Konstantinov V.M. Lesson planning for the textbook “Biology. Animals" for grade 7, Konstantinov V.M., Babenko V.G., Kumchenko V.S. / Konstantinov V.M. - M.: Ventana-Graf, 2005. - 304 p.
2. World Encyclopedia: Biology/ Ch. ed. M.V. Adamczyk: Ch. scientific Ed. V.V. Adamchik: Mn.: Modern writer, 2004. – 832 p.
3. Iontseva A.Yu. Biology in diagrams and tables / A.Yu. Iontseva, A.V. Torgalov. – M.: Eksmo, 2014. – 352 p.
4. Sadovnichenko Yu.A. Biology / Yu.A. Sadovnichenko. – M.: Eksmo, 2013. – 512 p.
5. Biology: a guide for applicants to universities: In 2 volumes. T.1. – 2nd ed., rev. and additional – M.: RIA “New Wave”: Publisher Umerenkov, 2012. – 512 p.

Images used:

Number of types: about 25 thousand.

Habitat: They live everywhere in humid environments, including the tissues and organs of other animals.

Structure: Flatworms are the first multicellular animals in which, during the course of evolution, bilateral symmetry, three-layer structure, and real organs and tissues appeared.

Bilateral(bilateral) symmetry - this means that an imaginary axis of symmetry can be drawn through the animal’s body, with the right side of the body being a mirror image of the left.

During embryonic development in three-layer animals have three layers of cells: outer - ectoderm, average - mesoderm, internal – endoderm. From each layer certain organs and tissues develop:

The skin (epithelium) is formed from the ectoderm and nervous system;

from the mesoderm - muscle and connective tissue, reproductive and excretory systems;

from the endoderm - the digestive system.

In flatworms, the body is flattened in the dorso-abdominal direction, there is no body cavity, the space between the internal organs is filled with mesoderm cells (parenchyma).

Digestive system includes the mouth, pharynx and blind intestine. Absorption of food and excretion of undigested residues occurs through the mouth. Tapeworms have a completely absent digestive system; they absorb nutrients over the entire surface of the body, being in the intestines of the host.

excretory organs – protonephridia. They consist of thin branching tubules, at one end of which there are flame (flickering) cells star-shaped, immersed in the parenchyma. A bunch of cilia (flickering flame) extends inside these cells, the movement of which resembles the flickering of a flame (hence the name of the cells). Flame cells capture liquid decay products from the parenchyma, and cilia drive them into the tubule. The tubules open on the surface of the body as an excretory pore, through which waste products are removed from the body.

Nervous system ladder type ( orthogon). It is formed by a large head paired nerve ganglion (ganglion) and six nerve trunks extending from it: two on the ventral side, two on the dorsal and two on the sides. The nerve trunks are connected to each other by jumpers. Nerves extend from the ganglion and trunks to organs and skin.

Reproduction and development:

Flatworms are hermaphrodites. Sex cells mature in the sex glands (gonads). A hermaphrodite has both male glands - testes, and female glands - ovaries. Fertilization is internal, usually cross-fertilization, i.e. worms exchange seminal fluid.

CLASS cilia worms

Milk planaria, a small aquatic animal, the adult is ~25 mm long and ~6 mm wide, with a flat, milky white body. At the front end of the body there are two eyes that distinguish light from darkness, as well as a pair of tentacles (chemical sense organs) necessary for searching for food. Planarians move, on the one hand, thanks to the work of the cilia covering their skin, and on the other hand, thanks to the contraction of the muscles of the skin-muscular sac. The space between the muscles and internal organs is filled with parenchyma, in which they meet intermediate cells, responsible for regeneration and asexual reproduction.

Planarians are predators that feed on small animals. The mouth is located on the ventral side, closer to the middle of the body, from it comes a muscular pharynx, from which three branches of a closed intestine extend. Having captured the victim, the planaria sucks out its contents with its throat. Digestion occurs in the intestines under the action of enzymes (intestinal), and intestinal cells are able to capture and digest pieces of food (intracellular digestion). Undigested food remains are removed through the mouth.

Reproduction and development. Ciliated animals are hermaphrodites. Cross fertilization. Fertilized eggs fall into a cocoon, which the worm lays on underwater objects. Development is direct.

CLASS FLUKES

4 - sporocyst; 5 - redia; 6 - cercariae; 7 - adolescary.

CLASS TAPPEWORMS

Bull tapeworm– a tapeworm, reaches a length of 4 to 12 meters. The body includes a head with suckers, a neck and a strobila - a band of segments. The youngest segments are located at the neck, the oldest are sacs filled with eggs, located at the posterior end, where they come off one by one.

Reproduction and development. The bovine tapeworm is a hermaphrodite: each of its segments has one ovary and many testes. Both cross-fertilization and self-fertilization are observed. The posterior segments, filled with mature eggs, open and are excreted with feces. Cattle (intermediate host) can swallow eggs along with grass; in the stomach, microscopic larvae with six hooks emerge from the eggs, which enter the blood through the intestinal wall and are carried throughout the animal’s body and carried into the muscles. Here the six-hooked larva grows and turns into Finn- a bubble containing the head of the tapeworm with its neck. A person can become infected with finches by eating undercooked or undercooked meat from an infected animal. In the human stomach, a head emerges from the finca and attaches to the intestinal wall. New segments bud from the neck - the worm grows. Bovine tapeworm secretes toxic substances that cause intestinal disorders and anemia in humans.

Development pork tapeworm has a similar character, its intermediate host, in addition to pigs and wild boars, can also be humans, then finches develop in its muscles. Development broad tapeworm is accompanied by a change of two intermediate hosts: the first is a crustacean (Cyclops), the second is a fish that has eaten the crustacean. The definitive host may be a person or a predator that eats the infected fish.

New concepts and terms: mesoderm, skin-muscle sac, tegument, hypodermis, reduction, protonephridia (flame cells), orthogon, strobila, ganglion, gonads, hermaphrodite, direct and indirect development, final and intermediate host, miracidium, cercaria, finna, segment, armed and unarmed tapeworm.

Questions for consolidation.

1. Who is called the intermediate host? Final?

6. Why is it dangerous to drink raw water or swim in bodies of water near livestock grazing? Why is it necessary to wash your hands with soap after interacting with animals?

7. For which worms is oxygen harmful?

8. What aromorphoses led to the appearance of the Flatworm type?

Lectures on zoology

Type Roundworms

Response plan:

· General characteristics of Roundworms

Body structure of human roundworm

· Reproduction and development of Ascaris human

· Classification of Roundworms, variety of species

· The importance of Roundworms in nature and human life