Animals; the most highly organized among all worms. For the first time, they have a set of organ systems characteristic of all higher groups of organisms, including mammals. Length from 2-3 mm to 3 m. The cylindrical or flattened body of annelids, as a rule, is clearly segmented. At the same time, partitions are formed in the body cavity, dividing it into separate segments. External and internal segmentation most often coincide, but sometimes only one internal segment corresponds to several external segments. More rarely, there is no segmentation. The first segment of the body is the head lobe, on which sensory organs can be located: antennae, palps, eyes.
The mouth opens on the lower surface of the second body segment. In polychaete worms, powerful chitinous jaws are formed in the oral cavity, capable of turning outward. They serve to capture and hold prey. In leeches, the mouth opening is surrounded by a sucker formed by the fusion of the first four segments. On the last segment of the body, the anus opens. On the sides of all segments, except the first and last, paired outgrowths develop - parapodia, which act as organs of locomotion. In oligochaete worms and some leeches they are modified into small bristles, which less often may be completely absent.
Annelids are three-layered animals that develop ectoderm, endoderm and mesoderm. From the latter, a secondary body cavity (coelom) is formed, filled with cavity fluid. Due to the fact that the fluid is under pressure, annelids maintain a constant body shape. In addition, the whole acts as the internal environment of the body, maintaining a constant biochemical regime. Annelids have a well-developed skin-muscle sac, consisting of skin epithelium and underlying circular and longitudinal muscles. Thanks to him, worms are able to perform a variety of movements.
The digestive system of annelids is continuous and consists of three sections: the foregut, midgut and hindgut. The anterior and posterior sections of the intestine develop from the ectoderm, and the middle section from the endoderm. Some species have paired salivary glands. The vast majority of annelids have a closed circulatory system. Only in some leeches it becomes open again, and in sipunculids it is absent. Paired ciliated funnels, which are repeated many times in each segment of the body, function as excretory organs in annelids. In this case, the funnel itself is located in one segment, and the excretory channel, passing through the partition between the segments, opens with an excretory opening on the side of the next segment of the body. The nervous system is represented by the peripharyngeal ring and the ventral nerve cord extending from it. On it, in each segment of the body, paired ganglia are located. Annelids are generally dioecious, but some species exhibit hermaphroditism. Development with metamorphosis, or direct.
About 12 thousand species, divided into 6 classes: primary rings,
Ringed worms live in fresh waters, seas, and soil. The body consists of ringed segments. About 9 thousand of their species are known, they are distinguished:
Class Polychaetes
Class Oligochaetes
Class oligochaetes
In annelids, for the first time, the body was divided into - round rings - segments.The body consists of a head lobe, a torso divided into separate segments, from 5 to 600 pieces, and an anal lobe. The skin-muscular sac consists of epithelium, which secretes outward the cuticle and abundant mucus and muscle fibers: circular and longitudinal, thanks to which the body is able to contract and lengthen. The body segments bear paired tufts of setae on their sides. In sexually mature individuals, a thickening appears in the anterior part of the body - a glandular girdle.
For the first time, the secondary body cavity appears - as a whole, it has its own walls of epithelium, filled with cavity fluid and divided by transverse partitions into segments. In general, it performs the functions of the internal skeleton, transports nutrients, and delivers metabolic products to the excretory organs.
Digestive system:
Mouth, located on the anterior segment of the body
Muscular throat
Esophagus
Goiter - an enlarged part of the esophagus
Stomach
The intestine ends with the anus located on the anal lobe.
Breathing is carried out through the covers of the body.
The excretory organs are metanephridia, of which there are two in each segment. They look like a funnel, the expanded end of which opens into a cavity. It is lined with ciliated epithelium and a convoluted tubule extends from it, ending in an excretory pore.
The circulatory system appears for the first time closed, no heart. Consists of the main blood vessels:
Dorsal (blood flows from the back end of the body to the front)
Abdominal (blood flows in the opposite direction)
They are connected to each other in each segment by annular vessels. The function of the heart is performed by thickened annular vessels located in segments 7-13. Capillaries form a dense plexus around the intestines (nutrition) and under the skin (gas exchange). 
The nervous system consists of:
Peripharyngeal nerve ring (suprapharyngeal and subpharyngeal nerve nodes connected by nerve cords).
The abdominal nerve chain (departs from the subpharyngeal nerve ganglion) with two close nodes in each segment, from which nerves extend to the tissues of the animal. 
The sense organs are well developed, with the exception of burrowing forms, which are located at the anterior end of the body (cephalization). These are touch, chemical sensitivity, light sensitivity.
The increasing complexity of the development of ringlets ensures more active and coordinated work of all systems and organs of the body, divided into segments, more complex behavior, and the successful development of new habitats.
Reproduction is asexual (fragmentation) and sexual. There are both dioecious and hermaphroditic species. Fertilization is external, development is direct or indirect.
Earthworm lives in soils rich in humus. The body has an elongated cylindrical shape and consists of 140-180 segments. The circular and longitudinal muscles of the worm's musculocutaneous sac act as antagonists and ensure movement and digging of burrows. The skin glands secrete a lot of mucus, which facilitates movement and ensures gas exchange.
It feeds on rotted plant debris, swallowing it along with the soil using its muscular pharynx. The ducts of calcareous glands flow into the esophagus, secreting substances that neutralize soil acids. In the goiter, food swells and carbohydrates are broken down under the influence of enzymes. In the muscular stomach, additional grinding of food occurs. The dorsal side of the midgut forms an invagination - typhlosol, which increases the absorptive surface of the intestine.
Earthworms are hermaphrodites; the gonads are located in several anterior segments of the body. External cross fertilization. The two worms exchange sperm, which flows into the partner's seminal receptacle. Eggs and sperm are released into the mucous membrane and fertilization occurs. The ends of the muff close, forming a cocoon, inside which the worms develop (direct development).
Earthworms have a high ability to regenerate.
Oligochaete worms, in particular earthworms, play a huge role in soil formation. They mix the soil, reduce its acidity, and increase fertility. Aquatic worms contribute to the self-purification of water bodies and serve as food for fish.
Class polychaetes
Most of them live in the seas; there are bottom-dwelling (sand-living) and free-living forms (nereids). On the sides of the body segment there is a pair of motor appendages with tufts of setae - parapodia. At the anterior end of the body there are sensory organs: various tentacles, eyes, olfactory pits. Many breathe using gills connected to parapodia. Most are dioecious. Fertilization of eggs occurs in water, development with transformation (there is a larva - trochophore).
Polychaete worms serve as food for fish, crustaceans, seabirds and mammals (an important link in food chains).
In annelids, according to modern scientific ideas, for the first time a body appeared, divided into sections. This feature was consolidated and further developed. From annelids came the following types:
Phylum Arthropod
Type Shellfish
Phylum Chordata.
Type of shellfish (soft-bodied) .
130 thousand species. Mollusks are predominantly marine animals; freshwater and terrestrial animals are rarely found. All mollusks have a bilaterally symmetrical body, soft, undifferentiated. Gastropods have asymmetry.
Main features of the structure:
- exoskeleton - shell.
- Heart and open circulatory system.
The body is not segmented and consists, as a rule, of the head, torso and legs. The body is surrounded by a large fold of skin - the mantle, which externalizes the shell.
Between the mantle and the body wall, a mantle plane is formed, into which the ducts of the digestive, excretory, and reproductive systems open. The musculature is represented by muscles, some of which are attached to the shell. The secondary cavity loses its supporting function and disintegrates. All that remains is the pericardial sac. The spaces between organs in the body of mollusks are filled with connective tissue.
The digestive system contains:
- The pharynx, the ducts of the salivary glands or grater open into it
- Esophagus (often dilated into a goiter)
- The stomach into which the liver ducts open
- Intestines
- The anus opens into the mantle cavity.
Breathing occurs through both gills and lungs.
The excretory organs of mollusks are the kidneys.
The heart consists of 1 or 2 atria and a muscular ventricle.
The nervous system is a scattered nodular type, consisting of several pairs of nerve ganglia from which nerves extend to various organs of the body. The nerve nodes are connected to each other by nerve trunks.
Sense organs are well developed in mollusks that lead an active lifestyle. There are quite complex eyes, organs of touch, chemical sense and balance. They reproduce only sexually; there are both hermaphrodites and dioecious ones. Development is direct or with metamorphosis.
Class Gastropods (snails).
Gastropods are the most numerous class of mollusks. They live in seas, fresh water bodies, and on land.
The body is enclosed in a solid shell in the form of a spiral. They have an asymmetrical body structure and spirals.
Great pond snail lives in stagnant fresh water bodies on plants.
The body is divided into head, torso and leg. The spirally twisted shell of the pond snail has a sharp top and holes - mouths. On the head there is a mouth, two movable tentacles - organs of touch, at the base of which there are eyes. The large foot has a flat, crawling sole. The digestive system includes the mouth (tongue with chitinous grater teeth or radula), pharynx, salivary glands, esophagus, stomach, intestines, liver, the duct of which opens into the stomach). The pond snail feeds on aquatic plants, which it scrapes with a grater.
Pond snails breathe with their lungs 7-9 times per hour, rising to the surface of the water and exposing the breathing hole outward.
The circulatory system is not closed. The heart is on the dorsal side, consists of both the atrium and the ventricle, the blood is colorless.
The excretory organ is the kidney with the ureter.
The nervous system is formed by five pairs of nerve ganglia, from which nerves extend to the organs and tissues of the body.
The snail is hermaphrodite. In one gonad, an egg and a sperm are simultaneously formed. Fertilization is internal, cross. Development is direct.
Class bivalve .
They live only in aquatic environments. The body is bilaterally symmetrical, the shell has two valves, and there is no head.
The toothless fish lives at the bottom of fresh water bodies, crawls with the help of its legs, burying its front blunt end into the ground, and its pointed rear end outward. The toothless body is located in the dorsal part of the shell and consists of a torso, legs, and head (sensory organs, pharynx, grater). The shell valves are connected by a ligament on the dorsal side and two special muscles - closures, which pass through the body of the animal. The toothless one lacks the tooth (“lock”) that others have. The mantle folds are adjacent to the shell valves; between them and the body there is a mantle cavity, in which there are two large gills, a mouth surrounded by oral lobes, and a leg. At the back, the mantle folds are closely pressed to each other, but two openings remain between them - chevrons:
1. bottom - water enters
2. upper - water comes out.
The current is created by cilia lining the mantle cavity and gills.
According to the type of nutrition of the toothless, the biofilter, protozoa, crustaceans, etc. enter the mantle cavity with a current of water and settle on the mucus secreted by the gills. It enters the mouth and further into the digestive system: oral lobes, mouth, esophagus, stomach, intestines, anus opens in the mantle cavity at the upper chevron. There is a digestive gland - the liver, the duct of which opens into the stomach. They breathe with gills.
The circulatory system is not closed (suction effect of the heart). The heart is located on the dorsal side of the body and consists of two atria and a ventricle.
Excretory system - two large kidneys on the sides of the heart and ureters.
The nervous system consists of three pairs of nerve ganglia:
· Above the esophagus
· Next to the posterior muscle - the closure muscle.
Sense organs are poorly developed.
The significance of bivalve mollusks is very diverse: the shells of freshwater pearl oysters are used to obtain mother-of-pearl. They are biofilters - this is their biological role.
Mussels, oysters, and scallops are eaten.
Bivalves are an important link in the food chain.
Class Cephalopods
Cephalopods are the most highly organized class among mollusks. These are octopuses, cuttlefish, squids, and there are also small forms. The body of cephalopods is bilaterally symmetrical, with a division into the head and torso; in primitive forms the shell is external, multi-chambered, in higher representatives it is internal and underdeveloped. Higher cephalopods have 8 tentacles equipped with suckers. Cephalopods are very mobile and use a reactive method of locomotion. A special adaptation of cephalopods is the ink gland. This “ink” is poisonous and paralyzes the olfactory organs of predators.
Annelids, a very large group, are the evolutionary descendants of flatworms. The most studied of them are polychaete worms living in the seas - polychaetes and oligochaete worms - Oligochaetes. The most famous representatives of oligochaetes are the earthworm and the leech. A characteristic feature of the structure of annelids is external and internal metamerism: their body consists of several, mostly identical, segments, each of which contains a set of internal organs, in particular a pair of symmetrically located ganglia with nerve commissures. As a result, the nervous system of annelids has the appearance of a “nervous ladder.”
A special place is occupied by representatives of the class of oligochaetes - earthworms, on which the main experiments were carried out related to the study of their reactions to various environmental agents and the development of conditioned reflexes. The nervous system of earthworms is presented in the form of nerve nodes - ganglia, located along the entire body in the form of a symmetrical chain. Each node consists of pear-shaped cells and a dense plexus of nerve fibers. Motor nerve fibers extend from these cells to the muscles and internal organs. Under the skin of the worm there are sensitive cells that are connected by their processes - sensory fibers - to the nerve ganglia. This type of nervous system is called chain, or ganglionic. The body of an earthworm consists of a number of segments. Each segment has its own nerve node and can respond to stimulation, being completely separated from the rest of the body, but all nodes are interconnected by jumpers, and the body acts as a single whole. The head node of the nervous system, located in the upper part of the head, receives and processes the greatest amount of irritation. It is much more complex than all other nodes of the worm's nervous system.
Movements of annelids
The motor activity of annelids is highly diverse and quite complex. This is ensured by highly developed muscles, consisting of two layers: the outer layer, consisting of circular fibers, and the inner layer, made of powerful longitudinal muscles. The latter extend, despite segmentation, from the anterior to the posterior end of the body. Rhythmic contractions of the longitudinal and circular muscles of the musculocutaneous sac provide movement. The worm crawls, stretching and contracting, expanding and contracting individual parts of its body. In an earthworm, the front part of the body elongates and narrows, then the same thing happens sequentially with the following segments. As a result, “waves” of muscle contractions and relaxations run through the worm’s body.
For the first time in the evolution of the animal world, annelids have genuine paired limbs: each segment has a pair of outgrowths called parapodia. They serve as organs of locomotion and are equipped with special muscles that move them forward or backward. Often parapodia have a branched structure. Each branch is equipped with a supporting seta and, in addition, a corolla of setae, which have different shapes in different species. Tentacle-shaped organs of tactile and chemical sensitivity also extend from the parapodia. The latter are especially long and numerous at the head end, where the eyes (one or two pairs) are located on the dorsal side, and the jaws are located in the oral cavity or on a special protruding proboscis. Thread-like tentacles at the head end of the worm may also participate in the capture of food objects.
Annelid behavior
Annelids live in seas and freshwater bodies, but some also lead a terrestrial lifestyle, crawling along the substrate or burrowing in loose soil. Marine worms are partly carried passively by water currents as part of plankton, but the majority of them lead a bottom-dwelling lifestyle in coastal zones, where they settle among colonies of other marine organisms or in rock crevices. Many species live temporarily or permanently in tubes, which in the first case are periodically abandoned by their inhabitants and then found again. Particularly predatory species regularly leave these refuges to “hunt”. The tubes are built from grains of sand and other small particles, which are held together by the secretions of special glands, thereby achieving greater strength of the buildings. Animals sitting motionless in tubes catch their prey (small organisms) by pushing and filtering water with the help of a corolla of tentacles that protrudes from the tube, or by driving a stream of water through it (in this case, the tube is open at both ends).
In contrast to sessile forms, free-living worms actively search for their food, moving along the seabed: predatory species attack other worms, mollusks, crustaceans and other relatively large animals, which they grab with their jaws and swallow; herbivores tear off pieces of algae with their jaws; other worms (the majority of them) crawl and rummage in the bottom mud, swallow it along with organic remains or collect small living and dead organisms from the bottom surface.
Oligochaete worms crawl and burrow in soft soil or bottom silt; some species are able to swim. In tropical rainforests, some oligochaetes even crawl onto trees. The bulk of oligochaete worms feed on deuterium, sucking up slimy silt or gnawing through the soil. But there are also species that eat small organisms from the surface of the ground, filter water or bite off pieces of plants. Several species lead a predatory lifestyle and capture small aquatic animals by sharply opening the mouth. As a result, the prey is sucked in with the flow of water.
Leeches swim well, making wave-like movements with their bodies, crawl, dig tunnels in soft soil, and some move on land. In addition to blood-sucking leeches, there are also leeches that attack aquatic invertebrates and swallow them whole. Terrestrial leeches that live in tropical rainforests lie in wait for their victims on land, in the grass or on the branches of trees and shrubs. They can move quite quickly. In the movement of terrestrial leeches along the substrate, suckers play an important role: the animal extends its body, then sticks to the substrate with the head sucker and pulls the rear end of the body to it, simultaneously contracting it, then sucks itself with the rear sucker, etc.
Experimental study of the behavior of annelids
Earthworms or earthworms are widespread throughout the globe. These animals play a huge role in soil formation, so they have long attracted the close attention of scientists of various profiles. Their behavior has also been studied quite well. Thus, the life activity of earthworms was described in detail by Charles Darwin. During his experiments, it turned out that they react differently to visual, tactile, olfactory and temperature stimuli. R. Yerkes and a number of other scientists studied the ability of earthworms to form simple skills. For this purpose, the method of developing defensive conditioned reactions in the T-shaped maze. The worms were trained to turn into the right or left arm of the maze. The unconditioned stimulus was an alternating current of varying intensity, and the conditioned stimulus was the maze itself, the elements of which were probably perceived by proprioceptive and tactile afferentation. The criterion for the development of the reflex was an increase in the number of turns into the arm of the maze, where the animals were not subjected to electrical stimulation. In the experiments of R. Yerkes, worms learned to correctly choose a side after 80–100 combinations (Fig. 15.3).
The presence of sensory organs helps earthworms distinguish between the simplest forms. So, in the process of storing food, they grab double pine needles by the base, and fallen leaves by the tops, by which they pull them into their burrow.
Even clearer conditioned reflexes manages to produce polychaete worms - polychaetes. Yes, y Nereis managed to develop stable conditioned reflexes to tactile stimulation, food, light and vibration. Analysis of the results showed that polychaetes develop reactions that have all the basic properties of true conditioned reflexes: an increase in the number of positive responses from experiment to experiment, a high maximum percentage of positive reactions (up to 80– 100) and the duration of their storage (up to 6–15 days).
It is very significant that the developed reaction faded away in the absence of reinforcement and was restored spontaneously.
Rice. 15.3
The revealed patterns of conditioned reflex activity of polychaetes correlate with the relatively differentiated brain of animals. Thus, true conditioned reflexes, as one of the sufficiently perfect mechanisms that determine acquired behavior, apparently appear for the first time in evolution in annelids.
- Tushmalova N. A. Basic patterns of the evolution of invertebrate behavior.
The type of annelids, uniting about 12,000 species, represents, as it were, a node in the family tree of the animal world. According to existing theories, annelids originate from ancient ciliated worms (turbellar theory) or from forms close to ctenophores (trochophore theory). In turn, arthropods arose from annelids in the process of progressive evolution. Finally, in their origin, annelids are related by a common ancestor to mollusks. All this shows the great importance that the type under consideration has for understanding the phylogeny of the animal world. From a medical point of view, annelids are of limited importance. Only leeches are of particular interest.
General characteristics of the type
The body of annelids consists of a head lobe, a segmented body and a posterior lobe. Segments of the body throughout almost the entire body have external appendages similar to each other and a similar internal structure. Thus, the organization of annelids is characterized by repeatability of structure, or metamerism.
On the sides of the body, each segment usually has external appendages in the form of muscular outgrowths equipped with bristles - parapodia - or in the form of bristles. These appendages are important in the movement of the worm. Parapodia in the process of phylogenesis gave rise to the limbs of arthropods. At the head end of the body there are special appendages - tentacles and sticks.
A developed skin-muscular sac consists of a cuticle, an underlying layer of skin cells and several layers of muscles (see Table 1) and a secondary body cavity, or whole, in which the internal organs are located. The coelom is lined with peritoneal epithelium and divided by septa into separate chambers. Moreover, in each body segment there is a pair of coelomic sacs (only the head and posterior lobes are devoid of coelom).
The coelomic sacs in each segment are located between the intestine and the body wall, they are filled with a watery fluid in which amoeboid cells float.
Overall it performs a supporting function. In addition, nutrients enter the coelomic fluid from the intestines, which are then distributed throughout the body. In the whole, harmful metabolic products accumulate, which are removed by the excretory organs. Male and female gonads develop in the walls of the coelom.
The central nervous system is represented by the suprapharyngeal ganglion and the ventral nerve cord. Nerves from the sensory organs pass to the suprapharyngeal node: eyes, balance organs, tentacles and palps. The abdominal nerve cord consists of nodes (one pair in each body segment) and trunks connecting the nodes to each other. Each node innervates all organs of a given segment.
The digestive system consists of the foregut, middle and hindgut. The foregut is usually divided into a number of sections: the pharynx, esophagus, crop and gizzard. The mouth is located on the ventral side of the first body segment. The hindgut opens with the anus on the posterior lobe. The intestinal wall contains muscles that move food along.
The excretory organs - metanephridia - are paired tubular organs, metamerically repeated in body segments. Unlike protonephridia, they have a through excretory canaliculus. The latter begins with a funnel that opens into the body cavity. Cavity fluid enters the nephridium through the funnel. A tubule of nephridium extends from the funnel, sometimes opening outward. Passing through the tubule, the liquid changes its composition; the final products of dissimilation are concentrated in it, which are released from the body through the external pore of nephridium.
For the first time in the phylogenesis of the animal world, annelids have a circulatory system. The main blood vessels run along the dorsal and ventral sides. In the anterior segments they are connected by transverse vessels. The dorsal and anterior annular vessels are capable of contracting rhythmically and perform the function of the heart. In most species, the circulatory system is closed: blood circulates through a system of vessels, nowhere interrupted by cavities, lacunae or sinuses. In some species the blood is colorless, in others it is red due to the presence of hemoglobin.
Most species of annelids breathe through skin rich in blood capillaries. A number of marine forms have specialized respiratory organs - gills. They usually develop on the parapodia or palps. Vessels carrying venous blood approach the gills; it is saturated with oxygen and enters the body of the worm in the form of arterial blood. Among annelids there are dioecious and hermaphroditic species. The gonads are located in the body cavity.
Annelids have the highest organization compared to other types of worms (see Table 1); For the first time, they have a secondary body cavity, a circulatory system, respiratory organs, and a more highly organized nervous system.
| Table 1. Characteristics of different types of worms | ||||||
| Type | Skin-muscle bag | Digestive system | Circulatory system | Reproductive system | Nervous system | Body cavity |
| Flatworms | Includes layers of longitudinal and circular muscles, as well as bundles of dorso-abdominal and diagonal muscles | From the ectodermal foregut and endodermal midgut | Not developed | Hermaphrodite | Paired brain ganglion and several pairs of nerve trunks | Absent, filled with parenchyma |
| Roundworms | Only longitudinal muscles | From the ectodermal anterior and posterior gut and the endodermal midgut | Same | Dioecious | Peripharyngeal nerve ring and 6 longitudinal trunks | Primary |
| From the external circular and internal longitudinal muscles | From the ectodermal foregut and hindgut and the endodermal midgut | Well developed, closed | Dioecious or hermaphrodite | Paired medullary ganglion, peripharyngeal nerve ring, ventral nerve cord | Secondary | |
|
Animals belonging to the type of annelids, or ringworms, are characterized by:
Annelids live in fresh and marine waters, as well as in soil. Several species live in the air. The main classes of the annelid phylum are:
Class polychaete ringletsFrom the point of view of phylogeny of the animal world, polychaetes are the most important group of annelids, since their progressive development is associated with the emergence of higher groups of invertebrates. The body of polychaetes is segmented. There are parapodia consisting of dorsal and ventral branches, each of which carries an antennae. The muscular wall of the parapodia contains thick supporting setae, and tufts of thin setae protrude from the apex of both branches. The function of parapodia is different. Typically these are locomotor organs involved in the movement of the worm. Sometimes the dorsal barbel grows and turns into a gill. The circulatory system of polychaetes is well developed and always closed. There are species with cutaneous and gill respiration. Polychaetes are dioecious worms. They live in the seas, mainly in the coastal zone. A typical representative of the class is the Nereid (Nereis pelagica). It is found in abundance in the seas of our country; leads a bottom lifestyle, being a predator, it captures prey with its jaws. Another representative, the sandbill (Arenicola marina), lives in the seas and digs holes. It feeds by passing sea mud through its digestive tract. Breathes through gills. Class oligochaete ringletsOligochaetes originate from polychaetes. The external appendages of the body are setae, which sit directly in the body wall; no parapodia. The circulatory system is closed; skin breathing. Oligochaete ringlets are hermaphrodites. The vast majority of species are inhabitants of fresh water and soil. A typical representative of the class is the earthworm (Lumbricus terrestris). Earthworms live in soil; During the day they sit in holes, and in the evening they often crawl out. Rummaging in the soil, they pass it through their intestines and feed on the plant debris contained in it. Earthworms play a large role in soil-forming processes; they loosen the soil and promote its aeration; they drag leaves into holes, enriching the soil with organic matter; deep layers of soil are removed to the surface, and surface layers are carried deeper. The structure and reproduction of an earthworm The earthworm has an almost round body in cross section, up to 30 cm long; have 100-180 segments or segments. In the anterior third of the earthworm's body there is a thickening - the girdle (its cells function during the period of sexual reproduction and egg laying). On the sides of each segment there are two pairs of short elastic setae, which help the animal when moving in the soil. The body is reddish-brown in color, lighter on the flat ventral side and darker on the convex dorsal side. A characteristic feature of the internal structure is that earthworms have developed real tissues. The outside of the body is covered with a layer of ectoderm, the cells of which form the integumentary tissue. The skin epithelium is rich in mucous glandular cells. Under the skin there is a well-developed muscle, consisting of a layer of circular muscles and a more powerful layer of longitudinal muscles located under it. When the circular muscles contract, the animal’s body elongates and becomes thinner; when the longitudinal muscles contract, it thickens and pushes the soil particles apart.
The digestive system begins at the front end of the body with the mouth opening, from which food enters sequentially into the pharynx and esophagus (in earthworms, three pairs of calcareous glands flow into it, the lime coming from them into the esophagus serves to neutralize the acids of rotting leaves on which the animals feed). Then the food passes into the enlarged crop, and a small muscular stomach (the muscles in its walls help grind the food). The midgut stretches from the stomach almost to the posterior end of the body, in which, under the action of enzymes, food is digested and absorbed. Undigested remains enter the short hindgut and are thrown out through the anus. Earthworms feed on half-rotten remains of plants, which they swallow along with the soil. As it passes through the intestines, the soil mixes well with organic matter. Earthworm excrement contains five times more nitrogen, seven times more phosphorus and eleven times more potassium than regular soil. The circulatory system is closed and consists of blood vessels. The dorsal vessel stretches along the entire body above the intestines, and below it - the abdominal vessel. In each segment they are united by a ring vessel. In the anterior segments, some annular vessels are thickened, their walls contract and pulsate rhythmically, thanks to which blood is driven from the dorsal vessel to the abdominal one. The red color of blood is due to the presence of hemoglobin in the plasma. Most annelids, including earthworms, are characterized by cutaneous respiration; almost all gas exchange is provided by the surface of the body, therefore earthworms are very sensitive to soil moisture and are not found in dry sandy soils, where their skin quickly dries out, and after rains, when there is a lot of water in the soil, they crawl to the surface. The excretory system is represented by metanephridia. Metanephridia begins in the body cavity with a funnel (nephrostom) from which a duct emerges - a thin loop-shaped curved tube that opens outward with an excretory pore in the side wall of the body. In each segment of the worm there is a pair of metanephridia - right and left. The funnel and duct are equipped with cilia, causing the movement of excretory fluid. The nervous system has a structure typical of annelids (see Table 1), two abdominal nerve trunks, their nodes are interconnected and form the abdominal nerve chain. The sense organs are very poorly developed. The earthworm does not have real organs of vision; their role is played by individual light-sensitive cells located in the skin. The receptors for touch, taste, and smell are also located there. Like hydra, earthworms are capable of regeneration. Reproduction occurs only sexually. Earthworms are hermaphrodites. At the front of their body are the testes and ovaries. Fertilization of earthworms is cross-fertilization. During copulation and oviposition, girdle cells on the 32-37th segment secrete mucus, which serves to form an egg cocoon, and protein fluid to nourish the developing embryo. The secretions of the girdle form a kind of mucous muff. The worm crawls out of it with its back end first, laying eggs in the mucus. The edges of the muff stick together and a cocoon is formed, which remains in the earthen burrow. Embryonic development of eggs occurs in a cocoon, and young worms emerge from it. Earthworm tunnels are located mainly in the surface layer of soil to a depth of 1 m; in winter they descend to a depth of 2 m. Through the burrows and tunnels of earthworms, atmospheric air and water penetrate into the soil, necessary for plant roots and the vital activity of soil microorganisms. During the day, the worm passes through its intestines as much soil as its body weighs (on average 4-5 g). On each hectare of land, earthworms process an average of 0.25 tons of soil every day, and over the course of a year they throw out 10 to 30 tons of soil they processed to the surface in the form of excrement. In Japan, specially bred breeds of fast-reproducing earthworms are bred and their excrement is used for biological soil cultivation. The sugar content of vegetables and fruits grown in such soil increases. Charles Darwin was the first to point out the important role of earthworms in soil formation processes. Annelids play a significant role in the nutrition of bottom fish, since in some places worms make up up to 50-60% of the biomass of the bottom layers of reservoirs. In 1939-1940 The Nereis worm was transplanted from the Azov Sea to the Caspian Sea, which now forms the basis of the diet of sturgeon fish in the Caspian Sea.
Leech classThe body is segmented. In addition to true metamerism, there is false ringing - several rings in one segment. There are no parapodia or setae. The secondary body cavity was reduced; instead there are sinuses and gaps between organs. The circulatory system is not closed; the blood passes only part of its way through the vessels and pours out of them into the sinuses and lacunae. There are no respiratory organs. The reproductive system is hermaphroditic. Medical leeches are specially bred and then sent to hospitals. They are used, for example, in the treatment of eye diseases associated with increased intraocular pressure (glaucoma), cerebral hemorrhage and hypertension. For thrombosis and thrombophlebitis, hirudin reduces blood clotting and promotes the dissolution of blood clots. |
1. In annelids, a circulatory system appears for the first time. 2. The circulatory system serves to transport oxygen and nutrients to all organs of the animal. 3. Annelids have two main blood vessels. Through the abdominal vessel, blood moves from the anterior end of the body to the posterior. 4. Blood moves through the spinal vessel from the posterior end of the body to the anterior. 5. The dorsal vessel passes above the intestine, the abdominal vessel - below it. In each segment, the dorsal and abdominal vessels are connected to each other by annular vessels.
Circulatory system 6. Annelids do not have a heart. Several thick annular vessels have muscular walls, due to the contraction of which blood moves. From the main vessels, thinner vessels depart, which then branch into the finest capillaries. The capillaries receive oxygen from the skin epithelium and nutrients from the intestines. And from other similar capillaries that branch in the muscles, “waste” is released. Thus, the blood moves all the time through the vessels and does not mix with the cavity fluid. Such a circulatory system is called closed. 7. There is an iron-containing protein in the blood, similar to hemoglobin.
Circulatory system of annelids 1. Annelids have a circulatory system for the first time. 2. The circulatory system is closed 3. two main blood vessels: abdominal and dorsal. They are connected at each segment by an annular vessel 4. There is no true heart
The circulatory system of mollusks: Unclosed (blood from the vessels enters the body cavity) A heart has appeared, which has increased the rate of blood circulation, which significantly increased the intensity of metabolic processes. Three-chambered or two-chambered heart (1 or 2 atria and a ventricle) the aorta departs from the heart, it branches into arteries Colorless blood is saturated with oxygen in the lung (gills) and returns to the heart through the veins Functions: blood carries oxygen and takes in carbon dioxide
Unlike other mollusks, cephalopods have an almost closed circulatory system. In many places (skin, muscles) there are capillaries through which arteries pass directly into veins. A highly developed circulatory system allows cephalopods to reach gigantic sizes. Only in the presence of a capillary system is the existence of very large animals possible, since only in this case is a complete supply of oxygen and nutrients to massive organs ensured. The blood is driven by three hearts. 1. The main one, consisting of a ventricle and two atria (the nautilus has four atria). The main heart pumps blood throughout the body. 2. And two gills. 3. Rhythmic contractions of the gill hearts push venous blood through the gills, from where it, enriched with oxygen, enters the atrium of the main heart. The heart rate depends on the water temperature. For example, an octopus at a water temperature of 22°C has a heart rate of 40-50 beats per minute. 4. There are special vessels to supply blood to the head. The blood of cephalopods is blue due to the presence of the respiratory pigment hemocyanin, which contains copper. Hemocyanin is produced in special gill glands.
The circulatory system in arthropods is not closed and is represented by the heart and large vessels, from which hemolymph (a fluid much like the blood of vertebrates) pours into the body cavity, washes the internal organs and returns to the heart. 1. The heart is capable of rhythmic contractions. Hemolymph enters it from the body cavity through the lateral openings, ostia, and washes the internal organs, supplying them with nutrients. 2. In crustaceans, hemolymph also performs a respiratory function. It contains oxygen-carrying substances - red hemoglobin or blue hemocyanin. There are special gill vessels for this purpose.
Circulatory system 1. When the heart contracts, the ostial valves close. 2. And the blood, moving through the arteries, enters the body cavity. Here it supplies oxygen and nutrients to the internal organs. 3. Saturated with carbon dioxide and metabolic products. 4. Blood then flows to the gills. 5. Gas exchange occurs there, and the blood, freed from carbon dioxide, is again saturated with oxygen. 6. After this, the blood enters the relaxed heart through the open ostia.
Circulatory system The circulatory system is not closed. Blood practically does not participate in the transfer of oxygen in insects. the long, tubular heart of insects is located on the dorsal side of the abdomen and is divided into several chambers; each chamber has openings with valves - ostia. Through them, blood from the body cavity enters the heart. adjacent chambers are connected to each other by valves that open only forward. Consecutive contraction of the chambers of the heart from the back to the front ensures the movement of blood.
Lancelet Circulatory system: closed, no heart, contracting walls of the abdominal aorta Function: blood carries oxygen and nutrients throughout the body, takes away decay products
Circulatory system of fish The circulatory system is closed, one circle of blood circulation, the heart is two-chambered (consists of a thin-walled atrium and a muscular ventricle) Venous blood is collected first in the venous sinus - an extension that collects blood from the venous vessels, then enters the atrium and is pushed out of the ventricle. Venous blood comes from the heart enters the abdominal aorta to the gills, arterial blood collects in the dorsal aorta. From all organs, venous blood enters the common venous sinus through the vessels.
Circulatory system of an amphibian Circulatory system. Two circles of blood circulation (large and small). Since the lungs have appeared, a pulmonary (lesser) circulation occurs. The heart of amphibians becomes three-chambered (formed by two atria and one ventricle), three pairs of arterial arches extend from it. Metabolism is not yet very intense; amphibians are poikilothermic (cold-blooded) animals.
The circulatory system of an amphibian Arterial blood enters the left atrium from the lungs through the pulmonary veins, and mixed blood enters the right atrium, since venous blood enters the vena cava from the internal organs, and the cutaneous veins bring arterial blood. In the ventricle, the blood is only partially mixed due to the presence of special separation mechanisms (various processes and the spiral valve of the conus arteriosus).
Circulatory system Systemic circulation. From the ventricle, blood enters three pairs of arterial vessels. When the ventricle contracts, venous blood is first pushed out, which fills the first two pairs of arteries. Blood with the maximum oxygen content enters the third pair of arteries, from which the carotid arteries depart, supplying blood to the brain. Then venous blood (from the internal organs through the vena cava) and arterial blood (through the cutaneous veins) enter the right atrium.
Circulatory system Pulmonary circulation. The pulmonary arteries carry oxygen-poor blood to the lungs, where gas exchange occurs, then the pulmonary veins carry arterial blood to the left atrium. Large branches depart from each pulmonary artery - cutaneous arteries, which carry blood to the skin, where it is oxidized and then enters the right atrium. Red blood cells in amphibians are large, biconvex, and have a nucleus. Metabolism is higher than that of fish, but not high enough to maintain a constant body temperature
Circulatory system There is a further separation of arterial and venous blood flow due to the appearance of an incomplete septum in the ventricle of the heart. The septum partially prevents the mixing of arterial and venous blood. Three vessels independently branch off from the ventricle: the pulmonary artery, which carries venous blood to the lungs, and the right and left aortic arches.
Circulatory system The systemic circulation begins with the aortic arches. The right aortic arch emerges from the left side of the ventricle and carries arterial, oxygenated blood. From it depart the carotid arteries, which carry blood to the brain, and the subclavian arteries, which supply blood to the forelimbs. The left aortic arch originates from the middle part of the ventricle and carries mixed blood. Both arches merge into the dorsal aorta, which supplies blood to the rest of the organs.
Circulatory system The small circle begins with the pulmonary artery, which arises from the right side of the ventricle. Venous blood is delivered to the lungs, gas exchange occurs there, and arterial blood returns through the pulmonary veins to the left atrium. Although the circulatory system is more advanced than that of amphibians, the metabolism is insufficient to maintain a constant body temperature, so reptiles do not have a constant body temperature and are poikilothermic.
Circulatory system. The heart becomes four-chambered, the septum divides the heart into two parts - right and left. Each part of the heart consists of an atrium and a ventricle. Venous blood returns to the right half of the heart through the vena cava (superior and inferior) from the systemic circulation. Pulmonary circulation. When the right ventricle contracts, venous blood flows through the pulmonary arteries into the lungs, where gas exchange occurs, and arterial blood through the pulmonary veins returns from the pulmonary circulation to the left atrium.
Circulatory system Great circle. Blood leaves the left ventricle through the right aortic arch. The carotid arteries, which carry blood to the head, and the subclavian arteries to the upper extremities, are separated from it. The right aortic arch passes into the dorsal aorta, supplying blood to the internal organs. The venous blood then collects in the vena cava and enters the right atrium. Unlike the circulatory system of reptiles, in birds blood from the heart to the organs in a large circle flows not through two arteries (the left and right aortic arches), but only through the right one. The oxygen capacity of the blood in birds is 2 times higher than in reptiles. The average body temperature of birds is about 42 degrees.
The circulatory system in the right half of the heart is venous, while in the left half it is arterial, i.e. there is no mixing of blood. The pulmonary circulation begins in the right ventricle, venous blood is carried through the pulmonary arteries to the lungs, where gas exchange occurs, and arterial blood through the pulmonary veins enters the left atrium. The systemic circulation begins in the left ventricle, the blood is ejected into the left aortic arch. Arteries supply blood to all internal organs. Venous blood enters the right atrium through the superior and inferior vena cava.
