Abstract: Characteristics of the types of worms: flat, round and annelid. Types of flatworms, roundworms and annelids Flatworms roundworms and annelids 4 options
All flatworms are three-layer animals (Fig. 79). They have a skin-muscular sac that forms the cover and muscles of the body. The excretory and digestive systems appear. The nervous system consists of two nerve ganglia and nerve trunks. Free-living worms have eyes and tactile lobes. All flatworms are hermaphrodites and lay eggs in a cocoon. Flatworms are divided into ciliated, tapeworms and flukes.
Rice. 79. Flatworms: 1 - liver fluke; 2 - pork tapeworm; 3 - echinococcus; round: 4 - roundworm, 5 - pinworm; ringed: 6 - leech, 7 - earthworm
Representative eyelash worms is free-living white planaria. This animal is 2 cm long, milky white in color, lives in ponds, slow-flowing rivers, and quiet creeks. Its body is covered with cilia, the main movement of which ensures the movement of the planaria along the bottom of the reservoir. Planaria is a predator, feeding on protozoa, coelenterates, daphnia and other small animals. The planaria's throat is capable of turning outward and, due to the suction cup, tightly attaching itself to the victim.
All eyelash worms have the ability to regenerate. Under unfavorable conditions, they can disintegrate into pieces, each of which is subsequently restored into a whole organism.
The length of echinococcus is only 1-1.5 cm. Humans can become infected with it from dogs and other animals. Finna echinococcus is capable of multiplying, forming daughter blisters. Sometimes it grows to the size of a walnut, and in some cases it is as big as a child’s head. This bubble can destroy tissue and can only be removed through surgery.
Annelids. These are more highly organized animals than those discussed earlier. The body of annelids is segmented. The nervous system of the nodal type and the excretory system are well developed, and a closed circulatory system appears. There are tactile and light-sensitive cells.
Best known earthworm. This worm lives in the soil, its body is segmented, on the underside there are bristles that are directly involved in movement. If you put an earthworm on paper, you can hear the rustling sound produced by the bristles as the worm moves. It refers to class of oligochaetes.
Worms do not have special respiratory organs. They breathe through their skin. Often after rain, earthworms crawl to the surface of the earth: rainwater floods the worm burrows, displacing oxygen from the soil, which makes breathing difficult.
Earthworms are bisexual animals, but they undergo cross-fertilization. When mating, two individuals come closer, overlap their anterior ends and exchange male reproductive products. Eggs are injected into a special belt - a coupling formed from mucus, on the 13th segment, which, moving with the coupling, are fertilized with sperm on the 9th segment. The clutch containing the fertilized eggs slides off the front and forms an egg cocoon. Eggs in a cocoon develop in the soil.
Earthworms are capable of regeneration. When a worm is cut in half, the missing part can be restored.
Earthworms feed on fallen leaves and grass, passing a large amount of soil through themselves, thereby loosening it, aerating it and enriching it with humus. They play a very important role in soil formation.
Lives in sewage polluted water bodies tubifex, serving as food for fish and purifying water from organic contaminants.
In our fresh water bodies there are false horse leech black and gray-green medicinal leech. U medical leech in the depths of the oral cavity there are three ridges with pointed chitinous teeth. They are located at the vertices of the triangle, with teeth facing each other. By sucking, the leech cuts through the skin with them, secreting hirudin, preventing blood clotting. Hirudin stops the development of blood clots, is useful for hypertension, sclerosis, strokes, and resolves subcutaneous hemorrhages.
Previously, medicinal leeches were widely used, but nowadays they have become very rare.
The large false horse leech attacks earthworms, mollusks, and tadpoles. It does not cause any harm to humans, although it sometimes attaches itself to the body of a person bathing in a pond using its rear suction cup.
| |
§ 58. Animal Kingdom. Multicellular organisms: sponges and coelenterates§ 60. Arthropods
on the topic: “Characteristics of types of worms: flat, round and annelid”
TYPE FLATWORMS
CLASS PLANARIA, OR CILIA WORMS
White, brown, and black planaria live in silted areas of lakes, ponds and streams. At the front end of their body two ocelli are noticeable (they distinguish light from darkness); The pharynx is located on the ventral side. Planarians are predators. They attack small aquatic animals, “crush” them under themselves and swallow them whole or tear them into pieces. They move thanks to the coordinated work of the cilia. The body length of freshwater planarians is 1-3 cm.
The world of marine ciliated worms is the richest and most diverse. Their large, wide leaf-shaped body has a wide variety of colors. In the moist litter of tropical forests live large soil planarians (bipalians), whose body length reaches 60 cm.
Internal structure and vital activity. The body of flatworms is covered with elongated cells with cilia. Deeper there are three layers of muscle fibers (circular, diagonal and longitudinal). Thanks to their contraction and relaxation, the worm lengthens or shortens, lifts one or another part of the body, and flattens. Under the muscles there is a mass of small cells - the main tissue, and in it - the internal organs. The digestive system consists of a mouth with a muscular pharynx and a three-branched intestine, the walls of which are formed by a single layer of flask-shaped cells capable of capturing food particles and digesting them. The glandular cells of the wall secrete digestive substances into the intestinal cavity. The resulting nutrients penetrate all cells of the body, and undigested food remains are removed through the mouth.
Ciliated worms breathe oxygen dissolved in water through the entire surface of the body. Substances that are unnecessary for the body, formed during the process of vital activity, are eliminated by entering the tubules, which begin with large stellate cells with bundles of cilia inside (they create a flow of fluid into the tubules). Small tubules are collected into one or two large tubules with excretory pores.
The nervous system of ciliated worms is formed by clusters of nerve cells - paired head nodes, nerve trunks and nerve branches extending from them. Most ciliated worms have eyes (from one pair to several dozen), tactile cells in the skin, and some have small paired tentacles at the anterior end of the body.
Reproduction of eyelash worms. Flatworms are usually hermaphrodites. Freshwater ciliated worms, such as planarians, lay fertilized eggs in cocoons formed from solidified mucus. The developed small worms break the walls of the cocoons and come out. In marine eyelash worms, fertilized eggs hatch into floating larvae, which then acquire the characteristics of adults.
CLASS FLUKES AND CLASS TAPEWORMS
The muscular and nervous systems of tapeworms are poorly developed, and the sensory organs are represented by sensitive skin cells. Their digestive system has disappeared: they absorb nutrients throughout the entire surface of the body from the host’s intestines.
The reproductive system is most developed in tapeworms. Almost all of them are hermaphrodites. Their last segments seem to be filled with eggs with developing embryos. The segments are separated from the body of the worm and come out with the feces of the owner or independently (due to muscle contraction). A sick person hatches up to 28 segments per day, containing up to 5 million eggs. Together with the grass, the eggs enter the stomach of the intermediate host - a cow (bovine tapeworm), a pig (pork tapeworm). In the stomach, six-hooked larvae emerge from the eggs, which penetrate the blood vessels of the intestine and then into the muscles. Here the larvae turn into fins, which look like a bubble the size of a pea. When a person eats undercooked or undercooked Finnish meat, he or she becomes the main host of the worm. In the human stomach, the head of the finna is turned out, and the bubble itself is digested. A small worm enters the intestine, attaches itself to its wall, and its neck begins to form segments.
The development of the wide tapeworm is associated with the change of two intermediate hosts (Cyclops crustaceans and fish). The main owner is a person.
Echinococcus- small worm (length up to 6 mm). Unlike tapeworms and tapeworms, the segments are not separated from its body. The main hosts of echinococcus are dogs, wolves, foxes, and cats; intermediate - sheep, cow, goat, deer, pig (maybe a person). In the liver, lungs, muscles, and bones of intermediate hosts, large blisters (a variety of Finns) develop, in each of which daughter and grandchild blisters with heads inside develop. The primary hosts become infected by eating meat with echinococcal blisters, and intermediate hosts by eating food contaminated with the feces of sick dogs, wolves and other primary hosts of echinococcus.
TYPE ROUND OR PRIMA CAVITY WORMS
Roundworms have a non-segmented, usually long body, round in cross section. On the surface of the skin there is a dense non-cellular formation of the cuticle. These worms developed a body cavity, formed as a result of the destruction of cells of the main tissue between the body wall and the internal organs (primary body cavity). The musculature of roundworms consists of a layer of longitudinal fibers. Therefore, they can only bend. The intestines of roundworms, which have the shape of a tube, begin with the mouth and end with the anus (anus).
Herbivorous nematodes live on the roots of onions, garlic, beans and some other garden plants (onion nematode), in underground shoots of potatoes (stem potato nematode), in various organs of strawberries (strawberry nematode). The length of their almost transparent body is about 1.5 mm. Nematodes use their piercing mouthparts to pierce plant tissues and inject them with substances that dissolve the contents of plant cells. They absorb dissolved substances using the expanded part of the esophagus, the muscular walls of which act like a pump. Food is digested in the intestines. Many nematodes live in the soil, feed on various plant debris and are of great importance in soil formation.
Roundworms live in the small intestine of their host. The body length of the female is up to 40 cm (males are smaller). Roundworms feed on semi-digested food. The eggs laid by females (about 200 per day) are excreted in human feces. In the external environment, mobile larvae develop in the eggs. Humans become infected with roundworm eggs by consuming poorly washed vegetables and food visited by flies.
In the host's intestine, the larvae emerge from the eggs, invade the blood vessels and enter the liver, heart and lungs. Grown larvae from the lungs enter the mouth and then into the intestines, where they become adults. Roundworms feed on the host's food, poison it with their secretions, cause the formation of ulcers on the intestinal walls, and in large numbers - intestinal obstruction and rupture of its walls.
Adult Trichinella (female body length is about 4 mm) live in the lumen of the small intestine, and the microscopic larvae they give birth penetrate into the muscles, where they grow, curl into a spiral and, having formed a capsule around themselves, enter a dormant state. The source of human infection is the meat of animals, especially pigs, which acquire Trichinella by eating small mammals, such as rats.
TYPE RINGED WORMS
GENERAL CHARACTERISTICS OF ANNELED WORMS
Ringed worms live in the seas, fresh water bodies, and soil. They have a long body, divided by transverse constrictions into ring-shaped segments (segments). External division corresponds to internal segmentation. The body cavity of these worms is lined with a layer of integumentary cells (secondary body cavity). Each segment contains a delimited section of this cavity. Annelids have a circulatory system, and many have a respiratory system. Their muscular, digestive, excretory, nervous systems and sensory organs are more advanced than those of flatworms and roundworms.
The skin of annelids consists of a single layer of integumentary cells (some of which secrete mucus). Under the skin there are circular and longitudinal muscles. The digestive system is noticeably divided into the oral cavity, pharynx, esophagus (in some, its expansion is formed - goiter), stomach (in some groups) and intestines. Undigested food remains are removed out through the anus. The circulatory system of annelids is formed by dorsal and ventral blood vessels connected to each other by ring vessels. Small blood vessels arise from these vessels. They branch and form a dense network of tiny vessels - capillaries - in the skin and internal organs. Blood (usually red) moves mainly due to the contraction and relaxation of the walls of the annular vessels that surround the esophagus. It transports the nutrients and oxygen that enter it to all organs of the body and frees the body organs from unnecessary metabolic products. The circulatory system of annelids is closed (the blood does not leave the blood vessels). Respiration in annelids occurs through the skin. Some sea worms have gills.
The release of substances (metabolic products) unnecessary for the body in earthworms occurs with the help of excretory tubes, beginning with funnels with cilia (a pair in each segment). The excretory tubes open outward on the ventral side of the next segment. In some annelids, the tubes begin with cells with a bunch of cilia inside.
The nervous system of annelids consists of paired suprapharyngeal and subpharyngeal nerve nodes, connected by nerve cords into a peripharyngeal ring, and nodes of the abdominal nerve chain (each segment of the worm contains a paired nerve ganglion). Nerves extend from ganglia to all organs of the body. Light and other stimuli act on sensitive cells. The excitation that arises in them is transmitted along nerve fibers to the nearest nerve node, and then through other nerve fibers to the muscles and causes their contraction. This is how one or another reflex is carried out. Most annelids lack sensory organs.
Among annelids there are both dioecious and hermaphrodites. The development of sea worms occurs with the larval stage.
The ability to regenerate in annelids is worse than in flatworms.
The phylum of annelids includes 9 thousand species. Main classes: Oligochaete worms and Polychaete worms.
CLASS POLYCHETATE WORMS
Habitats, structure and lifestyle.
Oligochaete worms live mainly in the soil (earthworms) and in fresh water bodies (tubifex). Earthworms (about 1,500 species) have a long body consisting of 80 or more rings. On the sides of each ring, except for the oral one, there are setae (usually two tufts). There are no sensory organs (there are olfactory, tactile, gustatory, and light-sensitive cells). Earthworms feed mainly on rotting organic matter and the bacteria they contain. Food is captured with the mouth located on the first segment of the body. Earthworms come to the soil surface at dusk and at night. They move by alternately contracting and relaxing the circular and longitudinal muscles. The bristles have a supporting role in moving and making passages in the soil. Moving in loose soil, the worm pushes its particles apart, and in dense soil passes them through the intestines. With the onset of drought or cold weather, earthworms go deep into the soil. Tubifex live at the bottom of reservoirs, forming dense settlements. The front part of their filamentous body (2/3) is usually located in a tube of mucus and soil particles, the back part is free and makes “breathing” movements. Tubifex worms feed on organic soil debris. Reproduction. Earthworms are hermaphrodites. Before laying eggs, two worms approach each other with their anterior ends of the body and exchange seminal fluid containing sperm, which enters their seminal receptacles. Then, when the eggs mature, a cocoon begins to form on the girdle of each worm (this is a glandular thickening of the skin of several specific segments): the girdle secretes mucus, which forms a muff. Contractions of the worm's body move the muff towards the anterior end of the body. It contains eggs and fluid with sperm. The muff turns into a cocoon, where fertilization of the eggs occurs. The developed worms break the cocoon and emerge from it.
CLASS POLYCHETATE WORMS
Polychaete worms include various types of nereids, sandworms, and serpules. Nereids live mainly in coastal parts of the seas, in muddy soil; Sandworms - in the minks they dug; serpuls sit in “houses” built from various materials. At their front end there is a plume of tentacles, with which they filter water.
Nereids are most diverse in the seas. They have a reddish or green color, cast in all the colors of the rainbow. The anterior segments of the body form a head with a mouth, palps and tentacles (tactile organs), two pairs of ocelli and two pits behind them (olfactory organs). On the sides of the body of Nereids, on the segments there are short, muscular paired lobe-like projections - parapodia with tufts of bristles. These are the limbs of Nereids. Nereids develop special skin outgrowths - gills.
Nereids are dioecious animals. Fertilization of eggs occurs in water. The eggs hatch into free-swimming larvae with a belt of cilia. Over time, the larvae take on the appearance of adult worms.
ORIGIN AND IMPORTANCE OF ANNELED WORMS
Origin. Scientists believe that ancient annelids evolved from ancient free-living flatworms. Proof of this is, for example, the presence of cilia in the larvae of marine annelids, excretory organs beginning with stellate cells with a ciliated flame, and the similarity of the nervous system with the nervous system of planarians. Polychaete worms are older than oligochaete worms, although they have the most complex structure. The simplification of the structure of oligochaete worms occurred mainly in connection with the transition to life in the soil.
Meaning. Nereids and other sea worms are the main food of many species of fish, crabs and other sea inhabitants; Many fish and freshwater invertebrates feed on tubifex; earthworms are the main food of moles, hedgehogs, toads, starlings and other land animals. By feeding on silt and various suspensions, annelids rid the water of excess organic matter. Earthworms and some other soil worms, by eating various plant debris and passing soil through their intestines, contribute to the formation of humus. The burrows they make are filled with air necessary for the breathing of plant roots and various soil-forming organisms living in the ground.
TYPES FLAT, ROUND AND ANNELED WORMS.
FOR ONE REPRESENTATIVE OF THE TYPES OF FLAT, ROUND AND ANNELED WORMS, SELECT THE APPROPRIATE CHARACTERISTICS:
1. Representatives
1. White planaria. 4. Ascaris.
2. Liver fluke. 5. Earthworm.
3. Bull tapeworm. 6. Nereid.
1. Type flatworms.
2. Type roundworms.
3. Type annelids.
1. Class of flukes.
2. Class tapeworms.
3. Class ciliated worms.
4. Class oligochaete worms.
5. Class polychaete worms.
4. Habitat.
1. They settle in organs rich in blood.
2. Settle in the intestines of humans and animals.
3. Lives in fresh water bodies: ponds, rivers, lakes.
4. Lives in salty bodies of water: seas and oceans.
5. Lives in soil rich in humus.
5. Body shape.
1. The body is elongated, round in cross section.
2. The body is flattened - leaf-shaped.
3. The body is flattened and elongated.
4. Body flattened-ribbon-shaped.
5. The body is elongated, oval in cross section.
6. Dividing the body into segments.
1. The body is divided by constrictions into segments.
2. There are no constrictions. The body is not divided into segments.
7. The presence of a cavity between organs.
1. Internal organs are located in a body cavity filled with
liquid.
2. There is no body cavity. Gaps between organs
filled with cells.
8. Coverings of the body.
1. The skin has numerous eyelashes.
2. The body segments have lobes with long bristles.
3. Short setae are located on the body segments.
4. There are no bristles or cilia on the body. The integument is smooth and
5. There are no bristles or cilia on the body. The integument is smooth and
9. Body musculature.
1. There are longitudinal, annular and dorso-ventral layers
2. There are longitudinal and circular elephant muscles.
3. There is only a longitudinal layer of muscles.
10. Nutrition.
1. They feed on the tissues of human and animal organs.
2. They eat ready-made, digested food.
3. They feed on rotted plant debris.
4. They feed on small invertebrates.
11. Digestive organs.
1. Mouth, pharynx, esophagus, intestines ending in anal
hole.
2. Mouth, pharynx, esophagus with goiter, stomach, intestines
ending in the anus.
3. Mouth, pharynx, esophagus, intestinal branches ending
4. There are no digestive organs. Food is absorbed through
the entire surface of the body.
12. Circulatory organs.
1. The circulatory system is closed. Consists of dorsal and
abdominal vessels with ring jumpers.
2. There are no circulatory organs.
13. Respiratory organs.
1. Breathes oxygen dissolved in water using gills.
2. There are no respiratory organs. Oxygen enters the body
across the entire surface of the body.
14. Nervous system.
1. Consists of the cerebral ganglion and nerves extending from it
trunks with branches.
2. Consists of the peripharyngeal nerve ring and extending from
it has nerve trunks with branches.
3. Consists of the peripharyngeal nerve ring and the abdominal
nerve cord with branches.
15. Sense organs.
1. Sense organs are well developed.
2. Sense organs are poorly developed.
16. Reproduction,
1. They reproduce asexually, falling apart into parts,
regenerating to a whole worm. Sexuality is also known
reproduction by fusion of sperm with eggs.
2. They reproduce only sexually. Animals are bisexual
Hermaphrodites.
3. They reproduce only sexually. Animals
dioecious.
17. Laying eggs.
1. Eggs are laid openly.
2. Eggs are laid in a cocoon.
18. Development.
1. Development is direct, proceeds without transformation.
2. Development is indirect, proceeds with transformation. Eat
larval stages. The final owner is man,
the intermediate host is cattle.
3. Development is indirect, proceeds with transformation. Eat
larval stages. Definitive host - large
cattle, intermediate host - gastropod.
4. Development is indirect, proceeds with transformation. Larva
free-floating in the water column.
There are three main types of worms: Flatworms, Roundworms and Annelids. Each of them is divided into classes into which types of worms are grouped based on the similarity of certain characteristics. In this article we will describe types and classes. We will also touch on their individual types. You will learn basic information about worms: their structure, characteristic features, role in nature.
Type Flatworms
Black, brown and live in silty areas of ponds, lakes and streams. At the front end of the body they have 2 ocelli, with the help of which they distinguish darkness from light. The pharynx is located on the ventral side. Planarians are predators. They hunt small aquatic animals, which they tear into pieces or swallow whole. They move thanks to the work of cilia. The body length of freshwater planarians ranges from 1 to 3 cm.
Their body is covered with elongated cells with special cilia (therefore they are also called ciliated worms). Deeper are 3 layers of muscle fibers - diagonal, circular and longitudinal. The worm (species related to planarians), due to their relaxation and contraction, shortens or lengthens, and can lift parts of the body. A mass of small cells is located under the muscles. This is the main tissue in which the internal organs are located. The mouth with a muscular pharynx, as well as the three-branched intestine, make up the digestive system. The intestinal walls are formed by a layer of flask-shaped cells. They capture food particles and then digest them. Digestive enzymes release glandular cells of the intestinal wall into the intestinal cavity. Nutrients resulting from the breakdown of food penetrate directly into the body tissues. Undigested residues are removed through the mouth.
Ciliated worms breathe oxygen dissolved in water. This process is carried out over the entire surface of the body. they consist of clusters of cells - paired head nodes, nerve trunks extending from them, as well as nerve branches. Planarians mostly have eyes (from 1 to several dozen pairs). They have tactile cells in their skin, and some representatives of this class have small paired tentacles at the anterior end of the body.
Class Flukes
Class Tapeworms
The nervous and muscular systems of this class are poorly developed. Skin cells represent their sensory organs. Their digestive system has disappeared: tapeworms absorb nutrients from the host’s intestines with the entire surface of their body.
Echinococcus
Class Nematodes
Nematodes are herbivorous worms that live on the roots of beans, garlic, onions and other garden plants, in underground shoots of potatoes (species Stem potato nematode), in the organs of strawberries (Strawberry nematode). The length of their almost transparent body is about 1.5 mm. With their piercing-type mouthparts, nematodes pierce plant tissue, after which they inject substances that dissolve the contents and walls of the cells. They then absorb the resulting substances using the expanded part of the esophagus. Its muscular walls act like a pump. Food is digested in the intestines. Many nematodes live in the ground and use plant debris as food. They play an important role in soil formation.
Roundworms
Its representatives live in fresh water bodies, seas, and soil. Their body is long, divided into ring-shaped segments (segments) by transverse constrictions. We are all familiar with the appearance of earthworms. Their length ranges from 2 to 30 cm. The body is divided into segments, which can be from 80 to 300.
Internal segmentation corresponds to external dissection. The body cavity of representatives of this type is lined with a layer of integumentary cells. A delimited portion of this cavity is located in each segment. Annelids have a circulatory system, and many of them also have a respiratory system. Their digestive, muscular, nervous, excretory systems, as well as sensory organs, are more advanced than those of round and flatworms. Their “skin” consists of a layer of integumentary cells. Beneath it are the longitudinal and circular muscles. In annelids, the digestive system is divided into the pharynx, oral cavity, esophagus, stomach (in certain groups), and intestines. Undigested food remains are removed through the anus.
Circulatory system of annelids
All types of annelids have a circulatory system formed by abdominal and dorsal blood vessels, which are connected to each other by ring vessels. Small vessels depart from the latter, which branch and form a network of capillaries in the internal organs and skin. Blood moves mainly due to the relaxation and contraction of the walls of the annular vessels covering the esophagus. It carries oxygen and nutrients supplied to it to all organs, and also relieves the body of metabolic products. Species of annelids are characterized by a closed circulatory system (this biological fluid is located within the vessels and does not flow into the body cavity). Breathing occurs through the skin. Some species have gills.
annelids
The nervous system of representatives of this type consists of paired subpharyngeal and suprapharyngeal nerve nodes, which are connected in a ring by nerve cords, as well as nodes of the chain (abdominal). A paired node is found in each segment of annelids. Nerves extend to all organs. Various stimuli (for example, light) affect sensitive cells. The excitation that arises in them is transmitted to the nearest nerve node along the nerve fibers, and then to the muscles (via other fibers) and causes their contraction. This is how reflexes are carried out. Most representatives of this type do not have sense organs.
Main classes of annelids
Ringed fish can be either hermaphrodite or dioecious. How many worms (species) does this type include? Today there are about 9 thousand of them, among which the main classes stand out: Polychaetes and Oligochaetes. The former live mainly in the soil (for example, such a type of earthworms as burrows), as well as in fresh water bodies (in particular, tubifex worms). Polychaete worms are a class that includes sandworms, nereids and serpules. Sandworms live in burrows they dig, Nereids live mainly in muddy soil, in coastal parts of the seas, Serpuls live in “houses” that they build from various materials.
Nereids
Nereids are the species of worms that are most diverse in the seas. Their color is green or reddish. The head is formed by the anterior segments of the body. She has palps, a mouth, tentacles (tactile organs), as well as 2 pairs of eyes and 2 pits located behind them (these are olfactory organs). On the segments on the sides of the body there are paired muscular short lobe-shaped projections with tufts of bristles. These are limbs. In addition, Nereids develop gills - special skin outgrowths. Often these are dioecious animals. Fertilization of eggs occurs in water, from which free-swimming larvae with a belt of cilia emerge. They eventually develop into adult worms.
The meaning of annelids
They are food for many types of crabs and fish (nereids and other sea worms). Earthworms are the main food of hedgehogs, moles, starlings, toads and other animals. Ringed fish, feeding on silt and various suspensions, rid the water of excess organic matter. In addition, earthworms and some other soil worms eat plant debris and also pass soil through their intestines. By doing this they contribute to the formation of humus.
on the topic: "Characteristics of types of worms: flat, round and annelid
TYPE FLATWORMS
CLASS PLANARIA, OR CILIA WORMS
White, brown, and black planaria live in silted areas of lakes, ponds and streams. At the front end of their body two ocelli are noticeable (they distinguish light from darkness); The pharynx is located on the ventral side. Planarians are predators. They attack small aquatic animals, “crush” them under themselves and swallow them whole or tear them into pieces. They move thanks to the coordinated work of the cilia. The body length of freshwater planarians is 1-3 cm.
The world of marine ciliated worms is the richest and most diverse. Their large, wide leaf-shaped body has a wide variety of colors. In the moist litter of tropical forests live large soil planarians (bipalians), whose body length reaches 60 cm.
Internal structure and vital activity. The body of flatworms is covered with elongated cells with cilia. Deeper there are three layers of muscle fibers (circular, diagonal and longitudinal). Thanks to their contraction and relaxation, the worm lengthens or shortens, lifts one or another part of the body, and flattens. Under the muscles there is a mass of small cells - the main tissue, and in it - the internal organs. The digestive system consists of a mouth with a muscular pharynx and a three-branched intestine, the walls of which are formed by a single layer of flask-shaped cells capable of capturing food particles and digesting them. The glandular cells of the wall secrete digestive substances into the intestinal cavity. The resulting nutrients penetrate all cells of the body, and undigested food remains are removed through the mouth.
Ciliated worms breathe oxygen dissolved in water through the entire surface of the body. Substances that are unnecessary for the body, formed during the process of vital activity, are eliminated by entering the tubules, which begin with large stellate cells with bundles of cilia inside (they create a flow of fluid into the tubules). Small tubules are collected into one or two large tubules with excretory pores.
The nervous system of ciliated worms is formed by clusters of nerve cells - paired head nodes, nerve trunks and nerve branches extending from them. Most ciliated worms have eyes (from one pair to several dozen), tactile cells in the skin, and some have small paired tentacles at the anterior end of the body.
Reproduction of eyelash worms. Flatworms are usually hermaphrodites. Freshwater ciliated worms, such as planarians, lay fertilized eggs in cocoons formed from solidified mucus. The developed small worms break the walls of the cocoons and come out. In marine eyelash worms, fertilized eggs hatch into floating larvae, which then acquire the characteristics of adults.
CLASS FLUKES AND CLASS TAPEWORMS
The muscular and nervous systems of tapeworms are poorly developed, and the sensory organs are represented by sensitive skin cells. Their digestive system has disappeared: they absorb nutrients throughout the entire surface of the body from the host’s intestines.
The reproductive system is most developed in tapeworms. Almost all of them are hermaphrodites. Their last segments seem to be filled with eggs with developing embryos. The segments are separated from the body of the worm and come out with the feces of the owner or independently (due to muscle contraction). A sick person hatches up to 28 segments per day, containing up to 5 million eggs. Together with the grass, the eggs enter the stomach of the intermediate host - a cow (bovine tapeworm), a pig (pork tapeworm). In the stomach, six-hooked larvae emerge from the eggs, which penetrate the blood vessels of the intestine and then into the muscles. Here the larvae turn into fins, which look like a bubble the size of a pea. When a person eats undercooked or undercooked Finnish meat, he or she becomes the main host of the worm. In the human stomach, the head of the finna is turned out, and the bubble itself is digested. A small worm enters the intestine, attaches itself to its wall, and its neck begins to form segments.
The development of the wide tapeworm is associated with the change of two intermediate hosts (Cyclops crustaceans and fish). The main owner is a person.
Echinococcus- small worm (length up to 6 mm). Unlike tapeworms and tapeworms, the segments are not separated from its body. The main hosts of echinococcus are dogs, wolves, foxes, and cats; intermediate - sheep, cow, goat, deer, pig (maybe human). In the liver, lungs, muscles, and bones of intermediate hosts, large blisters (a variety of Finns) develop, in each of which daughter and grandchild blisters with heads inside develop. The primary hosts become infected by eating meat with echinococcal blisters, and intermediate hosts by eating food contaminated with the feces of sick dogs, wolves, and other primary hosts of echinococcus.
TYPE ROUND OR PRIMA CAVITY WORMS
Roundworms have a non-segmented, usually long body, round in cross section. On the surface of the skin there is a dense non-cellular formation of the cuticle. These worms developed a body cavity, formed as a result of the destruction of cells of the main tissue between the body wall and the internal organs (primary body cavity). The musculature of roundworms consists of a layer of longitudinal fibers. Therefore, they can only bend. The intestines of roundworms, which have the shape of a tube, begin with the mouth and end with the anus (anus).
Herbivorous nematodes live on the roots of onions, garlic, beans and some other garden plants (onion nematode), in underground shoots of potatoes (stem potato nematode), in various organs of strawberries (strawberry nematode). The length of their almost transparent body is about 1.5 mm. Nematodes use their piercing mouthparts to pierce plant tissues and inject them with substances that dissolve the contents of plant cells. They absorb dissolved substances using the expanded part of the esophagus, the muscular walls of which act like a pump. Food is digested in the intestines. Many nematodes live in the soil, feed on various plant debris and are of great importance in soil formation.
Roundworms live in the small intestine of their host. The body length of the female is up to 40 cm (males are smaller). Roundworms feed on semi-digested food. The eggs laid by females (about 200 per day) are excreted in human feces. In the external environment, mobile larvae develop in the eggs. Humans become infected with roundworm eggs by consuming poorly washed vegetables and food visited by flies.
In the host's intestine, the larvae emerge from the eggs, invade the blood vessels and enter the liver, heart and lungs. Grown larvae from the lungs enter the mouth and then into the intestines, where they become adults. Roundworms feed on the host's food, poison it with their secretions, cause the formation of ulcers on the intestinal walls, and in large numbers - intestinal obstruction and rupture of its walls.
Adult Trichinella (female body length is about 4 mm) live in the lumen of the small intestine, and the microscopic larvae they give birth penetrate into the muscles, where they grow, curl into a spiral and, having formed a capsule around themselves, enter a dormant state. The source of human infection is the meat of animals, especially pigs, which acquire Trichinella by eating small mammals, such as rats.
TYPE RINGED WORMS
GENERAL CHARACTERISTICS OF ANNELED WORMS
Ringed worms live in the seas, fresh water bodies, and soil. They have a long body, divided by transverse constrictions into ring-shaped segments (segments). External division corresponds to internal segmentation. The body cavity of these worms is lined with a layer of integumentary cells (secondary body cavity). Each segment contains a delimited section of this cavity. Annelids have a circulatory system, and many have a respiratory system. Their muscular, digestive, excretory, nervous systems and sensory organs are more advanced than those of flatworms and roundworms.
The skin of annelids consists of a single layer of integumentary cells (some of which secrete mucus). Under the skin there are circular and longitudinal muscles. The digestive system is noticeably divided into the oral cavity, pharynx, esophagus (in some, its expansion is formed - goiter), stomach (in some groups) and intestines. Undigested food remains are removed out through the anus. The circulatory system of annelids is formed by dorsal and ventral blood vessels connected to each other by ring vessels. Small blood vessels arise from these vessels. They branch and form a dense network of tiny vessels - capillaries - in the skin and internal organs. Blood (usually red) moves mainly due to the contraction and relaxation of the walls of the annular vessels that surround the esophagus. It transports the nutrients and oxygen that enter it to all organs of the body and frees the body organs from unnecessary metabolic products. The circulatory system of annelids is closed (the blood does not leave the blood vessels). Respiration in annelids occurs through the skin. Some sea worms have gills.
The release of substances (metabolic products) unnecessary for the body in earthworms occurs with the help of excretory tubes, beginning with funnels with cilia (a pair in each segment). The excretory tubes open outward on the ventral side of the next segment. In some annelids, the tubes begin with cells with a bunch of cilia inside.
The nervous system of annelids consists of paired suprapharyngeal and subpharyngeal nerve nodes, connected by nerve cords into a peripharyngeal ring, and nodes of the abdominal nerve chain (each segment of the worm contains a paired nerve ganglion). Nerves extend from ganglia to all organs of the body. Light and other stimuli act on sensitive cells. The excitation that arises in them is transmitted along nerve fibers to the nearest nerve node, and then through other nerve fibers to the muscles and causes their contraction. This is how one or another reflex is carried out. Most annelids lack sensory organs.
Among annelids there are both dioecious and hermaphrodites. The development of sea worms occurs with the larval stage.
The ability to regenerate in annelids is worse than in flatworms.
The phylum of annelids includes 9 thousand species. Main classes: Oligochaete worms and Polychaete worms.
CLASS POLYCHETATE WORMS
Habitats, structure and lifestyle.
Oligochaete worms live mainly in the soil (earthworms) and in fresh water bodies (tubifex). Earthworms (about 1,500 species) have a long body consisting of 80 or more rings. On the sides of each ring, except for the oral one, there are setae (usually two tufts). There are no sensory organs (there are olfactory, tactile, gustatory, and light-sensitive cells). Earthworms feed mainly on rotting organic matter and the bacteria they contain. Food is captured with the mouth located on the first segment of the body. Earthworms come to the soil surface at dusk and at night. They move by alternately contracting and relaxing the circular and longitudinal muscles. The bristles have a supporting role in moving and making passages in the soil. Moving in loose soil, the worm pushes its particles apart, and in dense soil passes them through the intestines. With the onset of drought or cold weather, earthworms go deep into the soil. Tubifex live at the bottom of reservoirs, forming dense settlements. The front part of their filamentous body (2/3) is usually located in a tube of mucus and soil particles, the back part is free and makes “breathing” movements. Tubifex worms feed on organic soil debris. Reproduction. Earthworms are hermaphrodites. Before laying eggs, two worms approach each other with their anterior ends of the body and exchange seminal fluid containing sperm, which enters their seminal receptacles. Then, when the eggs mature, a cocoon begins to form on the girdle of each worm (this is a glandular thickening of the skin of several specific segments): the girdle secretes mucus, which forms a muff. Contractions of the worm's body move the muff towards the anterior end of the body. It contains eggs and fluid with sperm. The muff turns into a cocoon, where fertilization of the eggs occurs. The developed worms break the cocoon and emerge from it.
CLASS POLYCHETATE WORMS
Polychaete worms include various types of nereids, sandworms, and serpules. Nereids live mainly in coastal parts of the seas, in muddy soil; Sandworms - in the minks they dug; serpuls sit in "houses" built from various materials. At their front end there is a plume of tentacles, with which they filter water.
Nereids are most diverse in the seas. They have a reddish or green color, cast in all the colors of the rainbow. The anterior segments of the body form a head with a mouth, palps and tentacles (tactile organs), two pairs of ocelli and two pits behind them (olfactory organs). On the sides of the body of Nereids, on the segments there are short, muscular paired lobe-shaped outgrowths - parapodia with tufts of bristles. These are the limbs of Nereids. Nereids develop special skin outgrowths - gills.
Nereids are dioecious animals. Fertilization of eggs occurs in water. The eggs hatch into free-swimming larvae with a belt of cilia. Over time, the larvae take on the appearance of adult worms.
ORIGIN AND IMPORTANCE OF ANNELED WORMS
Origin. Scientists believe that ancient annelids evolved from ancient free-living flatworms. Proof of this is, for example, the presence of cilia in the larvae of marine annelids, excretory organs beginning with stellate cells with a ciliated flame, and the similarity of the nervous system with the nervous system of planarians. Polychaete worms are older than oligochaete worms, although they have the most complex structure. The simplification of the structure of oligochaete worms occurred mainly in connection with the transition to life in the soil.
Meaning. Nereids and other sea worms are the main food of many species of fish, crabs and other sea inhabitants; Many fish and freshwater invertebrates feed on tubifex; earthworms are the main food of moles, hedgehogs, toads, starlings and other land animals. By feeding on silt and various suspensions, annelids rid the water of excess organic matter. Earthworms and some other soil worms, by eating various plant debris and passing soil through their intestines, contribute to the formation of humus. The burrows they make are filled with air necessary for the breathing of plant roots and various soil-forming organisms living in the ground.
