Type roundworms and annelids. Lesson topic: "Flat

Annelids or annelids (lat. Annelida) are a type of highly organized invertebrate animals, characterized by the presence of a segmented coelom, which is responsible for external annulation. In the process of evolution, annelids evolved from ancient free-living flatworms.

The coelom is the cavity that separates the intestine from the body wall. It is a characteristic feature of ringed worms, since round and flat worms do not have it.

The most famous representatives of annelids for every person are leeches (subclass Hirudinea) and earthworms (suborder Lumbricina), which are also called earthworms. But in total there are more than 20 thousand species of these animals.

Taxonomy

Today, experts classify from 16 to 22 thousand as annelids. modern species animals. There is no single approved classification of ringlets. The Soviet zoologist V.N. Beklemishev proposed a classification based on the division of all representatives of annelids into two superclasses: non-girdle worms, which includes polychaetes and echiurids, and girdle worms, which includes oligochaetes and leeches.

Below is the classification from the World Register of Marine Species website.

• Class Polychaetes (Polychaetes). Representatives of the class have connected lateral appendages (parapodia) bearing chitinous setae; The name of the group is determined by the presence of a large number of setae per segment. Head with or without appendages. In most cases - dioecious; gametes are discharged directly into the water, where fertilization and development occur; free floating and are called trochophores. Sometimes they reproduce by budding or fragmentation. The class includes more than 6,000 species, which are divided into free-living and sessile forms.
• Class Girdle (Clitellata). Representatives of the class have an insignificant amount or no bristles on their body. There are no parapodia. They are characterized by the presence of a unique reproductive organ - the girdle, which is formed from the remains of the cocoon and performs protective function for fertilized eggs. The class has about 10,000 representatives.
  • Subclass Oligochaetes (Oligochetes). They live primarily in fresh water. They have setae that arise directly from the walls of the body, due to the small number of which (usually 4 on each segment) the subclass is called oligochaete. As a rule, they do not have appendages on the body. Hermaphrodites. Development is direct, there is no larval stage. There are about 3250 species.
  • Leech subclass. They inhabit mainly freshwater bodies, but there are also terrestrial and marine forms. There is a small sucker at the anterior end of the body and a large sucker at the posterior end. The fixed number of body segments is 33. The body cavity is filled with connective tissue. Hermaphrodites. Fertilized eggs are laid in a cocoon. Development is direct, there is no larval stage. There are about 300 species of representatives.

Class Echiura. This is a small group with only about 170 known species, all of which are exclusively marine inhabitants. Echiurids were recently classified as annelids after DNA examinations, but previously it was a separate type. The reason is that their body is different - it does not have segmentation, like those of ringed animals. In some sources, the Echiurides are considered not as a separate class, but as a subclass of the Polychaetes.

Spreading

Annelids, depending on the species, live on land, in fresh and salt water.

Polychaete worms usually live in sea ​​water(with the exception of some species that may also be found in freshwater bodies). They are food for fish, crayfish, as well as birds and mammals.

Oligochaete worms, to which the earthworm belongs, live in soil fertilized with humus or fresh water bodies.

Echiurids are distributed only in marine waters.

Morphology

The main characteristic of representatives of the Annelida phylum is considered to be the division of the body into a number of cylindrical segments, or metameres, the total number of which varies widely depending on the type of worm. Each metamer consists of a section of the body wall and a compartment of the body cavity with its internal organs. The number of outer rings of worms corresponds to the number of internal segments. The annelid body consists of a head region (prostomium); a body consisting of metameres; and a segmented posterior lobe called the pygidium. In some primitive representatives of this type the metamers are identical, or very similar to each other, each containing the same structures; in more advanced forms there is a tendency to consolidate certain segments and restrict certain organs to certain segments.

The outer shell of the annelid body (muscular sac) includes the epidermis, surrounded by a cuticle, as well as well-developed, segmentally located muscles - circular and longitudinal. Most annelids have short external setae composed of chitin. In addition, on each metamere, some representatives of this type of animal may have primitive limbs called parapodia, on the surface of which bristles and sometimes gills are located. The spatial movement of worms is carried out either through muscle contraction or movements of parapodia.

The body length of annelids varies from 0.2 mm to 5 m.

Basic general anatomical features of annelids in cross section

The digestive system of annelids consists of an unsegmented gut that runs through the middle of the body from oral cavity, located on the underside of the head, to the anus, located on the anal blade. The intestine is separated from the body wall by a cavity called the coelom. The segmented compartments of the coelom are usually separated from each other by thin sheets of tissue called septa, which perforate the intestine and blood vessels. With the exception of leeches, the whole of annelids is filled with fluid and functions as a skeleton, providing muscle movement, as well as transport, sexual, and excretory functions of the body. If the integrity of the worm's body is damaged, it loses the ability to move properly, since the functioning of the body's muscles depends on maintaining the volume of coelomic fluid in the body cavity. In primitive annelids, each compartment of the coelom is connected to the outside via channels for the release of germ cells and paired excretory organs (nephridia). In more complex species, both excretory and reproductive functions are sometimes served by one type of canals (and the canals may be absent in certain segments).

Circulatory system. Annelids developed a circulatory system for the first time in the process of evolution. Blood typically contains hemoglobin, a red respiratory pigment; however, some annelids contain chlorocruorin, a green respiratory pigment that gives the blood its corresponding color.

The circulatory system is usually closed, i.e. enclosed in well-developed blood vessels; in some species of polychaetes and leeches, an open-type circulatory system appears (blood and abdominal fluid mix directly in the sinuses of the body cavity). The main vessels - abdominal and dorsal - are connected to each other by a network of annular vessels. Blood is distributed in each segment of the body along the lateral vessels. Some of them contain contractile elements and serve as a heart, i.e. play the role of pumping organs that move the blood.

Respiratory system. Some aquatic annelids have thin-walled, feathery gills through which gases are exchanged between the blood and the environment. However, most representatives of this type of invertebrates do not have any special organs for gas exchange, and respiration occurs directly through the surface of the body.

Nervous system, as a rule, consists of a primitive brain, or ganglion, located in the head region, connected by a ring of nerves to the ventral nerve cord. In all metameres of the body there is a separate nerve ganglion.

The sense organs of ringed fish usually include eyes, taste buds, tactile tentacles and statocysts - organs responsible for balance.

Annelids reproduce sexually or asexually. Asexual reproduction is possible through fragmentation, budding or fission. Among the worms that reproduce sexually, there are hermaphrodites, but most species are dioecious. Fertilized ringed eggs usually develop into free-swimming larvae. Eggs earthly forms are enclosed in cocoons and larvae, like miniature versions of the adults.

The ability to restore lost body parts is highly developed in many multi- and oligochaete representatives of annelids.

Ecological significance

Earthworm is very important for maintaining soil condition

Charles Darwin, in his book The Formation of Vegetable Mold through the Action of Worms (1881), introduced the first scientific analysis influence of earthworms on soil fertility. Some of the worms dig burrows in the soil, while others live exclusively on the surface, usually in damp leaf litter. In the first case, the animal is able to loosen the soil so that oxygen and water can penetrate into it. Both surface and burrowing worms help improve soil in several ways:

• by mixing organic and mineral substances;
• by accelerating decomposition organic matter, which in turn makes them more accessible to other organisms;
• by concentrating minerals and converting them into forms that are more easily absorbed by plants.

Earthworms are also important prey for birds ranging in size from robins to storks, and for mammals ranging from shrews to badgers in some cases.

Terrestrial annelids in some cases can be invasive (brought into a certain area by people). In glacial areas North America For example, scientists believe that almost all native earthworms were killed by glaciers and the worms that are currently found in these areas (for example, Amynthas agrestis) were introduced from other areas, primarily from Europe, and in Lately, from Asia. Northern deciduous forests have been particularly negatively impacted by invasive worms through loss of leaf litter, decreased soil fertility, and changes in chemical composition soils and loss of ecological diversity.

Marine annelids may account for more than one-third of benthic animal species around coral reefs and in intertidal zones. Burrowing annelid species increase the penetration of water and oxygen into seafloor sediment, which promotes the growth of populations of aerobic bacteria and small animals.

Human interaction

Anglers find that worms are more effective baits for fish than artificial fly baits. In this case, the worms can be stored for several days in a tin can filled with damp moss.

Scientists study aquatic annelids to monitor oxygen levels, salinity and pollution environment in fresh and sea water.

The jaws of polychaetes are very strong. These advantages attracted the attention of engineers. Research has shown that the jaws of this genus of worms are made of unusual proteins that bind strongly to zinc.

On the island of Samoa, catching and eating one of the representatives of annelids - the Palolo worm - is a national holiday, and the worm itself is considered a delicacy by local residents. In Korea and Japan, the worms Urechis unicinctus from the class Echiuridae are eaten.

Representatives of annelids that are eaten

About 17 species of leeches are dangerous to humans.

Medical leeches are used for hirudotherapy, and a valuable remedy, hirudin, is extracted from pharmaceuticals.

Leeches can attach to a person’s skin from the outside, or penetrate internal organs (for example, the respiratory system or gastrointestinal tract). In this regard, two types of this disease are distinguished - internal and external hirudinosis. With external hirudinosis, leeches most often attach to human skin in the armpits, neck, shoulders, and calves.

Misostomidae on sea lily

TYPES FLAT, ROUND AND ANNELED WORMS.

FOR ONE REPRESENTATIVE OF THE TYPES OF FLAT, ROUND AND ANNELED WORMS, SELECT THE APPROPRIATE CHARACTERISTICS:

1. Representatives

1. White planaria. 4. Ascaris.

2. Liver fluke. 5. Earthworm.

3. Bull tapeworm. 6. Nereid.

1. Type flatworms.

2. Type roundworms.

3. Type annelids.

1. Class of flukes.

2. Class tapeworms.

3. Class ciliated worms.

4. Class oligochaete worms.

5. Class polychaete worms.

4. Habitat.

1. They settle in organs rich in blood.

2. Settle in the intestines of humans and animals.

3. Lives in fresh water bodies: ponds, rivers, lakes.

4. Lives in salty bodies of water: seas and oceans.

5. Lives in soil rich in humus.

5. Body shape.

1. The body is elongated, round in cross section.

2. The body is flattened - leaf-shaped.

3. The body is flattened and elongated.

4. Body flattened-ribbon-shaped.

5. The body is elongated, oval in cross section.

6. Dividing the body into segments.

1. The body is divided by constrictions into segments.

2. There are no constrictions. The body is not divided into segments.

7. The presence of a cavity between organs.

1. Internal organs are located in a body cavity filled with

liquid.

2. There is no body cavity. Gaps between organs

filled with cells.

8. Coverings of the body.

1. The skin has numerous eyelashes.

2. The body segments have lobes with long bristles.

3. Short setae are located on the body segments.

4. There are no bristles or cilia on the body. The integument is smooth and

5. There are no bristles or cilia on the body. The integument is smooth and

9. Body musculature.

1. There are longitudinal, annular and dorso-ventral layers

2. There are longitudinal and circular elephant muscles.

3. There is only a longitudinal layer of muscles.

10. Nutrition.

1. They feed on the tissues of human and animal organs.

2. They eat ready-made, digested food.

3. They feed on rotted plant debris.

4. They feed on small invertebrates.

11. Digestive organs.

1. Mouth, pharynx, esophagus, intestines ending in anal

hole.

2. Mouth, pharynx, esophagus with goiter, stomach, intestines

ending in the anus.

3. Mouth, pharynx, esophagus, intestinal branches ending

4. There are no digestive organs. Food is absorbed through

the entire surface of the body.

12. Circulatory organs.

1. The circulatory system is closed. Consists of dorsal and

abdominal vessels with ring jumpers.

2. There are no circulatory organs.

13. Respiratory organs.

1. Breathes oxygen dissolved in water using gills.

2. There are no respiratory organs. Oxygen enters the body

across the entire surface of the body.

14. Nervous system.

1. Consists of the cerebral ganglion and nerves extending from it

trunks with branches.

2. Consists of the peripharyngeal nerve ring and extending from

it has nerve trunks with branches.

3. Consists of the peripharyngeal nerve ring and the abdominal

nerve cord with branches.

15. Sense organs.

1. Sense organs are well developed.

2. Sense organs are poorly developed.

16. Reproduction,

1. They reproduce asexually, falling apart into parts,

regenerating to a whole worm. Sexuality is also known

reproduction by fusion of sperm with eggs.

2. They reproduce only sexually. Animals are bisexual

Hermaphrodites.

3. They reproduce only sexually. Animals

dioecious.

17. Laying eggs.

1. Eggs are laid openly.

2. Eggs are laid in a cocoon.

18. Development.

1. Development is direct, proceeds without transformation.

2. Development is indirect, proceeds with transformation. Eat

larval stages. The final owner is man,

the intermediate host is cattle.

3. Development is indirect, proceeds with transformation. Eat

larval stages. Definitive host - large

cattle, intermediate host - gastropod.

4. Development is indirect, proceeds with transformation. Larva

free-floating in the water column.

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Class-7

Item- biology

The purpose of the lesson: summarize and systematize students’ knowledge on the topic “Flat, Round, Annelid Worms” through game techniques.

Tasks:

• Educational: consolidation and deepening of students’ knowledge about the diversity, features of organization, structure, and vital activity of flat, round, and annelid worms.
• Educational: development of logical thinking techniques, activation of students’ cognitive activity.
• Educational: development of communication skills, a sense of responsibility, formation of a careful attitude towards one’s health.

Lesson type: lesson summary.

Lesson format: a game.

Equipment: PC, multimedia projector, screen, presentation.

During the classes

1. Organizing time(external and internal readiness of students).

2. introduction teachers.

In previous lessons we studied a group of animals called “worms”. What types of worms are included in this group? (Students name the types of flat, round, annelid worms). Today in the lesson we will generalize knowledge about the structure, life processes and significance of worms. We will generalize in the form of an intellectual game “Own Game”.

Rules of the game:

1. The class is divided into 3 teams. Each team chooses a captain who chooses a question from any section and any difficulty.
2. 30 seconds are given to discuss the answer to the question. For an early answer, the team receives 0.5 points.
3. If a team does not answer a question or answers incorrectly, the turn goes to the team that raised its hand first.
4. If a “pig in a poke” appears, the move goes to the next team in order.
5. The team with the most participants answering the questions receives an additional 2 points.
6. The right to start the game is determined by drawing lots.

3. Game.(Appendix. Presentation.).

Questions and assignments.

1). Indicate the name of the representative of the phylum Flatworms.

4). The sensory organs and nervous system of the pork and bovine tapeworm are poorly developed, and the digestive organs are completely absent. What do these signs indicate?

5). In the 19th century, the St. Petersburg doctor Weiss noticed that children who were prescribed to eat raw meat for medicinal purposes were often found to have tapeworms afterwards. Explain why?

6). Why can’t roundworms and soil nematodes stretch and shorten their bodies?

7). Tapeworms and roundworms live in the same environment - in the small intestine of the host, which contains ready-digested food. However, tapeworms do not have digestive organs, while roundworms have a mouth, pharynx, esophagus and intestines. Why?

8). At the end of the last century, one doctor, in an experiment carried out on himself, found out that larvae and subsequently adult worms do not develop from eggs just laid by a female roundworm and swallowed by a person. How can we explain the results obtained in the experiment?

9). It is known that if you try to pull out an earthworm crawling into its hole, you will tear it apart rather than pull it out. Why?

10). What conclusions can be drawn from the following facts:

earthworms avoid dry soil and always stay in moist soil;

Earthworms crawl out of their burrows onto the soil surface at night or during the day after rain.

eleven). Much is known about the activities of earthworms. For example, scientists believe that some remains of structures Ancient Rome ended up underground thanks to the work of earthworms. Explain how this happens?

12). Name the stages of development of the liver fluke.

13). List the organ systems of the milky white planaria.

14). Name the organ system shown. What is its function?

15). What is sexual dimorphism? How does a female roundworm differ from a male?

16). What organ system first appeared in the earthworm?

17). What is regeneration? Can it be attributed to the methods of earthworm reproduction? Explain your answer.

20). Indicate a representative of the type Roundworms (see task 1).

21). Name the representatives of the phylum Annelids. Indicate which class they belong to.

There lived a little worm in the world,
He was terribly lonely
I wandered alone all year round,
I only ate once a year...
The worm is a daring swimmer,
Despite being short in stature.
He was able to change color more than once -
For protection, without embellishment.
No bristles for movement
Only victims have no salvation -
There are suckers, hirudin.
Who is this gentleman?

Answers.

2). The presence of suckers, hooks, enormous fertility, a development cycle with a change of hosts, dense body coverings that are not digested in the host’s body.

3) Enormous fertility is associated with a low probability of eggs entering the body of a new host, and is an adaptation to the preservation of the species.

4) These organisms live in the host’s body, where they are protected from unfavorable conditions and provided with food. Living conditions are constant.

5) Raw meat may contain finns (larvae), the activation of which in the human intestine marks the beginning of the development of an adult worm.

6) The roundworm has only longitudinal muscles, so it can only twist its body. The shortening and elongation of the body is due to the presence of circular muscles.

7) The bovine tapeworm attaches to the intestines and absorbs food over the entire surface of the body. The roundworm has no organs of attachment; it is retained in the intestines, constantly moving towards the incoming food masses.

8) For normal development of larvae from eggs, certain conditions are necessary, including the presence of oxygen.

9) There are bristles on the body of an earthworm.

10) Worms do not have special respiratory organs; oxygen enters through moist skin.

11) Worms loosen the soil (make passages, burrows, pass it through themselves), so many structures settle.

12) 1 – adult worm, 2 – eggs, 3 – larva with cilia, 4 – larva in the intermediate host (snail), 5 – tailed larva, 6 – cyst.

13) Digestive, excretory, nervous, reproductive systems.

14) The nervous system, which provides communication with the external environment, irritability.

15) Sexual dimorphism is the external difference between a female and a male. The female roundworm is larger than the male.

16) Circulatory system.

17) Regeneration - restoration of lost parts of the body. Regeneration can be classified as a method of earthworm reproduction, as the number of individuals increases.

Through things and products contaminated with soil containing roundworm eggs;

• Into the intestines;
• Larva;
• To the lungs;
• In the digestive tract;
• In the intestines;
• In the intestines

19) Pinworm.

21) 1 - medical leech (Leeches), 2 - sandworm (Polychaetes), 3 - earthworm (Polichaetes).

22) Leech.

4. Reflection. Final words from the teacher.

Did you like this form of lesson organization?

Which questions did you find most interesting and informative?

Your wishes and suggestions.

5. Summing up. Jury speech.

There are three main types of worms: Flatworms, Roundworms and Annelids. Each of them is divided into classes into which types of worms are grouped based on the similarity of certain characteristics. In this article we will describe types and classes. We will also touch on their individual types. You will learn basic information about worms: their structure, characteristic features, role in nature.

Type Flatworms

Black, brown and live in silty areas of ponds, lakes and streams. At the front end of the body they have 2 ocelli, with the help of which they distinguish darkness from light. The pharynx is located on the ventral side. Planarians are predators. They hunt small aquatic animals, which they tear into pieces or swallow whole. They move thanks to the work of cilia. The body length of freshwater planarians ranges from 1 to 3 cm.

Their body is covered with elongated cells with special cilia (therefore they are also called ciliated worms). Deeper are 3 layers of muscle fibers - diagonal, circular and longitudinal. The worm (species related to planarians), due to their relaxation and contraction, shortens or lengthens, and can lift parts of the body. A mass of small cells is located under the muscles. This is the main tissue in which the internal organs are located. The mouth with a muscular pharynx, as well as the three-branched intestine, make up the digestive system. The intestinal walls are formed by a layer of flask-shaped cells. They capture food particles and then digest them. Digestive enzymes release glandular cells of the intestinal wall into the intestinal cavity. Nutrients resulting from the breakdown of food penetrate directly into the body tissues. Undigested residues are removed through the mouth.

Ciliated worms breathe oxygen dissolved in water. This process is carried out over the entire surface of the body. they consist of clusters of cells - paired head nodes, nerve trunks extending from them, as well as nerve branches. Planarians mostly have eyes (from 1 to several dozen pairs). They have tactile cells in their skin, and some representatives of this class have small paired tentacles at the anterior end of the body.

Class Flukes

Class Tapeworms

The nervous and muscular systems of this class are poorly developed. Skin cells represent their sensory organs. Their digestive system has disappeared: tapeworms absorb nutrients from the host’s intestines with the entire surface of their body.

Echinococcus

Class Nematodes

Nematodes are herbivorous worms that live on the roots of beans, garlic, onions and other garden plants, in underground shoots of potatoes (species Stem potato nematode), in the organs of strawberries (Strawberry nematode). The length of their almost transparent body is about 1.5 mm. With their piercing-type mouthparts, nematodes pierce plant tissue, after which they inject substances that dissolve the contents and walls of the cells. They then absorb the resulting substances using the expanded part of the esophagus. Its muscular walls act like a pump. Food is digested in the intestines. Many nematodes live in the ground and use plant debris as food. They play an important role in soil formation.

Roundworms

Its representatives live in fresh water bodies, seas, and soil. Their body is long, divided into ring-shaped segments (segments) by transverse constrictions. We are all familiar with the appearance of earthworms. Their length ranges from 2 to 30 cm. The body is divided into segments, which can be from 80 to 300.

Internal segmentation corresponds to external dissection. The body cavity of representatives of this type is lined with a layer of integumentary cells. A delimited portion of this cavity is located in each segment. Annelids have a circulatory system, and many of them also have a respiratory system. Their digestive, muscular, nervous, excretory systems, as well as sensory organs, are more advanced than those of round and flatworms. Their “skin” consists of a layer of integumentary cells. Beneath it are the longitudinal and circular muscles. In annelids, the digestive system is divided into the pharynx, oral cavity, esophagus, stomach (in certain groups), and intestines. Undigested food remains are removed through the anus.

Circulatory system of annelids

All types of annelids have a circulatory system formed by abdominal and dorsal blood vessels, which are connected to each other by ring vessels. Small vessels depart from the latter, which branch and form a network of capillaries in the internal organs and skin. Blood moves mainly due to the relaxation and contraction of the walls of the annular vessels covering the esophagus. It carries oxygen and nutrients supplied to it to all organs, and also relieves the body of metabolic products. Species of annelids are characterized by a closed circulatory system (this biological fluid is located within the vessels and does not flow into the body cavity). Breathing occurs through the skin. Some species have gills.

annelids

The nervous system of representatives of this type consists of paired subpharyngeal and suprapharyngeal nerve nodes, which are connected in a ring by nerve cords, as well as nodes of the chain (abdominal). A paired node is found in each segment of annelids. Nerves extend to all organs. Various stimuli (for example, light) affect sensitive cells. The excitation that arises in them is transmitted to the nearest nerve node along the nerve fibers, and then to the muscles (via other fibers) and causes their contraction. This is how reflexes are carried out. Most representatives of this type do not have sense organs.

Main classes of annelids

Ringed fish can be either hermaphrodite or dioecious. How many worms (species) does this type include? Today there are about 9 thousand of them, among which the main classes stand out: Polychaetes and Oligochaetes. The former live mainly in the soil (for example, such a type of earthworms as burrows), as well as in fresh water bodies (in particular, tubifex worms). Polychaete worms are a class that includes sandworms, nereids and serpules. Sandworms live in burrows they dig, Nereids live mainly in muddy soil, in coastal parts of the seas, Serpuls live in “houses” that they build from various materials.

Nereids

Nereids are the species of worms that are most diverse in the seas. Their color is green or reddish. The head is formed by the anterior segments of the body. She has palps, a mouth, tentacles (tactile organs), as well as 2 pairs of eyes and 2 pits located behind them (these are olfactory organs). On the segments on the sides of the body there are paired muscular short lobe-shaped projections with tufts of bristles. These are limbs. In addition, Nereids develop gills - special skin outgrowths. Often these are dioecious animals. Fertilization of eggs occurs in water, from which free-swimming larvae with a belt of cilia emerge. They eventually develop into adult worms.

The meaning of annelids

They are food for many types of crabs and fish (nereids and other sea worms). Earthworms are the main food of hedgehogs, moles, starlings, toads and other animals. Ringed fish, feeding on silt and various suspensions, rid the water of excess organic matter. In addition, earthworms and some other soil worms eat plant debris and also pass soil through their intestines. By doing this they contribute to the formation of humus.

ZOOLOGY

FLAT, ROUND AND RINGED WORMS

METHODOLOGICAL INSTRUCTIONS FOR LABORATORY EXERCISES

INTRODUCTION

Worms (Vermes) are a vast and diverse phylum of invertebrate animals, with elongated tubular, round or flat soft-skinned bodies. Worms are one of the oldest and most widespread animals. The term "worms" occupied a prominent place in the invertebrate system until recently. Under this term, not only flat, round and annelid worms, but also a number of adjacent groups were combined into one general type of worms (Vermes). Currently, worms have lost their classification significance. However, the concept itself has not lost its everyday zoological meaning.

By “worms” we mean organisms that have an elongated body shape, devoid of limbs and a clearly formed head, equipped with strong muscles in the form of a skin-muscular sac, which provides the body bending movement typical of worms. The locomotor organs of worms are not articulated or absent at all; the body is naked or covered with needles, bristles, and eyelashes. The skin of some worm species secretes mucus or tube lime. Many worms have simple eyes, soft filaments on the head, or segmented filaments and ties. Some worms have respiratory organs and a vascular system. Many worms are dioecious, others are hermaphrodites.

The most poorly organized worms are the lowest turbellaria- in many structural or physiological features they are close to the coelenterates, and the higher ones - annelids- are just as close to arthropods.

Worms are divided into 7 classes:
1) flatworms (orders: ciliated worms, flukes and tapeworms), 2) nemerteans, 3) roundworms, 4) spinyworms, 5) bristlejaws, 6) annelids and 7) rotifers

1. Flatworms.

1.1. Generalcharacteristic

Taxonomy

Animal Kingdom (Animalia)

Subkingdom Multicellular (Metаzoa)

Type Flatworms (Plathelminthes)

Class Ciliated worms (Turbellaria)

Order Triramoidae (Tricladida)

Species: milky pshnaria (Dendrocoeliumlacteum)

Class Digenetic flukes (Trematoda)

Order Fasciolidae (Fasciolida)

Species: liver fluke (Fasciolahepatica)

lanceolate fluke (Dicrocoeliumlanceatwn)

cat fluke (Opistorchisfelineus)

Class Monogenetic flukes (Monogenea)

Order Gyrodactylidae (Gyrodactylidea)

Species: frog fluke (Polystomaintegerrimum)

1.2. Morphological overview

Class Ciliated or Turbellaria

More than 3,000 species of turbellaria are known, living in seas, fresh waters and moist soil.

Let's consider the morphology of ciliated worms using the example of a typical representative - milk planaria (Dendrocoelium lacteum) (Fig. 1).

Rice. 1. Milky white planaria

1 – eyes; 2 – mouth; 3 – pharynx; 4 – intestinal branches

It got its name from the color of the body, reaching a length of up to 3 cm. The head part of the body is as if cut off, the back part is pointed. There is a pair at the front eye in the form of black dots, and on the sides there are outgrowths in the form of blades, under which on the ventral side there is suction pit, acting as a fixation organ for the worm. There are two openings in the middle of the ventral side of the body: oral And sexual. The latter is somewhat shifted posteriorly. 8 pairs open on the back excretory openings.

During the day, planarians sit under various underwater objects: stones, rotting plant leaves, driftwood. As night falls, planarians scatter in search of prey. When moving, these animals can lengthen and shorten their bodies, and some can swim. The typical method of movement of planaria is gliding along the substrate, reminiscent of crawling. snails, but faster. All planarians are predators and the main components of their diet are small crustaceans, worms, and insect larvae.

The body integument of the milk planaria is presented skin-muscle bag. The role of the skin plays here single-layer ciliated epithelium. Its cells are cylindrical in shape and bear on their surface cilia, representing outgrowths of cell protoplasm. Synchronized vibrations of the cilia facilitate the movement of turbellaria. Among the epithelial cells there are special rod-shaped formations - Rhabdites. The functions of rhabditis are not fully understood. It is known that they can be thrown out out, and swelling in water, they cover the body of the worm with mucus. Elitelial cells are located on basement membrane, separating it from the muscle layer. Below the basement membrane is a layer transverse muscle fibers. Below it is a layer oblique (diagonal) muscle fibers And longitudinal muscles, well developed. In addition, the entire thickness of the body is penetrated dorsoventral (dorsoventral) muscle bundles. All muscles are represented by smooth muscle tissue.

Thus, the ciliated epithelium, basement membrane and muscle layers form skin-muscle bag, in which all the internal organs of the animal are placed (Fig. 27).

The internal space between the walls of the bag is filled pyrenchyma, consisting of connective tissue cells. On the ventral side of the body, closer to the back of it, is located mouth opening, supplied with obturator muscles. The mouth leads into an enlarged cavity where the pharynx, capable of extending like a proboscis from its mouth and capturing prey. The pharynx continues in intestines, having a branched structure (hence the name of the order). One of the branches of the intestine is directed to the head of the body, and the other two are directed to the back. Each branch is divided into secondary, tertiary, quaternary, etc. branching, which greatly increases the absorption surface of the intestine. Intestinal epithelial cells are flask-shaped and have the ability to capture food particles and digest them (so-called digestive phagocytosis). Undigested foods are released into the intestinal cavity, from where strong contractile muscle movements are removed out through the mouth. The dairy planaria does not have a respiratory system. Breathing occurs diffusely through the body.

The nervous system consists of paired cephalic ganglia and those departing from them nerve trunks. The cephalic ganglia, connecting with each other, form the so-called. "brain". Short branched branches extend forward from it head nerves. Stretching back from the cephalic ganglia are the two most developed ventral nerve trunk and less developed dorsal The abdominal trunks are connected to each other by means of transverse ring-shaped constrictions (commissur), also covering the spinal nerve trunks. This type of nervous system is called staircase, or orthogonal In addition, numerous lateral nerve cords.

Sense organs are represented in pairs eye And head blades. The entire skin, as well as the head lobes, has a sense of tactility. Chemical irritations are perceived by long, motionless cilia scattered throughout the planarian's body. Suitable for eyelashes sensory processes nerve cells. The organs of vision are eyes, consisting of pigment glass, into the cavity of which the light-sensitive part of the receptors protrudes. Nerve fibers depart from them and go to the “brain”. The pigment glass faces its concave side towards the surface of the body, so light first passes through the receptors, and then through their photosensitive parts. These eyes are called converted or inverted.

The excretory system is presented protonephridia(from the Greek “protos” - simple, primary and “nephros” - kidney). They start out special (fiery) cells from which they come excretory tubules(one from each cell). Inside the cell, a bundle protrudes into the initial part of the tubule eyelashes, when moving, it resembles the play of flame. Through the thinned cell wall, dissimilation products enter the tubule with a fluid current excited by the movements of the cilia bundle. The excretory products then enter main excretory channels, formed by the fusion of tubules, opening outwards with excretory openings. Protonephridia are of ectodermal origin, and their function is more to regulate osmotic pressure than to release metabolic products. This explains the absence of protonephridia in marine turbellarians, the secretion products of which are removed by special cells - amebocytes, which come out through the integument of the body.

Sexually, the milk planaria is hermaphrodite. The male reproductive system consists of 200–300 vesicle-shaped testes, located closer to the sides of the body. Efferent tubules testes flow into vas deferens, merging into seminal vesicle. It starts at the bottom ejaculatory duct, passing through the copulatory organ - cirrus and opening at its end. Cirrus is placed in a special container - cirrus bursa, or cirrus pocket. The female reproductive system consists of two ovaries, their excretory ducts And accessory glands. From ovaries, located near the head of the body, extend long oviducts, connecting in an unpaired vagina. The latter opens outward at the cirrus bursa genital cloaca. In addition, there is copulatory bursa, serving to fill the partner’s sperm during cross-fertilization. Some turbellaria, including the milk planaria, are capable of asexual reproduction by dividing the body into metameric parts.

Fertilization in planaria is internal. In cross-fertilization, each partner inserts its cirrus into the copulatory bursa of the other, from which the sperm enters the genital cloaca, where fertilization of the eggs occurs. A set of such eggs is covered in secretions yolk cells, which hardens and forms cocoon, attached by a worm to underwater objects. The cocoon has a round shape and contains from 5 to 42 eggs.

Development in freshwater and terrestrial forms is direct, without metamorphosis. Marine turbellaria hatch from eggs müllerian larva, possessing radial symmetry in the early stages of development. Then the larva settles to the bottom and turns into a typical worm.

Class Digenetic flukes, or Trematodes

Flukes range in length from a few millimeters to 1.5 meters (these latter are found in sharks). The body shape is often leaf-shaped or ribbon-shaped. At the anterior end of the body on the ventral side there is oral sucker in the form of a muscular rounded roller. Second sucker - abdominal– found in most flukes and located closer to the middle part of the worm’s body. Suckers are fixation organs trematodes in the host's body. At the bottom of the oral sucker opens mouth, but initially it was believed that both suckers lead into the mouth, which is why the incorrect name for these animals arose - flukes (Distoma).

The covers of trematodes are called tegument. Upper layer epithelium does not have cilia, cell membranes and nuclei, but contains a large number of mitochondria and dense formations - cuticular spines, being additional organs of fixation. The epithelium is located on basement membrane, permeated with cytoplasmic strands connecting it to the layer submerged epithelium. The cells of the latter have clear boundaries and contain nuclei. Below the basement membrane is a layer ring And longitudinal muscles. Parenchyma, filling the space between the internal organs in the skin-muscle sac, it is structured similarly to that of ciliated worms.

The digestive system of flukes is presented mouth opening, which is located at the bottom of the oral sucker. Next comes the muscular pharynx, continuing in a narrow esophagus. It turns into a bibranched blind-ending midgut, stretching along the sides of the body. In some trematodes, the midgut has lateral protrusions, which increases its absorption surface.

The nervous system of digenetic flukes consists of a paired cerebral ganglion, from which nerve cords arise. Three pairs of nerve trunks extend to the back of the body: abdominal, dorsal And lateral, interconnected by transverse Commissurimi. Therefore, the nervous system of trematodes, as well as turbellarians, staircase type. Of all the nerve cords, the abdominal ones are the best developed. Sense organs represented skin receptors and small eyes. The latter function only in trematode larvae.

Excretory system protonephridyl type and consists of a pair of main excretory channels, branching on lateral tubules, which end stellate cells (arthrocytes) with bunches flickering eyelashes. The main channels in the back of the body connect to form bladder(not in all trematodes), which opens outwards through the opening of the excretory system.

The reproductive system of trematodes has a complex structure. The vast majority of flukes are hermaphrodites; only a few species are dioecious. The male reproductive system is represented by two round, lobed or tree-like branches testes with those departing from them vas deferens. The latter merge and form ejaculatory duct. It passes through the copulatory organ (cirrus) and opens at its end. Like turbellarians, trematode cirrus is located in copulatory bursa capable of protruding outward from male genital opening. The female reproductive system consists of an unpaired ovary, in which eggs are formed, and from zheltochnikov, where nutrient-rich yolk cells. Ovarian duct - oviduct and the ducts of the zheltochniks flow into a small reservoir - ootype Fertilization of eggs occurs in it, which are then surrounded by yolk cells that flow through the vitelline ducts. Opens in ootype seminal receptacle, where sperm obtained from other individuals through cross-fertilization is stored. There are clusters in the wall of the ootype putamen glands– Melisa Taurus, which secrete substances for fertilized eggs that form dense shells around them. In this form, eggs from the ootype enter a long duct - uterus It opens outwards female genital opening next to that of the copulatory organ. Excess sperm and yolk cells that accumulate in the trematode ootype are released into external environment through a short duct - Laurerov channel, opening on the dorsal side of the worm's body.

In many species, in eggs located in the uterus, it begins embryonic development larvae, so an egg with an already formed larva enters the external environment. This is advantageous in the sense that the developing larvae emerge completely ready for independent life.

Trematodes obtain the energy they need for life as a result of the breakdown of glycogen deposited in their tissues, which sometimes accounts for up to 65% of body weight.

Marita – sexually mature helminth .

Miracidium– the first larval stage of most trematodes.

Sporocyst– the second larval stage of trematodes, capable of parthenogenetic reproduction.

Redium– the third larval stage of trematodes, capable of parthenogenetic reproduction.

Cercaria– fourth larval stage of trematodes.

Adolescaria (metacercaria)– the fifth larval stage of trematodes, capable of causing disease when it enters the body of the final host (the so-called invasive larva). Adolescary turns into marita.

Additional host– second intermediate host.

Let us consider the development cycles of two trematodes: the liver and lanceolate flukes.

Rice. 2. Liver fluke

1 – ovary; 2 – 3 – testes; 4-5 – zheltochnik; 6 -7 – seminal ducts; 8 - seed pipe; 9 – seminal duct in the cirrus; 10 – cirrus; 11 – bursa; 12 – oviduct; 13 – 14 – vitelline ducts; 15 – uterus; 16 – Melissa body

It has a sac-like shape and contains germ cells inside, from which the next generation of larvae then develops, parthenogenetically. redia. They have an elongated body shape and one oral sucker. Inside the redia, by parthenogenesis, they are formed church car They have oral and ventral suckers, an esophagus and intestines. Cystogenic (cyst-producing) glands are located on the sides of the body. Cercariae are equipped with a tail appendage, often twice the length of the larva itself. Cercariae emerge from the mollusk into the water, swim freely, then attach to a suitable substrate (coastal plants, surface water film) and encyst. In this case, the body of the cercarium becomes rounded, and the caudal process disappears. This stage is called adolescary and is invasive. Definitive hosts become infected when drinking water, eating coastal vegetation, or fresh hay, where adolescaria are present. In the intestine of the final host, the shells of the Adolescaria cysts dissolve and the latter penetrate the intestinal wall, enter the blood vessels and are carried into the liver, where they penetrate into its parenchyma and turn into young fascioli. After 35–40 days, they penetrate from the liver parenchyma into the bile ducts and become sexually mature. The disease caused by fascioli is called fascioliasis.

Lanceolate fluke (Dicrocoelium lanceatum) (Fig. 3).

Rice. 3. Lanceolate fluke

1 – oral sucker; 2 – abdominal sucker; 3 – intestines; 4 – copulatory organ (cirrus) in the bag; 5 - ovary; 6 – zheltochnik; 7 – vitelline ducts; 8 – testes; 9 – vas deferens; 10 – uterus; 11 – ootype; 12 – pharynx; 13 – semen receptacle

Class Monogenetic flukes

Monogenetic flukes (Monogenea) are ecto- and endopasites of fish, amphibians and reptiles.

Most of them have an elongated and flattened body, at the rear end of which there is a special attachment apparatus in the form of a disk with suction cups, hooks and valves. At the front end of the body there are also fixation organs - small suckers and blades.

The body covers of monogenetic flukes are not fundamentally different from those of trematodes.

mouth, muscular short throat esophagus and branched or unbranched intestines.

The nervous system is organized according to the orthogonal type, the sensory organs are poorly developed.

protonephridia and excretory canals ending in two excretory pores in the front of the body.

Sexually, monogenea are hermaphrodites. There is one several testes, from which they depart vas deferens. By merging with each other they form seminal vesicle. The female reproductive system consists of one ovary, well developed zheltochnikov, short uterus And ootype. In the front part of the worm's body is located genital opening, into which the uterus and male copulatory organ, armed with chitinoid needles and hooks.

Let's consider life cycles monogeneas using the example of the frog's salivator, Dactylogyrus and Gyrodactylus.

Rice. 4. Frog fluke

1 – mouth; 2 - pharynx; 3 – ovary; 4 – intestines; 5 - attachment disk; 6 – hooks; 7 – suction cups

2. Tapeworms

2.1. general characteristics

Taxonomy

Animal Kingdom (Animalia)

Subkingdom Multicellular (Metazoa)

Type Flatworms (Plathelminthes)

Class Tapeworms (Cestoda)

Chain Squad (Cyclophyllidea)

Species: pork tapeworm (Taeniasolium)

bovine tapeworm (Taeniarhynchussaginatus)

cucumber tapeworm (Dipylidiumcaninum)

dwarf tapeworm (Hymenolepisnana)

Echinococcus (Echinococcusgranulosus)

alveococcus (Alveococcusmultilocularis)

sheep brain (Multicepsmulticeps)

moniesia (Monieziaexpansa)

Lentets squad (Pseudophyllidea)

Types: wide tapeworm (Diphyllobothriumlatum)

Ligulp (Ligulaintestinalis)

2.2. Morphological overview

The body of tapeworms consists of heads (scolex), necks and the body itself, or strobila The organs of attachment are located on the scolex - suckers, whisk chitinized hooks, proboscis, bothria (suctioncracks) And botridia (clefts with septa).

Each type of cestode is characterized by its own attachment apparatus, which is the most important feature for systematic identification. With the help of fixation organs, tapeworms are held on the inner wall of the intestine of the final host. The neck, an unsegmented area of ​​the body behind the scolex, is a growth zone, forming a strobile. The latter consists of separate fragments - members, or proglottid. The body length of tapeworms ranges from several mm to tens of meters, and the number of strobile segments ranges from 2–5 to several hundreds and thousands.

The body of cestodes is covered with a typical skin-muscular sac, similar in structure to that of trematodes. On the surface of the outer cytoplasmic layer there are countless hair-like projections (microtrichium). They perform the function of fixation and serve to absorb digestive enzymes from the host. Located under the basement membrane annular And longitudinal layers smooth muscle fibers. Many cestodes also have dorsal-abdominal muscle bundles. The space between the internal organs is filled parenchyma, consisting of connective tissue cells.

The nervous system of tapeworms is represented by paired cephalic ganglion with longitudinal longitudinal ones extending from it forward and backward nerve trunks (5 steam). The most developed pair abdominal trunks, passing near the canals of the excretory system. Longitudinal trunks are connected to each other transverse commissures(typical orthogonal system).

Excretory system protonephridial type. It consists of many scattered in the parenchyma ciliated cells, with protrusions extending from them literal tubules. They fall at four main longitudinal canals, interconnected by jumpers in each segment of the strobilus. Longitudinal canals open at the end of the last segment.

The reproductive system of cestodes is hermaphrodite and resembles flukes as such. In the segments of the upper part of the strobilus, the genitals are not developed (immaturesegments). The male and female reproductive systems are formed in the segments of the middle part, which is why these segments are called hermaphroditic. In the back. parts of the strobile are located mature cocks with a greatly expanded uterus, filled with eggs, and atrophied other organs of the reproductive system.

The largest of the cestodes produce a colossal number of eggs during their life. Thus, over the course of 20 years of life, a bull tapeworm produces about billion eggs.

Fertilization in tapeworms occurs both crosswise and by self-fertilization, with the copulatory organ of one segment being inserted into the vagina of another, or, bending, into the vagina of the same segment.

Most cestodes develop with a change of hosts, and in some groups in the development cycle there is a change of two hosts (intermediate and final), in others - three (intermediate, additional and final).

Most tapeworms have clearly defined body segmentation, however, there are also those in which the segmentation is not pronounced. These are representatives of the families Ligulidae, Triaenophoridae, Cyathocephalidae. The tapeworm's scolex has suction slits (batria), sometimes armed with chitinized hooks. The strobile may consist of 3–4 thousand segments. The uterus of tapeworms open type, located in the middle part of the progloggida. Testes and gall bladders are numerous.

All cestodes are biohelminths, i.e. their development occurs with the participation of one (chain tapeworm) or two (tape tapeworm) intermediate hosts. In the body of the latter, cestodes are in the form of larvae with different structure. The main types of tapeworm larvae (Finn) are: cysticercus, acenurus, echinococcus, alveococcus, cysticercoid and plerocercoid.

A cysticercus is a vesicular formation filled with clear liquid and surrounded by a connective tissue capsule. Inside the bladder, one embryonic scolex with or without suckers and hooks is attached to its wall.

The cenurus is a bubble of a similar structure with the difference that on its inner membrane there is not one, but many scolex.

Echinococcus is a single-chamber bladder with dense walls consisting of several membranes. The inner shell produces daughter bubbles with grandchildren formed in them, etc. Scolexes are located both on the inner walls of the bladders and in the fluid filling the fin.

Cysticercoid is a microscopic larva that has an expanded anterior part with a folded inward (invaginated) scolex. The rear part - the cercomere - in the form of a caudal appendage bears embryonic hooks.

A procercoid is a tapeworm larva with an elongated body, having embryonic bothria at the anterior end and a cercomere with hooks at the posterior end.

Plerocercoid is a tapeworm larva sometimes up to 1 m long with bothria at the anterior end of the body.

3. Primary cavity. Roundworms

3.1 General characteristics

Taxonomy

Animal Kingdom (Animalia)

Subkingdom Multicellular (Metazoa)

Type Primary cavity (Nemathelminthes)

Class Roundworms, or nematodes (Nematoda)

Species: human roundworm (Ascarislumbricoides)

pork roundworm (Ascarissuisj

roundworm (Parascaris equorum)

neoascarids (Neoascarisvitulbfum)

toxocara (Toxocaracanis)

toxascarida (Toxascarisleonina)

chicken roundworm (Ascaridiagalli)

pork whipworm (Trichocephalussuis)

trichinella (Trichinellaspiralis)

Rishta Medina (Dracunculusmedinensis)

pinworm baby (Enterobiusvermicularis)

horse pinworm (Oxyurisequi)

3.2. Morphological overview

More than 12,000 species of nematodes are known, living in seas, fresh waters, soil and living organisms. The body length of roundworms varies from up to 8 meters.

Let's consider the external and internal structure nematode bodies using the example of the horse roundworm.

The body of the roundworm is fusiform, round in cross section (Fig. 5). The anterior and posterior parts of the body are narrowed. The outside of the body is covered cuticle, resembling collagen in composition and, therefore, very elastic. Cuticle formation occurs as a result of cell activity hypodermis(modified single-layer epithelium). The cuticle consists of several layers of cells, and bottom layer has a fibrous syncytial structure, lies under the hypodermis basement membrane – a noncellular structure that separates the epithelial layer from the muscular layer. Most nematodes have 4 longitudinal lines along their body: two on the sides and one on the dorsal and ventral sides. On the inner surface, the hypodermis forms thickenings in the form of 4 rollers, corresponding to longitudinal lines. IN side bolsters gi subdermis the channels of the excretory system pass through, and in dorsal And abdominal – main nerve trunks. Under the basement membrane lies a layer longitudinal muscles. Each muscle cell is made up of plasmatic process, sarcoplasmic sac(the cell body itself) and contractible part. The hypodermal rollers divide the muscle layer into 4 longitudinal strips. The plasmatic processes of muscle cells are directed either towards the dorsal or ventral ridge of the hypodermis .

Rice. 5. Cross section of the body of a female roundworm

1- cuticle, 2- hypodermis, 3- longitudinal muscles, 4- plasmatic processes of muscle cells, 5- dorsal ridge of the hypodermis, 6- dorsal nerve trunk, 7- lateral ridge of the hypodermis, 8- excretory canal, 9- uterus, 10- ovary , 11-abdominal ridge of the hypodermis, 12-abdominal nerve trunk, 13-oviduct, 14-intestine, 15-primary body cavity.

Therefore, it is generally accepted that the muscle layer is divided into dorsal and abdominal antagonist muscles. The cuticle, hypodermis and layer of longitudinal muscles make up the skin-muscle bag is not matod. It forms inside primary body cavity where the organs of the digestive and reproductive systems are located. The body cavity of roundworms is called primary, because. formed by reduction of parenchyma. Inside, the primary cavity is filled with liquid contents. Cavity fluid contains organic acids (butyric, valeric, caproic, etc.) formed as a result of anaerobic breakdown of glycogen. The primary cavity fluid creates excess pressure in the roundworm’s body, and if for some reason a rupture of the roundworm’s body wall occurs inside the host’s body, then the cavitary fluid of the helminth that spills out causes excruciating pain.

The digestive system of roundworm consists of front, middle And hindgut. The foregut begins mouth, located at the anterior end of the body and surrounded by three lips. Mouth leads to throat. The pharynx passes into the anterior part of the midgut, often called esophagus, within the walls of which lie esophageal glands. In some nematodes, such as pinworms, the posterior part of the esophagus forms a flask-shaped expansion - bulbus, which is a systematic feature of the suborder oxyurat (pinworms). The midgut is lined with columnar epithelium with villi on the inner surface. In the protoplasm of intestinal epithelial cells, reserve nutrients are deposited in the form of glycogen grains. The content of the latter in the dried state reaches 32%. The hindgut, like the foregut, is lined from the inside with a cuticle and ends anus, where in males the opening of the reproductive system opens. There is no respiratory system. Respiration occurs anaerobically due to the breakdown of nutrients. Some authors provide data on the presence of a respiratory pigment in roundworms, similar to mammalian hemoglobin.

The nervous system consists of peripharyngeal nerve ring and those departing from him nerve trunks. The nerve ring surrounds the anterior part of the esophagus and gives off 6 short nerve trunks to the front and 6 long nerve trunks to the back, of which dorsal And abdominal most developed and occur in the hypodermal ridges. Both trunks are connected to each other in the form of half rings by numerous jumpers - commissures.

The sensory organs of nematodes are poorly developed. Around the mouth, and in males at the rear end of the body are located tactile tubercles And bristles. On the sides of the head end of the body lie amphids- chemical sense organs.

The excretory system has a very unique structure. In the lateral ridges the hypodermis passes excretory channels, starting blindly at the back of the body and merging into median unpaired canal, which opens as an excretory duct behind the lips. According to histological data, these canals represent one giant cell (the so-called cervical gland) with the nucleus lying at the level of the anterior part of the esophagus. The nucleus of this cell is called syncarion. Two pairs lie on the lateral ridges of the hypodermis phagocytic cells. From the cavity fluid, these cells absorb decay products and foreign bodies. Insoluble particles accumulate in phagocytic cells and are not removed from them anywhere throughout the life of the roundworm.

Sexually, most nematodes are dioecious. The reproductive system of the female horse roundworm consists of thin, thread-like pairs ovaries, which, expanding, turn into oviducts, where egg formation occurs. Oviducts without visible boundaries go to the steam room uterus, the trunks of which, merging, form an unpaired vagina, opening genital opening on the ventral side of the body. The male has a single filamentous testis, passing without sharp boundaries into a channel of larger diameter – vas deferens. Under the intestine, it goes posteriorly and forms seminal vesicle, where sperm accumulates. The bladder narrows into a thin muscular tube – seventh channel, draining into the hindgut. The steam room opens there too copulatory bursa (genital bursa), which holds two cutlery needles, or spicules. They protrude out through the anus and serve as auxiliary organs during copulation.

Parascarid eggs released into the external environment under favorable conditions (temperature 18–20 °C and humidity of at least 60%) become invasive within 7–14 days. Larvae emerge from the eggs in the horse's intestines, where the eggs end up with food or water. Through the intestinal mucosa, the larvae penetrate the blood vessels and are carried by the bloodstream into the lungs. In the pulmonary alveoli, the larvae grow, molt and migrate to the bronchi. It's annoying respiratory tract and reflex cough. Together with sputum, parascarid larvae enter the oral cavity and are swallowed. In the intestine they develop to the sexually mature stage and begin to reproduce. The period of development of parascarids to sexual maturity is about 2 – 2.5 months. In the development cycle of the horse roundworm there is no intermediate host, so it is classified as a group geohelminths. The development of human and pork roundworms occurs in a similar way.

The baby pinworm (Enterobius vermicularis) (Fig. 6) reaches a length of up to 1 cm.

Rice. 6. Female baby pinworm

1 – mouth; 2 – cuticular thickenings; 3 – esophagus; 4 – bulb; 5 – genital opening; 6 – uterus filled with eggs; 7 – midgut; 8 – ovary; 9 – anus; 10 – tail

4.Annelids

4.1. general characteristics

The body of annelids is elongated and consists of segments shaped like rings. Most annelids are characterized by coincidence of the boundaries of external and internal segmentation. The skin-muscular sac consists of the cuticle, hypodermal epithelium, circular and longitudinal muscles of the internal lining of the body cavity (coelothelium). A characteristic feature of the morphology of annelids is the presence of a secondary body cavity (coelom). The nervous system is represented by the suprapharyngeal ganglion, the peripharyngeal ring and the ventral nerve cord. The digestive system consists of the foregut, midgut and hindgut ending in the anus. The circulatory system is closed; the role of the heart is played by one or more blood vessels. Breathing is carried out over the entire surface of the body or gills. The excretory system is of the protonephridial type. Among the ringed worms There are dioecious animals and hermaphrodites. In sea ringlets, development occurs with metamorphosis according to the following scheme: egg – trochophore larva – adult worm.

Taxonomy

Animal Kingdom (Animalia)

Subkingdom Multicellular (Metazoa)

Type Annelids (Annelida)

Class Polychaetes (Polychaeta)

Kinds: nereis(Nereis diversicolor)

sandstone(Arenicola marina)

ClassOligochaetes(Oligochaeta)

Kinds: rainworm(Lumbricus terrestris)

tubifex(Tubifex tubifex)

enchytraeus(Enchytraeus albidus)

ClassLeeches(Hirudinea)

SquadProboscisleeches(Rhynchobdellida)

Kinds: fishleech(Piscicola geometra)

cochlearleech(Glossosiphonia complanata)

TroopLawless,

or Jaw leeches(Arhynchobdellida,seuGnathobdettida)

View: medicalleech(Hirudo medicinalis)

4.2. Morphological overview

Class Polychaetes

The body of polychaete worms is spindle-shaped, slightly compressed in the dorsoventral direction. External segmentation is well expressed, the number of segments ranges from 5 to 800. In this regard, few-segmented and multi-segmented forms of annelids are distinguished. Front of the body ( prostomium) and back - (pygidium) are special, non-metameric formations. The body segments are equivalent in both external and internal structure.

Prostomium carries a pair palps, or palp, a couple tentacles (antennae) And antennae (cirrh)(Fig, 7).

Rice. 7. Nereis parapodia

1 – dorsal antenna; 2 – lobes of the dorsal branch of the parapodia; 3 – bristles; 4 – lobes of the ventral branch of the parapodium; 5 – abdominal barbel; 6 – ventral branch of parapodia; 7 – supporting bristles; 8 – dorsal branch of parapodia

On the sides of the body there are paired lateral outgrowths - parapodia, serving to move the animal along the bottom. They consist of dorsal And abdominal lobes, from the base of which they extend dorsal And abdominal antennae, performing tactile and olfactory functions. Each of the blades has tufts bristles, formed by a chitin-like substance.

The body of polychaetes is covered with thin cuticle, secreted by single-layer skin epithelium. The muscular system of polychaetes is presented circular And longitudinal layers of muscles. The inner surface of the longitudinal muscle fibers is lined with single-layer epithelium bordering on whole, or secondary body cavity. The whole is filled with watery liquid with amoeboid cells, which perform a phagocytic function.

Digestive system presented mouth, pharynx with protruding chitinized jaws (foregut), middle And hindgut.

Respiration of polychaetes occurs over the entire surface of the body or through gills.

The circulatory system consists of dorsal And abdominal vessels, interconnected ring vessels, capillaries And gaps. The circulatory system is closed, the movement of blood occurs due to the contraction of the walls of the spinal vessel. Some polychaetes have red blood due to the presence of an iron-containing pigment, similar in composition to mammalian hemoglobin.

The excretory system consists of metanephridia, located in pairs in body segments.

The nervous system consists of cerebral ganglia(more often than two), paired peripharyngeal nerve rings (connectives) and doubles abdominal nerve trunk. Each segment of the body contains a pair of ganglia from which nerve endings arise. The sensory organs are epithelial sensory cells, antennae, palps, parapodia antennae, statocysts and eyes.

Sexually, most polychaetes are dioecious. Sexual dimorphism is not always expressed. Polychaetes reproduce both sexually and asexually. The last method of reproduction occurs by budding. Polychaete worms are characterized by a clearly expressed repair(restoration of lost body parts). The development of polychaetes follows the scheme: egg - trochophore larva - metatrochophore - adult worm.

The sizes of polychaetes range from 1 mm to 3 meters. Worms of the genus Palolo are used as food in Indonesia and serve as excellent bait for fishing; polychaetes are the main food items for sturgeon and crabs.

Class Oligochaetes

Oligochaete worms, or oligochaetes, are characterized by the absence of palps, parapodia and gills. Sexually hermaphrodites. About 3,400 species of madocchaetes live in fresh waters and soil.

The body of oligochaetes is highly elongated and cylindrical. Dimensions range from 0.5 to 3 meters.

On the front of the body there is a small movable blade - prostomium, without eyes, antennae or palps. Each body segment, except the first, is equipped with small bristles. The anus opens on the posterior segment - pygidium.

The outside of the body of oligochaetes is covered cuticle, under which is located epithelium

Rice. 9. Cross section of an earthworm

1 – pharynx; 2 – esophagus; 3 – goiter; 4 – muscular stomach; 5 - midgut; 6 – dorsal blood vessel; 7 – ring blood vessel; 8 – testes; 9 – seed-receiver; 10 – seed sacs; 11 – seed tubes with seed funnels; 12 – ovary; 13 – oviduct; 14 – metanephridia; 15 - cuticle with epidermis; 16 – circular muscles; 17 – longitudinal muscles; 18 – bristles; 19 – coelothelium; 20 – whole; 21 – typhlosol; 22 – midgut; 23 – metanephridia; 24 – abdominal blood vessel; 25 - ventral nerve cord; 26 - dorsal blood vessel

In earthworms, ducts open into the esophagus calcareous glands, which secrete lime to neutralize humic acids, contained in the soil and vegetable material. Dorsal part midgut forms an internal protrusion - typhlosol, shaped like a clover leaf on a cross section of a worm. Thanks to this formation, the absorption surface of the intestine increases.

The circulatory system is structured similarly to that of polychaetes. In addition to the pulsating dorsal vessel, blood movement is supported by contractions of several annular vessels in the anterior part of the worm's body. In the skin, blood vessels form a dense network of capillaries, which greatly facilitates the breathing of animals.

The excretory system is represented by segmentally located metanephridia. They are found in each segment of the body, and the funnels of the metanephridia open into the cavity of one segment, and the excretory ducts pass through the next segment, breaking off outward on the lateral parts of the worm's body.

The nervous system of oligochaetes consists of paired suprapharyngeal ganglia, peripharyngeal nerve rings And ventral nerve cord. The sense organs are represented by light-sensitive cells scattered over the surface of the skin.

Sexually, oligochaete worms are hermaphrodites. Fertilization cross, those. one individual plays the role of a female, and the other - a male. Mucus is secreted in the girdle area, where eggs are laid. The resulting mucous membrane slides through the anterior end of the worm's body, passing into the area of ​​the sperm receptacles. They squeeze the sperm in them into the mucus of the egg cocoon, where fertilization of the eggs occurs. The egg cocoon is shed by the worm, its edges collapse and slightly harden. Embryos develop in the eggs, which then turn into young worms and begin to live in the soil. Sometimes earthworms have asexual reproduction by dividing the body into two parts - architomy. Subsequently, the missing body parts are regenerated.

Leech class (Hirudinea)

The body of leeches is segmented, but the external segmentation often does not correspond to the internal (true) one. Typically, there are 3 to 5 external segments per internal segment. Leeches are characterized by the presence front, surrounding the mouth, and rear, larger suckers.

The skin-muscle sac is represented by a dense cuticle, under which is located epithelium with mucous and pigment cells. Muscles are made up of a layer ring and highly developed longitudinal muscle fibers. The internal space between the organs is filled parenchyma.

The digestive system of leeches consists of a front sucker lying on the bottom mouth, opening into the oral cavity, pharynx, esophagus, midgut and hindgut. In proboscis leeches, the pharynx forms a muscular tube - proboscis, capable of protruding from the mouth when attacking prey. Jawed leeches have three muscular ridges on the walls of the oral cavity: one dorsal and two lateral. Along the edges of each cushion sits a row chitinized cloves, the combination of which forms the jaw. When attacked, the leech uses its jaw to cut through the host's skin and suck the animal's blood from the resulting wound. The throats open salivary glands, secreting protein substance hirudin, having properties to prevent blood clotting. Therefore, wounds made by leeches bleed heavily. Blood can remain in the leech's intestines for several months. The pharynx continues into a narrow and short esophagus, opening into the lumen of the midgut, often called stomach. In a medicinal leech, it forms 10–11 pairs of lateral protrusions or pockets. The last pair of stomach pouches are particularly large and extend to the back of the body. The bases of the last bags open into a narrow hindgut, ending anus above the posterior sucker.

The nervous system of leeches is presented suprapharyngeal And subpharyngeal ganglia, ventral nerve cord On the front part of the leech on the dorsal side there are 1–5 pairs of simple eye And goblet organs(the latter act as chemoreceptors).

Breathing in sea leeches is carried out using gills, in freshwater and terrestrial animals - through the skin.

Due to the loss of the coelom, leeches lack a true circulatory system. Its functions are performed system of lacunae, representing the remains of the secondary body cavity. Lacunae are connected to each other anastomoses. Distinguish dorsal, abdominal And lateral lacunae. The abdominal nerve cord is located inside the abdominal lacuna. Contractions of the walls of the lacunae promote the circulation of coelomic fluid. Some leeches contain hemoglobin And amoeboid cells, possessing the ability of phagocytosis.

The excretory system of leeches is of the metanephridial type.

Sexually, leeches are hermaphrodites. Male genital organs are presented metamerically located testes, from which short ones extend seminiferous tubules, then merging into vas deferens. The latter open in seminal vesicles, from which sperm comes ejaculatory ducts, and of them - in channel of the copulatory organ. Some leeches do not have a copulatory organ and the sperm is released out into spermatophore– a package of sperm glued together with a special secretion. Slermatophore attaches to abdomen partner leeches near the female genital opening. In other forms, the spermatophore can be completely inserted into vagina or attach to the skin. Female genital organs are represented by one pair ovaries, short oviducts And vagina, lying behind the male genital opening on the ventral side. Fertilized eggs are laid in a cocoon, which is formed, like in earthworms, as a result of the secretion of mucous secretion by the glands of the girdle. Leech cocoons are attached to various underwater objects. Some wear a cocoon on their belly.

The development of leeches is characterized by the absence of a free-swimming larva. The eggs develop into larvae that swim in the cocoon fluid using the ciliary apparatus. After metamorphosis, the larvae turn into young leeches and emerge from the cocoon.

Leeches have been used in medicine since ancient times. For these purposes they use different kinds jaw leeches, but highest value has a medicinal leech. In 1840, more than 25 million leeches were caught in the reservoirs of France, using them for almost all diseases. Currently, leeches are used only in the treatment of hypertension and thrombophlebitis.