What body symmetry do flatworms have? Flatworms - general characteristics

FASCIOLESSIS

· Blood fluke: 1. Schistosoma blood - Schistosoma haematobium

2. Schistosoma Maisoia - Schistosome mansoni

3. Schistosoma japonica - Schistosoma japonicum

SCHISTOSOMIASIS

· Opisthorchus (cat or Siberian fluke) - Opisthorchis felineus

Opisthorchiasis

· Clonorchis (Chinese fluke) - Clonorchis sinensis

CLONORCHOSIS

· Paragonim (pulmonary fluke) - Paragonimus westermani

PARAGONIMOSIS

Type Flatworms: general characteristics(PLATHELMINTHES)

The phylum Flatworms includes the following classes: Ciliated worms (Turbellaria), Flukes (Trematoda), Tapeworms (Cestoda), etc.

1. The type of flatworms is represented by bilaterally symmetrical (bilateral) animals, through whose body only one plane of symmetry can be drawn. Bilateral symmetry first appears in this group of invertebrates.

Flatworms have three layers. During the process of ontogenesis, they form not two, as in coelenterates, but three germ layers. Between the ectoderm, which forms the integument, and the endoderm, from which the intestines are built, they also have an intermediate germ layer - mesoderm. Their body in most cases is elongated and flattened in the dorso-ventral direction (takes the form of a leaf, plate, ribbon).

2 . Important Feature the structure of flatworms is the presence of a skin-muscular sac. This is the name of the combination of the epithelium and the complex system of muscle fibers located directly below it. These fibers, often breaking up into several layers (circular, longitudinal), cover the entire body of the animal under the epithelium in the form of a continuous sac, and are not divided into separate muscle bundles for a more special purpose, as in higher bilateral animals (arthropods, mollusks). The contraction of the muscular elements of the musculocutaneous sac is responsible for the characteristic “worm-like” movements of Plathelminthes.

3 . The body of flatworms does not have a cavity - they are cavityless, or parenchymatous, animals: the space between internal organs filled with connective tissue of mesodermal origin, or parenchyma containing numerous cells. Parenchyma occupies all the spaces between organs, and its role is diverse. It has a supporting role, serves as a place for storing reserve nutrients, plays an important role in metabolic processes, etc.

5 . The nervous system consists of a paired cerebral ganglion and nerve trunks extending from it posteriorly, connected by annular bridges. Two longitudinal trunks (lateral or abdominal) reach special development. Flatworms develop a central regulatory apparatus nervous system.

6 . The circulatory and respiratory systems are absent.

7 . For the first time, special excretory organs appear, built like the so-called protonephridia. They are represented by a system of branched tubules ending in the parenchyma with a special stellate cell with a bunch of cilia. Protonephridia communicate with the external environment using special excretory openings.

8. The reproductive system of flatworms is hermaphrodite; usually formed a complex system ducts that serve to excrete reproductive products, and organs appear that provide the possibility of internal fertilization.

Basic aromorphoses, ensuring the emergence and development of flatworms are the following:

Development in embryogenesis of the third germ layer - mesoderm;

The emergence of muscle, connective, epithelial and nervous tissues;

The emergence of the nodal nervous system, digestive, excretory and reproductive organ systems;

The emergence of bilateral symmetry.

Just like coelenterates, flatworms have a closed intestine with only one opening: the entrance, which is also the anus. Flatworms do not have a circulatory or respiratory system.

Comparative characteristics of classes of flatworms.

Flatworms are a type of relatively simple, segmented, soft-bodied invertebrate, bilaterally symmetrical animals that do not have a body cavity (space between organs). This group includes 25,000 species. Of these, more than 3,000 are found in Russia. Most of them parasitize the body of humans and other mammals, but there are also free-living species.

Representatives of the type Flatworms are characterized by the fact that in the process of evolution they acquired three layers, bilateral symmetry, differentiated tissues and organs.

The three-layer structure is that during the process of embryonic development, three germ layers are formed in the animal: endoderm (inner), mesoderm (middle) and ectoderm (outer).

Classification

The phylum Flatworms are divided into 7 classes:

• Tape;
• Gyrocotylides;
• Cilia;
• Trematodes;
• Monogenea;
• Cestodoformes;
• Aspidogastra.

The table below discusses the features and most common representatives of these groups.

Table 1

Due to this way of life, their nervous system and sensory organs are practically undeveloped, and there is no digestive system.

They have a thick body. At the rear end is special body for attachment in the form of a disk - haptor.

They have powerful muscles and cilia to facilitate movement. Well developed sense organs.

They have a leaf-shaped form.

There is no digestive system. The nervous system is not very well developed.

They have an attachment disk, which is located on the ventral side. It consists of several rows of suction cups.

They have a special attachment organ - a rosette, which is located at the back.

Reasons for the increase in infection cases

In developed countries:

In less developed countries:

• people often cannot afford the energy resources needed to adequately cook food;
• poorly designed water supply and irrigation systems that provide additional distribution channels;
• unsanitary conditions and the use of human feces to fertilize the soil and enrich fish farm ponds;
• Some medications become ineffective and continue to be used.

While poorer countries are still struggling with unintentional infections, in developed countries cases of deliberate self-infection with tapeworms have been reported among dieters desperate for quick weight loss.

Pests

In northwestern Europe including British Isles, there are concerns about the spread of New Zealand planaria (Arthurdendyus triangulatus) and the Australian worm Australoplana SANGUINEA, which prey on earthworms, which may lead to deterioration of soil quality. A. triangulatus is believed to have reached Europe in containers of plants imported from botanical gardens.

Human use

Two species of planarians have been successfully used in the Philippines, Indonesia, Hawaii, New Guinea and Guam to control the population growth (introduction) of the African snail species Achatina gigantea, which has begun to displace native snails in these regions. The number of unwanted snails has decreased, but it is not known exactly what role the spread of planarians played in this. Although it is believed that this has had a greater effect than other biological methods, there are now concerns that these planarians themselves could become a serious threat to their native snails.

Free-living species

Structural features

table 2

Theory for preparation for block No. 4 of the Unified State Exam in biology: with system and diversity of the organic world.

Type Flatworms

Flatworms- a type of the most primitive three-layered animals. Unlike coelenterates, they develop a third (middle) germ layer - mesoderm.

The body shape of flatworms, as the name of the type suggests, is flattened. They are bilaterally symmetrical, that is, only one plane of symmetry can be drawn through the body. This type of symmetry first appears during evolution in flatworms.

The body is not segmented; at the anterior end there is a mouth opening that leads into the intestinal cavity. In this, flatworms are similar to coelenterates. However, unlike them, in the body of flatworms one can distinguish not just diffusely scattered cells different types, but already clearly formed tissues. Tissues form organs, organs form systems: digestive, excretory, nervous And sexual.

Respiratory organs and circulatory system are absent. The exchange of gases occurs directly through the integument of the body, so the flat shape of the body advantageously increases the surface area for gas exchange.

The space between the internal organs and the body wall is filled parenchyma – unspecialized tissue from the middle germ layer, mesoderm. Parenchyma serves to store and transport substances, maintains the shape of the worm's body and serves as a support for internal organs.

Integument and muscles

Epithelial and muscle tissues are separate, separated by a layer of connective tissue. Together these three tissues form the body wall of the worms, called skin-muscle bag. Typically, the outer layers of muscle cells are ring-shaped, that is, when they contract, the body of the worm narrows and elongates. The inner layers of muscles have a longitudinal arrangement, with their help the worm can shorten and bend in different directions. In addition, there are dorsoventral (dorsoventral) bunches muscles - they connect the abdominal and dorsal parts of the animal. When they contract, the body flattens.

Digestive system

The digestive system consists of the foregut ( throats), formed by the ectoderm, and the middle endodermal intestine, in which digestion actually occurs. There is no hindgut or anus, so the remains of undigested food are returned to the environment through the mouth opening.

The nervous system of flatworms is much more complex than that of coelenterates. Here are its characteristic differences:

• nerve cells are collected in ganglia, which in turn are connected into nerve trunks;
• nerve cells are located deeper in the body, which allows them to be protected;
• is happening cephalization, that is, ganglia located closer to the head play a more important role in controlling the body;
• oligomerization nerve centers, that is, their number decreases as the body becomes more complex.

In the anterior part of the body there is a large cerebral ganglion, from which two nerve trunks extend posteriorly. The trunks are connected by transverse bridges, which is why this system received the name orthogon(meaning orthogonal, that is, perpendicular arrangement of nerve trunks).

Excretory system

Waste products, often toxic to cells, accumulate in tissue fluid. Unlike coelenterates, flatworms do not have the ability to secrete metabolic products directly into the external environment; this requires a separate system.

The excretory system consists of branching tubules of ectodermal origin - protonephridia. Each tubule ends with a star-shaped cell - cyrtocyte. There are bundles of cilia on the cyrtocytes. When the cilia beat, reminiscent flickering flame, there is a movement of tissue fluid into the protonephridia tubules. All tubules empty into larger ducts that open on the surface of the body excretory openings. Thus, the liquid with metabolic products gets out.

In some species, the excretory ducts expand at the back of the body to form the bladder. Metabolic products accumulate and concentrate in it. With the help of the excretory system, excess fluid can also be removed from the worm’s body, which is especially important for freshwater forms. Without this mechanism, freshwater worms simply would not be able to maintain water-salt balance.

Reproductive system

Most flatworms are hermaphrodites. Their gonads are located deep in the body, and the germ cells are excreted through ducts. The organization of the reproductive system can vary significantly among representatives of different species.

Male gonads - testes. From them to the copulatory organ ( cirrus) there are vas deferens. The female reproductive system contains ovaries, zheltochniks, oviducts and vagina, opening into the genital cloaca. The yolk sacs are similar in structure to the ovaries, but contain yolk cells– sterile eggs with a large supply of nutrients for the future egg.

Classification

Flatworms include five classes, of which school course Only three are considered.

Class Ciliated worms (Turbellaria)

There are more than 3,500 species in the class. Unlike other flatworms, most turbellarians are free-living. Characteristic representatives of the class are planaria (milk, brown, mourning, black, etc.). They live in fresh water, are found in large numbers in stagnant and slow-flowing reservoirs, hiding under stones or plant leaves. The sizes of eyelash worms range from 2-3 mm to 30 cm.

The body is flat, thickened in the middle. There may be outgrowths at the anterior end. With the help of cilia and a skin-muscle sac, worms can crawl on various surfaces or swim. The mouth opening is usually located in the middle part of the body.

The turbellarian epithelium contains scattered unicellular glands that secrete a mucous or protein secretion. The mucus probably helps in movement and attachment to the substrate and serves for protection. The protein secretion can be toxic, which repels other predatory animals.

Most eyelash worms are predators. They have a retractable throat, with which they can swallow prey or tear off pieces from it. If the victim's body is covered with a chitinous shell, the worm throws digestive enzymes out and softens the hard covers. Interestingly, planarians can use the “weapons” of coelenterates: when a worm eats a hydra, its stinging cells do not split, but migrate through the body wall, ending up in the epithelium of the worm, protecting it from enemies.

Since turbellaria lead an active lifestyle, their sense organs are quite well developed. The entire body is covered with special long sensitive cilia, sensilla. They perceive mechanical or chemical irritations. Also, almost all ciliated animals have balance organs and two or more photosensitive eyes, which are located in the head area or evenly along the edge of the body.

Ciliated worms are hermaphrodites, fertilization is internal, most often cross-fertilization, that is, partners take turns fertilizing each other. Sperm is usually injected into the genital cloaca, but sometimes directly into the body of the worm (in this case, the copulatory organ pierces the partner’s integument). After this, the sperm move towards the eggs and fertilize them.

Development can be direct (an individual similar to an adult emerges from the egg) or with metamorphosis (a larva with cilia emerges from the egg).

Turbellaria regenerate well: from a small piece of the body a full-fledged adult organism can develop. When unfavorable conditions occur, planaria tend to fall apart and wait out in this form. long time. After conditions improve, new organisms regenerate from the pieces. This is an example of asexual reproduction in ciliated worms.

Class Flukes (Trematoda)

The nervous system is formed by a pair of cephalic ganglia. Two bridges connecting the ganglia form the peripharyngeal nerve ring. Nerve trunks extend forward and backward from the ring.

Trematodes are hermaphrodites. In all flukes, the female reproductive system is represented by one branching ovary, vitelline and shell glands. Their ducts empty into a sac-like cavity, which continues into the uterus. The uterus opens into the genital cloaca. Nearby is the copulatory organ, which receives sperm from two testes (rarely from one).

During fertilization, the seed enters the genital cloaca, from where sperm move towards the eggs. Fertilized eggs are surrounded by yolk cells, covered with a shell and begin to move out of the uterus.

The life cycle of flukes is complex: the worm goes through several stages of development with a change of hosts. Adult animal ( Marita), capable of sexual reproduction, lives in the main host - a vertebrate. After fertilization, the eggs are released into the external environment and enter the water (most often with the host’s feces). Comes out of an egg in water miracidium, a larva with cilia.

Miracidium actively swims and looks for an intermediate host, a mollusk of a certain species. For example, for the liver fluke the intermediate host is small pond snail. Having penetrated the mollusk with the help of a special proboscis, the larva loses its cilia and becomes immobile. sporocyst. The sporocyst divides asexually, resulting in the formation of many larvae of a new generation. They feed on the tissues of the mollusk and continue to reproduce. As a result, they come out of the mollusk cercariae- larvae with tails, similar to adult maritas. Cercariae attach to the leaves of coastal plants and become encysted. Cyst can wait for a long time until the host animal eats it. A person can become infected if they drink raw water with broken cysts.

The body resembles a thin ribbon and consists of a head, neck and many segments. Due to their segmented structure, tapeworms are also called tapeworms. The length of worms can reach 20-30 m. Such large individuals are called tapeworms, because they usually occur only singly.

On the head there are suction cups and hooks, with the help of which the worm clings tightly to the intestinal wall. The neck is followed by many segments, each of which lives and develops independently.

The digestive system of tapeworms is completely reduced: animals live in the intestines and absorb food processed by the host’s enzymes through the body surface.

Respiration is anaerobic, so when nutrients are oxidized, glucose is not completely broken down. Products of incomplete breakdown are excreted and poison the host's body.

Each segment of the worm contains organs of the excretory and reproductive systems. The nervous system is extremely poorly developed: two nerve trunks run along the sides, and tactile cells are scattered in the epithelium.

Tapeworms are hermaphrodites. The genital organs develop gradually: the youngest segments located next to the head may not have them at all. A large number of testes with ducts are formed in the parenchyma, which merge into a common vas deferens. The ovary is one, large, consisting of several lobules.

Both cross-fertilization and self-fertilization are possible, in which sperm are introduced into the vagina of an adjacent or even one’s own member. As the eggs mature, the segment matures and may eventually break away from the worm's body. The eggs are shed in the host's feces and can settle on plant leaves.

When an egg is ingested by an intermediate host, it produces oncosphere, a larva with six hooks. For bovine tapeworm (Taeniarhynchus saginatus) intermediate hosts are artiodactyls, for pork tapeworm (Taenia solium)– pigs, dogs, hares and rabbits. Once in the animal's intestine, the oncosphere drills through its wall and enters the bloodstream, settling in some organ. There the larva transforms into Finn and waits for it to enter the body of the next owner. Infection usually occurs when the primary host eats the intermediate host. A person can become infected by eating undercooked meat.

In the intestine, the head of the worm turns out of the finna and attaches to the intestinal wall. Young segments separate from the neck, the body of the tapeworm grows.

Type Flatworms has about 12.5 thousand species. In a type, classes are distinguished (i.e., type classification):

1. Eyelash worms, or Turbellaria (3 thousand centuries) - all free-living in the sea or in fresh water bodies. Representative – Planaria milky.

The organs of attachment are located on the scolex - suction pits bothria(y Lentets wide), suckers (Tapeworm bullish), hooks (Tapeworm pork). The structure of the head, especially the organs of attachment, is very diverse, therefore these organs are often used in the systematic determination of cestodes. With the help of an armed head, cestodes attach to the inner wall of the host's intestine.

at the beginning the strobiles are called hermaphroditic. They contain well-developed both male and female reproductive systems. In the hermaphroditic segments, eggs and sperm are actively produced, and fertilization occurs in them. The size of the segments increases with distance from the neck. At the posterior end of the body the segments are already mature, containing only a queen beetle filled with eggs. The number of segments that make up the body of the cestode varies within very wide limits. There are cestodes that consist of one segment; there are very few such species; in the majority, the number of segments is in the tens and hundreds; in some species it can reach several thousand. In accordance with this, the total body length of cestodes is very different.

Veils. Covered body of tapeworms tegument(this is a type of submerged epithelium without cilia). However, unlike flukes, the tegument of tapeworms forms many microscopic hairy outgrowths - microtrichium, increasing the absorption area of ​​nutrients. Just like flukes, the tegument of tapeworms is dense, well protecting the worm from the digestive juices of the host’s intestines. The tegument firmly fuses with the muscle fibers located underneath it, forming skin-muscular bag. Tapeworms do not have any organs of locomotion other than the musculocutaneous sac. The internal organs are located in the skin-muscle sac. Connective tissue lies between the internal organs parenchyma.

Nervous system – orthogon(see flukes).

Circulatory and respiratory systems are missing.

Excretory system protonephridial type (see flukes).

Reproduction and development. Tapeworms - hermaphrodites. The reproductive system is structured in the same way as in flukes. In growing hermaphroditic segments, almost all the space is occupied by reproductive organs. The act of fertilization involves either two individuals (cross-fertilization) or different segments of the same strobila (self-fertilization). In mature segments, the uterus grows greatly, it is filled with eggs, and all other parts of the reproductive system in mature segments are atrophied. Eggs secreted by mature segments (in Lentets wide) or mature segments detached from the strobila (in Tapeworm bullish, Tapeworm pork, Echinococcus), are released into the environment with the excrement of the host animal. The fertility of cestodes is extremely high, for example, Tapeworm bullish or Tapeworm pork(otherwise called tapeworms) produces about 600 million eggs per year, and for

type Flatworms class Tapeworms

Questions for self-control.

Name the aromorphoses of the Flatworm type.

Name the classification of the type Flatworms.

Explain the body structure of tapeworms.

How does excretion occur in tapeworms?

What is the type of nervous system in tapeworms called, what is its structure?

What is the structure of the reproductive system in tapeworms?

Tell us the lifestyle and development cycle of Bovine tapeworm, Porcine tapeworm, Echinococcus, Broad tapeworm, Sheep brainworm, Moniesia, Ligulidae.

Indicate the definitive hosts for the Bovine tapeworm, Porcine tapeworm, Echinococcus, Broad tapeworm, Sheep brainworm, Moniesia, Ligulata.

How do the definitive hosts become infected with Bovine tapeworm, Porcine tapeworm, Echinococcus, Broad tapeworm, Sheep brainworm, Moniesia, Ligulinaceae.

Specify the intermediate hosts for the Bovine tapeworm, Porcine tapeworm, Echinococcus, Broad tapeworm, Sheep brainworm, Moniesia, Ligulin.

What internal organs are located in each segment?

What is Finna? Is it possible to see her?

Why do tapeworms have well-developed reproductive organs?

Why can mature segments separated from a tapeworm move independently?

Why is the worm not digested in the host's intestines?

Imagine what would happen if a person accidentally swallowed a segment of, for example, a bovine tapeworm with mature eggs?

type Flatworms class Tapeworms

Rice. Bull tapeworm: head and segments.

Rice. Wide tapeworm: strobila.

type Flatworms class Tapeworms

Rice. Covers of tapeworms.

1 - hair growths of the tegument - microtrichia; 2 - basement membrane; 3 - circular muscles; 4 - longitudinal muscles; 5 - nuclei of hypodermal cells.

Rice. Development of pork tapeworm.

1 - head; 2 - neck; 3 - strobile; 4 - segments (proglottids); 5 - hooks; 6 - suction cups; 7 - oncosphere - larva with six hooks; 8 - Finns in pork meat (partially opened); 9 - young tapeworm form turned inside out. Table 1. Tapeworms of great economic importance

Table. 1. Tapeworms of economic importance (continued)

DRAWINGS THAT SHOULD BE DONE IN THE ALBUM

(7 pictures in total)

Lesson topic: Type Flatworms -Plathelminthes.

Flatworms include a class of invertebrates (ciliated free-living, tapeworms, cestodes), which have a bilaterally symmetrical, longitudinally flattened body shape. Unlike coelenterates, flatworms have 3 layers in their body structure:

1. Ectoderm (outer germinal layer of skin).
2. Endoderm (inner layer).
3. Mesoderm is the intercavity germ layer.

Structural features

Flatworms do not have a so-called body cavity. The space between the upper and lower layers is filled by parenchyma (connective tissue formed from mesoderm). Flatworms do not have a full-fledged excretory system. For example, in planaria, which belongs to the free-living flat ciliated species, the excretory organs replace the tubes emerging from the stellate cells, which are located in the parenchyma. They contain long, constantly oscillating cilia, which create a fluid flow directed towards the exit. The tubes permeate the entire body of the planaria, merge into 2 tubules and end with holes on the back of the worm. Through them, liquid comes out, with harmful products dissolved in it.

Another structural feature of flatworms is their reproductive system. All of them are hermaphrodites, but despite this, cross mating is more often used for fertilization. The peculiarity of planaria in this regard is the additional ability to reproduce by division. If an adult is cut in half, a new full-fledged worm will grow from each half. This feature is characteristic of another genus. For example, round free-living worms, such as California red worms, which many are accustomed to calling earthworms.

Classification

• ciliary;
• gyrocotylides;
• Monogenaeans;
• cestodoformes;
• aspidogastra;
• trematodes;
• cestodes.

Free-living predators

Gyrocotylides infect chimaera fish that live at depths of more than 500 meters. Due to the peculiarities of their habitat, the development cycle of these flatworms has not been sufficiently studied.

Trematodes

Cestodes

• wide tape;
• rat tapeworm;
• pork tapeworm;
• bovine tapeworm;
• dwarf tapeworm;
• cucumber tapeworm;
• sheep brain;
• echinococcus.

All these species are united by a similar structure - the scolex, the segments growing from it, in which eggs mature as the worm develops. Mature segments (proglottids) are separated from the body of the helminth and excreted with feces. The main interspecies difference lies in the size of tapeworms and their locations in the host’s body.

Diseases

Most often, people become infected with echinococcus, porcine, bovine, dwarf tapeworms and tapeworms, which cause the diseases described below.

Echinococcosis

Echinococcus is the most dangerous helminth for humans from the class of cestodes. It affects the lungs and liver, and its larvae can enter the brain through the bloodstream.

In advanced cases, drug treatment is ineffective. Hydatid cysts are removed surgically.

Taeniasis and cysticercosis

Teniarinhoz

The disease begins to develop when bovine tapeworm eggs enter the body. Characteristic signs infection is a disruption of the gastrointestinal tract, deterioration of well-being: fatigue, nausea (vomiting). Without treatment, anemia (anemia) progresses.

Hymenolepiasis

A disease caused by the dwarf tapeworm. The main symptoms are similar to those of teniarinchiasis. The acute stage of the disease is accompanied by sudden weight loss due to constant nausea, vomiting and pain in the lower abdomen.

Diphyllobothriasis

Patients are most often concerned about the following manifestations:

• Nausea, accompanied by cramping pain in the intestinal area.
• Increased salivation.
• Anorexia due to loss of appetite (a person may for a long time not feel hungry, and then vice versa - constantly want to eat).
• Fatigue, rapid heartbeat, dizziness (symptoms of anemia).
• Irritability, nervousness, numbness of limbs, depression.

In the later stages of the disease, there may be an enlargement of the spleen, liver and acute pain in the epigastrium during meals. A large number of proglottid can cause intestinal blockage.

Schistosomiasis

Paragonimiasis