Class ciliated worms. Presentation of "flatworms" Type roundworms

Class Ciliated worms
Ciliated worms are the most primitive group of lower worms; represented mainly by free-living forms. Body length varies from 5 mm to 50 cm. Turbellaria have the shape of a spindle, ribbon or drop and are covered with ciliated epithelium; glandular cells on the surface of the body secrete mucus.
The class Ciliated worms includes about 3,000 species living in marine and fresh water bodies, rarely in soil. A representative of free-living ciliated worms is the white (milk) planaria, which lives in fresh water bodies
Appearance and covers. The body of ciliated worms is elongated and leaf-shaped. Dimensions vary from a few millimeters to several centimeters. The body is colorless or white. Most often, eyelash worms are colored in different colors by grains of pigment located in the skin.
The excretory system first appears as a separate system. It is represented by two or several channels, each of which opens outward at one end, and the other strongly branches, forming a network of channels of various diameters. The thinnest tubules or capillaries at their ends are closed by special cells - stellate.
From these cells, bundles of cilia extend into the lumen of the tubules. 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.
The sense organs of ciliated worms are relatively well developed. The entire skin serves as an organ of touch. In some species, the function of touch is performed by small paired tentacles at the anterior end of the body.
The balance sense organs are represented by closed sacs - statocysts, with auditory pebbles inside. The organs of vision are almost always present. There may be one pair of eyes or more
The main feature of the nervous system of ciliated worms in comparison with coelenterates is the concentration of nervous elements at the anterior end of the body with the formation of a double node - the cerebral ganglion, which becomes the coordinating center of the entire body. Longitudinal nerve trunks, connected by transverse annular bridges, extend from the ganglion
The reproductive system is quite diverse in structure. It can be noted that, in comparison with coelenterates, ciliated worms have special excretory ducts for removing germ cells out. Ciliated worms are hermaphrodites. Fertilization is internal.
Reproduction. In most cases, sexually. In most worms, development is direct, but in some marine species development occurs with metamorphosis.
However, some eyelash worms can also reproduce asexually through transverse fission. At the same time, regeneration of missing organs occurs in each half of the body.

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Slide 1

Apollinaria Eyelash worms

Slide 2

In lakes, ponds, ditches on underwater objects, stones, in the axils of plant leaves.

Habitat

Slide 3

The skin-muscle sac contains all the internal organs. It consists of one layer of integumentary cells (epithelium), bearing cilia, and three types of muscles located underneath them: annular, oblique, longitudinal. The space between the skin-muscle sac and the organs is filled with parenchyma cells

Skin-muscle bag

Slide 4

It is represented by two sections of the intestine: the anterior (mouth and pharynx) and the middle (highly branched and blindly closed). The mouth is on the ventral side and leads into the muscular pharynx. The worm that has fed on the whole has a branched intestine visible through the integument. In the intestines, food is digested and absorbed, and undigested remains are eliminated through the mouth. The intestine is closed, there is no anus

Digestive system

Slide 5

Excretory system - protonephridia. The removal of waste products from tissues and organs occurs through numerous tubules. The tubule begins with cells with a bunch of cilia. Thanks to the movement of these cilia, liquid metabolic products flow from the tubules into two large longitudinal excretory canals.

Excretory system

Slide 6

Circulatory, respiratory and nervous systems

There is no circulatory or special respiratory system. Worms breathe through the surface of their bodies, extracting oxygen from the water. Therefore, eyelash worms live in clean, oxygen-rich water.

In the anterior part of the body, nerve cells form a paired head nerve ganglion, from which nerve trunks extend, giving numerous branches of nerves to organs and tissues. There are organs of vision, taste, smell, touch, and balance.

Class Ciliated worms, or turbellaria (lat. Turbellaria) - a class of the flatworm type. There are over 3500 species. These are predominantly free-living flatworms, less often parasitic. Their body is covered with ciliated epithelium. Dimensions range from microscopic to 30-40 cm. Most free-living species of ciliated worms are found in seas and fresh waters, a smaller number are found in damp places on the land surface, in the soil. The most famous are representatives of the order three-branched, or planarians, a large group (a subtype of lower worms or an independent type) of invertebrate, bilaterally symmetrical, free-living or parasitic animals. The length of P. h. is from 0.1 mm to several meters. The body is usually flattened (hence the name), oval or more or less elongated; whole or divided into a number of segments (tapeworms); in parasitic forms it is equipped with organs of attachment to the “host” in the form of suckers, proboscis, hooks, etc. The body wall is represented by a skin-muscular sac. The skin is formed by a single-layer epithelium covered with cilia (in free-living P. h.) or the so-called. submerged epithelium. The muscles consist of annular, longitudinal and oblique layers that provide the “worm-like” movement of the animal. There is no body cavity, the space between the skin-muscle sac and the internal organs is filled with connective tissue - parenchyma. The mouth opening is located on the ventral side of the body or on its anterior, less often at the posterior end. Most forms have an intestine, but some do not (intestinal turbellaria), and digestion occurs in the central part of the parenchyma. In tapeworms (parasitic parasites), which also lack an intestine, nutrition occurs by absorbing juices from the intestines of the “host” over the entire surface of the body. P. h. does not have an anal opening. The nervous system consists of the brain, which lies in the front of the body, and several paired longitudinal nerve trunks, of which the lateral ones usually reach the greatest development. The sense organs of free-living forms are tactile papillae or tentacles, eyes, and the organ of balance is the statocyst. There is no circulatory system. Skin breathing. Excretory organs - Protonephridia. P. h. - hermaphrodites; have complex reproductive ducts; The ovaries in most forms are divided into the ovaries themselves (producing eggs) and the vitelline cells (producing cells that serve to nourish the embryo). In free-living P. h. development is direct or with metamorphosis; in the latter case, a Müllerian larva is formed. For parasitic P. h., as a rule, a complex development cycle is characteristic - with alternation of free and parasitic larvae and even generations of different structures. Free-living P. h. live in the seas, fresh waters and on land; parasitic - external or internal parasites of other animals, as well as humans. Lit.: Guide to Zoology, vol. 1, M. - L., 1937; Beklemishev V.N., Fundamentals of comparative anatomy of invertebrates, 3rd ed., vol. 1-2, M., 1964; Dogel V. A., Ciliary worms

Coelenterates mainly have radial symmetry; we will consider bilaterally symmetrical animals. This is a huge group, including about 99% of all animals, including flatworms, roundworms and annelids, mollusks and arthropods, chordates and many others (Fig. 1).

Rice. 1. Bilaterally symmetrical animals

Their body is characterized by bilateral symmetry and the presence of three cell layers: ectoderm, mesoderm and endoderm (Fig. 2). Coelenterates had only two cell layers.

Rice. 2. Bilateral symmetry and cell layers

In most bilaterally symmetrical animals, it is always possible to distinguish the anterior and posterior ends of the body, as well as the ventral and dorsal sides. Some bilaterally symmetrical animals secondarily lose this type of symmetry, for example, echinoderms.

Flatworms are considered to be the most ancient in origin, i.e., a primitive group of bilaterally symmetrical animals (Fig. 3).

Rice. 3. Flatworms

Flatworms do not have a specialized respiratory system, so their bodies are flat. In order for each cell to receive oxygen and release carbon dioxide, that is, for effective gas exchange, it is necessary that the cell be close to the external environment, which is why large flatworms have a body that is usually flat, like paper (Fig. 4).

Rice. 4. Representative of flatworms

Under the integument there are several layers of muscle, together they form a musculocutaneous sac. Flatworms do not have an internal body cavity, it is all filled with cells, all organs are united into systems: the digestive, excretory, reproductive and nervous systems of the organs. There is no circulatory system; nutrients are distributed directly through the intestines when present. The intestine is blindly closed and communicates with the environment only through the mouth.

The nervous system is represented by nerve ganglia located in the anterior part of the body, cerebral ganglia and nerve trunks extending from them, connected by jumpers (Fig. 5).

Rice. 5. Nervous system of flatworms

Some free-living flatworms have primitive organs of vision and balance. Discharge is carried out using special tubules and through the entire surface of the body. The body of a flatworm contains testes and ovaries, that is, male and female reproductive organs (Fig. 6).

Rice. 6. Reproductive organs of some flatworms

Such animals are called hermaphrodites. An interesting feature of most flatworms is the presence of a complex egg. It consists of a fertilized egg and several yolk cells, all of these cells together are covered with a hard protective membrane.

The organism in which an adult worm lives and reproduces sexually is called final owner.

The class Ciliated worms (Fig. 7) includes about three thousand mostly free-living species, with sizes ranging from microscopic to 30-40 centimeters.

Rice. 7. Class Ciliated worms

They live in sea or fresh waters, sometimes in humid land habitats. The integument of these representatives always has cilia, which help them swim or move along the bottom (Fig. 8).

Rice. 8. Eyelash worms

The sense organs of ciliated worms are much better developed than those of representatives of other classes; they often have an organ of balance. The olfactory organs are important, since with their help most ciliated worms hunt. Almost all ciliated worms have eyes (Fig. 9).

Rice. 9. Eyelash worm eyes

Ciliated worms are hermaphrodites and usually undergo cross-fertilization. Development is direct - a larva emerges from the egg, outwardly similar to the adult organism.

The ability of flatworms to regenerate is clearly expressed; accordingly, there is also asexual reproduction - a constriction appears on the body of the worm, which gradually divides its entire body into two parts.

The most famous are representatives of the order Planaria (Fig. 10), small flatworms found in freshwater bodies, where they crawl among aquatic plants.

Rice. 10. Planaria

In northern and central Russia, the milky-white planaria is very common, the largest among the rest (Fig. 11). Its length reaches three centimeters, the dark branched intestines clearly shine through its white covers, and a pair of eyes can be discerned on the head.

Rice. 11. Milky white planaria

Planarians move extremely smoothly and evenly due to the beating of cilia and small contractions of the body. They feed mainly on small aquatic animals.

The intestine has an extremely branched shape (Fig. 12), which is especially clearly visible in the milky white planaria if you observe it with a magnifying glass.

Rice. 12. Intestine of a milky white planaria

Planaria reproduce by laying eggs, which are immersed in a common protective cocoon. The main protective device of the planarians themselves is the mucus that abundantly covers their body. Planaria have extremely pronounced regeneration.

Rice. 13. Class Flukes

Typically, one of the hosts is a gastropod and the other is a vertebrate (Fig. 14).

Rice. 14. The owners of the flukes

Flukes produce a large number of eggs; the final host is a vertebrate; in its body, flukes can be found in the liver, intestines, gall bladder, and organs of the excretory system. The sizes of flukes range from several tens of microns to several centimeters. The body is flattened, leaf-shaped, there are two suckers - oral and ventral. The oral opening is located at the bottom of the oral sucker. The intestines are closed. The integument of flukes does not have cilia.

The nervous system is basic for representatives of the type. Discharges occur through the surface of the body and with the help of tubules. Flukes are mostly hermaphrodite, but dioecious species are also found.

The eggs formed after the crossing of worms are hatched into the external environment with the feces or urine of the host, and a larva emerges from the egg, capable of swimming using the beating of cilia. For further development, it must infect a gastropod, inside which the larva undergoes metamorphosis and reproduces asexually (Fig. 15).

Rice. 15. Life cycle of the liver fluke

Then, dispersal larvae emerge from the body of the intermediate host and infect the definitive hosts (Fig. 16).

Rice. 16. Life cycle of the liver fluke

Rice. 17. Liver fluke (fluke)

It causes the disease fasciliosis, which manifests itself as hepatic colic and cholecystitis; this disease is common among sheep.

The adult worm is hermaphrodite and can reach three centimeters in length. Development occurs with the change of one intermediate host - a freshwater snail; infection of the final host occurs when ingesting water or food with its cysts. In the intestine, the cyst bursts, the young fluke comes out and penetrates the liver.

We learned about bilaterally symmetrical animals, examined the type Flatworms and its two classes - the Ciliated worms class and the Flukes class; in the next lesson we will complete the topic “Flatworms”.

Bibliography

1. Latyushin V.V., Shapkin V.A. Biology Animals. 7th grade. - Bustard, 2011.
2. Sonin N.I., Zakharov V.B. Biology. Diversity of living organisms. Animals. 7th grade. - M.: Bustard, 2009.
3. Isaeva T.A., Romanov N.I. Biology, 7th grade. - M.: Russian Word, 2013

1. Internet portal “shkolo.ru” ()
2. Internet portal “bono-esse.ru” ()
3. Internet portal “biolka.narod.ru” ()

Homework

1. Name the features of flatworms.
2. Name the most famous representatives of the class Ciliated worms.
3. Describe the lifestyle of worms of the class Flukes.

Slide 1

Slide text:

Apollinaria

Eyelash worms

Slide 2

Slide text:

In lakes, ponds, ditches on underwater objects, stones, in the axils of plant leaves.

Habitat

Slide 3

Slide text:

The skin-muscle sac contains all the internal organs. It consists of one layer of integumentary cells (epithelium), bearing cilia, and three types of muscles located underneath them: annular, oblique, longitudinal.
The space between the skin-muscle sac and the organs is filled with parenchyma cells

Skin-muscle bag

Slide 4

Slide text:

It is represented by two sections of the intestine: the anterior (mouth and pharynx) and the middle (highly branched and blindly closed). The mouth is on the ventral side and leads into the muscular pharynx. The worm that has fed on the whole has a branched intestine visible through the integument. In the intestines, food is digested and absorbed, and undigested remains are eliminated through the mouth. The intestine is closed, there is no anus

Digestive system

Slide 5

Slide text:

Excretory system - protonephridia. The removal of waste products from tissues and organs occurs through numerous tubules. The tubule begins with cells with a bunch of cilia. Thanks to the movement of these cilia, liquid metabolic products flow from the tubules into two large longitudinal excretory canals.

Excretory system

Slide 6

Slide text:

Circulatory, respiratory and nervous systems

There is no circulatory or special respiratory system. Worms breathe through the surface of their bodies, extracting oxygen from the water. Therefore, eyelash worms live in clean, oxygen-rich water.

In the anterior part of the body, nerve cells form a paired head nerve ganglion, from which nerve trunks extend, giving numerous branches of nerves to organs and tissues. There are organs of vision, taste, smell, touch, and balance.