1. In annelids, a circulatory system appears for the first time. 2. 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 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. Saturates carbon dioxide and products of exchange. 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 heart chambers 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. From the heart, venous blood 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 the vena cava from internal organs venous blood enters, 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 Big circle blood 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 they branch carotid arteries 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. The carotid arteries, which carry blood to the brain, depart from it and subclavian arteries, supplying 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 right side 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.
Annelids are the most highly organized type of worms. Includes from 12 thousand (according to old sources) to 18 thousand (according to new) species. According to the traditional classification, annelids include three classes: polychaetes, oligochaetes, and leeches. However, according to another classification, polychaetes are considered in the rank of class, and oligochaetes and leeches are included in the rank of subclasses in the class Zyaskovye; In addition to these groups, other classes and subclasses are also distinguished.
The body length of annelids, depending on the species, varies from a few millimeters to more than 5-6 meters.
In progress embryonic development ectoderm, mesoderm and endoderm are formed. Therefore, they are classified as three-layered animals.
In the process of evolution, annelids have a secondary body cavity, i.e. they are secondary cavities. The secondary cavity is called in general. It forms inside the primary cavity, which remains in the form of lumens of blood vessels.
The coelom develops from the mesoderm. Unlike the primary cavity, the secondary cavity is lined with its own epithelium. In annelids, the whole is filled with fluid, which, among other things, performs the function of a hydroskeleton (supporting shape and support during movement). Coelomic fluid also transports nutrients, and metabolic products and germ cells are excreted through it.
The body of annelids consists of repeating segments (rings, segments). In other words, their body is segmented. There can be several or hundreds of segments. The body cavity is not single, but is divided into segments by transverse partitions (septa) of the epithelial lining of the coelom. In addition, two coelomic sacs (right and left) are formed in each ring. Their walls touch above and below the intestine and support the intestines. Between the walls there are also blood vessels and a nerve cord. Each segment has its own nodes of the nervous system (on the paired abdominal nerve trunk), excretory organs, gonads, and external outgrowths.
The head lobe is called the prostomium. The back part of the worm's body is the anal lobe, or pygidium. The segmented body is called the torso.
The segmented body allows annelids to grow easily by forming new rings (this occurs posterior to the anal lobe).
The appearance of a segmented body is an evolutionary progress. However, annelids are characterized by homonomic segmentation, when all segments are approximately the same. In more highly organized animals, segmentation is heteronomous, when the segments and their functions are different. At the same time, in annelids, the formation of the head section of the body is observed by fusion of the anterior segments with a simultaneous increase in the cerebral ganglion. This is called cephalization.
The body walls, like those of lower worms, are formed by a skin-muscular sac. It consists of skin epithelium, a layer of circular and a layer of longitudinal muscles. Muscles achieve more powerful development.
Paired organs of movement emerged - parapodia. They are found only in polychaete annelids. They are outgrowths of a skin-muscular sac with tufts of bristles. In the more evolutionarily advanced group of oligochaetes, the parapodia disappear, leaving only the setae.
The digestive system consists of the foregut, midgut and hindgut. The walls of the intestine are formed by several layers of cells, they contain muscle cells, thanks to which food moves. The foregut is usually divided into the pharynx, esophagus, crop and gizzard. The mouth is located on the ventral side of the first body segment. The anus is located on the caudal blade. The process of absorption of nutrients into the blood occurs in the midgut, which has a fold on top to increase the absorption surface.
Characterized by a closed circulatory system. Previous types of worms (flat, round) did not have a circulatory system at all. As already mentioned, the lumen of blood vessels is the former primary cavity of the body, whose cavity fluid began to perform the functions of blood. Circulatory system roundworms consists of a dorsal vessel (in which blood moves from the tail blade to the head), an abdominal vessel (blood moves from the head blade to the tail), half rings connecting the dorsal and abdominal vessels, small vessels, departing to various bodies and fabrics. Each segment contains two half rings (left and right). The closed circulatory system means that blood flows only through the vessels.
Blood moves due to the pulsation of the walls of the spinal vessel. In some oligochaete worms, in addition to the dorsal one, some annular vessels contract.
Blood carries nutrients from their intestines and oxygen supplied through the integument of the body. The respiratory pigment, which reversibly binds oxygen, is found in the blood plasma and is not contained in special cells, as in vertebrates, for example, the hemoglobin pigment is found in red blood cells. Pigments in annelids can be different (hemoglobin, chlorocruarine, etc.), so the color of blood is not always red.
There are representatives of annelids that do not have a circulatory system (leeches), but in them it has been reduced, and a respiratory pigment is present in the tissue fluid.
Although annelids do not have respiratory system and usually breathe over the entire surface of the body, gas transport is carried out by the circulatory system, and not by diffusion through tissue fluid. Some marine species primitive gills are formed on the parapodia, in which there are many small blood vessels located close to the surface.
The excretory organs are represented by metanephridia. These are tubes that have a funnel with cilia at the end located inside the body (in the coelom). On the other side, the tubes open outward through the surface of the body. In every segment ringworm There are two metanephridia (on the right and on the left).
The nervous system is more developed compared to roundworms. In the head lobe, a pair of fused nodes (ganglia) form something like a brain. The ganglia are located on the peripharyngeal ring, from which the paired abdominal chain extends. It contains paired nerve ganglia in each body segment.
Sense organs of annelids: tactile cells or structures, a number of species have eyes, chemical sense organs (olfactory pits), and an organ of balance.
Most annelids are dioecious, but some are hermaphrodites. Development is direct (a small worm emerges from the egg) or with metamorphosis (a floating trochophore larva emerges; typical for polychaetes).
Annelids are thought to have evolved from worms with undifferentiated bodies, similar to ciliated worms (a type of flatworm). That is, in the process of evolution, two other groups of worms evolved from flatworms - round and annelid.
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 The structure of annelids is external and internal metamerism: their body consists of several, for the most part 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 cephalic ganglion of the nervous system, located at the top of the head, receives and processes greatest number irritations. It is much more complex than all other nodes of the worm's nervous system.
Movements of annelids
The locomotor 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 stretches 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 true 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 having different types different shape. 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 can 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. Sea worms are carried somewhat passively by water currents as component plankton, but most of them lead a benthic 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 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 the right choice sides 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.
Annelids, also called annelids, include great amount species of animals. Their body consists of numerous repeating elements, which is why they got their name. The general characteristics of annelids unite about 18 thousand different species. They live on land in the soil and on the surface in tropical rainforests, in the seawater of the oceans and the fresh water of rivers.
Classification
Annelids are a type of invertebrate animal. Their group is called protostomes. Biologists distinguish 5 classes of annelids:
Belt, or leeches;
Oligochaetes (most famous representative of this class - earthworm);
Polychaetes (peskozhil and nereid);
Misostomidae;
Dinophylids.
Considering general characteristics annelids, you understand their importance biological role in soil processing and aeration. Earthworms loosen the soil, which is beneficial for all surrounding vegetation on the planet. To understand how many of them there are on earth, imagine that in 1 sq. meter of soil is aerated with 50 to 500 annelids. This increases the productivity of agricultural land.
Annelids are one of the main links in the food chains of ecosystems both on land and in the oceans. They feed on fish, turtles, birds and other animals. Even people use them as a supplement when breeding commercial fish species in both fresh and sea waters. Fishermen use worms as bait on a hook when catching fish with a fishing rod.
Everyone knows about the meaning medical leeches, which suck blood from sore spots, relieving a person of hematomas. People have long understood their medicinal value. Leeches are used for hypertension, increased blood clotting. Leeches have the ability to produce hirudin. This is a substance that reduces blood clotting and dilates the vessels of the human circulatory system.
Origin
Studying the general characteristics of annelids, scientists found that they have been known since the Cambrian period. Considering their structure, biologists came to the conclusion that they originated from a more ancient type of lower flatworms. The similarity is obvious in certain structural features of the body.
Scientists believe that the main group of polychaete worms appeared first. In the process of evolution, when this type animals moved to life on the surface and in fresh water bodies, and oligochaetes appeared, later called leeches.
Describing the general characteristics of annelids, we note that this is the most progressive type of worms. It was they who first developed the circulatory system and the ring-shaped body. On each segment, paired organs of movement appeared, which later became the prototype of the limbs.
Archaeologists have found extinct annelids that had several rows of calcareous plates on their backs. Scientists believe that there is a certain connection between them and mollusks and brachiopods.
general characteristics
In grade 7, the type of annelids is studied in more detail. All representatives have enough characteristic structure. Both from the front and from the back the body looks the same and symmetrical. Conventionally, it is divided into three main sections: the head lobe, numerous segments of the central part of the body and the posterior or anal lobe. The central segmented part, depending on the size of the worm, can include from ten to several hundred rings.
General characteristics of annelids include information that their sizes vary from 0.25 mm to a length of 5 meters. The movement of worms is carried out in two ways, depending on its type. The first way is through contraction of the body muscles, the second is with the help of parapodia. These are the bristles found in polychaete worms. They have lateral bilobed projections on the walls of the segments. In oligochaete worms, organs such as parapodia are absent altogether or have separately growing small bundles.
Structure of the head blade
Annelids have sensory organs located at the front. These are eyes, olfactory cells, which are also present on the tentacles. Ciliary fossae are organs that distinguish between the effects of various odors and chemical irritants. There are also hearing organs that have a structure reminiscent of locators. And, of course, the main organ is the mouth.
Segmented part
This part represents the same general characteristic of the type of annelids. The central region of the body consists of rings, each of which represents a complete independent part body. This area is called the coelom. It is divided into segments by partitions. They are noticeable when viewed appearance. The outer rings of the worm correspond to the internal partitions. It is on this basis that the worms received their main name - annelids, or ringworms.
This division of the body is very important for the life of the worm. If one or more rings are damaged, the rest remain intact, and the animal regenerates in a short period of time. The internal organs are also arranged according to the segmentation of the rings.
Secondary body cavity, or coelom
The structure of annelids has the following general characteristic: the skin-muscle sac has coelomic fluid inside. It consists of the cuticle, dermal epithelium and circular and longitudinal muscles. The fluid contained in the body cavity maintains a constant internal environment. All the main functions of the body are carried out there: transport, excretory, musculoskeletal and sexual. This liquid is involved in the accumulation of nutrients, removes all waste, harmful substances and sexual products.
The type of annelids also has common characteristics in the area of body cell structure. The upper (outer) layer is called the ectoderm, followed by the mesoderm with a secondary cavity lined with its cells. This is the space from the body walls to the internal organs of the worm. The fluid contained in the secondary body cavity, thanks to pressure, maintains the constant shape of the worm and plays the role of a hydroskeleton. The last inner layer is called endoderm. Since the body of annelids consists of three shells, they are also called three-layered animals.
Worm food system
General characteristics of annelids in grade 7 briefly describe the structure digestive system the body of these animals. In the front part there is a mouth opening. It is located in the first segment from the peritoneum. All digestive tract has a through system of structure. This is the mouth itself, then there is a peripharyngeal ring that separates the worm’s pharynx. The long esophagus ends in the goiter and stomach.
The intestine has a common characteristic for the class of annelids. It consists of three departments with different purposes. These are the foregut, middle and hindgut. The middle compartment consists of endoderm, and the rest are ectodermal.
Circulatory system
The general characteristics of annelids are briefly described in the 7th grade textbook. And the structure of the circulatory system can be seen in the schematic image above. Vessels are indicated in red. The figure clearly shows that the circulatory system of annelids is closed. It consists of two long longitudinal vessels. These are dorsal and ventral. They are connected to each other by the annular vessels present in each segment, which resemble veins and arteries. The circulatory system is closed; blood does not leave the vessels and does not pour into the body cavities.
The color of blood in different types of worms can be different: red, transparent and even green. This depends on the properties of the chemical structure of the respiratory pigment. It is close to hemoglobin and has different oxygen content. Depends on the habitat of the ringed worm.
The movement of blood through the vessels is carried out due to contractions of some sections of the spinal and, less commonly, annular vessels. After all, they don’t. The rings contain special contractile elements in these vessels.
Excretory and respiratory systems
These systems in the type annelids (the general characteristics are briefly described in the 7th grade textbook) are associated with the skin. Respiration occurs through the skin or gills, which in marine polychaete worms are located on the parapodia. The gills are branched, thin-walled projections on the dorsal lobes. They can be different shapes: leaf-shaped, pinnate or bushy. The inside of the gills is permeated with thin blood vessels. If the worms are small-chaete, then respiration occurs through the moist skin of the body.
The excretory system consists of metanephridia, protonephridia and myxonephridia, located in pairs in each segment of the worm. Myxonephridia are the prototype of the kidneys. Metanephridia have the shape of a funnel located in the coelom, from which a thin and short channel brings the excretory products out in each segment.
Nervous system
If we compare the general characteristics of roundworms and annelids, the latter have a more advanced nervous system and sensory organs. They have a cluster nerve cells above the peripharyngeal ring of the anterior lobe of the body. The nervous system consists of ganglia. These are suprapharyngeal and subpharyngeal formations connected by nerve trunks into a peripharyngeal ring. In each segment you can see a pair of such ganglia of the ventral chain of the nervous system.
You can see them in the figure above. They are marked yellow. Large ganglia in the pharynx play the role of the brain, from which impulses diverge along the abdominal chain. The worm's sensory organs also belong to the nervous system. He has a lot of them. These are the eyes, the organs of touch on the skin, and the chemical senses. Sensitive cells are located throughout the body.
Reproduction
Describing the general characteristics of the type of annelids (class 7), one cannot fail to mention the reproduction of these animals. They are mostly heterosexual, but some have developed hermaphroditism. The latter include the well-known leeches and earthworms. In this case, conception occurs in the body itself, without fertilization from the outside.
In many polychaetes, development occurs from the larva, while in other subspecies it is direct. The gonads are located under the coelomal epithelium in each or almost every segment. When these cells rupture, the germ cells enter the coelom fluid and are excreted through the organs excretory system out. For many, fertilization occurs on outer surface, and in underground soil worms - inside.
But there is another type of reproduction. In conditions favorable for life, when there is a lot of food, individuals begin to grow individual body parts. For example, several mouths may appear. Subsequently, the rest grows. The worm breaks down into several separate parts. This asexual species reproduction, when a certain part of the body appears, and the rest regenerate later. An example is the ability of Aulophorus for this type of reproduction.
In the article you learned in detail all the main characteristics of annelids, which are studied in the 7th grade of school. We hope it is detailed description These animals will help you learn more easily.
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 that great importance, which has the type in question 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 skin-muscular sac is developed, which 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 placed between the intestine and the body wall and are filled watery liquid, 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. As a whole they accumulate harmful products metabolism, 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 | |
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Animals belonging to the type of annelids, or ringworms, are characterized by:
Annelids live in fresh and sea waters, as well as in the 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 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 organic substances; deep layers of soil are removed to the surface, and superficial 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. Characteristic feature 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. Skin epithelium 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 residues 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 areas. sandy soils, where their skin soon 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 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. Earthworms undergo 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 path 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. Used, for example, in the treatment of eye diseases associated with enlargement intraocular pressure(glaucoma), with cerebral hemorrhage and hypertension. For thrombosis and thrombophlebitis, hirudin reduces blood clotting and promotes the dissolution of blood clots. |
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