Conclusion parasitic flatworms. Flukes are parasitic flatworms

Development usually occurs with metamorphosis, less often - without it.

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

Structure and vital functions

The body shape of flatworms is very diverse. Most of them are leaf-shaped or ribbon-shaped. In tapeworms, the body is usually divided into a number of segments. The body length of flatworms ranges from a few millimeters to 18 m.

The musculature of the skin-muscle sac is composed of two layers of muscle fibers: the outer circular and the inner longitudinal. In addition, individual bundles of muscle fibers run obliquely through the parenchyma from the dorsal side of the body to the ventral side. This muscle structure allows the worm to perform various movements, as well as extend and contract the body in length.

The body cavity is filled with a loose mass of connective tissue cells - parenchyma, in the spaces between which interstitial fluid circulates. The parenchyma contains the digestive, excretory and genital organs.

The circulatory system, like all primitive animals, is absent.

The reproductive system is hermaphroditic and very complex. Typically, this system, in addition to the testes and ovaries, includes various appendage formations that ensure the process of fertilization of eggs with sperm, supplying the egg with the nutrients necessary for the development of the embryo and creating protective shells around the egg.

The development of flatworms occurs in most cases with metamorphosis, when the animal goes through a series of larval stages before reaching maturity. Much less often their development occurs without such complex

Another class belongs to flatworms - these are tapeworms, which, in turn, are divided into orders of tapeworms and tapeworms.

These worms differ from roundworms in that they have an intermediate host in whose body their larvae develop. As a rule, fish and animals become intermediate hosts.

Tapeworms in the sexually mature state are inhabitants of the intestines of vertebrates. At the anterior end of the body there is a head - the scolex, which is an organ of attachment, behind it there is a growth zone; the body is divided into segments, or proglottids. Hermaphrodite. The intestines are reduced.

Tapeworms have a head with four suckers, with the help of which the worms attach to the intestinal walls. Next comes the growth zone, or neck, from which the segments originate. As the neck grows, a distinct transverse constriction appears on it, separating the posterior portion, which turns into a proglottid.

The uterus does not have an excretory opening, which means that it is practically impossible to detect eggs in feces; eggs without a lid.

As the helminth grows, new segments gradually push back the previously formed ones. Thus, in the front of the body there are the youngest segments, and at the end - the oldest, most mature.

In the process of moving the segments further from the neck, they mature, their shape changes and internal structure. Young segments are the smallest. Gradually their size increases, their reproductive system changes, which young, newly formed segments are completely deprived of. Many segments connected to each other resemble a chain, which can contain from 3 to several thousand segments.

As already mentioned, tapeworms do not have a digestive system; they absorb food over the entire surface of the body.

Life cycle tapeworm disease occurs with a change of hosts and with larval stages. The permanent hosts are vertebrates and humans, and the intermediate hosts are vertebrates and invertebrates.

Type Roundworms

Character traits type organizations are as follows:

1. The body is thin, cylindrical, elongated and pointed at the ends. In cross section it is round (which gives the type its name).

2. The skin-muscle bag consists of an outer multilayer cellular structure the cuticle, the single-layer epithelium located underneath it and a layer of longitudinal muscle fibers, thanks to the contractions of which the body can bend like a snake.

3. The body cavity is primary, filled with liquid under greater than atmospheric pressure. Cavity fluid gives the body elasticity and thus acts as a hydroskeleton. It also provides transport of nutrients and waste products.

4. For the first time in the animal world, the digestive system is represented through a digestive tube, divided into three sections - the foregut, middle and hindgut. The anterior section begins with the oral opening leading to the oral cavity and pharynx, which can work as a pump. The pharynx is separated from the midgut by a valve. In the midgut, food is digested and absorbed. The midgut is followed by the ectodermal hindgut, which opens on the ventral side of the body, the anus.

5. Excretory system It is represented by a pair of lateral longitudinal canals, merging under the pharynx into one duct and opening on the ventral side of the body with an excretory opening. The final waste products accumulate in the cavity fluid, and from it enter the excretory canals.

6. The nervous system is represented by a circular peripharyngeal ganglion and several longitudinal nerve trunks extending from it, connected to each other by semicircular nerve bridges. There are organs of taste and touch, and free-living roundworms have light-sensitive eyes.

7. Roundworms are dioecious animals that reproduce only sexually. In roundworms, males and females are externally distinguishable (sexual dimorphism). The reproductive system has a tubular structure: the female has paired ovaries, oviducts, uterus and unpaired vagina, the male has an unpaired testis, vas deferens, ejaculatory duct, copulatory apparatus. Fertilization is internal, development usually occurs with incomplete transformation (with the larval stage).

Figure 11.6. Appearance(a) and internal structure (b) of roundworms: 1 - mouth opening; 2 - pharynx; 3 - intestines; 4 - vagina; 5 - uterus; 6 oviduct; 7-ovary; 8 - ejaculatory duct; 9 - testis; 10 - vas deferens.

The development cycle is complex, associated with the release of eggs into the external environment and migration of larvae in the human body. Fertilized eggs, covered with dense protective shells, enter the soil from the human intestine. In the presence of oxygen and sufficient high temperature The larva develops in them within about a month. The egg becomes contagious (invasive). With contaminated water and food, eggs enter the small intestine of a person. Here the larvae are freed from the shell, pierce the intestinal mucosa with their elastic body and penetrate the blood vessels. With the blood flow through the portal and inferior vena cava, they enter the right atrium, right ventricle and the lungs (via the pulmonary arteries). From the lung tissue they penetrate into the bronchi, from them into the trachea, and then into the pharynx. During migration, the larvae develop in the presence of oxygen. From the pharynx they enter the intestines, where they complete their development cycle. Life expectancy is about a year.

Roundworms are ubiquitous and have a high number of individuals, which indicates the biological progress of this group of animals. Their ancestors are considered to be ancient eyelash worms.

Group composition and characteristic representatives Eyelash worms (Turbellaria); Monogenea, or monogenetic flukes; Tapeworms (Cestoda); Cestodaria (Cestodaria); Gyrocotyloidea; Trematoda, or (formerly) digenetic flukes; Aspidogastrea.

Structure A distinctive feature of flatworms is the body flattened in the dorsal-ventral direction. Unlike coelenterates, in flatworms there is a third layer of cells, the mesoderm, located between the ectoderm and endoderm. Therefore, they are called three-layer animals that do not have a body cavity (it is filled with parenchyma and a loose cell mass in which the internal organs are placed).

Planaria is a predator. Its pharynx is a catching apparatus, which, through the mouth located on the ventral side, protrudes outward, penetrates the prey and sucks out its contents. Digestion of food occurs in the branched intestine. Undigested residues are expelled through the mouth. The planaria breathes over the entire surface of its body. The excretory organs consist of a system of branched tubules located on the sides of the body. Liquid harmful metabolic products are eliminated through excretory pores.

Nerve cells are collected in two nerve trunks, which are connected by thin bridges. At the anterior end of the body, they form a thickening nerve ganglion, from which nerve processes extend to the sensory organs (eyes and organs of touch) and to the posterior end of the body. The reproductive organs are two oval ovaries and numerous testes, develop in the body of one individual and form reproductive cells, eggs and sperm. Animals whose bodies contain both female and male reproductive organs are called hermaphrodites. Their fertilization is internal, cross-fertilization, after which the planaria lays cocoons with eggs. Her development is direct.

Almost all tapeworms are hermaphrodites, characterized by high fertility and development with a change of hosts. Each segment of the bovine tapeworm has one ovary and many testes. The eggs mature in the oldest, posterior segments, which break off and are released with feces. Further development of the eggs will occur if they are ingested by cattle along with the grass. In the stomach of a cow, larvae emerge from the eggs, which, boring through the intestinal walls, enter the blood.

Flatworms include representatives such as flukes.

All types of helminths of this type have a flattened body, tongue-shaped or leaf-shaped. Flatworms have well-developed digestive, nervous, excretory and reproductive systems, but lack circulatory and respiratory systems.

The digestive system of fluke helminths consists of the mouth, pharynx, esophagus and two intestinal canals. Digestion and absorption of food occurs in the intestines. The anus is absent, and undigested food remains are thrown out through the mouth. Tapeworms do not have a digestive system.

Flukes, or trematodes, have one sucker on the front end of the body (the mouth is located deep in the sucker), the second on the stomach (in the fluke subclass).

There is a species of flukes that have many suckers or at the rear end of the body there is a whole disk for suction (multi-mouths).

Flukes feed on the contents of the host's intestines, blood, mucus, and epithelium. Their digestion is extracellular, enzymatic. The organ of excretion is a richly developed aquifer system. The water driven by the cilia flushes excretory products from the excretory canals.

Flukes lack a circulatory system and respiratory organs, as well as sensory organs.

The nervous system consists of two nerve ganglia located at the anterior end of the body and nerve trunks extending from them. The sense organs include nerve endings (sensilla).

The vast majority of representatives are hermaphrodites, except for blood flukes (schistosomas) - they are dioecious. Fluke eggs are light yellow to dark brown in color and have a cap on one of the poles. During examination, eggs are found in duodenal contents, feces, urine, and sputum.

The first intermediate host of flukes are various mollusks, the second host is fish and amphibians. The definitive hosts are various vertebrates.

The life cycle of polymouths is extremely simple: after leaving the fish, a larva emerges from the egg, which after a short period of time again attaches itself to the fish and turns into an adult worm. Flukes have a more complex development cycle, changing 2-3 hosts.

The sizes of flukes range from 1 mm to 1.5 m.

The name given to helminths was not entirely accurate, since they do not suck anything out of the body, but they cause enormous harm.