Number of species: about 25 thousand.

Habitat: They live everywhere in humid environments, including the tissues and organs of other animals.

Structure: Flatworms are the first multicellular animals in which, in the course of evolution, bilateral symmetry, three-layer structure, real organs and tissues appeared.

Bilateral(bilateral) symmetry - this means that an imaginary axis of symmetry can be drawn through the animal's body, while the right side of the body will be a mirror image of the left.

During embryonic development, three-layer animals are laid three layers of cells: outer - ectoderm, average - mesoderm, internal - endoderm. Certain organs and tissues develop from each layer:

from the ectoderm, the skin (epithelium) and the nervous system are formed;

from the mesoderm - muscle and connective tissues, reproductive, excretory systems;

from the endoderm digestive system.

In flatworms, the body is flattened in the dorsal-abdominal direction, there is no body cavity, the space between the internal organs is filled with mesoderm cells (parenchyma).

Digestive system includes the mouth, pharynx and blindly closed intestine. The absorption of food and the excretion of undigested residues occurs through the mouth. In tapeworms, the digestive system is completely absent; they absorb nutrients from the entire surface of the body, being in the intestines of the host.

excretory organs - protonephridia. They consist of thin branching tubules, at one end of which are fiery (flickering) cells star-shaped, immersed in the parenchyma. A bundle of cilia (flickering flame) departs inside these cells, the movement of which resembles the flickering of a flame (hence the name of the cells). Flame cells capture liquid decay products from the parenchyma, and cilia drive them into the tubule. The tubules open on the surface of the body with an excretory pore through which decay products are removed from the body.

Nervous system ladder type ( orthogon). It is formed by a large head paired ganglion (ganglion) and six nerve trunks extending from it: two on the ventral side, two on the dorsal and two on the sides. Nerve trunks are interconnected by jumpers. From the ganglion and trunks, nerves depart to the organs and skin.

Reproduction and development:

Flatworms are hermaphrodites. Sex cells mature in the sex glands (gonads). Hermaphrodite has both male glands - testes, and female - ovaries. Fertilization is internal, usually cross, i.e. worms exchange seminal fluid.

CLASS CILIATION WORMS

Dairy planaria, a small aquatic animal, the adult has a length of ~25 mm and a width of ~6 mm, the body is flat, milky white. At the front end of the body are two eyes that distinguish light from darkness, as well as a pair of tentacles (chemical sense organs) necessary for finding food. Planarians move, on the one hand, thanks to the work of the cilia covering their skin, on the other hand, due to the contraction of the muscles of the skin-muscular sac. The space between the muscles and internal organs is filled with parenchyma, in which intermediate cells responsible for regeneration and asexual reproduction.

Planarians are carnivores that feed on small animals. The mouth is located on the ventral side, closer to the middle of the body, from it comes a muscular pharynx, from which three branches of a closed intestine depart. Having captured the victim, the planaria sucks out its contents with its throat. Digestion occurs in the intestine under the action of enzymes (intestinal), intestinal cells are able to capture and digest pieces of food (intracellular digestion). Undigested food remains are removed through the mouth.

Reproduction and development. Ciliary - hermaphrodites. Cross fertilization. Fertilized eggs fall into a cocoon, which the worm lays on underwater objects. The development is direct.

CLASS FLUES

4 - sporocyst; 5 - redia; 6 - cercariae; 7 - adolescarium.

CLASS TAPE WORMS

Bull tapeworm- a tapeworm, reaches a length of 4 to 12 meters. The body includes a head with suckers, a neck and a strobile - a tape of segments. The youngest segments are at the neck, the oldest are sacs filled with eggs, located at the posterior end, where they come off one by one.

Reproduction and development. Bull tapeworm is a hermaphrodite: in each of its segments there is one ovary and many testes. Both cross-fertilization and self-fertilization are observed. The posterior segments, filled with mature eggs, open and, with feces, are brought out. Cattle (intermediate host) can swallow eggs along with grass, in the stomach microscopic larvae with six hooks come out of the eggs, which enter the bloodstream through the intestinal wall and spread throughout the body of the animal and enter the muscles. Here the six-hooked larva grows and turns into Finn- a vial, inside of which there is a tapeworm head with a neck. A person can become infected with fincas by eating undercooked or undercooked meat from an infected animal. In the human stomach, a head emerges from the finca, which is attached to the intestinal wall. New segments bud from the neck - the worm grows. Bull tapeworm allocates toxic substances that cause intestinal disorders and anemia in humans.

Development pork tapeworm has a similar character, its intermediate owner, in addition to a pig and a wild boar, can also be a person, then Finns develop in its muscles. Development wide ribbon is accompanied by a change of two intermediate hosts: the first is a crustacean (cyclops), the second is a fish that has eaten a crustacean. The definitive host may be a human or a predator that has eaten the infected fish.

New concepts and terms: mesoderm, musculocutaneous sac, tegument, hypodermis, reduction, protonephridia (flame cells), orthogon, strobili, ganglion, gonads, hermaphrodite, direct and indirect development, definitive and intermediate host, miracidium, cercaria, finna, segment, armed and unarmed tapeworm.

Questions for reinforcement.

1. Who is called the intermediate host? final?

6. What is dangerous to drink raw water swimming in water bodies near grazing? Why is it important to wash your hands with soap after interacting with animals?

7. For which worms is oxygen harmful?

8. What aromorphoses led to the appearance of the type Flatworms?

Lectures on zoology

Type Roundworms

Answer plan:

· general characteristics roundworms

The structure of the body of Ascaris human

Reproduction and development of Ascaris human

Classification of roundworms, variety of species

The value of roundworms in nature and human life

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 features buildings:

• 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.
• excretory system 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 aquatic environment. Further, the development cycle follows one of two options. Cercariae are transformed into cysts directly in 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 allergic reaction(skin rash, itching).

Integuments of the body Outside, the body is covered with a single-layer epithelium. In ciliary worms, or turbellaria, the epithelium consists of cells that carry cilia. Flukes, monogeneans, cestodes, and tapeworms lack ciliated epithelium for most of their lives (although ciliated cells may occur in larval forms); their covers are represented by the so-called tegument, in a number of groups bearing microvilli or chitinous hooks. Tegumented flatworms belong to the Neodermata group. Flatworms can regenerate 6/7 of their body.

Musculature Under the epithelium there is a muscular sac, consisting of several layers of muscle cells that are not differentiated into individual muscles (a certain differentiation is observed only in the region of the pharynx and genital organs). The cells of the outer muscle layer are oriented across, the inner - along the anterior-posterior axis of the body. The outer layer is called the layer of circular muscles, and the inner layer is called the layer of longitudinal muscles.

Nervous system and sensory organs The nervous system is represented by nerve nodes located in the anterior part of the body of the worm, cerebral ganglia and nerve columns extending from them, connected by jumpers. The sense organs, as a rule, are represented by separate skin cilia - processes of sensitive nerve cells. Some free-living representatives of the type, in the process of adapting to living conditions, acquired light-sensitive pigmented eyes - primitive organs of vision and organs of balance.

Structure The body is bilaterally symmetrical, with clearly defined head and tail ends, somewhat flattened in the dorsoventral direction, in large representatives it is strongly flattened. The body cavity is not developed (with the exception of some phases life cycle tapeworms and flukes). The exchange of gases is carried out through the entire surface of the body; respiratory organs and blood vessels are absent.

Questions: How many flatworms live in Russia? What are the body coverings of flatworms? What kind of muscles? What are the sense organs? Briefly describe the structure of the body. How do flat people eat? How do they breathe? How do they reproduce?

Interesting Facts 1. By digesting, flatworms are able to "learn". A group of scientists made unusual discovery regarding the abilities of flatworms. It turns out that if planar worms are first taught to go through the maze, then grind them into a puree and let other worms eat it, then such worms will be able to go through this maze the first time.

Interesting facts 2. Different-sex species of worms - schistosomes are inseparable throughout life. The female lives in the pocket of the male all her life.

Interesting facts 3. Almost all types of flatworms can turn inside out. 4. And here are some more interesting facts about flatworms. For example, flatworms are truly almost immortal. If you cut off a very small piece from the worm, approximately 1/100 of the whole worm, it is still able to recover to the whole organism.

Interesting facts 5. On the skin of some planarians living in fresh water, scientists have found nettle cells, which are very similar to stinging cells found in coelenterates. It turns out that these cells really belonged to coelenterates, which subsequently ate the ciliary worms. Stinging cells are not digested by worms. They get into their skin and serve to carry protective function and attacks.

L i

7. Type flatworms

1. Fill in the summary table in your notebooks throughout the study of representatives of all types of worms

	1	2	3
Type of worms	flat	Round	ringed
Habitat	freshwater and marine waters, terrestrial wet environments, some inside animals and plants	The soil, fresh water, seas, animals and plants (parasites)	Fresh and marine water bodies, soil, there are parasites
Nutrition	The mouth opening is the pharynx-gut. The remains are removed through the mouth opening.	mouth opening, digestive system through in the form of a tube, anus	Mouth, pharynx, esophagus, midgut, hindgut, anus
Breath		Breathe with the entire surface of the body, there is no respiratory system	through the wet surface of the body or with the help of gills
Circulation	is absent	is absent	closed or partially closed circulatory system contracting walls of blood vessels
Selection	Branched tubules ending in parenchyma with stellate cells	modified skin glands, phagocytic cells	altered segmental glands found in every segment of the body
reproduction	Hermaphrodites. Sex glands: testes and ovaries.	dioecious	hermaphrodites and dioecious

2. Is the statement true: "Adult parasitic worms have cilia"?

3. Find in the text of the paragraph a description of the skin-muscle sac. Explain why it is called that.

Under the integumentary tissue is the skin muscles - this is a musculocutaneous sac, inside which the internal organs are located.

4. Remember the internal structure of the coelenterates. Compare the internal structure of coelenterates and flatworms. Note any complications.

Flatworms do not have an internal cavity, and the internal organs, combined into systems, are located inside the skin-muscle sac.

5. Write down the definitions of the concepts:

Bilateral symmetry - an imaginary axis of symmetry can be drawn through the animal's body and the right side is, as it were, mirror reflection left

Intermediate host - an organism in which worm larvae develop and reside for some time

suckers, hooks, proboscis

Worms produce many eggs in order to survive. Many eggs die either without finding an intermediate host, or when they enter the body of an unusual animal.

8. Specify the characteristics corresponding to each class of flatworms

A - class Eyelash worms
B - class Flukes
B - class Tapeworms

Answer:
A - 1, 7, 9, 6
B - 2, 3, 8, 11
B - 2, 4, 5, 8, 10

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. Body colorless or white color. 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 certain form and for muscle attachment. The combination of muscles and epithelium forms 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. Except listed species muscle fibers for ciliary worms are characteristic 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 aqueous humor, which allows the transfer of products from the intestine to internal organs and 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 at 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 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 different diameter. 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 some marine species development occurs with metamorphosis. However, some ciliary worms can reproduce and asexually through cross division. At the same time, in each half of the body, regeneration missing organs.