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

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

Differences between flatworms and roundworms

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

Diversity of classes of flatworms

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

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	During its entire life, the worm has one host, to which it arrives as a free-swimming larva
Cestodoids		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 ownership occur several times over the course of life cycle 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 larvae)
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 emerge 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 death. 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 with warm water and 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.

Let's start the description with a little wince. worms.

What can we do if such trump cards are available in the thick “deck” of the natural diversity of life forms? I write “trump cards” not only because “ worms ". The evolution of multicellularity from bilayers led to significantly more perfect forms

organisms with a three-layer body structure. And then nature had to tinker for a long time, creating not just one, but entire ones. 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-layered) K l

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.. Eyelash worms. A. With. With. s

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……………………….. Flukes……………………….. Tapeworms

……………………………………………….. White planaria….

Liver fluke …… …………… Bovine tapeworm ___________________________________________________________________________________ More than 15 thousand species

……..
Habitat : marine and fresh water bodies, wet soil, human and animal bodies. Structure: bilaterally symmetrical . For the first time, embryos develop – thirdgerm layer mesoderm

………..
, from which parenchymal cells and the muscular system develop. Body flattened. Body coverings and muscular system: skin-muscular sac - made of single-layer epithelium (maybe be with eyelashes) and

three layers smooth muscles (circular, longitudinal and oblique).Movement:

contraction of muscles (flukes, tapeworms) or movement of cilia and muscles (cilia worms). Body cavity:absent.

, internal organs are located inparenchyma Digestive system: has two sections - anterior (mouth, pharynx) and middle (branches intestines). The intestine is closed, no anal opening and food residues are removedthrough the mouth . In tapeworms digestive system absent —.

- absorption of food by all cells of the body. As you remember, this is one of their forms biological progress Excretory system: appears for the first time , formed by a system of tubules. One end begins in the parenchyma stellate cell. with a bunch of cilia, and the other flows into excretory duct Channels. are combined into one or two common channels ending excretory poresElementary.

the unit of the system isprotonephridia Nervous system: from suprapharyngeal ganglia (ganglia), and longitudinal nerves trunks(related.

crossbars ladder type) Sense organs: touch Andchemosensitive cells. Free-living animals have organs vision…………..

And balance. Reproductive system:To reproductive system: testes, vas deferens, ejaculatory duct and copulatory organ.Women's reproductive system: ovary, oviduct,

uterus, zheltochniki.1. Appearance of the third germ layer -.
mesoderm
2. The appearance of the excretory system - protonephridia. 3. Emergence of the nervous system.

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ladder type Who has questions about the article to Biology tutor via Skype .

, comments, wishes - please comment

a brief description of 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 blindlyexcretory	system
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 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 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 - ciliary 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 . Most often, eyelash worms are colored grains in different colors pigment

, embedded in the skin. Body covered single-layer ciliated epithelium . In the integument there are, 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 an 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 for muscle attachment. The combination of muscles and epithelium forms 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. Except listed types muscle fibers are characteristic of ciliated worms 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 internal organs and transfer of metabolic products to the excretory system. In addition, parenchyma can be considered as supporting tissue.

There is no body cavity. Inside there is spongy tissue - parenchyma 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 large forms intestines presented 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 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.

The cerebral ganglion and the nerve trunks coming from it 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 first 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 various diameters. The thinnest tubules or capillaries are closed at their ends 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.

§ 1 Habitats and external structure of flatworms

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

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

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

§ 2 Internal structure of flatworms

Speaking about the internal structure of this type of animal, it must be remembered that the circulatory and respiratory systems are absent. They are characterized by aerobic or anaerobic respiration. Oxygen enters the body through the entire surface of the body.

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

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

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

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

§ 3 Taxonomy of Flatworms

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

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

List of used literature:

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

Images used:

All worms can be divided into three types (flat, annelid, round), each of which has its own characteristic features. This type refers to invertebrate animals that lack a body cavity and have bilateral symmetry.

Patients who want to get rid of helminths often ask for natural remedies with the least side effects. In such cases, I recommend this remedy.

The main signs of the type of flatworms

• digestive;
• nervous;
• sexual;
• excretory.

This type has several systems and even the rudiments of organs

Circulatory system

Not present, but the function of blood is performed by the parenchyma, consisting of connective cells. It is she who transports nutrients in the body.

Digestive system

Quite simplified, consists of the pharynx and intestines.

The pharynx is powerful and can:

• suck in;
• twist and envelop its victim.

The intestine consists of two sections - anterior and middle, most often branched. It has a closed structure, so that all undigested waste exits through the mouth. The mouth opening is located closer to the middle of the worm's body.

Free worms are mostly predators and they even have a peculiar device for capturing prey. This system is not observed in all classes; more primitive worms do not have it. For example, tapeworms feed on the entire surface.

Excretory system

The excretory system is quite large and consists of many tubules that unite and lead to excretory pores.

The parenchyma contains special cells that drive harmful substances into the tubules. For humans, these excretory products are very dangerous and toxic, along with poison.