A type of annelids is an earthworm. A short description of the type of annelids. Reproductive system and development

Initial level of knowledge:

kingdom, type, cell, tissues, organs, organ systems, heterotroph, predation, saprophyte, detritophage, eukaryotes, aerobes, symmetry, body cavity, larva.

Response plan:

General characteristics of annelids
Body structure of annelids
Reproduction and development of annelids
Classification of annelids, variety of species
Features of the structure and development of worms of the Maloshchitelkovye class on the example of an earthworm
Characteristics of the class Multi-plate
Characteristics of the class Leech
Origin of annelids

General characteristics of annelids

Number of species: about 75 thousand.

Habitat: in salt and fresh waters, found in soil. Aquatic ones crawl along the bottom, burrow into silt. Some of them lead a sedentary lifestyle - they build a protective tube and never leave it. There are also planktonic species.

Structure: bilaterally symmetrical worms with a secondary body cavity and a body divided into segments (rings). In the body, the head (head lobe), trunk and caudal (anal lobe) sections are distinguished. The secondary cavity (as a whole), in contrast to the primary cavity, is lined with its own internal epithelium, which separates the coelomic fluid from the muscles and internal organs. The fluid acts as a hydroskeleton, and also participates in metabolism. Each segment is a compartment containing the external outgrowths of the body, two coelomic sacs, nodes of the nervous system, excretory and genital organs. Annelids have a musculocutaneous sac, consisting of one layer of skin epithelium and two layers of muscles: annular and longitudinal. On the body there may be muscular outgrowths - parapodia, which are organs of movement, as well as bristles.

Circulatory system first appeared during evolution in annelids. It is of a closed type: blood moves only through the vessels, not getting into the body cavity. There are two main vessels: dorsal (carries blood from back to front) and abdominal (carries blood from front to back). In each segment, they are connected by annular vessels. The blood moves due to the pulsation of the dorsal vessel or "hearts" - the annular vessels of 7-13 body segments.

No respiratory system... Ringed worms are aerobes. Gas exchange occurs across the entire surface of the body. Some polychaetae developed cutaneous gills - outgrowths of parapodia.

For the first time in the course of evolution, multicellular excretory organs - metanephridia. They consist of a funnel with cilia and an excretory canal located in the next segment. The funnel faces the body cavity, the tubules open on the surface of the body with an excretory pore through which the decay products are removed from the body.

Nervous system formed by the periopharyngeal nerve ring, in which the paired epopharyngeal (cerebral) ganglion is especially developed, and the abdominal nerve chain, consisting of paired abdominal nerve nodes in each segment. From the "cerebral" ganglion and nerve chain nerves depart to organs and skin.

Sense organs: eyes - organs of vision, palps, tentacles (antennae) and antennae - organs of touch and chemical sense are located on the head lobe in polychaetae. In small-bristled animals, the sense organs are poorly developed due to the underground lifestyle, but the skin contains light-sensitive cells, organs of touch and balance.

Reproduction and development

They reproduce sexually and asexually - by fragmentation (division) of the body, due to the high degree of regeneration. In polychaetal worms, budding is also found.
Polychaetes are dioecious, while those with few bristles and leeches are hermaphrodites. Fertilization is external, in hermaphrodites - cross, i.e. worms exchange semen. Freshwater and soil worms develop directly, i.e. young individuals emerge from the egg. In marine forms, development is indirect: a larva, a trochophore, emerges from the egg.

Representatives

Type Ringed worms are divided into three classes: Polychaetae, Malobeta, Leech.

Small-bristled worms (oligochaetes) mainly live in the soil, but there are also freshwater forms. A typical representative living in the soil is the earthworm. It has an elongated, cylindrical body. Small forms - about 0.5 mm, the largest representative reaches almost 3 m (giant earthworm from Australia). Each segment has 8 bristles, located in four pairs on the lateral sides of the segments. Clinging to the irregularities of the soil, the worm moves forward with the help of the muscles of the skin-muscular sac. As a result of feeding on rotting plant residues and humus, the digestive system has a number of features. Its anterior section is divided into the muscular pharynx, esophagus, goiter, and gizzard.

The earthworm breathes throughout its entire surface due to the presence of a dense subcutaneous network of capillary blood vessels.

Earthworms are hermaphrodites. Fertilization is cross. The worms attach themselves to each other with their ventral sides and exchange semen, which enters the seminal receptacles. After that, the worms disperse. In the front third of the body there is a girdle, which forms a mucous muff, eggs are laid in it. As the sleeve moves through the segments containing the spermatozoa, the eggs are fertilized with sperm belonging to another individual. The sleeve is thrown off through the front end of the body, thickens and turns into an egg cocoon, where young worms develop. Earthworms are characterized by a high ability to regenerate.

Longitudinal section of the body of the earthworm: 1 - mouth; 2 - pharynx; 3 - esophagus; 4 - goiter; 5 - stomach; 6 - intestine; 7 - periopharyngeal ring; 8 - abdominal nerve chain; 9 - "hearts"; 10 - dorsal blood vessel; 11 - abdominal blood vessel.

The importance of oligochaetes in soil formation. Charles Darwin noted their beneficial effect on soil fertility. Dragging plant residues into the burrow, they enrich it with humus. Laying passages in the soil, they facilitate the penetration of air and water to the roots of plants, loosen the soil.

Polychaetae. Representatives of this class are also called polychaetes. They live mainly in the seas. The articular body of polychaetes consists of three sections: the head lobe, the segmented body, and the posterior anal lobe. The head lobe is armed with appendages - tentacles and bears small eyes. The next segment contains a mouth with a pharynx, which can turn outward and often has chitinous jaws. On the segments of the body there are bifurcated parapodia, armed with bristles and often having branchial outgrowths.

Among them there are active predators that can swim quite quickly, bending their bodies in waves (nereids), many of them lead a burrowing lifestyle, making long burrows in the sand or silt (sandworms).

Fertilization is usually external, the embryo turns into a larva characteristic of polychaetes - a trochophore, which actively swims with the help of cilia.

Class Leeches unites about 400 species. In leeches, the body is elongated and flattened in the dorsal-abdominal direction. At the front end, there is one mouth sucker on the back - another sucker. They do not have parapodia and setae, they swim, bending their body in waves, or "walk" on the ground or leaves. The body of the leeches is covered with cuticles. Leeches are hermaphrodites, direct development. They are used in medicine, because due to the release of the protein hirudin by them, the development of blood clots that clog the blood vessels is prevented.

Origin: annelids evolved from primitive, similar to flat ciliary worms. From the polychaetae came the few bristles, and from them - the leeches.

New concepts and terms:, polychaetes, oligochaetes, general, segments, parapodia, metanephridia, nephrostome, closed circulatory system, cutaneous gills, trochophora, hirudin.

Questions for consolidation:

• Why did annelids get this name?
• Why are annelids also called secondary cavities?
• What structural features of annelids indicate their higher organization compared to flat and round worms? What organs and organ systems first appear in annelids?
• What is characteristic of the structure of each body segment?
• What is the significance of annelids in nature and human life?
• What are the structural features of annelids in relation to their lifestyle and habitat?

Literature:

1. Bilich G.L., Kryzhanovsky V.A. Biology. Complete course. In 3 volumes - Moscow: Onyx 21st Century Publishing House LLC, 2002
2. Biology: A guide for university applicants. Volume 1. - M .: New Vol-na Publishing House LLC: ONIKS Publishing House CJSC, 2000.
3. Kamensky, A.A. Biology. Reference manual / A. A. Kamenskiy, A. S. Maklakova, N. Yu. Sarycheva // Full course of preparation for exams, tests, tests. - M .: CJSC "ROSMEN-PRESS", 2005. - 399s.
4. Konstantinov V.M., Babenko V.G., Kuchmenko V.S. Biology: Animals: A Textbook for 7th grade students of a comprehensive school / Ed. V.M. Konstantinova, I.N. Ponoma-roar. - M .: Ventana-Graf, 2001.
5. Konstantinov, V.M.Biology: animals. Textbook. for 7 cl. general education. schools / V. M. Konstantinov, V. G. Babenko, V. S. Kuchmenko. - M .: Ventana-Graf, 2001 .-- 304s.
6. Latyushin, V.V. Biology. Animals: textbook. for 7 cl. general education. institutions / V. V. Laktyushin, V. A. Shapkin. - 5th ed., Stereotype. - M .: Bustard, 2004 .-- 304s.
7. Pimenov A.V., Goncharov O.V. Biology manual for university applicants: Electronic textbook. Scientific editor Gorokhovskaya E.A.
8. Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers .: Sara-tov, Lyceum Publishing House, 2005.
9. Taylor D. Biology / D. Taylor, N. Green, W. Stout. - M.: Mir, 2004. - Vol. 1. - 454p.
10. Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for university entrants. T.2. - M .: LLC "New Wave Publishing House", 1998.
11. www.collegemicrob.narod.ru
12. www.deta-elis.prom.ua

Circulatory system of annelids

The annelids (Annelida) are the most highly organized worms with a whole.

In most species, the circulatory system is closed; it is based on the dorsal and abdominal vessels, connected by annular vessels that resemble arteries and veins. Depending on the type of respiratory pigments, some annelids have red blood, while others have colorless or green blood.

The vessels of the circulatory system carry red blood. The dorsal vessel has the ability to pulsate, that is, contractile movements of the walls and usually drives the blood from back to front.

Ringed worm. Photo: daz smith

Special vessels, covering the intestinal tube and located metamerically in each segment (rings of the body), transfer blood to the abdominal vessel, which is not capable of independent pulsation. The blood moves in it from front to back. In addition to these directions of blood currents, the vessels that carry blood from the spinal vessel to the parapodia are important. These are parapodial vessels. In parapodia, blood vessels acquire the character of capillaries, where blood oxidation occurs, which is in close contact with the oxygen of the external environment. The dorsal vessel reaches the prostomium, the abdominal vessel ends at the level of the pharynx, that is, it is somewhat shorter. The skin is also intensively supplied with capillary blood vessels. At the same time, the intestinal tube and all internal organs, as well as disseminations, are also abundantly irrigated with blood.

Nervous system of annelids

The nervous system is much better developed than in the previously considered types of worms: its ganglia are larger, the trunks are thicker and contain a greater number of nerve cells. Its fine structure, as it was revealed by modern electron microscopic studies, is complex. It should be especially noted that the central nervous system in lower worms is still closely connected with the epidermis, while in ringlets it is completely separated from the outer integument and is isolated from the surrounding tissues by well-developed outer membranes, which greatly improves its work.

The central part of the typical nervous system of the annulus consists of the cerebral ganglion (brain), lying on the dorsal side of the anterior end of the body above the pharynx, two periopharyngeal trunks (connectives) extending from the brain, which pass to the ventral side, where they join and form the suboesophageal ganglion. The abdominal chain departs from the latter, forming a ganglion in each segment (more often in the middle part of it), which explains the name given to it.

In lower species, there are two types of cephalic ganglia, from each of which a thin trunk with small ganglia in each segment extends along the ventral side to the posterior end of the body. Both shafts are connected by transverse bridges. This system is called the ladder nervous system. The latter is less centralized, simpler in fine structure, and to some extent similar to the nervous systems of the lower worms. The foregoing allows us to conclude that the typical central nervous system of annulus developed in the process of evolution from the ladder system.

Each ganglion of the abdominal chain innervates the organs of the segment in which it is located, and coordinates their work. The cephalic ganglion, periopharyngeal connectives and the suboesophageal ganglion innervate the sensory organs, parts of the digestive and other systems located in the anterior part of the body. It should be especially noted that the head ganglion through the rest of the central nervous system (periopharyngeal connectives, suboesophageal ganglion and abdominal chain) coordinates the work of all parts of the body of the worms, and this brain function is much more pronounced in annelids than in lower worms. However, due to the relative independence of the metameric ganglia, the parts of the annulus body, separated from the prostomium, retain motor and other functions for quite a long time.

Ringed worms. Photo: Jacob Levine

Many rings in the abdominal chain have long, thick fibers formed by the process of one nerve cell or the processes of several nerve cells. These fibers, often called giant fibers, facilitate the rapid conduction of nerve stimuli.

In the central nervous system of the worms under consideration, there are neurosecretory cells that secrete hormones that affect various vital processes (reproduction, development, etc.) of annulus. Similar cells are found in lower-standing animals, but in the latter they are diffusely scattered along the central nervous system, and in higher worms they form clusters.

The sense organs are diverse, most of them are concentrated in the skin of the anterior part of the body. Tactile sensations are perceived by the endings of nerve cells with fine hairs. Organs that respond to various chemical stimuli are usually located in special pits of the prostomium, the most sensitive of them are located near the mouth and play an important role in obtaining food. Light-sensitive cells are scattered throughout the skin. At sea. polychaete ringlets and most leeches have eyes of varying complexity. Some polychaete worms have organs of balance, similar in structure to the corresponding organs of jellyfish and other lower animals. In some species, organs associated with the abdominal chain and performing the same functions as the lateral line organs of fish have been found.

In the supraopharyngeal ganglion, it is planned, but it does not yet become permanent, its division into sections, each of which is associated with certain sensory organs (eyes, chemical receptors, etc.).

The complication of the development of the nervous system of ringlets in comparison with the same systems of the previously considered types of multicellular animals (starting with coelenterates - approx. Site) provides a more active and coordinated work of all systems and organs, more complex behavior, successful development of new habitats.

In the phylogenetic series of annelids, there are groups with well-developed sense organs (polychaete worms). In these animals, three sections are distinguished in the supraesophageal ganglion. The anterior part innervates the tentacles, the middle part innervates the eyes and antennae. Finally, the hindquarters develop in connection with the improvement of the chemical senses.

The developed nervous system and musculature allow ringlets to lead a varied life and use different types of plant and animal food. They are characterized by all types of reflexes, they are capable of conditioned reflex learning and have an associative memory, which allows them to exhibit relatively complex behavior.

The body of which consists of repeating segments, or rings (hence their name - annelids).

General brief characteristics of annelids:

• there is a secondary body cavity (whole);
• the outside of the body is covered with cuticle secreted by the ectoderm.
• there is a circulatory system;
• the nervous system is represented by a paired epopharyngeal ganglion connected by jumpers to the abdominal nerve chain (usually double);
• excretory organs are located in each ring and are formed from the ectoderm, they are equipped with cilia;

Structure

The elongated body of annelids is, as it were, assembled from segment rings, the segments are separated by internal septa; but they are not completely independent, since along the entire body there is a through intestine with oral and anal openings, the abdominal trunk of the nervous system and the trunks of a closed circulatory system. These organ systems, penetrating the septa one after the other, stretch through the entire body of annelids. Each ring-segment has a secondary body cavity (whole). Most of the segments bear outside, on the right and left, two bundles of bristles - organs for movement or fixation in tubes. In leeches, the bristles are secondarily lost.

Secondary body cavity (whole)

The secondary body cavity (whole) is of mesodermal origin. It is surrounded by a mesodermal membrane and is filled with fluid. The cavity occupies the space between the walls of the body and the intestinal tube. The main part of the mesoderm lining the secondary cavity is the muscles that make up the body wall. They provide the movement of the animal. In addition, the muscles of the intestinal wall, contracting alternately, push food.

The secondary body cavity performs the following functions:

The secondary body cavity to one degree or another is a characteristic feature for all types of multicellular animals that follow in the evolutionary development, starting with annelids.

Classification

Ringed worms are a numerous types of worms with a more complex body structure in comparison with flat and primary cavity worms. It is divided into three classes: Polychaetae, Girdle (including the subclasses Small-bristled worms and Leeches), Misostomids.

Origin

According to a comparative study of the structure of worms, annelids evolved from primitive whole worms, similar to flat ciliary worms. Important evolutionary acquisitions of annelids are the secondary body cavity (whole), the circulatory system, and the division of the body into separate rings (segments). Polychaetal annelids are the ancestral group of the rest of annelids. From them, during the transition to freshwater and terrestrial life, the small-bristle worms separated. Leeches are descended from small-bristled worms.

On this page material on topics:

• Abstract on the topic annelids short most important

• All about flatworms in brief

• Annel worms report

• A short message about annelids

• Circulatory system... The vessels of the circulatory system carry red blood. The dorsal vessel has the ability to pulsate, that is, contractile movements of the walls and usually drives the blood from back to front.

  Special vessels, covering the intestinal tube and located metamerically in each segment (rings of the body), transfer blood to the abdominal vessel, which is not capable of independent pulsation. The blood moves in it from front to back. In addition to these directions of blood currents, the vessels that carry blood from the spinal vessel to the parapodia are important. These are parapodial vessels. In parapodia, blood vessels acquire the character of capillaries, where blood oxidation occurs, which is in close contact with the oxygen of the external environment. The dorsal vessel reaches the prostatemind, the abdominal vessel ends at the level of the pharynx, that is, it is somewhat shorter. The skin is also intensively supplied with capillary blood vessels. At the same time, the intestinal tube and all internal organs, as well as disseminations, are also abundantly irrigated with blood.

  
  

  :

  1 — nerves to palps. 2 — nerves to the antennae (pyrrus), 3 — the supraopharyngeal ganglion, 4, 5 — the periopharyngeal nerve ring, 6 — the nerves of the abdominal nerve chain, 7. — the beginning of the abdominal nerve chain

  

  ... I - the pharynx and the buccal region are retracted; II - the buccal region is inverted, the pharynx is pushed forward:

  1 - buccal: department, 2 - pharynx

  

  ... The pharynx (1) with large jaws is extended outward

  Respiratory system... The capillaries of the circulatory system of the parapodia and the skin are very important in the respiratory processes of Nereis, while there are no special branchial outgrowths in the species of this genus.

  Excretory system... In Nereis it consists of paired metanephridia. They are absent only in five anterior metameres and three or four posterior ones. Nereis metanephridias are very typical. Each metanephridium consists of a glandular metanephridial body in the form of a sac, pierced by a convoluted nephridial canal. This channel begins even outside the body of metanephridium in the cavity of the corresponding coelomic sac with a funnel, or nephrostomy. The nephrostomy rapidly narrows into a canal, which penetrates the wall of the dissepiment lying in front of it and enters the cavity of the next coelomic sac (anterior to the previous one), where the metanephridium body itself lies. Inside the metanephridial body, the anterior part of the nephridial canal(closest to the nephrostomy) carries thin cilia, which work in concert and drive the fluid in the tube of the nephridial canal forward to the external outlet, i.e. into the external environment. This posterior part of the nephridial canal carries no cilia. The outer opening of the nephridial canal is called the nephrvopore. Thus, the liquid content of metanephridium, penetrating into the nephridial canal from the coelom, is excreted through the nephropore. This is the anatomy of metanephridium. As for its function, it consists in the removal of liquid metabolic products through the nephridial canal, which are partially accumulated in the form of grains in the coelomic cavity.

  According to the classification, ringed worms belong to the group of invertebrates, the type of primorsomes, with a secondary body cavity (whole).

  The type of annelids (or annelids) includes 5 classes: girdle worms (leeches), small-bristled (earthworm), polychaete (nereid, sandworm) worms, misostomids, dinophilids. This type includes about 18 thousand species of worms. Free-living ringlets are common throughout our planet; they live in freshwater and salt water bodies, soil.

  This group includes typical representatives of ringworms - small-bristled worms and leeches. Aeration and loosening of 1 square meter of soil is carried out on average from 50 to 500 rings. The marine forms of annelids, which are found at different depths and throughout the entire territory of the World Ocean, are distinguished by a variety. They play an important role in the food webs of marine ecosystems.

  Ringed worms have been known since the Middle Cambrian.

  It is believed that they descended from the lower flatworms, since certain features of their structure indicate the similarity of these groups of animals. Polychaetal worms are distinguished as the main class of the annelid type. From them later in the course of evolution in connection with the transition to a terrestrial and freshwater way of life, there were few bristles, which gave rise to leeches.

  All annelids have a characteristic structure.

  The main characteristic: their bilaterally symmetrical body can be conditionally divided into a head lobe, a segmented body and a posterior (anal) lobe. The number of trunk segments can range from tens to several hundred. Sizes vary from 0.25 mm to 5 m. At the head end of the rings, there are sensory organs: eyes, olfactory cells and ciliary fossa that react to the action of various chemical stimuli and perceive odors, as well as hearing organs that have a structure similar to locators.

  The senses can also be located on the tentacles. The body of annelids is divided into ring-shaped segments. Each segment in a certain sense is an independent part of the whole organism, since the whole (secondary body cavity) is divided by partitions into segments in accordance with the outer rings.

  Therefore, this type is given such a name - "annelids". The significance of this division of the body is enormous. When damaged, the worm loses the contents of several segments, the rest remain intact, and the animal quickly regenerates.

  Metamerism (segmentation) of internal organs, and, accordingly, organ systems of annelids is due to the segmentation of their bodies. The internal environment of the annulus organism is the coelomic fluid, which fills the whole in the skin-muscular sac, consisting of the cuticle, skin epithelium and two muscle groups - annular and longitudinal. In the body cavity, the biochemical constancy of the internal environment is maintained, and the transport, sexual, excretory, and musculoskeletal functions of the body can be realized.

  In more ancient polychaete worms, each segment of the body has parapodia (paired primitive limbs with bristles). Some types of worms move by contraction of muscles, while others, using parapodia.

  The mouth opening is on the ventral side of the first segment. Digestive system of annelids through.

  The intestine is divided into the anterior, middle and hind colon. The circulatory system of annelids is closed, consists of two main vessels - the dorsal and the abdominal, which are interconnected by annular vessels like arteries and veins. The blood of this type of worm can be of different colors in different species: red, green, or clear. It depends on the chemical structure of the respiratory pigment in the blood. The breathing process is carried out by the entire surface of the worm's body, but some species of worms already have gills.

  The excretory system is represented by paired protonephridia, metanephridia, or myxonephridia (prototypes of the kidneys) present in each segment. The nervous system of annelids includes a large nerve ganglion (the prototype of the brain) and a ventral nerve cord of smaller ganglia in each segment. Most annelids are dioecious, but some have developed hermaphroditism a second time (like an earthworm and leech).

  Fertilization is carried out inside the body or in the external environment.

  The annelids are very important. Their important role in food chains in natural habitats should be noted. On the farm, people began to use marine species of ringlets as a food base for growing valuable commercial fish species, for example, sturgeon.

  The earthworm has long been used as bait in fishing, as food for birds. The benefits of earthworms are immense as they aerate and loosen the soil, which increases crop yields. In medicine, leeches are widely used for hypertension, increased blood clotting, since they secrete a special substance (hirudin), which has the property of reducing blood clotting and expanding blood vessels.

  Related articles:

  Worms
  2. Flatworms
  3. Roundworms
  4. Small bristles

  Features of the structure of annelids

  Ringworms are the most highly organized worms. They are the most progressive type of worm. The features that distinguish this type of worm from other types are the presence of celoma and the metameric structure. Based on this, annelids can be called coelomic animals with a high organization.

  In addition, annelids play a very important role in the biocenosis.

  They are ubiquitous. The most variety is the marine forms of rings. An important role is played by annelids living in the earth and decomposing complex organic compounds.

  Also, rings play an important role not only in the biocenosis of nature, but also for human health. For example, leeches, on which hirudotherapy is based, help to heal patients from rather complex diseases without the use of medicines.

  If we dwell in more detail on the structure of annelids, we can find that some annelids have heightened vision, and the eyes can be located not only on the head, but also on the body, tentacles.

  Also, this type of worm has developed taste sensations, and, based on the research of biological scientists, they have the beginnings of logical thinking. This is because worms can find sharp corners.

  If we consider the internal structure, then we can also note a lot of features that indicate the progressive structure of annelids.

  An example of this is the fact that most annelids are dioecious, only a small part are hermaphrodites. Development with metamorphosis occurs in polychaetal worms and without metamorphosis in small-bristled and leeches.

  The circulatory system of the annelid worm type also has a special structure, because the pumping of blood is carried out by the vessels. In addition, the circulatory system is closed, which in turn also speaks of the progressive features of the structure of annelids.

  Also, the most important difference between annelids and all major types of worms is the appearance of a brain located dorsally above the pharynx.

  Of particular interest is the reproduction of annelids and ways to attract individuals of the opposite sex. One of these ways is glow. Worms use it not only for reproduction, but also for protection. They lure predators to themselves and, with the help of the glow, teach them to eat parts of the body that are unimportant for the worm, which it can easily restore without damage to the body.

  If we consider the classes of worms, some of which are described in detail in the coursework, you can also highlight certain features of each class.

  The most varied in shape and color are polychaete worms, most of which live in the seas.

  Most of them lead a burrowing lifestyle, burrowing into the substrate or attaching to it. Sessile polychaetes and crawling polychaetes are also known. They move through the bristles, which are often brightly colored in all colors of the rainbow.

  When considering the next group, you can also see the structural features associated with the way of life of worms.

  And if in the previous case, polychaetes were characterized by a large number of bristles for swimming and burrowing in silt, then the small bristles are characterized by an unseparated head section, a streamlined body, a small number of bristles, all this is associated with a burrowing lifestyle, because many small bristles live in earth, water and single individuals at sea.

  Leeches have the same adaptations for feeding on the blood of various animals: chitinous serrated plates, a large number of glands that secrete mucus, and the presence in the body of an enzyme that anesthetizes the bite and liquefies the victim's blood.
  Echiurids are sea burrowing worms.

  Their body, unlike all other classes of worms, is not segmented and is often equipped with a proboscis.

  Features of the organization of the Earthworm

  Body structure	The body is elongated, round, segmented. The symmetry is bilateral, the abdominal, dorsal sides of the body, the anterior and posterior ends are distinguished. There is a secondary body cavity lined with epithelium and filled with fluid. Movement with the help of the skin-muscle bag.
  Digestive system	Digestive system - mouth opening pharynx about the esophagus goiter stomach middle intestine posterior intestine anal opening, glands.
  Respiratory system. Circulatory system. Excretory system	The circulatory system is closed and consists of blood vessels. There are larger vessels - hearts that push blood. Blood contains hemoglobin. The cavity fluid provides a connection between the circulatory system and cells. Full body breathing. The excretory system contains a pair of nephridia in each segment.
  Nervous system, sense organs	Nodal type: paired head ganglion, paired periopharyngeal traction connecting with the abdominal. Many annelids have sense organs: eyes, olfactory pits, organs of touch. In dogworms (in connection with the underground way of life), the sense organs are represented by tactile and light-sensitive cells over the entire surface of the body.
  Reproduction	Dissolved or secondary hermaphrodites. Fertilization is cross, internal (in aquatic forms in water). Direct development. Some marine annelids are metamorphosed and have a swimming larva. Capable of regeneration.

  Question 1. What features of ringed worms allowed them to inhabit most of the planet?

  Ringed worms acquired a number of structural and physiological features that allowed them to survive in a variety of environmental conditions.

  Firstly, in annelids, specialized organs of movement appeared, which gave a relative independence from the physical properties of the habitat.

  These are parapodia in polychaetes, which provide movement in the water column and along the bottom, and setae in oligochaetes, which help in movement in the soil.

  Secondly, in annelids, the nervous system and sense organs have reached significant development. That allows you to increase the activity of your lifestyle.

  Thirdly, in annelids, mechanisms are observed that make it possible to tolerate unfavorable environmental conditions.

  For example, diapause is characteristic of soil oligochaetes (see the answer to the question

  2), and some types of leeches are capable of falling into suspended animation (see answer to question 2).

  Question 2. What adaptations do ringed worms have for enduring adverse conditions?

  How does this happen?

  In soil species, in the case of unfavorable conditions, the worms crawl to the depth, curl up into a ball and, having secreted mucus, form a protective capsule, diapause occurs in them - a state in which the processes of metabolism, growth and development slow down.

  Leeches living in cold waters can fall into anabiosis in winter - a state of the organism in which life processes are so slowed down that all visible manifestations of life are absent.

  Question 3.

  What allows scientists to classify polychaetes, oligochaetes and leeches to the same type?

  All of these animals have a number of characteristics that characterize their belonging to one type - annelids. All of them are multicellular animals with an elongated worm-like body, which has bilateral symmetry and consists of separate rings (segmental structure).

  The inner cavity of these worms is divided by partitions into separate segments, inside which there is liquid.

  Searched on this page:

  • What features of annelids allowed them to inhabit most of the planet
  • mucus formation allowing soil worms to tolerate adverse conditions
  • what is common in adaptations to the transfer of unfavorable conditions in protozoa and oligochaetes
  • which allows scientists to classify polychaetes oligochaetes and leeches to the same type
  • what features of annelids allowed them to populate a large

  We invite you to visit the site

  Encyclopedia "Animal Life" (1970)
  

  To the beginning of the encyclopedia

  By the first letter
  BINANDTOHABOUTPRFROMTFU

  TYPE ANNELIDES

  TO annelids belong primary annulus, polychaete and small-bristle worms, leeches and echiurids.

  In the type of annelids, there are about 8 thousand species. These are the most highly organized representatives of the worm group. The sizes of the rings range from fractions of a millimeter to 2.5 m. Mostly these are free-living forms. The ring body is subdivided into three parts: the head, the ring body, and the anal lobe. Such a clear division of the body into sections is not present in animals standing lower in their organization.

  The head of the rings is equipped with various sensory organs.

  Many ringlets have well-developed eyes. Some have particularly keen eyesight and their lens is capable of accommodation. True, the eyes can be located not only on the head, but also on the tentacles, on the body and on the tail. Ringworms also have developed taste sensations. On the head and tentacles, many of them have special olfactory cells and ciliary fossa that perceive various smells and the action of many chemical stimuli.

  Ringworms have well-developed hearing organs, arranged like locators. Recently, in the marine ringlets, echiurids, hearing organs have been opened, very similar to the lateral line organs in fish.

  With the help of these organs, the animal subtly distinguishes the slightest rustles and sounds, which are heard much better in water than in air.

  The body of the rings is made up of rings, or segments. The number of rings can reach several hundred. Other rings consist of only a few segments. Each segment to some extent represents an independent unit of the whole organism.

  Each segment includes parts of vital organ systems.

  Special organs of movement are very characteristic of ringlets. They are located on the sides of each segment and are called parapodia. The word "parapodia" means "like legs." Parapodia are lobe-like outgrowths of the body, from which bundles of bristles protrude outward. In some pelagic polychaetes, the length of the parapodia is equal to the diameter of the body. Parapodia are not developed in all ringlets. They are found in primary annelids and polychaete worms.

  In small bristles, only bristles remain. Primitive leech acantobedella has bristles. The rest of the leeches do without parapodia and setae in motion. Have echiurid no parapodia, and setae only at the posterior end of the body.

  Parapodia, nodes of the nervous system, excretory organs, sex glands and, in some polychaetes, paired intestinal pockets are systematically repeated in each segment. This internal segmentation coincides with the external annulus. The multiple repetition of body segments is called the Greek word "metamerism".

  Metamerism arose in the course of evolution in connection with the elongation of the body of the ancestors of ringlets. The lengthening of the body necessitated multiple repetitions, first of the organs of movement with their muscles and nervous system, and then of the internal organs.

  

  The segmented secondary body cavity, or the whole, is extremely characteristic of annulus. This cavity is located between the intestines and the body wall. The body cavity is lined with a continuous layer of epithelial cells, or cellothelium.

  These cells form the layer that covers the intestines, muscles, and all other internal organs. The body cavity is divided into segments by transverse septa - disseminations. A longitudinal septum - mesentery passes along the midline of the body, which divides each compartment of the cavity into the right and left parts.

  The body cavity is filled with liquid, which in its chemical composition is very close to sea water. The fluid filling the body cavity is in continuous motion. The body cavity and cavity fluid perform important functions. The cavity fluid (like any fluid in general) is not compressed and therefore serves as a good "hydraulic skeleton".

  By the movement of the cavity fluid, various nutritious products, secretions from the endocrine glands, as well as oxygen and carbon dioxide, which are involved in the process of respiration, can be transported inside the body of the rings.

  Internal partitions protect the body in case of severe injuries and ruptures of the body wall.

  For example, an earthworm that is cut in half does not die. The septa prevent the fluid from flowing out of the body. The inner partitions of the rings, thus, protect them from death. Naval ships and submarines also have internal hermetic partitions. If the board is punctured, then the water poured into the hole fills only one damaged compartment. The rest of the compartments, not flooded with water, retain the buoyancy of the damaged ship.

  Likewise, in ringlets, the violation of one segment of their body does not entail the death of the entire animal. But not all annelids have well-developed septa in the body cavity. For example, in echiurids, the body cavity does not have partitions. A puncture of the wall of the echiurida's body can lead to her death.

  In addition to the respiratory and protective role, the secondary cavity serves as a receptacle for reproductive products, which mature there before being excreted.

  Rings, with few exceptions, have a circulatory system. However, they have no heart. The walls of large vessels contract themselves and push blood through the thinnest capillaries.

  In leeches, the functions of the circulatory system and the secondary cavity coincide so much that these two systems are combined into a single network of gaps through which blood flows. Some ringlets have colorless blood, while others have a green pigment called chlorocruorin. Often the rings have red blood, similar in composition to that of vertebrates.

  Red blood contains iron, which is part of the pigment in hemoglobin. Some rings, burrowing into the ground, experience an acute oxygen deficiency.

  Therefore, their blood is adapted to bind oxygen especially intensively. For example, the polychaete Magelona papillicornis has a developed pigment hemerythrin, which contains five times more iron than hemoglobin.

  In ringlets, in comparison with lower invertebrates, metabolism and respiration proceed much more intensively. Some polychaete ringlets develop special respiratory organs - gills. In the gills, a network of blood vessels branches out, and through their wall oxygen enters the bloodstream, and then is carried throughout the body.

  The gills can be located on the head, on the parapodia and on the tail.

  The annular pass-through intestine consists of several sections. Each section of the intestine has its own specific function. The mouth leads to the throat. Some ringlets have strong horny jaws and denticles in the pharynx, which help to grip live prey more tightly. In many predatory ringlets, the pharynx is a powerful weapon of attack and defense.

  The esophagus follows the pharynx. This section is often equipped with a muscular wall. Peristaltic muscle movements slowly push food into the following sections. In the wall of the esophagus there are glands, the enzyme of which is used for the primary processing of food.

  The midgut follows the esophagus. In some cases, goiter and stomach are developed. The midgut wall is formed by the epithelium, which is very rich in glandular cells, which produce a digestive enzyme. Other cells in the midgut absorb the digested food. In some rings, the midgut is in the form of a straight tube, in others it is curved in loops, while others have metameric outgrowths on the sides of the intestine.

  The hind gut ends with the anus.

  Special organs - metanephridia - are used to excrete liquid metabolic products. Often they serve to bring out the germ cells - sperm and eggs. Metanephridia begins with a funnel in the body cavity; from the funnel there is a convoluted channel, which opens outward in the next segment.

  Each segment contains two metanephridia.

  Rings reproduce asexually and sexually. Asexual reproduction is common in aquatic ringlets. At the same time, their long body breaks up into several parts. After a while, each part rebuilds the head and tail.

  Sometimes a head with eyes, tentacles, and a brain forms in the middle of the worm's body even before it splits. In this case, the separated parts already have a head with all the necessary sense organs. Polychaetes and oligochaetes are relatively good at restoring lost body parts. Such ability is not possessed by leeches and echiurids. These rings have lost their segmented body cavity. This is partly why, apparently, they lack the ability to reproduce asexually and restore lost parts.

  Fertilization of eggs in marine rings occurs most often outside the body of the mother's body. In this case, males and females simultaneously eject sex cells into the water, where fertilization takes place.

  In marine polychaete ringlets and echiurids, crushing of fertilized eggs leads to the development of a larva, which is not at all similar to adult animals and is called trochophora.

  Trochophora lives for a short time in the surface layers of water, and then settles to the bottom and gradually turns into an adult organism.

  Freshwater and terrestrial rings are most often hermaphrodites and have a direct development.

  There is no free larva in freshwater and terrestrial rings. This is due to the fact that fresh water has a completely different salt composition than sea water. For the development of life, sea water is more favorable. Fresh water even contains some poisonous pones (for example, magnesium) and is less suitable for the development of organisms.

  Therefore, the development of freshwater animals almost always occurs under the cover of special low-permeable shells. Even denser shells - shells - are formed in the eggs of ground rings.

  The dense shells here protect the eggs from mechanical damage and from drying out under the scorching rays of the sun.

  The practical importance of annelids is growing more and more in connection with the development of the intensity of biological research.

  In the USSR, for the first time in the history of world science, acclimatization of some invertebrates has been carried out to strengthen the food supply of the sea. For example, the polychaete Nereis, acclimatized in the Caspian Sea, has become the most important food item for sturgeon and other fish.

  Earthworms not only serve as bait for fishing and food for birds.

  They bring great benefits to humans, loosening the soil, making it more porous. This promotes free penetration of air and water to the plant roots and increases crop yields.

  Digging in the ground, the worms swallow pieces of soil, grind them and throw them on the surface well mixed with organic matter. The amount of soil carried to the surface by worms is amazingly large. If you spread the soil over the entire surface of the land, plowed by earthworms every 10 years, you would get a layer of fertile land 5 cm thick.

  Leeches are used in medical practice for hypertensive diseases and the threat of hemorrhage.

  They let the substance hirudin into the blood, which prevents blood clotting and promotes the expansion of blood vessels.

  Ring type includes several classes. The most primitive are marine primary rings - archiannelids.

  Polychaetae and echiurids - the inhabitants of the sea. Small bristle rings and leeches - mainly inhabitants of fresh water and soil.

  To the beginning of the encyclopedia