What body shape do flatworms have. The main reasons for the increase in cases of invasion

flatworms- three-layer animals with bilateral (two-sided) symmetry, the body of which is covered with a skin-muscle sac, and the space between internal organs filled with parenchyma.

Systematics. Type flatworms combines several classes, the main of which are: Class Ciliary worms (turbellaria), Class Flukes (trematodes), class Monogeneans, class Tapeworms(cestodes).

Body shape. The vast majority of flatworms have a flattened body in the dorsal-abdominal direction. Ciliary worms, trematodes and monogeneans most often have a leaf-shaped or worm-shaped undivided body. The tape-like body of cestodes is usually divided into a head (scolex), a neck and a strobila, consisting of segments.

Dimensions. Ciliary worms rarely reach large sizes - 5-6 cm (one species - up to 35 cm). The body length of most species of the class is measured in millimeters. The sizes of trematodes lie approximately in the same range. Monogeneans are usually small - a few millimeters. Cestodes are the longest invertebrates and their length sometimes reaches 30 m. Among tapeworms there are also dwarfs - only 3-4 mm.

Adult trematodes, cestodes and monogeneans lead an attached lifestyle, but they are able to change the place of attachment. With the help of suction cups and contractions of the body, trematodes and monogeneans can move. Cestodes living in the intestines constantly have to overcome its peristalsis. They do this by reducing the entire body, or parts of it.

Parenchyma. The space between the skin-muscular sac and the internal organs is filled with a special tissue - the parenchyma, so that the body cavity in flatworms is absent. The parenchyma is a derivative of the third germ layer - the mesoderm. Parenchyma cells have many intertwining processes. Dorso-ventral muscles and muscles and special muscles pass through the parenchyma, providing the mobility of individual organs. The functions of the parenchyma are very diverse. It provides support for the body, complex metabolic processes, nutrients are stored in its cells. Other types of worm body cells can form from parenchyma cells.

Digestive system. In general, the digestive system consists of two sections - the foregut and midgut. The foregut includes the mouth, pharynx, and esophagus. The hindgut and anus are always absent. Undigested residues are removed through the mouth opening.

The digestive tract begins with a mouth opening, which is located terminally at the anterior end of the body or on its ventral side. The oral cavity leads to the pharynx, which in some groups of worms can turn outward (ciliary worms). Behind the pharynx is the esophagus of various lengths, which continues into the blindly closed intestine.

The structure and degree of development of the intestine are varied. In ciliary worms, the intestine may be completely absent, or it may form two or three branches. In some trematodes, it is straight and looks like a small bag, while in most flukes, the intestine bifurcates. Sometimes both intestinal trunks merge, forming a kind of intestinal ring. At large species(fasciola) intestinal trunks form many lateral branches. In many monogeneans, the gut forms a dense network.

All tapeworms lack a digestive system.

excretory system. To remove excess fluid and harmful metabolic products from the body, flatworms use special cells and a system of channels. The thinnest tubules penetrate the parenchyma of the worm. Gradually merging with each other, they form thicker channels that open on the surface of the body with an excretory pore. The beginning of a thin tubule forms an excretory cell, from which several long flagella ("flickering flame") depart into the cavity of the tubule, which are in constant motion and ensure the movement of fluid in the channels. Such a formation is called protonephridia, and this type of excretory system is called prononefridial. Gradually, the liquid with metabolic products is ejected through the excretory pores, which can be from one to two to 80. different types.

Some ciliary worms lack protonephridia. In this case, the excretory function is performed by the intestines and parenchyma.

Nervous system. In some of the most primitive ciliary worms, the nervous system is diffuse. However, most flatworms have supraesophageal ganglia (usually paired), from which several longitudinal nerve trunks depart. These trunks are interconnected by transverse bridges - commissures. This type of nervous system is called the orthogon.

Sexual system. Almost all flatworms are hermaphrodites. The only exceptions are some flukes (schistosomes) and a few ciliary worms. But their separateness is a secondary phenomenon.

The male reproductive system is represented by testes, the number and shape of which are very diverse. Trematodes, for example, usually have two compact (rarely branched) testicles. In ciliary worms, cestodes and monogenes, from 1-2 compact to many tens of small vesicles. Thin vas deferens depart from the testes, merging into the vas deferens. The vas deferens flows into the copulatory organ different structure, which can turn out of the male genital opening. This hole can be located either on the flat side of the worm (most common) or on the side (taeniae).

The female reproductive system is complex and very diverse. In the general case, there are paired or unpaired ovaries of various shapes that produce eggs. The ducts of the ovaries (oviducts) and special glands - vitelline glands - merge, forming an extension in most species - the ootype. The ducts of various additional glands (shell and others) also flow there. Fertilization of eggs occurs either in the ootype or in the uterus. The uterus also serves as the site of the final formation of eggs. The uterus either opens outwards with the female genital opening through which eggs are laid (most flatworms) or has no communication with the environment (some cestodes). In the latter case, the eggs get outside only after the destruction of the tissues of the joint.

In ciliary worms, trematodes and monogeneans, there is only one reproductive complex. In cestodes, male and female gonads are located in each segment of the worm, and in some species, 2 reproductive complexes are located in each segment.

Reproduction. In flatworms, sexual reproduction predominates. Despite hermaphroditism, self-fertilization is rare. Most often, cross-fertilization occurs when two partners are involved. In rare cases, partners grow together (spikes). In cestodes, cross-fertilization occurs both between two individuals and segments of one worm. In dioecious flukes of schistosomes, the male and female live together all their lives (up to 30 years). In this case, the male wears the female in a special fold.

In a number of ciliary worms, asexual reproduction is described, when an individual is laced into two parts, from which new worms are formed. Asexual reproduction in the form of budding is known in cestodes both in adulthood (budding of segments) and in larvae (formation of scolexes in larval bubbles).

Development. The ontogenesis of flatworms is very diverse and differs greatly among representatives of different classes.

A fertilized egg of a number of ciliary worms undergoes complete uneven spiral crushing. The gastrula is formed by immigration. Further development is either direct (an adult worm is immediately formed from the egg), or metamorphosis occurs (a larva covered with cilia comes out of the egg, which turns into an adult animal).

In monogeneans, cleavage is also completely uneven, gastrulation occurs by epiboly. Then all cell boundaries disappear, resulting in the formation of syncytium, in which the laying of tissues and organs of the future larva takes place. The development of larvae in different species at different temperatures can vary from 3 to 35 days. The larva that emerged from the egg is very mobile due to the ciliary epithelium. In the future, it attaches to its host and there the formation of an adult organism takes place. Some species have live birth. In this case, the embryo develops in the uterus of the mother's organism to the state of an adult organism within 4-5 days. Interestingly, at the time of birth, a young worm already has a developing embryo in its uterus, in which another one develops.

The trematode egg undergoes complete uniform (or uneven) crushing. Subsequently, a larva covered with cilia is formed in the egg - miracidium. In one case, it emerges from its shell in the water and searches for a suitable intermediate host, which is always a mollusc. In another case, the exit occurs directly in the digestive tract of the mollusk that swallowed the egg. In the tissues of the mollusk, the miracidium sheds its ciliary cover and turns into a maternal sporocyst, which subsequently begins to reproduce: it gives birth to several dozen daughter sporocysts. Both maternal and daughter sporocysts are devoid of intestines. Daughter sporocysts form inside themselves a certain number of larvae of the next generation - cercariae, which already have two suckers and a tail. In some cases, the maternal or daughter sporocyst gives birth to larvae with intestines - redia, which in turn form cercariae that emerge from the mollusk. The number of generations of larvae in mollusk tissues can be different. Thus, from miracidia alone, in the end, from several tens to several tens of thousands of cercariae can form.

Cercariae of other species look for additional hosts - arthropods, fish and others, penetrate into them and encyst, forming an infective larva - metacercariae. When the definitive host eats an additional infection occurs. For example, a person becomes infected with a cat fluke (opisthorchis) when eating insufficiently processed fish of the carp family (roach).

The development of cestodes can proceed with the change of three or two hosts.

Origin. Flatworms are most likely descended from ancestors similar to the planula-shaped larvae of some coelenterates. However, for obvious reasons, no paleontological evidence was found for this - the too delicate body of such animals could not be preserved in a fossil state.

Despite the external simplicity of these worms, their body is a rather complex and not fully understood mechanism.

flatworms ( Latin name Plathelminthes or Platyhelminthes) are a group of worm-like invertebrates without a body cavity. At the same time, the body of these organisms is flattened, and the free space between the body wall and internal organs is filled with parenchyma (undifferentiated connective tissue).

In relation to volume, the surface area of ​​the body of these helminths is large, so the metabolism in the body can be maintained using the diffusion mechanism. At the same time, these worms do not have a circulatory system..

Group composition: what classes are included?

The group includes seven classes of helminths:

The body of the worms is covered with a single layer of epithelium. At the same time, it is worth noting the high regenerative capabilities of flatworms. So, the vast majority of representatives of this group can regenerate up to 6/7 of their body.

Under the epithelium, a muscle sac is fixed, which is several layers of muscle cells that are not distributed into individual muscles. There is an outer (annular) and inner (longitudinal) layer of muscles.

All representatives of flatworms, except for cestodes and tapeworms, have a pharynx. The pharynx passes into the intestine (digestive parenchyma), which is closed in the final part. Several representatives of large turbellarians have anal pores.

Helminths have a primitive nervous system, which is a cluster of nerve nodes that are located in the anterior segment of the body. In addition, the nervous system is also represented by the cerebral ganglia, from which the nerve columns branch, interconnected by jumpers.

Osmoregulation (the mechanism for maintaining a constant osmotic pressure) is carried out by protonephridia, which are branching canals that pass into one or two excretory canals. The release of toxic and poisonous substances from the body of helminths occurs due to the passage of fluid through protonephridia or through parenchyma cells (atrocytes).

The reproductive system of helminths implies a division into two sexes: male and female. Worms have testes and ovaries; males also have copulatory organs (organs for internal fertilization). Moreover, all representatives of the group, except for some species of dioecious flukes, are hermaphrodites.

The most famous representatives

Flatworms have six of the most studied and described representatives (separate groups or individuals). In total, there are more than 25 thousand species of flatworms, 3000 of which live in Russia and the CIS countries.

structural features

Body flatworms has clearly defined fabrics of all 4 main types, from which organs and organ systems are formed. The shape of the body is flattened in the dorsal-abdominal direction, has the form of a sheet, plate, ribbon, and the like.

Symmetry bilateral (bilateral), appeared in the process of evolution as an adaptation to active image life. In the body, the main and tail end, dorsal and abdominal parts are already distinguished.

germ layers - ectoderm, endoderm and mesoderm. In the process of embryonic development, a third germ layer is laid, which occurs for the first time in flatworms. Mesoderm - the middle germinal layer, characteristic of the embryos of multicellular three-layer animals.

Cavity the body is absent, the gaps between the organs are filled with parenchyma. Parenchyma- loose connective tissue, which performs various functions: storage nutrients, their transportation, excretion of metabolic products, maintaining the shape of the body, etc.

Features of life processes

Support carried out thanks to the cells of the parenchyma and the musculocutaneous sac.

Motion provided by smooth muscles, which are formed along the annular, longitudinal and diagonal muscle fibers.

Transport of substances through the body occurs by diffusion. There is no circulatory system in all flatworms.

Selection carried out with the participation excretory system. Appears in the process of evolution for the first time and is built according to the type of protonephridia. Protonephridia - excretory organs of some invertebrates, which consist of tubules, beginning with star-shaped cells, from which cilia are directed into the lumen of the tubules. Metabolic products can accumulate in special cells of the parenchyma.

Function regulation implemented with the participation nervous system nodal (ganglionic) type, which is divided into central (CNS) then peripheral (PNS). The CNS consists of the head ganglion and nerve trunks connected by annular septa. The PNS is represented by nerve processes and nerve endings. In flatworms, only unconditioned reflexes are known.

reproduction sexual, which is carried out by the reproductive system of female and male organs. In most flatworms, the reproductive system hermaphroditic. Hermaphrodites are organisms that have both female and male sex organs. Fertilization is internal, may be cross or due to self-fertilization.

Regeneration well developed in free-living species.

Type Flatworms has about 12.5 thousand species. Classes are distinguished in a type (i.e. type classification):

1. Eyelash worms, or Turbellaria (3 thousand years old) - all free-living in the sea or in fresh water. Representative - Planaria dairy.

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

the beginning of the strobili are called hermaphroditic. They contain a well-developed male and female reproductive system. In hermaphroditic segments, eggs and spermatozoa 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 uterus stuffed with eggs. The number of segments that make up the body of the cestode varies over a very wide range. 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.

Covers. The body of tapeworms is covered tegument(this is a type of submerged epithelium without cilia). However, unlike flukes, the tegument of tapeworms forms many microscopic hair outgrowths - microtrichium, increasing the area of ​​absorption of nutrients. As with flukes, the tegument of tapeworms is dense, well protecting the worm from the digestive juices of the host's intestines. The tegument is firmly fused with the muscle fibers located under it, forming skin-muscular bag. Tapeworms have no organs of locomotion, except for the skin-muscle sac. The musculoskeletal sac contains the internal organs. Between the internal organs lies connective tissue parenchyma.

Nervous system – orthogon(see flukes).

Circulatory and respiratory systems missing.

excretory system protonefridial type (see flukes).

Reproduction and development. Tapeworms - hermaphrodites. The reproductive system is also arranged like that of flukes. In the growing hermaphroditic segments, almost the entire space is occupied by the reproductive organs. Either two individuals participate in the act of fertilization (cross-fertilization), or different segments of one strobila (self-fertilization). In mature segments, the uterus grows strongly, it is full of 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 strobili (in chain bullish, chain pork, Echinococcus), with the excrement of the host animal are excreted in environment. The fecundity of cestodes is extremely high, for example, Tapeworm bullish or Tapeworm pork(otherwise called tapeworms) produces about 600 million eggs a year, and for

type Flatworms class Tapeworms

Questions for self-control.

Name aromorphoses of the type Flatworms.

Name the classification of the type Flatworms.

Describe the structure of the body of tapeworms.

How does excretion occur in tapeworms?

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

What is the structure of the reproductive system in tapeworms?

Tell the lifestyle and development cycle of the bovine tapeworm, pork tapeworm, Echinococcus, wide Lentets, Sheep brain, Moniesia, Remnets.

Indicate the final hosts for the bovine tapeworm, pork tapeworm, Echinococcus, broad tapeworm, Sheep brain, Moniesia, Remnets.

How does the infection of the final hosts of the bovine tapeworm, pork tapeworm, Echinococcus, wide Lentets, Sheep brain, Moniesia, Remnets occur.

Indicate the intermediate hosts for bovine tapeworm, pork tapeworm, Echinococcus, broad tapeworm, Sheep brain, Moniesia, Remnets.

What internal organs are located in each segment?

What is a finna? Can you see her?

Why do tapeworms have well-developed reproductive organs?

Why can mature segments separated from the tapeworm move independently?

Why is the worm not digested in the intestines of the host?

Imagine what happens if a person accidentally swallows a segment, for example, a bull tapeworm with mature eggs?

type Flatworms class Tapeworms

Rice. Bull chain: head and segments.

Rice. Ribbon wide: strobila.

type Flatworms class Tapeworms

Rice. Integuments of tapeworms.

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

Rice. The development of the pork tapeworm.

1 - head; 2 - neck; 3 - strobili; 4 - segments (proglottids); 5 - hooks; 6 - suckers; 7 - oncosphere - larva with six hooks; 8 - Finns in pork meat(partially opened); 9 - a young tape form turned out of the Finn. Table 1. Tapeworms of great economic importance

Table. 1. Tapeworms of Economic Importance (continued)

DRAWINGS TO BE DONE IN THE ALBUM

(total 7 drawings)

Lesson topic: Type Flatworms -Platehelminthes.