flatworms

We can meet free-living species in the seas or fresh waters. In total, 5500 species of flatworms are known.

The phylum flatworms are usually represented by three classes:

• flukes,
• eyelash worms,
• Tape worms.

Body structure of flatworms

When considering the body of a flatworm, one can determine its right and left sides, abdominal and dorsal, i.e. it is bilaterally symmetrical.

With the help of the abdominal part, the worm can move on a hard surface. Thanks to the nerve cells and organs responsible for the perception of chemicals, as well as the organs of vision located at the head end of the body, flatworms have the opportunity to better navigate in space.

The intestinal system of a flatworm is very simple, it consists of the anterior, caecum and middle intestine.

However, flatworms become the first owners of excretory organs, the function of which is to remove excess water, metabolic products, and also regulate osmotic pressure.

Flatworms are hermaphrodites. The reproductive system of flatworms is represented by the sex glands, ducts and yolks.

Class Ciliary worms

The most typical representative of this class is the predator dairy planaria, which is a free-living flatworm. The habitat of planaria is stagnant fresh water.

Planarians feed on insect larvae, snails, and small crustaceans. Planarians have a well-developed ability to regenerate.

Flukes class

A representative of this class of flatworms is a liver fluke, whose habitat is the ducts of the liver of cattle and humans.

The development cycle occurs with a change of host and alternation of generations.

Together with the feces, the mature egg enters the water, after a short development a larva appears, it penetrates into the body of the intermediate host (small pond snail), where it turns into a sporocyst, and then a redia.

Such a long period of development is evidence that the ancestors of flukes were free-living.

Tapeworms

The body of a tapeworm consists of a head, neck and segments, which are alternately interconnected.

A typical representative of the bull tapeworm, the ultimate owner of which is a man.

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The purpose of the lesson is to analyze the basic features of this type of animal and the first two of its three classes.

In the previous lesson, we analyzed the type of Ki-shech-but-lost-nye. They have ra-di-al-ny sim-met-ryu. And this year we are on-chi-on-it once-a-thief about two-sided-sim-metric animals.

Two-sided-sim-metric - a huge group, more than 99% of animals belong to them. Including these are flatworms, ringworms and roundworms, mollyus-ki, members-no-one-hundred-no-gie, choir-to-vye and many others. etc. Their body is characterized by two-sided symmetry and the presence of three cellular layers: ek-to-der-we, me-zo- der-we and en-to-der-we. Here, I remind you that the intestinal-but-on-lost cell-layers had only two. In most bilaterally symmetrical animals, one can distinguish between the anterior and posterior ends of the body, as well as the abdominal and spinal ny side of the body. Some-rye, one-on-one, again morning-chi-va-yut two-sided symmetry, as, for example, needle-skin.

The most ancient in terms of origin, with-mi-tiv-noy group-sing two-sided-symmetric-metric animals are considered flatworms. This type combines worm-like demons-of-the-night calls that do not have a body. Flatworms live in saline and fresh waters; some species have adapted to life in wet earthly places-to-obi-ta-ni-yah, many pa-ra-zi-ti-ru -yut on different groups of animals.

The body length of flatworms lies in the range from 0.5 mm to 20 m. The body consists of several cellular layers. The outer integumentary layer of free-but-living flatworms has cilia. Pa-ra-zi-ti-che-sky pre-hundred-vi-te-lei has no res-no-cheque.

Why do pre-hundred-vi-the-types, like right-vi-lo, have a flat body? The fact is that they have no special breathing system. In order for each cell to be able to receive sour and give off carbon-le-sour gas (i.e., for gas-to-ob-me-on) , it must-on-ra-la-gat-sya not far from the external environment. The body of large flatworms is usually flat, like boom-ma-ha.

Under the integumentary tissue, there are several layers of mu-sku-la-tu-ry. Mu-sku-la-tu-ra and the blood layer together form a skin-but-muscle-shoulder sac. Flatworms don’t have internal-ren-it in the lo-sti, the whole body is half-not-but cells-ka-mi. Or-ga-ny ob-one-not-us in the system-ste-we. In flatworms, you have a pi-sche-va-ri-tel-naya, you-de-li-tel-naya, nervous and in a lo-vaya si-ste-we or- g-nov.

The blood-ve-nos-naya si-ste-ma they don’t have, and the pi-ta-tel-nye things are dis-pro-country-ny-ut-sya right in the ki- shech-ni-ku (when he is). The gut blindly closes and communicates with the environment only through the mouth. Free-bod-but-living-woo-ing flatworms pi-ta-yut-sya pre-im-s-stvenno-but like predators. Pa-ra-zi-ti-che-pi-ta-yut-sya either with the help of the mouth, or vpi-you-vaya pi-ta-tel-studies through the entire top -ness of the body.

The nervous system is represented by the nerve-knots-la-mi, dis-lo-women-us-mi in the anterior part of the body, the brain-go- you-mi gang-gli-i-mi and from-go-da-schi-mi from them nerve-us-mi-stol-ba-mi, connect-nen-us-mi re-re-mych-ka- mi. In some free-bod-but-living-woo-shy flat worms, once you have pri-mi-tiv-nye organs of vision and or-ga-na equal -but-ve-siya.

You-de-le-nie implement-la-et-xia with the help of special channels, as well as through the surface of the body. In the or-ha-bottom-me of the flatworm, they have both male (se-men-no-ki) and female (egg-no-ki) or-ga-ny times -many. Such animals are na-zy-va-yut-xia ger-ma-fro-di-ta-mi. In-te-res-naya feature of the most-shin-stva of flatworms - is it so-called-zy-va-e-my-th-complex-th egg. It consists of a fertilized egg-cell and several bilious cells. All these cells together are covered by a single protective shield speed.

For pa-ra-zi-ti-che-sky flatworms, ha-rak-te-ren is a complex life cycle. Or-ga-nism, in some-rum time-vi-va-yut-sya and on-ho-dyat-sya for some time, li-chin-ki, na-zy-va-et-sya pro-me-zhu-precise ho-zya-i-nom. Or-ga-nism, in some-rum lives and multiplies an adult worm, na-zy-va-et-sya-windows nom.

At the present time, there are about 25 thousand species to the type of flatworms. You-de-la-ut up to 9 classes, out of some 6 representations-le-us-key-chi-tel-but pa-ra-zi-ti-che-ski-mi-vi -yes. We consider only three classes of flatworms.

Class Res-nich-nye worms

This class counts over 3500 species, predominantly free-but-living-woo. Sizes of pre-hundred-vi-te-lei - from micro-ro-co-pi-che to 30-40 cm. Most of the species are found in the seas and press -ny waters, a few - in wet places on the top of the land or in the soil.

The pre-hundreds of this class have eyelashes on the top of the body. Res-nich-ki-m-ga-yut float or re-re-move along the bottom. Large worms re-re-move-ga-yut-sya mainly due to waves-but-different movements of the body.

In the layers of ciliary worms, there are a lot of one-but-clear glands. Some-rye-le-zy you-ra-ba-you-va-yut special-ci-al-gra-nu-ly, some-rye when you break -whether-va-yut-sya on-ru-zhu and when co-cos-but-ve-nii with water form protective mucus. Thanks to this, the ciliary worms practically don’t eat other animals.

Pi-sche-va-ri-tel-naya si-ste-ma to-free-but once-but-about-time-on in pre-de-lah class-sa. The pain-shin-stvo of the pre-hundred-vi-te-lei of the class is a predator-ni-ki. Ob-on-ru-alive the victim, the worm on-roof-va-et with his body, after which you-va-et. At the same time, there are species, pi-ta-yu-schi-e-sya in-do-ros-la-mi or leading a pa-ra-zi-ti-che-sky way of life.

Or-ga-ny senses in ciliary worms, once you are significantly better than in other classes. Some species have an equal organ. The most important role is played by the organs of obscenity, since with the help of the sense of smell, almost all of them hunt. Almost all ciliated worms have eyes.

Res-nich-nye worms - ger-ma-fro-di-you. Most of the pro-is-ho-dit has a re-re-cross-blank-to-your-re-nie. The development is direct, that is, from the egg you-go-dit or-ga-nism, similar to an adult animal. Ciliary worms can also multiply in a demonic way. At the same time, on the body, it appears-yav-la-et-sya in-pe-river-naya pe-re-heavy-ka, in a degree-pen-but once-de-la-yu-shaya belly-here-noe on two parts. Brightly you-ra-same-on the ability to re-ge-not-ra-tion.

The most-bo-lea-of-the-west-na-mi are-la-yut-xia before-a-hundred-vi-te-whether from-a-row-yes plan-on-riy. These are small flatworms, some of which are in a hundred-yan-but meet in fresh-water-water-to-e-max, where they are half-for- yut among water races. In the north and middle in the lo-se of Russia, very often you meet a mo-loch-no-white plan-na-riya, the largest among others (up to 3 cm long). Through it, so-ver-shen-but white in-cro-you clearly see-sve-chi-va-et-dark-y-y-y-y-ki-shech-nick. On the head, you can see a pair of eyes.

Plan-on-rii re-re-dvi-ga-ut-sya through-you-tea-but smoothly and equally-but-by-measure-but due to res-no-check. Pi-ta-yut-sya in the basis of new chalk-ki-mi waters-us-mi live-here-us-mi. Ki-shech-nick has a through-you-tea-but branched-line form, something especially ben-but ho-ro-sho can be observed at milk-no- white plan-on-rii, if you look at it through a magnifying glass.

Once-a-many-m-yut-sya plan-on-rii eggs-tsa-mi, someone-rye-key-che-us in a cocoon. Behind the shield with the means of the plan-on-rii, their mucus is, for some reason, abundantly, but covers the body. These worms have through-you-tea-but raz-vi-tuyu re-ge-not-ra-tion.

So-sal-shchi-ki class

Worms of this class lead a pa-ra-zi-ti-che-sky way of life. Like many other couples, they have a complex life cycle. It includes, as a rule, at least three co-le-tions and pro-te-ka-et in several ho-zya-e-wahs. Usually, one of the hosts is a bru-ho-no-gy mole-lusk, and the other is like a nocturnal one. So-sal-shchi-ki pro-from-the-dyat a large number of eggs.

Window-cha-tel-ny ho-zya-in - in the sound of the night. In the or-ga-niz-me ho-zya-and-on adult worms can-go-die-sya in the ki-shech-ni-ke, pe-che-ne, gall bladder-zy-re , or-ga-nah you-de-li-tel-noy si-ste-we and in many other places. Their sizes are from ten microns to several san-ti-meters. The body is leaf-shaped, flattened. As a rule, they have two attachments - ro-to-vai and abdominal. At the bottom of the ro-to-howl of the pri-suc-ki races-on-lo-the-same-but ro-to-th-hole. Ki-shech-nick for-mknu-ty.

In-cro-you co-sal-shchi-kov do not have res-no-check. Nervous si-ste-ma - ha-rak-ter-naya for the type. You-de-le-nie - through the cross-you of the body and you-de-li-tel-nye ka-na-ly.

The pain-shin-stvo of so-sal-schi-kov is ger-ma-fro-di-you, but there are also di-del-but-po-lye. Ob-ra-zu-yu-shchi-e-sya after the worm-wei-scraping of the eggs, you-into the external environment with the feces or urine of the host.

From the egg you-go-dit li-chin-ka, able to swim with the help of b-e-niya res-no-check. For further development, it must-on-ra-zit bru-ho-no-ho-go-mol-lus-ka. Inside it, there is a li-chin-ka pre-ter-pe-va-et me-ta-mor-fo-zy and times-many-m-e-xia. Then from the body of the pro-me-zhu-exact-no-ho-zya-and-on you-ho-dyat races-se-li-tel-li-chin-ki, some-rye for-ra- zha-yut windows-cha-tel-nyh ho-zya-ev.

In total, opi-sa-but about 7200 species of sal-shchi-kov. Some species - pa-ra-zi-you che-lo-ve-ka, you-zy-va-yu-schy dangerous for-bo-le-va-nia.

Ras-look-rim as an example of a pe-che-night-twist, someone-para-ra-zi-ti-ru-et in pe-che- nor the bile ducts warm-blooded. She-za-va-et for-bo-le-va-nie fas-tsio-lez with pe-che-night-us-mi-li-ka-mi and ho-le-qi-sti-tom. Ras-pro-country-not-on among the sheep. An adult is ger-ma-fro-dit, usually up to 3 cm in length. nym ho-zya-i-nom - fresh water snail. For-ra-the-windows-cha-tel-no-go-ho-zya-and-on pro-is-ho-dit when pro-gla-you-va-nii with water or food in-ko-i- the current stage of pa-ra-zi-ta.

abstract source - http://interneturok.ru/ru/school/biology/7-klass/zhivotnye-ploskie-chervi/ploskie-chervi?seconds=0&chapter_id=79

video source - http://www.youtube.com/watch?v=vGLlqFriMns

video source - http://www.youtube.com/watch?v=ZqtXc9ZRtvo

video source - http://www.youtube.com/watch?v=6xy5QEwPwLw

video source - http://www.youtube.com/watch?v=lUq4T2IWBgU

video source - http://www.youtube.com/watch?v=z20mVcfg8_0

video source - http://www.youtube.com/watch?v=d_wz-R-5KUY

video source - http://www.youtube.com/watch?v=DGMS94Abgz4

video source - http://www.youtube.com/watch?v=TIz4ynRB1gE

video source - http://www.youtube.com/watch?v=IEDzPe6AoQ0

presentation source - http://ppt4web.ru/biologija/ploskie-chervi3.html

http://nsportal.ru/shkola/biologiya/library/2013/01/17/tip-ploskie-chervi

http://www.animals-wild.ru/bespozvonochnye-zhivotnye/972-ploskie-chervi.html

With a little frown, let's start the description worms. What to do if there are such trump cards in the thick "deck" of the natural diversity of life forms.

I write "trump cards" not only because " worms". The evolution of multicellularity from two-layer has led to much more perfect forms of organisms with a three-layer body structure. And then nature had to tinker for a long time, creating not one, but whole.

Somehow it even becomes a shame for all mammals, which represent only a separate class of organisms in the type of chordates. And here, "some kind of worms" - and whole three types: flatworms, roundworms and annelids.

Well, let's start everything in order, so:

……………… Type Flatworms (three layers)

…………………………………. K l . a. with. with. s

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.. Ciliary worms……………………….. Flukes……………………….. Tapeworms

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White planaria…. Liver fluke …… …………… Bull tapeworm ________________________________________________________________________________________________

……………………………………………….. More than 15 thousand species

Habitat : marine and fresh water bodies, moist soil, human and animal organisms.

……..
Structure: bilaterally symmetrical . For the first time in embryos, a the third germ layer – mesodermfrom which parenchymal cells and the muscular system develop. Body flattened.

………..
Integuments of the body and muscular system: skin-muscular sac - from a single-layer epithelium (may be with eyelashes) and three layers smooth muscles (circular, longitudinal and oblique).

Motion: muscle contraction (flukes, tapeworms) or movement of cilia andmuscles (ciliary worms).

body cavity: is absent , the internal organs are located inparenchyma.

Digestive system:has two sections - anterior (mouth, pharynx) and middle (branches intestines). The bowel is closed anal opening is missing and leftover food is removed. through the mouth. At the tapeworms digestive system is absent- absorption of food by all cells of the body. As you remember, this is one of the forms of biological progress -.

excretory system: appears for the first time formed by a system of tubules. one end starts in the parenchyma stellate cell with a bunch of cilia, and the other flows into excretory duct. ducts combined into one or two common channels ending excretory pores. Elementary unit of the system areprotonephridia.

Nervous system:from supraesophageal ganglions(ganglia) and longitudinal nerves trunks, related cross jumpers(ladder type).

Sense organs: touch and chemosensitive cells. Free-living people have organsvision and balance.…………..

reproductive system: to usually hermaphrodites.Men'sreproductive system: testes, vas deferens, ejaculatory duct and copulatory organ. Women'sreproductive system: ovary, oviduct, uterus, yolk glands.

1. The appearance of the third germ layer -mesoderm.
2. The appearance of the excretory system - protonephridia.
3. Emergence of the nervous system ladder type.

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Who has questions about the article to biology tutor via skype, comments, wishes - please in the comments .

Subcutaneous worm rishta

There are worms that live in human blood. These include schistosomes. Their main habitat is blood vessels. However, they are able to penetrate into various organs, causing symptoms of damage to the genitourinary system, liver, and kidneys.

In the blood may be the larvae of some helminths. For example, in tapeworms, this is how they spread through the organism of the intermediate host. With the blood flow, the larvae migrate to various organs, where they are fixed and form cysts containing the heads of adult worms. The latter, when they enter the digestive tract of the final host, attach to the intestinal wall, giving rise to a sexually mature individual.

Flatworms: general characteristics

The body of flatworms is capable of performing complex and varied movements.

All flatworms have common structural features:

• The outer cover is represented by the cuticle. In free-living individuals, it is covered with cilia, the surface of the body of worms is usually smooth.
• Under the outer cover there are several layers of muscle fibers.
• There is no body cavity.
• The digestive system has only one opening - the mouth. The intestine ends blindly. Some worms are completely devoid of digestive organs. So, tapeworms, which absorb nutrients with the whole body from the intestinal lumen of the host, do not need them.
• There is no circulatory system and blood, as well as respiratory organs.
• The excretory system is represented by a network of tubes that permeate the entire body.
• The nervous system is primitive. Near the pharynx there are several ganglia, from which nerve trunks connected by jumpers depart. The sense organs are formed only in free-living individuals and some worms at the larval stages of development.

The system that is really well developed is the sexual system. Flatworms are hermaphrodites. Reproduction is possible with the participation of 2 individuals or by self-fertilization.

flukes

The development cycle of trematodes is one of the most complex. Miracidia emerge from eggs released into the environment. In water, the latter feel comfortable and exist for some time as free-living organisms. The next stage is the introduction of miracidia into the first intermediate host. The larva does this with the help of a special cutting apparatus on the head. The host is usually a mollusk.

Their life cycle can take place in several hosts and is accompanied by a regular alternation

Here miracidia turns into a sporocyst, which gives rise to the next stage of the development cycle - redia. Those, in turn, are the precursors of cercariae, which leave the intermediate host and re-enter the aquatic environment. Further, the development cycle follows one of two options. Cercariae are transformed into cysts directly in the external environment (attached to algae) or in the body of the second intermediate host (mollusk, fish, amphibian).

These are the longest worms with a transparent shell

Infection of the final host occurs when it eats the infected organs of the intermediate host. The cycle of development ends with the attachment of the head from the cyst to the intestinal wall and the development of an adult worm. The latter can reach considerable sizes (for example, a wide tapeworm grows up to 10 m long).

For flukes, a person is the final host, but for tapeworms it can also be an intermediate host.

What symptoms occur when a person is infected with a helminth? The clinic of the disease is due, first of all, to which organ was affected. Sexually mature worms usually live in the intestines, therefore, in the general picture of the disease, symptoms characteristic of digestive disorders prevail: nausea, gas formation, stool disorders, and abdominal pain.

Helminths secrete waste products that, getting into the bloodstream, cause poisoning and symptoms of intoxication (fever, fatigue, and others). In addition, they are perceived by the immune system as an allergen. Therefore, helminthiases are often accompanied by symptoms of an allergic reaction (skin rash, itching).

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

Structural features Body sizes from 2-3 mm to 20 m. The body is elongated and flattened in the dorsal-abdominal direction; has a ribbon-like or leaf-like shape. The presence of developed organ systems is characteristic: muscular, digestive (absent in ribbon), excretory nervous and sexual.

Integuments of the body and the muscular system The cells of the epithelium and muscles 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: annular, 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 (ciliary worms).

The digestive system has two sections - anterior (mouth, pharynx) and middle (intestinal branches). The intestine is closed blindly, the posterior intestine and anus are absent. Undigested food remains are removed through the mouth. Tapeworms have no digestive system (represented by separate digestive cells).

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

Nervous system. Sense organs. It consists of supraglottic ganglions (ganglia) and longitudinal nerve trunks that run along the body and are connected by transverse nerve bridges. Sense organs - touch and chemical sense. Free-living people have organs of touch and balance.

Hepatic fluke Hepatic flukes, usually up to 3 cm long, 1.3 cm wide. Hepatic flukes of the order Opisthorchis cause opisthorchiasis, early symptoms - liver enlargement, allergic reactions and gastrointestinal disturbances; late stage symptoms - pain radiating to the back, biliary colic, headaches and dizziness, insomnia. Treatment is with anthelmintic, choleretic and enzyme preparations. High frequency electromagnetic radiation is also used.

Development cycle The life cycles of different genera are different. In species of the genus Fasciola, development occurs with one intermediate host (freshwater snail), and infection of the final host occurs when swallowed with water or eaten with coastal plants of the resting stage - adolescaria. In species of the genera Opisthorchis and Clonorchis, the second intermediate host is freshwater fish, and infection of the final host occurs by eating raw fish with invasive stages. In species of the genus Dicrocoelium, terrestrial lung snails and ants serve as intermediate hosts, and infection of the final host (usually a herbivore) occurs when an infected ant is eaten with grass.

Bull tapeworm (tapeworm) It affects cattle and humans, causing teniarinhoz. Tapeworm infestation is particularly prevalent in equatorial Africa, Latin America, 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 laying of the reproductive apparatus begins at about the 200th segment. Length of mature proglottids mm, width 5-7 mm. The scolex (head section) is equipped with 4 suckers without hooks (therefore unarmed). The life span of bovine tapeworm in the human intestine, if no deworming measures are taken, is years. A tapeworm produces ~ 600 million eggs per year, ~ 11 billion in a lifetime.

Development cycle Segments containing eggs are excreted from the human intestine (the main host). Together with the grass, they enter the stomach of the cow (intermediate host). Six hooked larvae emerge from the eggs, which penetrate into the blood vessels of the intestine and then into the muscles. In the muscles, the larva turns into Finns (a vial with a tapeworm head inside). When a person eats poorly processed finny meat, the tapeworm head attaches to the intestinal wall and begins to produce segments.

Structural features Bilaterally symmetrical. Sizes from a few 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. Body filiform, fusiform, non-segmented, round in cross section.

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

The excretory system is represented by 1-2 skin glands (modified protonephridia). These are large cells, from which two channels depart on the sides of the cell. At the posterior end of the body, the channels end blindly, and in front they open into the external environment with an excretory pore.

Nervous system. Sense organs Ladder-type nervous system. It is represented by the head nerve nodes (ganglia), the peripharyngeal nerve ring and several nerve trunks (dorsal and abdominal), median transverse bridges. The sense organs are represented by the organs of touch and chemical sense. Marine forms have light-sensitive receptors. Scheme of the roundworm nervous system: 1 - oral papillae with tactile endings and the nerves that innervate them, 2 - peripharyngeal nerve ring, 3 - lateral head 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

Ascaris human Ascarids are large roundworms, their length can reach 40 centimeters. Most often affect the organs of the gastrointestinal tract, causing ascariasis. The favorite habitat of adults is the small intestine. Roundworms are bisexual worms. Ascaris females can produce more than 200 thousand eggs per day. Fertilized eggs from the human intestine enter the soil. They develop larvae. Infection occurs when drinking water from open reservoirs, eating poorly washed vegetables, fruits that have eggs with larvae. In the human body, the larva migrates: once in the intestine, it perforates its walls and enters the blood stream.

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

Integuments of the body 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 muscles (outer annular and inner longitudinal) and a single-layer epithelium of the secondary body cavity. With the contraction of the circular muscles, the body of the worm becomes long and thin, with the contraction of the longitudinal muscles, it shortens and thickens.

Body cavity Secondary - whole (has an epithelial vystilka). In most, the body cavity is divided by transverse partitions corresponding to body segments. The cavity fluid is a hydroskeleton and an 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, goiter), 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.

The circulatory system is closed. There are two vessels: dorsal and abdominal, connected in each segment by annular vessels. Through the dorsal vessel, blood moves from the posterior end of the body to the anterior, along the abdominal vessel from front to back. The movement of blood is carried out due to the rhythmic contractions of the walls of the spinal vessel and the annular vessels ("heart") in the pharynx. Many people have red blood.

The excretory system is of the Metanephidial type. Metanephridia look like tubes with funnels, two in each segment. The funnel, surrounded by cilia, and convoluted tubules are in one segment, and a short tubule that opens outwards with an opening - an excretory pore - is in the next segment.

Nervous system. Sense organs. It is represented by supraglottic and subpharyngeal nerve nodes (ganglia), which are connected to the peripharyngeal nerve ring and the abdominal nerve chain, consisting of paired nerve nodes 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 hermaphodites. Sex glands develop only in certain segments. Insemination is internal. The type of development is direct. Asexual reproduction is carried out by budding and fragmentation (due to regeneration). Marine representatives are dioecious. Development with metamorphosis, trochophore larva.

a brief description of

Habitat and appearance	Size 10-15 mm, leaf-shaped, live in ponds and slow-flowing reservoirs
body cover and musculocutaneous sac	The body is covered with a single layer (ciliary) epithelium. The superficial muscle layer is annular, the inner one is longitudinal and diagonal. There are dorso-abdominal muscles
body cavity	The body cavity is absent. Inside is spongy tissue - parenchyma
Digestive system	Consists of the anterior (pharynx) and the middle, which has the appearance of highly branched trunks ending blindly
excretorysystem	Protonephridia
Nervous system	The brain ganglion and the nerve trunks coming from it
sense organs	Tactile cells. One or more pairs of eyes. Some species have balance organs
Respiratory system	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 ciliary worms are planaria(Fig. 1).

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

general characteristics

Appearance and covers . The body of ciliary worms is elongated, foliate. Sizes vary from a few millimeters to several centimeters. The body is colorless or white. Most often, ciliary worms are painted in various colors with grains. pigment embedded in the skin.

body covered single layer ciliated epithelium. The covers have skin glands scattered throughout the body or collected in complexes. Of interest is the variety of skin glands - rhabdit cells, which contain light-refracting rods rabdites. 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 is formed on the surface of the worm, possibly playing a protective role.

Skin-muscular sac . 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 is made up of several layers smooth muscle fibers. The most superficial 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 defined body cavity ciliary worms do not. All gaps between organs are filled parenchyma- loose connective tissue. The small spaces between the parenchyma cells are filled with an aqueous liquid, which allows the transfer of products from the intestine to the internal organs and the transfer of metabolic products to the excretory system. In addition, the parenchyma can be considered as a supporting tissue.

Digestive system ciliary worms blindly closed. Mouth also serves for swallowing food, and for throwing out undigested food. The mouth is usually located on the ventral side of the body and leads to throat. In some large ciliary worms, such as freshwater planaria, the mouth opening opens into pharyngeal pocket, in which is muscular throat, able to stretch and protrude out through the mouth. midgut in small forms of ciliary worms is channels branching in all directions, and in large forms, the intestines are represented three branches: one front, going to the front end of the body, and two rear running along the sides to the posterior end of the body.

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

sense organs ciliary worms are relatively well developed. organ of touch whole skin serves. In some species, the function of touch is performed by small paired tentacles at the anterior end of the body. Sense organs of balance represented by closed sacs - statocysts, with hearing stones inside. organs of vision are almost always available. The eye may be one pair or more.

excretory system for the first time appears as separate system. It is represented two or multiple channels, each of which one end opens outwards, a the other is strongly branched, forming a network of channels of various diameters. The thinnest tubules or capillaries at their ends are closed by special cells - stellate(see fig. 1, D). From these cells in the lumen of the tubules depart bunches of cilia. Due 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 varied in structure. It can be noted that in comparison with coelenterates in ciliary worms special excretory ducts appear for

expelling germ cells. Eyelash worms hermaphrodites. Fertilization - internal.

Reproduction. In most cases in a sexual way. For most worms direct development, but in some marine species development occurs with metamorphosis. However, some ciliary worms can reproduce and asexually through transverse fission. At the same time, in each half of the body, regeneration missing organs.