Flatworms: structural features, types and general characteristics. Habitat of flatworms Habitat and habitat of flatworms

test yourself 1. name the main groups included by the type of flatworms and the characteristic distinguishing features using the example of representatives of each

2. what lifestyle do the representatives lead? various groups flatworms? How are the structural features of worms related to the image life. And the habitat?

1) Name the main groups included in the phylum Flatworms and their characteristic distinctive features using the example of representatives of each group.

2) what kind of lifestyle do representatives of different groups of flatworms lead? How are the structural features of worms related to their lifestyle and habitat?

.Name the main classes of the type Flatworms and their characteristic distinctive features using the example of representatives of each class. 2.What kind of life do they lead?

representatives various classes? How are the structural features of worms related to their lifestyle and habitat? 3. Using the example of the structural features of flat, round and annelid worms, list the signs of increased complexity of organization compared to coelenterates. 4.What diseases cause flatworms? What is their prevention? 5.What structural features and lifestyle are characteristic of representatives of the Roundworm type? 6.Why did annelids get this name? What is characteristic of the structure of each segment? 7. Based on what characteristics do annelids belong to more complexly organized animals than those previously studied?

11 Flatworms a) have bilateral symmetry b) a skin-muscular sac c) a special excretory system d) all answers are correct

12 The body cavity of the roundworm a) filled with connective tissue b) filled with liquid c) filled with air d) absent
13 In each segment of the earthworm’s body, a) nerve ganglia are repeated b) excretory tubes c) annular blood vessels d) all answers are correct
14 An earthworm has a) sense of smell b) taste c) hearing d) no special sense organs
15 An earthworm breathes a) in an oxygen-free environment b) with atmospheric air c) both options are possible d) there is no respiration
16 The shell of the common pond snail is covered with a layer of a) lime b) horn-like substance c) chitin d) silicon
17 In the circulatory system of the pond snail there are
a) two-chamber heart and one circle of blood circulation b) two-chamber heart and an open circulatory system c) an open circulatory system, the function of the heart is performed by two vessels in the front part of the body d) a single-chamber heart and an open circulatory system
18 Gastropods include a) naked slug b) livebearer c) bitinia d) all answers are correct
19 The chitinous cover of arthropods performs the functions of a) protection b) thermoregulation c) gas exchange d) all answers are correct
20 The cancer heart has a) two sections: an atrium and a ventricle b) three sections: two atria and one ventricle c) one section d) there is no heart
21 Nervous system in cancer it consists of a) suprapharyngeal ganglion b) subpharyngeal ganglion c) ventral nerve cord d) all answers are correct
22 The abdomen of the cross spider has a) three segments b) five segments c) non-segmented structure d) none of the answers is correct
23 The process of digestion in the cross spider:
a) intracavitary b) partially extracavitary c) completely extracavitary d) liquid components are digested outside the digestive system, and solid ones in the spider’s stomach
24 The body of arthropods consists of:
a) head, chest and abdomen b) head and torso c) cephalothorax and torso d) head, chest and abdomen; cephalothorax and abdomen.
25 In insects, the number of pairs of motor limbs can be equal to
a) 3 b) 4 c) 5 d) all answers are correct
26 Oxygen reaches insect tissues through diffusion through
a) walls of capillaries b) walls of trachea c) walls of pulmonary sacs d) enters first into the trachea, then into the capillaries
27 Pisces belong to the type:
a) achordates b) hemichordates c) chordates
28 The body is covered with bony scales: a) only in cartilaginous fish b) only in bony fish c) in all fish, with rare exceptions
29 Fish's eyes are always open because they:
a) the eyelids have grown together and turned into a transparent membrane b) the eyelids are absent c) the eyelids are motionless
30 The spinal cord in fish is located
a) under the spine b) in the spinal canal, which forms the upper arches of the vertebrae c) above the spine
31 Circulatory system in fish
a) closed b) open c) open in cartilaginous and closed in bone
32 Fish body temperature
a) constant, and does not depend on the temperature of the medium b) variable, but does not depend on the temperature of the medium c) not constant and depends on the temperature of the medium
33 skin in reptiles
a) has sebaceous glands b) dry (without glands) c) has a small number of glands that secrete mucus
34 The heart of reptiles
a) three-chamber b) three-chamber, except for crocodiles c) four-chamber
35 Fertilization in reptiles
a) external b) internal c) both external and internal
36 Snakes
a) legless lizards b) snakes c) a special group of reptiles
37 In all mammals, the thoracic cavity is separated from the abdominal septum
a) anthema b) ganglion c) diaphragm d) cuticle
38 Does not apply to the skeleton of the lower limb next element
a) tarsus b) femur c) tibia d) radius
39 Animals are characterized by radial symmetry of the body
a) mollusks b) flatworms c) coelenterates d) fish
40 Eliminate unnecessary things
a) scapula b) clavicle c) crow bones d) humerus
41 Bird Science is
a) poultry b) ornithology c) cynology d) zoology
42 Keel on the sternum of birds
a) promotes cutting through air during flight b) increases the area of ​​attachment of the pectoral muscles c) does not matter as an adaptation to flight
43 What digestive organs arose in birds due to their lack of jaws and teeth
a) goiter b) glandular section of the stomach c) muscular section of the stomach d) small intestine
44 Mammals spread across the Earth due to the fact that
a) were small in size b) fed their young with milk c) were warm-blooded d) all answers are correct
45 Fabrics first appeared in
a) protozoa b) coelenterates c) flatworms d) annelids
46 Darwin's theory states that all organisms
a) unchangeable and created higher powers b) were first created and then evolved naturally c) arose and

1) name the main systematic groups of the type of flatworms and their characteristic distinctive features using the example of representatives of each group.

Worms are a fairly common species on earth. Roundworms differ from flatworms both in appearance and in the structure of internal vitals. important 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 their life cycle 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

• A 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.

How are they different?

What's in 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 are flukes, paragonims and schistosomes, echinococci, roundworms, hookworms, and 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 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 a difference in the clinical picture for the period of invasion and a later period. Entering the human body at the metacercaria stage, the helminth develops until the stage of sexual maturity, and then for many years lives in its usual localization places.

In the 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 peculiarity is associated with pathological changes in the 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.

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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 is an effective drug that is preferable to the outdated 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 a protective covering, 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 a large 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), located one 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.

Brief description

Habitat and appearance	Dimensions 10-15 mm, leaf-shaped, live in ponds and low-flowing reservoirs
Body cover and skin-muscle bag	The body is covered with single-layer (ciliated) epithelium. The superficial muscle layer is circular, the inner layer is longitudinal and diagonal. There are dorso-abdominal muscles
Body cavity	There is no body cavity. Inside there is spongy tissue - parenchyma
Digestive system	Consists of the anterior section (pharynx) and the middle section, which looks like highly branched trunks ending blindly
excretorysystem	Protonephridia
Nervous system	The cerebral ganglion and the nerve trunks coming from it
Sense organs	Tactile cells. One or more pairs of eyes. Some species have balance organs
Respiratory organs	No. Oxygen is supplied through the entire surface of the body
Reproduction	Hermaphrodites. Fertilization is internal, but cross-fertilization - two individuals are needed

Typical representatives of eyelash worms are planarians(Fig. 1).

Rice. 1.Morphology of flatworms using the example of milk planaria. A - appearance of planaria; B, C - internal organs (diagrams); D - part of a cross section through the body of a milk planaria; D - terminal cell of the protonephridial excretory system: 1 - oral opening; 2 - pharynx; 3 - intestines; 4 - protonephridia; 5 - left lateral nerve trunk; 6 - head nerve ganglion; 7 - peephole; 8 - ciliated epithelium; 9 - circular muscles; 10 - oblique muscles; 11 - longitudinal muscles; 12 - dorsoventral muscles; 13 - parenchyma cells; 14 - cells forming rhabdites; 15 - rhabdites; 16 - unicellular gland; 17 - a bunch of eyelashes (flickering flame); 18 - cell nucleus

General characteristics

Appearance and covers . The body of ciliated worms is elongated, leaf-shaped. Dimensions vary from a few millimeters to several centimeters. The body is colorless or white. More often eyelash worms colored grains in different colors pigment, embedded in the skin.

Body covered single-layer ciliated epithelium. In the integument there are skin glands, scattered throughout the body or collected in complexes. Of interest are the types of skin glands - rhabditis cells, which contain light-refracting rods Rhabdites. They lie perpendicular to the surface of the body. When the animal is irritated, the rhabdites are thrown out and swell greatly. As a result, mucus forms on the surface of the worm, possibly playing a protective role.

Skin-muscle bag . Under the epithelium is basement membrane, which serves to give the body a certain shape and to attach muscles. The combination of muscles and epithelium forms a single complex - skin-muscle sac. The muscular system consists of several layers smooth muscle fibers. Most superficially located circular muscles, somewhat deeper - longitudinal and the deepest - diagonal muscle fibers. In addition to the listed types of muscle fibers, ciliary worms are characterized by dorso-abdominal, or dorsoventral, muscles. These are bundles of fibers running from the dorsal side of the body to the ventral side.

The movement is carried out due to the beating of the cilia (in small forms) or the contraction of the skin-muscular sac (in large representatives).

Clearly expressed body cavities ciliated worms do not. All spaces between organs are filled parenchyma- loose connective tissue. The small spaces between the parenchyma cells are filled with aqueous fluid, which allows the transfer of products from the intestines to the internal organs and the transfer of metabolic products to the excretory system. In addition, parenchyma can be considered as supporting tissue.

Digestive system eyelash worms blind. Mouth also serves for swallowing food, and for throwing out undigested food debris. The mouth is usually located on the ventral side of the body and leads into throat. In some large ciliated worms, such as the freshwater planaria, the mouth opening opens into pharyngeal pocket, in which it is located muscular throat, capable of stretching and protruding out through the mouth. Midgut in small forms of ciliated worms it is canals branching in all directions, and in large forms the intestine is represented three branches: one front, going to the front end of the body, and two rear, running along the sides to the rear end of the body.

Main feature nervous system ciliated worms compared to coelenterates is concentration of nerve elements at the anterior end of the body with the formation of a double node - the cerebral ganglion which becomes coordinating center of the whole body. They depart from the ganglion longitudinal nerve trunks, connected by transverse ring jumpers.

Sense organs in ciliated worms they are relatively well developed. Organ of touch All skin serves. In some species, the function of touch is performed by small paired tentacles at the anterior end of the body. Balance sense organs represented by closed sacs - statocysts, with hearing stones inside. Organs of vision are almost always available. There may be one pair of eyes or more.

Excretory system for the first time appears as separate system . She is presented two or several channels, each of which one end opens outwards, A the other is heavily branched, forming a network of channels of various diameters. The thinnest tubules or capillaries at their ends are closed by special cells - star-shaped(see Fig. 1, D). From these cells, they extend into the lumen of the tubules bunches of eyelashes. Thanks to their constant work, there is no stagnation of fluid in the body of the worm; it enters the tubules and is subsequently excreted. The excretory system in the form of branched canals closed at the ends by stellate cells is called protonephridia.

Reproductive system quite diverse in structure. It can be noted that, in comparison with coelenterates, ciliated worms special excretory ducts appear For

excretion of germ cells. Eyelash worms hermaphrodites. Fertilization - internal.

Reproduction. In most cases sexually. Most worms direct development, but some marine species development occurs with metamorphosis. However, some eyelash worms can reproduce and asexually through transverse division. In this case, in each half of the body there is regeneration missing organs.

Structural features Bilaterally symmetrical - a single symmetry cavity divides the body into left and right halves. Development occurs from three germ layers: ectoderm, endoderm and mesoderm. Third germ layer appears for the first time during evolution and gives rise to the development of parenchymal cells that fill the gaps between organs and the muscular system. Left half Right half

Structural features Body dimensions from 2-3 mm to 20 m. The body is elongated and flattened in the dorsal-ventral direction; has a ribbon-like or leaf-shaped form. It is characterized by the presence of developed organ systems: muscular, digestive (absent in ribbon-like), excretory, nervous and reproductive.

Integument of the body and the muscular system Epithelial and muscle cells are separate formations. The skin-muscle sac consists of a single-layer epithelium (in aquatic forms the epithelium has cilia) and three layers of smooth muscles: circular, longitudinal and oblique). Some representatives also have dorso-abdominal muscles. Movement is provided by muscle contraction (flukes and tapeworms) or by cilia of the integumentary epithelium and muscle contraction (ciliated worms).

The digestive system has two sections - the anterior (mouth, pharynx) and middle (branches of the intestine). The intestine is closed blindly, the hind intestine and anus are absent. Undigested food remains are removed through the mouth. Tapeworms do not have a digestive system (represented by individual digestive cells).

Excretory system Formed by a system of tubules, one end of which begins in the parenchyma with a stellate cell with a bunch of cilia, and the other ends into the excretory duct. The duct is united into one or two common channels, ending with excretory pores.

Nervous system. Sense organs. It consists of suprapharyngeal nerve ganglia (ganglia) and longitudinal nerve trunks running along the body and connected by transverse nerve bridges. Sense organs - touch and chemical sense. Free-living animals have organs of touch and balance.

Liver fluke Liver flukes usually reach 3 cm in length and 1.3 cm in width. Liver flukes of the order Opisthorchis cause opisthorchiasis, early stage symptoms are liver enlargement, allergic reactions and gastrointestinal disorders; symptoms of the late stage - pain radiating to the back, biliary colic, headaches and dizziness, insomnia. Treatment is with anthelmintic, choleretic and enzyme preparations. Also applies electromagnetic radiation high frequency.

Development cycle The life cycles of different genera differ. In species of the genus Fasciola, development occurs with one intermediate host (a freshwater snail), and infection of the final host occurs when ingested with water or eaten with coastal plants of the dormant stage - Adolescaria. In species of the genera Opisthorchis and Clonorchis, the second intermediate host is freshwater fish, and infection of the definitive host occurs when eating raw fish with invasive stages. In species of the genus Dicrocoelium, land pulmonate snails and ants serve as intermediate hosts, and infection of the final host (usually a herbivore) occurs when an infected ant eats grass.

Bovine tapeworm (tapeworm) Affects cattle and humans, causing teniahrynchiasis. Infection with bovine tapeworm is especially common in equatorial Africa, Latin America, in the Philippines and parts of Eastern Europe. An adult bull tapeworm consists of more than 1000 segments and reaches 4-40 meters in length. The formation of the reproductive apparatus begins approximately from the 200th segment. The length of mature proglottids is mm, width is 5-7 mm. The scolex (head section) is equipped with 4 suckers without hooks (therefore unarmed). The lifespan of a bovine tapeworm in the human intestine, if no deworming measures are taken, is years. The tapeworm produces ~600 million eggs per year, and ~11 billion over its lifetime.

Development cycle Segments containing eggs are released from the human intestine (the main host). Together with the grass, they enter the stomach of the cow (intermediate host). The eggs hatch into six-hooked larvae that penetrate the blood vessels of the intestine and then into the muscles. In the muscles, the larva turns into finn (a vesicle with the head of the tapeworm inside). When a person consumes poorly processed fino meat, the head of the tapeworm attaches to the intestinal wall and begins to produce segments.

Structural features Bilaterally symmetrical. Sizes from several micrometers (soil) to several meters (sperm whale nematode). They have a non-segmented body with a dense cuticle. The ciliary cover is partially or completely reduced. The body is filiform, fusiform, unsegmented, round in cross section.

The digestive system is formed by the foregut, middle and hindgut. The foregut is differentiated into sections: the mouth with cuticular lips, the pharynx and the esophagus. The midgut and hindgut are not divided into sections. The digestive tract ends with the anus.

Excretory system Represented by 1-2 skin glands (modified protonephridia). These are large cells from which two channels extend on the sides of the cell. At the posterior end of the body, the canals end blindly, and in front they open into external environment excretory at times.

Nervous system. Sense organs Nervous system of the ladder type. It is represented by the head nerve ganglia (ganglia), the peripharyngeal nerve ring and several nerve trunks (dorsal and ventral), and median transverse bridges. The sense organs are represented by the organs of touch and chemical sense. Marine forms have photosensitive receptors. Diagram of the roundworm nervous system: 1 - oral papillae with tactile endings and the nerves innervating them, 2 - peripharyngeal nerve ring, 3 - lateral cephalic ganglia, 4 - abdominal nerve trunk, 5 - lateral nerve trunks, 6 - ring nerves, 7 - posterior ganglion , 8 - sensitive papillae with corresponding nerves, 9 - anus, 10 - dorsal nerve trunk

Human roundworm Roundworms are large roundworms, their length can reach 40 centimeters. Most often they affect the gastrointestinal tract and cause ascariasis. The favorite habitat of adults is the small intestine. Roundworms are bisexual worms. Female roundworms can produce more than 200 thousand eggs per day. Fertilized eggs from the human intestine enter the soil. Larvae develop in them. Infection occurs by drinking water from open reservoirs, eating poorly washed vegetables and fruits that contain eggs with larvae. In the human body, the larva migrates: once in the intestine, it drills through its walls and enters the bloodstream.

Structural features Bilateral symmetry of the body. Dimensions from 0.5 mm to 3 m. The body is divided into the head lobe, trunk and anus. Polychaetes have a separate head with eyes, tentacles and antennae. The body is segmented (external and internal segmentation). The body contains from 5 to 800 identical ring-shaped segments. The segments have the same external and internal structure(metamerism) and perform similar functions. Metameric structure determines high degree regeneration.

Body integument and muscular system The body wall is formed by a skin-muscular sac, consisting of a single-layer epithelium covered with a thin cuticle, two layers of smooth muscle (external circular and internal longitudinal) and single-layer epithelium of the secondary body cavity. When the circular muscles contract, the body of the worm becomes long and thin; when the longitudinal muscles contract, it shortens and thickens.

Body cavity Secondary - coelom (has epithelial lining). In most, the body cavity is divided by transverse partitions corresponding to body segments. Cavity fluid is a hydroskeleton and internal environment; it is involved in the transport of metabolic products, nutrients and reproductive products.

The digestive system consists of three sections: anterior (mouth, muscular pharynx, esophagus, crop), middle (tubular stomach, midgut) and posterior (hindgut, anus). The glands of the esophagus and midgut secrete enzymes to digest food. Absorption occurs in the midgut.

Circulatory system is closed. There are two vessels: dorsal and abdominal, connected in each segment by ring vessels. Blood moves through the dorsal vessel from the rear end of the body to the front, and through the abdominal vessel from front to back. The movement of blood is carried out thanks to the rhythmic contractions of the walls of the spinal vessel and the annular vessels (“heart”) in the pharynx. Many people have red blood.

Excretory system of Metanefidial type. Metanephridia look like tubes with funnels, two in each segment. A funnel surrounded by cilia and convoluted tubules are located in one segment, and a short tubule opening outward with an opening, the excretory pore, is in the adjacent segment.

Nervous system. Sense organs. It is represented by suprapharyngeal and subpharyngeal nerve ganglia (ganglia), which are connected into a peripharyngeal nerve ring and an abdominal nerve chain, consisting of paired nerve ganglia in each segment, connected by longitudinal and transverse nerve trunks. Polychaetes have organs of balance and vision (2-4 eyes). Most have only olfactory, tactile and light-sensitive cells.

Reproduction and development Soil and freshwater forms are mainly hermaphoditic. The gonads develop only in certain segments. Insemination is internal. Type of development - direct. Asexual reproduction carried out by budding and fragmentation (due to regeneration). Marine representatives are dioecious. Development with metamorphosis, larva-trochophore.

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 belong to 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 (with no 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 their cross-sectional body has a 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.

Class name	Habitat		Life cycle
Monogenea (flukes)	With the help of an attachment disk at the rear end of the worm, Monogenea attaches to the gills of fish and the skin of amphibians and turtles	Very small, on average no more than 1 mm	Throughout its life, the worm has one host, to which it arrives as a free-swimming larva
Cestodoformes		Length ranges from 2.5 to 38 cm	The larvae develop in the body of crustaceans when the eggs are swallowed. After a crustacean is eaten by an aquatic vertebrate, the adult specimen easily moves from the intestine of the new host into the body cavity, where it lives and reproduces.
Aspidogastra	Live in the bodies of mollusks, freshwater and marine fish	An adult rarely reaches a size of more than 15 mm	Changes of hosts occur several times during the life cycle of worms
Trematodes (flukes)			They have several owners throughout their life. The larva lives initially and subsequently dies. Ingested by ingestion of cercariae (ready to colonize the organs of the final host larva)
Gyrocotylides		From 2 to 20 cm	Hypothetically, the larvae first develop in the body of the intermediate host, and only then move into the fish. But due to the fact that chimeric fish are deep-sea, the hypothesis has not been confirmed experimentally
Tape	The habitat of flatworms is the intestines of mammals and humans, to the wall of which they firmly adhere with the help of their heads	They can reach sizes up to 10 m.
Ciliary	Mostly free-living worms, they live in fresh and salt water bodies, sometimes in moist soil	Body length ranges from microscopic sizes to 40 cm	A larva similar to an adult worm emerges from the egg, living among plankton until it grows

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 striking representative is the 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.