Question 1. What are the structural features of annelids?
Structural features of annelids:
- the body consists of separate rings - segments;
- all organs, with the exception of the digestive system, are also segmented;
- segments are separated by partitions of mesodermal origin - septa;
- a longitudinal partition passes along the midline of the body, which divides each compartment of the cavity into the right and left parts;
- segments can be specialized to perform certain functions;
- the body wall is a skin-muscular sac formed by: 1) epithelium, outside of which there is a thin cuticle; 2) annular and longitudinal layers of muscles; some worms have parapodia;
- there is a secondary body cavity (as a whole), filled with liquid;
- the circulatory system is closed;
- breathing is carried out by the entire surface of the body (some marines have gills - epithelial outgrowths of the dorsal branches of parapodia);
- excretory organs - metanephridia, located in pairs in each segment;
- the nervous system is represented by a near-pharyngeal nerve ring formed by the supra-pharyngeal and sub-pharyngeal ganglia (nerve nodes); - two nerve trunks originate from the nerve ring, brought together on the ventral side of the body, in each segment the trunks form nerve nodes with nerves extending from them;
- the sense organs are located on the head: eyes, organs of touch, organs of chemical sense; there are sensitive cells in the body.
Question 2. What are parapodia?
Parapodia are muscular mobile outgrowths of the body, located in pairs on each segment of the body and serving mainly as organs of locomotion, i.e., being primitive limbs. Parapodia have two branches - dorsal and ventral.
Question 3. How are the internal organs located in the body of an annelids?
The internal organs are located segment by segment. Only the digestive tube is not segmented.
Question 4. Describe the structure of the circulatory system in annelids.
The circulatory system is closed. Blood moves through the dorsal (forward) and abdominal (backward) vessels, which communicate with annular vessels in each segment. The first five annular vessels pulsate, providing the movement of blood. The blood is colorless, red or green; some forms contain hemoglobin. Some groups do not have a circulatory system.
Question 5. How do annelids breathe?
Breathing is carried out in most cases by the entire surface of the body. However, some forms have special epithelial outgrowths of the dorsal branch of parapodia - skin gills.
Question 6. What departments does the digestive system of the earthworm consist of?
The digestive system is end-to-end, complex, consists of the following sections: pharynx, esophagus, stomach and intestine, sometimes with lateral outgrowths. The digestive system ends at the anus.
Question 7. Name the organs for excretion of rings.
Excretory organs - metanephridia. The metanephridium consists of a funnel with cilia and an excretory tubule. The cilia of the funnel drive fluid into the tubule leading to another segment. The tubule is surrounded by blood vessels that carry out the reverse absorption of the necessary substances, and opens with an outlet on the side of the body of the worm. The metanephridia of annelids are prototypes of the nephrons of chordates.
Question 8. What classes are united by the type of annelids?
The following classes belong to the type of annelids: Polychaetes, Low-bristle, Leeches.
Question 9. How do low-bristle worms differ from polychaete worms?
The oligochaetes have no lateral outgrowths of the body, there are few setae, the head is not isolated, there are no tentacles and eyes. Simplifications in the structure of oligochaetes are associated with a burrowing lifestyle in the soil.
Question 10. How does the earthworm reproduce?
During sexual reproduction, two animals are attached by the ventral sides, the heads are facing each other. Fertilization is preceded by mating, during which the spermatozoa of each of the two worms pass into the spermatheca of the other. The worms disperse. The belts of both worms secrete mucus, dressing them in the form of sleeves in which eggs are laid. The clutch begins to move towards the head of the worm. During the passage of the clutch past the 10th and 1st segments, spermatozoa obtained from another worm are squeezed into the clutch, with which the eggs are fertilized. The muff with the fertilized eggs then slides over the head. The sleeve then becomes denser (its holes shrink) and turns into an egg cocoon in which young worms develop. In the absence of a sexual partner, self-fertilization occurs.
Question 11. What are the structural features of leeches?
Features of the structure of leeches: no setae and parapodia; the number of segments is constant; have suction cups at the anterior and posterior ends of the body; the mouth, located in the center of the anterior sucker, is armed with three very strongly serrated plates - "jaws"; the voluminous midgut forms a series of paired sac-like outgrowths on the sides - reservoirs for storing blood, which the leech sucks. When biting through the skin, leeches inject a substance into the wound - hirudin, which prevents blood clotting. Therefore, in medicine, leeches are used for hypertension, hemorrhages, thrombosis and other diseases, for the treatment of which it is necessary to reduce blood clotting and remove some of it from the bloodstream.
Question 12. Tell us about the significance of annelids in nature.
Ringlets are common in salt and fresh waters, where they serve as food for many vertebrates (marine polychaetes); found in the soil, participating in the soil-forming process (earthworm). Increase soil fertility. They are a food base for many carnivores.
The solution contains answers to the questions of the educational edition and is made in an easy-to-read PDF format.
Annelids belong to the subsection of coelomic animals Coelomata), a group (supertype) of protostomes (Protostomia). It is characteristic for the primordials:
- The primary mouth (blastopore) of the embryo (gastrula) passes into from an adult animal or the definitive mouth is formed in place
- primary mouth.
- The mesoderm is usually formed teloblastically.
- Covers are single layered.
- The skeleton is external.
- The following types of animals are protostomes: annelids (Annelida), molluscs (Mollusca), arthropods (Arthropoda), onychophora (Onychophora).
- Annelids are a vast group of animals, about 12 thousand species are known. They are inhabitants of the seas, fresh water bodies, inhabit the land.
The main features of the type:
- The body consists of a head lobe (prostomium), a segmented trunk, and an anal lobe (pygidium). The metamerism of the external and internal structure is characteristic.
- The body cavity is secondary, in most animals it is well developed. The blades are devoid of coelom.
- The skin-muscular sac is developed, represented by the epithelium and muscles, circular and longitudinal.
- The intestine consists of three sections, the salivary glands are developed.
- Excretory system of nephridial type.
- The circulatory system is of a closed type, in some groups it is absent.
- The respiratory system is either absent, animals breathe with the entire surface of the body, some representatives have gills.
- The nervous system consists of a paired brain and a ventral nerve chain or ladder.
- Annelids are dioecious or hermaphrodites.
- Crushing of eggs on a spiral type, deterministic.
- Development with metamorphosis or direct.
Annelids General characteristics
Latin name Annelida
Type annelids, or rings, is a very important group for understanding the evolution of higher invertebrates. It includes about 8700 species. Compared with the considered flat and roundworms, and even with nemerteans, annelids are much more highly organized animals.
The main feature of the external structure of the rings is metamerism, or body segmentation. The body consists of a more or less significant number of segments, or metameres. The metamerism of rings is expressed not only in the external, but also in the internal organization, in the repetition of many internal organs.
They have a secondary body cavity - generally absent in lower worms. The body cavity of the annulus is also segmented, that is, it is divided by partitions more or less in accordance with the external segmentation.
At rings there is a well-developed closed circulatory system. Excretory organs - metanephridia - are located segmentally, and therefore are called segmental organs.
Nervous system consists of a paired supraoesophageal ganglion, called the cerebrum, connected by circumoesophageal connectives to the ventral nerve cord. The latter consists of a pair of longitudinally approximated trunks in each segment, forming ganglia, or nerve nodes.
Internal structure
musculature
Under the epithelium is a muscular sac. It consists of external circular and internal longitudinal muscles. Longitudinal muscles in the form of a continuous layer or divided into ribbons.
Leeches have a layer of diagonal muscles, which are located between the annular and longitudinal. Dorso-abdominal muscles are well developed in leeches. Wandering polychaetes have developed parapodial flexors and extensors, derivatives of the annular muscles. The annular musculature of oligochaetes is more developed in the anterior eight segments, which is associated with lifestyle.
body cavity
Secondary or general. The body cavity is lined with coelomic or perineal epithelium, which separates the cavity fluid from tissues and organs. Each body segment of polychaetes and oligochaetes has two coelomic sacs. On the one hand, the walls of the sacs adjoin the muscles, forming a somatopleura, on the other hand, to the intestines and to each other, a splanchnopleura (intestinal leaf) is formed. The splanchnopleura of the right and left sacs forms the mesentery (mesenterium) - a two-layer longitudinal septum. Either two or one septum is developed. The walls of the sacs facing the neighboring segments form dissipations. Dissepiments disappear in some polychaetes. Generally absent in prostomium and pygidium. In almost all leeches (with the exception of bristle-bearing ones), the parenchyma between the organs is generally preserved in the form of lacunae.
Functions of the coelom: supporting, distributive, excretory, and in polychaetes - sexual.
The origin of the whole. Four hypotheses are known: myocoel, gonocoel, enterocoel and schisocoel.
Digestive system
Represented by three departments. Digestion is abdominal. The pharynx of predatory polychaetes is armed with chitinous jaws. The ducts of the salivary glands open into the throat of annelids. Leech glands contain the anticoagulant hirudin. In earthworms, ducts of calcareous (morren) glands flow into the esophagus. The composition of the foregut of earthworms includes, in addition to the pharynx and esophagus, goiter and muscular stomach. The absorption surface of the middle intestine increases due to outgrowths - diverticulum (leeches, part of polychaetes) or typhlosol (oligochaetes).
excretory system
Nefridial type. As a rule, each segment has two excretory canals, they begin in one segment and open with an excretory pore in the next segment of the body. The excretory organs of polychaetes are the most diverse. Polychaete worms have the following types of excretory system: protonephridia, metanephridia, nephromixia, and myxonefridia. Protonephridia are developed in larvae, they begin with terminal club-shaped cells with a flagellum (solenocytes), then the nephridial canal. Metanephridia begin with a funnel with a nephrostomy, inside
funnels are located cilia, followed by a duct and nephropore. Protonephridia and metanephridia are ectodermal in origin. Nephromyxia and mixonephridia are the fusion of the ducts of the protonephridium or metanephridium with the coelomoduct - the genital infundibulum. Coeloducts of mesodermal origin. The excretory organs of oligochaetes and leeches are metanephridia. In leeches, their number is much less than that of body segments (the medical leech has 17 pairs), the separation of the funnel from the canal is characteristic. In the excretory canals of nephridia, ammonia is converted into macromolecular compounds, and water is absorbed as a whole. Annelids also have “kidneys” of accumulation: chloragogenic tissue (polychaetes, oligochaetes) and botryoid tissue (leeches). They accumulate guanine, uric acid salts, which are removed from the coelom through nephridia.
The circulatory system of annelids
Most annelids have a closed circulatory system. It is represented by two main vessels (dorsal and abdominal) and a network of capillaries. The movement of blood is carried out due to the contraction of the walls of the spinal vessel; in oligochaetes, ring hearts also contract. The direction of blood flow along the dorsal vessel from back to front, abdominal - in the opposite direction. The circulatory system is developed in bristle-bearing and proboscis leeches. In jawed leeches, there are no vessels; the function of the circulatory system is performed by the lacunar system. The process of functional replacement of one organ by another, different in origin, is called organ substitution. The blood of annelids is often colored red due to the presence of hemoglobin. Primitive polychaetes have no circulatory system.
Respiratory system
Most breathe with the entire surface of the body, some polychaetes and some leeches have gills. The respiratory organs are evaginated. The gills of polychaetes by origin are a modified dorsal antennae of parapodia, leeches are skin outgrowths.
Nervous system and sense organs
The structure of the nervous system includes: a paired cerebral (supraglottic) ganglion, connectives, subpharyngeal ganglia and the abdominal nerve chain or ladder-type nervous system. The abdominal trunks are connected by commissures. The evolution of the nervous system went in the direction of transforming the ladder-type nervous system into a chain, immersing the system into the body cavity. Nerves extending from the central system make up the peripheral system. There is a different degree of development of the supraesophageal ganglion, the brain is either monolithic or separate departments. For leeches, the fusion of the ganglia of the segments that make up the suckers is characteristic. Sense organs. Polychaetes: epithelial sensory cells, antennae, nuchal organs, parapodial antennae, statocysts, organs of vision (goblet or bubble type eyes). Sense organs of oligochaetes: light-sensitive cells, some inhabitants of the water have eyes, chemical sense organs, tactile cells. Leeches: goblet organs - chemical sense organs, eyes.
Classification
The type of rings is divided into several classes, of which we will consider four:
1. Multibrush rings (Polychaeta)
2. Echiurida (Echiurida)
Echiurids are an extremely modified group of annulus, the internal organization of which differs from that of polychaetes in an unsegmented coelom, the presence of one pair of metanephria.
The trochophore larva of Echiuridae is of the greatest importance for establishing the unity of the origin of Echiurids with polychaetes.
At the bottom of the sea, among the stones in the silt, sand, there are peculiar animals, but in appearance they very little resemble annelids, primarily due to their lack of segmentation. This includes such forms as Bonellia, Echiurus and some others, in total about 150 species. The body of the female Bonellia, living in the crevices of stones, has the shape of a cucumber and carries a long non-retractable trunk, forked at the end. The length of the trunk can be several times the length of the body. A groove lined with cilia runs along the trunk, and a mouth is located at the base of the trunk. With the flow of water through the groove, small food particles are brought to the mouth. On the ventral side of the anterior part of the body of Bonellia there are two large setae, while in other Echiurids, at the posterior end, there is also a corolla of small setae. The presence of setae brings them closer to the annulus.
3. Small-bristle rings (Oligochaeta)
Small-bristle rings, or oligochaetes, are a large group of rings, including about 3100 species. They undoubtedly descend from polychaetes, but differ from them in many essential features.
The overwhelming majority of oligochaetes live in the soil and at the bottom of fresh water bodies, where they often burrow into silty soil. In almost every fresh water body you can find the Tubifex worm, sometimes in huge numbers. The worm lives in silt, and sits with its head end buried in the ground, and its rear end constantly oscillates.
Soil oligochaetes include a large group of earthworms, an example of which is the common earthworm (Lumbricus terrestris).
Oligochaetes feed mainly on plant foods, mainly on the decaying parts of plants that they find in the soil and in the silt.
Considering the features of oligochaetes, we will have in mind mainly the common earthworm.
4. Leeches (Hirudinea) >> >>
Phylogeny
The problem of the origin of the rings is very controversial, there are various hypotheses on this issue. One of the most common hypotheses to date was put forward by E. Meyer and A. Lang. It is called the turbellar theory, since its authors believed that the polychaete rings originate from turbellarian-like ancestors, that is, they associated the origin of the rings with flatworms. At the same time, supporters of this hypothesis point to the phenomenon of the so-called pseudometamerism observed in some turbellarians and expressed in the repetition of certain organs along the length of the body (intestinal outgrowths, metameric arrangement of the gonads). They also point to the similarity of the larva of the trochophore of the annulus with the Müllerian larva of turbellaria and to the possible origin of metanephridia by changing the protonephridial system, especially since the larva of the annulus - trochophores - and the lower annulus have typical protonephridia.
However, other zoologists believe that annelids are closer to nemerteans in a number of ways and that they are descended from nemertean ancestors. This point of view is developed by N. A. Livanov.
The third hypothesis is called the trochophore theory. Its supporters produce rings from the hypothetical ancestor of the trochozoon, which has a trochophore-like structure and descends from ctenophores.
As for the phylogenetic relationships within the four classes of annelids considered, they now seem to be quite clear.
Thus, annelids, which are highly organized protostomes, apparently originate from ancient protostomes.
Undoubtedly, not only modern polychaetes, but also other groups of annelids originated from ancient polychaetes. But it is especially important that polychaetes are a nodal group in the evolution of higher protostomes. Mollusks and arthropods originate from them.
Meaning of annelids
Polychaete worms.
Food for fish and other animals. Mass species play the greatest role. Introduction of polychaetes of the Azov nereid into the Caspian Sea.
Human food (palolo and other species).
Purification of sea water, processing of organic matter.
Settlement on the bottoms of ships (serpulids) - reduction in speed.
Small-bristle worms.
Oligochaetes - inhabitants of water bodies are the food of many animals, they are involved in the processing of organic matter.
Earthworms - animal food and human food. Gallery
Class Polychaetes, Class Low-bristle, Class Leeches
Question 1. Describe the structural features of annelids.
Characteristic features of the type Annelids:
The body is always segmented (segmentation in the internal structure is the repetition of many internal organs).
They have a secondary body cavity - the whole.
The circulatory system is closed.
The nervous system consists of the peripharyngeal nerve ring and the ventral nerve cord. The supraglottic node is the "brain".
The sense organs are located on the head segments.
Organs promoting locomotion are setae (in oligochaetes, 8 on each segment) and parapodia with tufts of setae (in polychaetes).
Question 2. What are parapodia? What do you think their evolutionary significance is?
Parapodia - lateral outgrowths of the body in polychaete worms, arranged in pairs and serving as organs of movement. Evolutionarily, parapodia are the precursors of limbs.
Question 3. Describe the structure of the circulatory system of annelids.
The circulatory system is closed, consisting of vessels, some of which have contracting walls (“hearts”), which ensures blood circulation. Some groups do not have a circulatory system. The blood of a number of forms contains hemoglobin (a red blood protein containing iron and transporting oxygen from the respiratory system to the tissues).
Question 4. Describe the organs of excretion of rings.
The excretory system is represented by segmentally arranged metanephridia. Their funnel faces the body cavity, and the other end opens outward.
Question 5. How does the earthworm reproduce?
Earthworms are hermaphrodites, but they cross fertilize. The two worms approach each other and exchange spermatozoa, which go into their spermatozoa. Then a mucous muff is formed on the body of each worm. With muscle contractions, the worm moves it to the front end of the body. When the muff passes by the openings of the ovarian ducts and sperm receptacles, eggs and sperm enter it. Then the muff slips off the worm and closes into a cocoon, where small worms develop from the fertilized eggs.
Question 6. What classes are united by the type of annelids?
Type Annelids combines several classes, of which the three main ones are Polychaete, Low-bristle and Leeches.
Question 7. Why are some annelids called polychaetes, while others are called low-bristle? How are oligochaetes different from polychaetes?
Small-bristle worms are one of the subclasses of annelids. The brightest and most familiar representative of the taxon is the most trivial Earthworm.
Polychaete worms are one of the subclasses of annelids. The most famous representatives of the taxon are sandworm and nereid. Sometimes animals are called polychaetes, which in Greek means "a lot of hair."
The difference between low-bristle worms and polychaetes
There are fewer species of oligochaetes than polychaetes. The first are only 3 thousand species, the second - about 10 thousand.
The maximum size of polychaetes exceeds the maximum size of oligochaetes, reaching 3 meters.
Animals have different habitats. Small bristle worms live mainly in the ground, most polychaete worms prefer warm and salty water bodies.
Oligochaetes perceive oxygen with the entire surface of the skin, polychaetes breathe with the help of pseudo-gills-setae.
Small-bristle - hermaphrodites, polychaetes - dioecious animals.
The oligochaetes that emerge from the egg are similar to their parents. Polychaetes go through the larval stage.
Olympians devour dead leaves and corpses, most polychaetes are active predators.
Question 8. When and from whom did the first annelids originate? What major changes accompanied the appearance of the type? Discuss with the class what the meaning of these transformations is. Record the results of the discussion in your notebook.
Annelids are descended from free-living flatworms. From the common ancestors of worms, under the influence of evolutionary factors, annelids also originated. An important point in their evolution is the division of the body into segments (rings). In connection with the active movement of annelids, a circulatory system appeared, supplying the body with nutrients and oxygen. Ancient annelids had a more complex structure compared to other worms.
Question 9. Make a table "Comparative characteristics of the structure of organs and systems in flat, round and annelids" (work in small groups).
Comparative characteristics of the structure of organs and systems in flat, round and annelids
The most famous representatives of annelids for each 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.
Systematics
To date, experts attribute from 16 to 22 thousand modern animal species to the type of annelids. There is no single approved classification of rings. The Soviet zoologist V.N. Beklemishev proposed a classification based on the division of all representatives of annelids into two superclasses: girdleless, which includes polychaetes and echiurids, and girdle, including oligochaetes and leeches.
The following is a classification from the World Register of Marine Species website.
Table of biological taxonomy of annelids
| Class* | Subclass | Infraclass | Detachment |
| Polychaete worms, or polychaetes (lat. Polychaeta) | |||
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| Polychaeta incertae sedis (disputed species) | |||
| Sedentaria | Canalipalpata |
|
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| Scolecida (Scolecida) |
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| Palpata |
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| Errantia (sometimes called Aciculata) |
|
||
| Belt class (Clitellata) | Leeches (Hirudinea) | Acanthobdellidea | |
|
|||
|
Small-bristle worms (Oligochaeta) |
|
||
|
Echiuridae (Echiura) |
|
There is also a superclass Annelida incertae sedis, which includes controversial species. There, according to the World Register of Marine Species, such a controversial group as Myzostomidae (Myzostomida), which other classifications refer to polychaete worms or even separate into a separate class, also entered as a detachment.
- Class Polychaete(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 dumped directly into the water, where fertilization and development take place; floating freely and are called trochophores. Sometimes they reproduce by budding or fragmentation. The class includes more than 6000 species, which are divided into free-living and sessile forms.
- Class Poyaskovye (Clitellata). Representatives of the class on the body have a small number or no bristles at all. Parapodia are absent. They are characterized by the presence of a unique reproductive organ - a girdle, which is formed from the remains of a cocoon and performs a protective function for fertilized eggs. The class has about 10,000 representatives.
- Subclass Small-bristle(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 was called low-setae. Appendages on the body, as a rule, do not have. Hermaphrodites. Development is direct, there is no larval stage. There are about 3250 species.
- Subclass Leeches. They inhabit mainly freshwater reservoirs, 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 types of representatives.
Class Echiuridae (Echiura). This is a small group with only about 170 known species, all of which are exclusively marine life. Echiurids were recently classified as annelids after DNA examinations, but earlier it was a separate type. The reason is that their body is different - it does not have segmentation, like annelids. In some sources, the Echiurids are considered not as a separate class, but as a subclass of Polychaetes.
Spreading
Annelids, depending on the species, live on land, in fresh and salt water.
Polychaete worms, as a rule, live in sea water (with the exception of some species that can also be found in freshwater bodies). They are food for fish, crayfish, as well as birds and mammals.
Small-bristle worms, to a subclass of which the earthworm belongs, live in soil fertilized with humus or fresh water.
Echiurides are distributed only in marine waters.
Morphology
The main characteristic of representatives of the Annelida type is considered to be the division of the body into a number of cylindrical segments, or metameres, the total number of which, depending on the type of worm, varies widely. Each metamere consists of a section of the body wall and a section of the body cavity with its internal organs. The number of outer rings of worms corresponds to the number of inner segments. The body of annelids consists of the region of the head (prostomium); a body consisting of metameres; and a segmented posterior lobe called the pygidium. In some primitive representatives of this type, the metameres are identical, or very similar to each other, each containing the same structures; in more advanced forms, there is a tendency to consolidate some segments and restrict certain organs to certain segments.
The outer shell of the body of annelids (skin-muscular sac) includes the epidermis surrounded by the cuticle, as well as well-developed, segmentally located muscles - annular and longitudinal. Most annelids have external short setae composed of chitin. In addition, on each metamere, some representatives of this type of animals may have primitive limbs called parapodia, on the surface of which setae and sometimes gills are located. The spatial movement of the worms is carried out either through muscle contraction or movements of the parapodia.
The body length of annelids ranges from 0.2 mm to 5 m.
The main general anatomical features of annelids in cross section Digestive system Annelids consists of an unsegmented intestine that runs through the middle of the body from the oral cavity, located on the underside of the head, to the anus, located on the anal lobe. The intestine is separated from the body wall by a cavity called the whole. The segmented compartments of the coelom are usually separated from each other by thin sheets of tissue called septa that perforate the gut and blood vessels. With the exception of leeches, in general, representatives of annelids are filled with liquid and function as a skeleton, providing muscle movement, as well as transport, sexual, and excretory functions of the body. When the integrity of the body of the worm is damaged, it loses the ability to move properly, since the functioning of the muscles of the body 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 by means of 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 the same type of canals (the canals may be absent in certain segments).
Circulatory system. In annelids, for the first time in the process of evolution, a circulatory system appeared. Blood usually contains hemoglobin, a red respiratory pigment; however, some annelids contain chlorocruorin, a green respiratory pigment that gives blood its 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 - the abdominal and dorsal - are interconnected 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 breathing 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 node.
The sense organs of annelids typically include eyes, taste buds, tactile tentacles, and statocysts, organs responsible for balance.
reproduction annelides occur either sexually or asexually. Asexual reproduction is possible through fragmentation, budding, or division. Among worms that reproduce sexually, there are hermaphrodites, but most species are dioecious. The fertilized eggs of marine annelids usually develop into free-swimming larvae. The eggs of terrestrial forms are encased in cocoons and larvae, like miniature versions of the adults.
The ability to restore lost body parts is highly developed in many annelids with many and few bristles.
Ecological significance
The earthworm is very important for maintaining the condition of the soil Charles Darwin, in The Formation of Vegetable Mold through the Action of Worms (1881), presented the first scientific analysis of the influence of earthworms on soil fertility. Some of the worms burrow in the soil, while others live exclusively on the surface, usually in wet 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 the decomposition of organic substances, 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 the glacial regions of North America, for example, scientists believe that almost all native earthworms were killed by glaciers and the worms currently found in these regions (such as Amynthas Agrestis) were introduced from other areas, primarily from Europe. , and more recently, from Asia. Northern hardwood forests have been particularly affected by invasive worms through loss of leaf litter, reduced soil fertility, changes in soil chemistry, and loss of ecological diversity.
Marine annelids can make up over one-third of benthic animal species around coral reefs and in intertidal areas. Burrowing annelids increase the infiltration of water and oxygen into the seabed sediment, which promotes the growth of populations of aerobic bacteria and small animals.
Human interaction
Anglers believe 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 wet moss.
Scientists study aquatic annelids to monitor oxygen levels, salinity and environmental pollution in fresh and sea water.
The jaws of polychaetes are very strong. These advantages have attracted the attention of engineers. Research has shown that the jaws of this genus of worms are made up 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 the locals. In Korea and Japan, Urechis unicinctus worms from the Echiuridae class are eaten.
Representatives of annelids, which are eaten Cases of using leeches for medicinal purposes were known as early as China around 30 AD, India around 200 AD, ancient Rome around 50 AD, and then throughout Europe. In the medical practice of the 19th century, the use of leeches was so widespread that their stocks in some areas of the world were depleted, and some regions imposed restrictions or bans on their export (while the medicinal leeches themselves were considered an endangered species). More recently, leeches have been used in microsurgery for transplantation of organs and their parts, skin areas. In addition, scientists argue that the saliva of medical leeches has an anti-inflammatory effect, and some anticoagulants contained in it prevent the growth of malignant tumors.
About 17 species of leeches are dangerous for humans.
Medical leeches are used for hirudotherapy, and a valuable remedy is extracted from pharmacies - hirudin Leeches can attach to the skin of a person from the outside, or penetrate into internal organs (for example, the respiratory or gastrointestinal tract). In this regard, there are two types of this disease - internal and external hirudinosis. With external hirudinosis, leeches are most often attached to human skin in the armpits, neck, shoulders, and calves.
Misostomida on sea lily The main characteristic features of annelids are:
Secondary, or coelomic, body cavity;
The appearance of the circulatory and respiratory systems;
Excretory system in the form of metanephridia.
a brief description of
|
Habitat |
Marine and freshwater, terrestrial and underground animals |
|
body structure |
The body is elongated, worm-like, metameric structure. Bilateral symmetry. Three-layer. Polychaetes have parapodia |
|
body integuments |
Cuticle. Each segment has 8 or more setae for locomotion. There are many glands in the skin. In the skin-muscle sac, longitudinal and transverse muscles |
|
body cavity |
The secondary cavity of the body - as a whole, is filled with a liquid that acts as a hydroskeleton |
|
Digestive system |
Mouth, pharynx, esophagus, goiter, stomach, intestines, anus |
|
Respiratory system |
Breathing with the entire surface of the body. Polychaetes have external gills. |
|
Circulatory system |
closed. One circle of blood circulation. There is no heart. blood red |
|
excretorysystem |
A pair of tubules in each metamere - metanephridia |
|
Nervous system |
Periopharyngeal nerve ring, ladder-type abdominal nerve cord |
|
sense organs |
Tactile and photosensitive cells, polychaetes have eyes |
|
Reproductive system and development |
Hermaphrodites. Cross fertilization. Development without metamorphosis. Fertilization is internal. Polychaete dioecious, external fertilization, development with metamorphosis |
The main classes of the type are Small-bristle, Polychaete, Leeches.
A.G. Lebedev "Preparing for the exam in biology"
Basic aromorphoses:
1. The appearance of a secondary cavity of the body-coelom.
2. Metomeric structure of the body.
3. The emergence of a closed circulatory system.
4. The excretory system is of the methonephridial type.
5. More highly organized nervous system and sense organs.
6. The emergence of the respiratory system.
7. The emergence of organs of movement.
General characteristics of annelids.
An extensive group of animals, including about 12k species.
They live mainly in the seas, as well as in fresh waters and on land.
They are characterized by the following features of the organization:
1. Metamyria (correct repetition of organs similar to each other along the axis of the animal's body). Outwardly, this is expressed in the fact that the entire body of the worm is divided by constrictions into separate segments (rings). Therefore, annelids are also called ringworms. Along with the external, there is an internal segmentation, which is expressed in the repetition of many internal organs.
As a result, each segment to some extent represents an independent unit of a complete system.
Metamyria can be homonomous (all segments are the same) and heteronomous (if the segments differ from each other). Annelids are characterized mainly by homonomous segmentation.
Metamyria arose with the need to increase mobility by building muscle and muscle mass in length. However, this raises a new problem - managing and increasing the number of organs in order to ensure a full life.
Thus, the biological meaning of metamyria as a whole is:
a) solving the problem of body control;
b) all vital processes are intensified, as the same organs are repeated;
c) the margin of biological strength increases;
d) due to the presence of metomeric, annelids are capable of regeneration.
From an evolutionary point of view, segmentation opens the way for specialization and differentiation of cells, which leads to a reduction in energy costs. And the emergence of heteronomous segmentation. The occurrence of heteronomous segmentation is observed in some annelids, for example, in nereids.
2. For the first time in annuli, the process of cefollization is noted, that is, the formation of the head section.
3. The musculocutaneous sac is well developed.
Due to this, annelids make complex undulating and peristatic movements. An important role is played by the lateral outgrowths of the body-paropodia, which are the organs of movement. Parapodia is another way to increase the mobility of annelids. Paropodiums are best developed in polychaete annulus.
In oligochaete worms and leeches, paropodia have undergone, to one degree or another, reduction.
4. Annelids have a secondary body cavity, the coelom. Unlike the primary body cavity of the schizocoel, the coelom is lined with a special coelomic epithelium. In fact, it is an internal organ and has its own walls.
The whole, as well as the whole body of annelids, is segmented.
5. The digestive system is well differentiated into sections.
Some species have salivary glands. The anterior and posterior intestines are of ectodermal origin, the middle of endodermal origin.
6. The main excretory organs are the metanephridia. This is an open excretory system associated with the whole and providing not only the function of excretion, but also the regulation of the water regime.
Metanephridia are arranged in segments. In this case, the metanephridial funnel is located in one segment, and the excretory canal opens in the adjacent segment.
7. Most annelids have a closed circulatory system. This means that blood flows only through the vessels and there is a network of capillaries between arteries and veins.
8. Breathing is carried out through the skin, but some representatives have new respiratory organs - gills.
The dorsal parapodia tendril turns into a gill.
9. The nervous system consists of paired dorsal cerebral ganglia and the ventral nerve cord.
Paired dorsal along the brain are divided into anterior, middle and posterior ganglion. This is different from the previous groups of worms.
10. The sense organs are better developed than in flat and roundworms.
There are eyes capable of accommodation in many rings. The organs of touch, the organs of balance (statocysts), the organs of chemical sense, and in some also the organs of hearing, arranged like locators.
Annelids are mostly dioecious, but hermaphroditism is often observed. Development often proceeds with metamorphosis. A typical sea ring larva is called a trochophora (cilia-bearing).
Thus, in annelids, progressive features of organization can be traced: the presence of a coelom, metamerism of the structure, the appearance of a circulatory system, methonephridia, a more highly organized nervous system and sensory organs. Along with these features, there are signs that bring them closer to lower worms (primitive signs: the trochophore larva has a primary body cavity, protonifridia, an orthogonal nervous system, and in the early stages of development, a blind intestine).
These features are also found in adult rings from primitive groups.
The type includes 3 classes:polychaete class or polychaete worms, olegochaete class or oligochaete worms, leech class.
Polychaete class (Polychaete worms)
The central class of annelids, characterized by the largest number of species.
Some annelids swim freely in water, for example, nereids, others burrow into the sand, for example, sandworms. There are sessile polychaetes living in calcareous pipes, for example, serpulids and Aphrodites crawling along the bottom.
External structure of polychaetes.
The body consists of a head section, a segmented trunk, and an anal lobe (pegidia).
The head section is formed by the head lobe, the prostomium and the oral segment, the peristomium. Many polychaetes have ocelli and sensory appendages on their heads. For example, a Nereid has 2 pairs of eyes, tentacles, two-segmented palps, and olfactory pits. On the peristomium below there is a mouth, and on the sides there are several pairs of antennae. The body consists of segments, the number of which can reach up to 800.
Homonomic segmentation is best expressed in free-moving vagrant polychaetes. Heteronomic segmentation is inherent in sessile and partly burrowing forms.
On the body segments are paropodia, with the help of which polychaetes swim, crawl or burrow into the ground. Each paropodium consists of a basal part and two lobes: the dorsal (notopodium) and the ventral (neuropodium). At the base of the paropodia on the dorsal side there is a dorsal antennae, and on the ventral side there is a ventral antennae. In some species, the dorsal barnacle of the paropodium develops into feathery gills. Paropodia armed with tufts of setae composed of organic matter similar to chitin.
One of the setae of each lobe is most developed and is called an aciculum. This is a base bristle. Muscles are attached to its base, setting the entire bundle in motion. In some species leading a burrowing or attached lifestyle, paropodia are reduced. The anal lobe does not bear any appendages.
Skin-muscle bag.
The body of polychaetes is covered with a monosyllabic epithelium, which exposes a thin cuticle to the surface. The epithelium may be ciliated. It is rich in single-celled glands that secrete mucus and substances from which many sessile polychaetes build their tubes. Under the epithelium lies the annular and longitudinal muscles. The longitudinal muscles form 4 highly developed bands: 2 on the dorsal side and 2 on the ventral side.
In addition, there are oblique muscles that run obliquely from the dorsal part of the skin-muscle sac to the abdominal. The secondary cavity of the body is the whole. In fact, it is a sac filled with abdominal fluid, which is separated from all tissues and organs by coelomic epithelium of mesodermal origin.
Thus, the longitudinal muscles, intestines and internal organs are covered with a single layer of epithelium.
Another feature of the coelom in polychaetes is its metomeric structure.
This means that each segment of the polychaete's body essentially has its own cavity, completely separated from the cavities of neighboring segments by special partitions consisting of a two-layer epithelium.
In addition, the coelomic cavity in each segment is completely divided into right and left halves by a longitudinal, also two-layer septum. Inside this septum passes the intestines, and above and below the intestines, also inside this septum, are the dorsal and abdominal blood vessels.
That is, in each internal segment of polychaetes there are 2 coelomic sacs. The epithelial walls of these sacs are closely adjacent on one side to the muscles of the skin-muscular sac, and on the other to the intestines and to each other, covering the intestine and blood vessels on both sides. This part of the walls of the coelomic sacs is called the dorsal and abdominal mesentery or mesentery.
In general, it performs several functions:
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1. Let's continue to fill in the table.
2. Let us explain the above statement.
Annelids for the first time have a secondary body cavity and a cellular structure of the skin. The circulatory system appears in the internal structure. The excretory system is represented by more developed metanephridia. Most of the rings are free-living, some have a semblance of legs - parapodia. All are bilaterally symmetrical. There are sense organs.
Let's write about the protective function of partitions.
Each segment of annelids is separated by a septum and has a complete set of nerve nodes, nephridia, annular vessels and gonads. If the integrity of one segment is broken, this affects the vital activity of the worm to a small extent.
4. Let us list the structural features of the annulus.
Some types of rings have parapodia and setae for locomotion.
Those species that do not have parapodia have bristles or their body is covered with mucus for better gliding. The muscular system of all rings is represented by annular and longitudinal muscles.
5. Let's finish the schemes.
a) Digestive system of the rings
b) Nervous system of rings
c) Sense organs of rings
6.
Let's write about the division of the body of the ring.
Regeneration can occur and the worm will restore the lost parts. That is, asexual reproduction will occur.
7. Let's write an answer about the formation of a belt.
Maybe. In some polychaete worms living in the seas and belonging to the type Annelids, reproduction occurs in water, fertilization is external.
But in most rings, reproduction occurs with the help of a girdle.
8. Let's explain the relationship.
There is a direct relationship between the number of eggs laid and the care of offspring. Some polychaetes lay few eggs, and the female guards them. This means that the annelids are more advanced than the previous types of worms.
We list the ways of feeding polychaetes.
Among the polychaete worms there are predators that feed on small marine animals. There are omnivores that filter water and feed on plants.
10. Let's finish the sentences.
The development of polychaetes occurs with the alternation of life forms.
Their larvae do not look like adults. Each life form performs different functions: reproduction, resettlement, self-preservation. In some polychaetes, care for offspring is observed.
11. Let's finish the scheme.
The value of polychaetes in nature
Filter water.
2. They are fish food.
3. They feed on the remains of dead animals.
12. Let's write the differences in the nutrition of different worms.
The oligochaete worms feed on organic matter from the plant residues of the soil, and among the polychaetes there are predators, omnivores, and herbivores.
Let us write the common adaptations of protozoa and oligochaetes.
To endure unfavorable conditions, many protozoa form a cyst, and oligochaetes form a protective capsule, and fall into diapause. These formations are similar in their functions.
14. Denote the structure of the earthworm in the figure. Let's make a conclusion.
Conclusion: The primary cavity of the body is the supporting one. It contains a liquid that gives the body of the worm elasticity.
We list the features of leeches.
1) Constant number of body segments (33)
2) The presence of suction cups for attaching to the body of the victim or the substrate.
3) Absence of bristles on the body.
4) All leeches live in the aquatic environment.
16. Let's name the types of nutrition of leeches.
17. Define the type and class of worms. 
Let us explain the peculiarity of leeches.
In leeches, the nervous system is better developed.
19. Let us explain the statement.
The statement is not correct. Leeches are very sensitive to the purity of water and die when it is contaminated. Oligochetes, on the other hand, endure water pollution and can live in such reservoirs for a long time.
Write an answer about hirudias.
Hirudin is necessary to prevent blood clotting on the wound of the victim and in the stomach of the leech itself. If it is not produced, the leech will not be able to feed, as the blood will clot.
21. Let's name the role of leeches in medicine.
Leeches are used in medicine to reduce blood pressure in hypertension and the threat of hemorrhage, stroke.
Let us indicate the characteristics of the classes of annelids.
Classes like Annelids.
A - 1, 2, 8, 10, 16
B - 4, 6, 11, 12, 17
B - 3, 5, 7, 9, 14, 15
Let's write down the answers to the crossword number 1.
Answers:
1. Capsule
2. Belt
3. Polychaetes
4. Cavity
5. Chain
6. Oligochetes
7. Chain
8.
Breath
Keyword: rings
Type Annelids
Aromorphoses of the type:
1) the presence of organs of movement;
2) the appearance of respiratory organs and a closed circulatory system;
3) secondary body cavity.
The type of annelids covers about 8000 species of higher worms, which have a much more complex organization than the previous types.
The main features of the type:
The body of the worms is composed of a head lobe (prostomium), a segmented trunk, and a posterior anal lobe (pygidium). Sensory organs are located on the head lobe.
There is a well-developed skin-muscular sac.
3. In annelids, for the first time, a secondary body cavity or coelom appears (the space between the body wall and internal organs with its own epithelial lining, which separates the cavity fluid from all surrounding tissues and organs). It is divided into chambers according to external segmentation.
4. The mouth opening lies on the ventral side of the first segment of the body.
The digestive system consists of the oral cavity, pharynx, midgut and hindgut, which opens with an anus at the end of the anal lobe.
5. Most have a well-developed closed circulatory system.
6. The functions of excretion are performed by metanephridia.
Metanephridia are called open excretory organs, in contrast to closed protonephridia.
Metanephridia begins with a more or less expanded funnel - nephrostomy, seated with cilia and opening into the cavity of the segment. From the nephrostomy, the nephridial canal begins, which passes into the next segment. Here, the canal forms a complex tangle and opens with an excretory opening to the outside.
The nervous system consists of paired supra- and sub-pharyngeal ganglia associated with the peripharyngeal nerve ring and the ventral nerve cord. The latter is a pair of longitudinally approximated trunks, forming nerve nodes in each segment.
The most primitive annelids are dioecious; some have secondarily hermaphroditism.
9. The crushing of the egg is of a spiral type.
10. In the lower representatives of the type, development proceeds with metamorphosis, a typical larva is a trochophore.
According to the most common view, annelids are descended from lower non-segmented worms.
The type is divided into three classes - Small-bristle (representative of the earthworm), Polychaetes (nereis, sandworm) and Leeches.
It is believed that in the course of evolution, polychaetes gave rise to arthropods.
1. Flatworms:
a) two-layer animals;
b) three-layer animals.
Specify the organs of excretion in bovine tapeworm:
a) protonephridia;
b) metanephridia;
3. Intermediate host of the liver fluke:
a) a cow
b) small pond snail;
c) a person.
4. The complication of roundworms compared to flatworms is associated with the appearance of:
a) three-layer structure of the body;
b) nervous system;
c) hermaphroditism;
d) through the digestive system.
a) type Roundworms;
b) class Tapeworms;
c) Flukes class?
How many layers of muscle do roundworms have?
a) one; b) two; at three o'clok.
7. How many segments does the body of an earthworm have?
a) 20-30; 6)250; c) up to 180; d) 50.
8. Among annelids, only:
a) oligochaetes; b) polychaetes; c) leeches.
Polychaetes are characterized by (-en; -o):
a) dichotomy;
b) hermaphroditism;
c) budding.
10. What is the body cavity of a Nereid:
a) intestinal; b) primary;
c) secondary; d) filled with parenchyma
Literature
R.G. Zayats, I.V. Rachkovskaya and others. Biology for entrants. Minsk, Unipress, 2009, p. 129-177.
2. L.N. Pesetskaya. Biology.
Minsk, "Aversev", 2007, p.195-202.
3. N.D. Lisov, N.A. Lemeza and others. Biology. Minsk, "Aversev", 2009, pp. 169-188.
4. E.I. Shepelevich, V.M. Glushko, T.V. Maksimov. Biology for schoolchildren and entrants. Minsk, "UniversalPress", 2007, pp. 404-413.