What kind of skin does an earthworm have? Features of the body structure of an earthworm
Target: Study the external structure of an earthworm.
Equipment: live earthworms, Petri dishes (disposable cups), tweezers, filter paper, magnifying glasses, onion pieces.
Progress
The stages of laboratory work that students do and record at their workplaces are reproduced on the multimedia board.
1. Examine the body of an earthworm.
Determine the size of the worm's body (length and thickness) using a ruler (bio_2007_053_p,:1.1, 1.2)
The body length of an adult earthworm is usually 15–20 cm.
Determine the segmentation of the body. Find out whether the body is segmented the same throughout the entire body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.: hint)
Identical segments.
Determine the shape of the body, find out how the dorsal side of the body differs from the abdominal side.
Convex (dorsal) and flat (ventral)
Determine body color. Find out how the dorsal side of the body differs from the ventral side.
Find the anterior (more pointed, closest to the girdle - thickening at the anterior end of the body) (bio_2007_053_p,:1.3; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.1) and posterior (blunter) ends of the body (bio_2007_053_p,:1.4),
The anterior end of the worm's body with a mouth opening. A small movable lobe in front of the mouth is located on the ventral side of the body. An earthworm has neither eyes nor tentacles.
The posterior end of the worm's body with the anus. belt Determine on which body segments the girdle is located. (bio_2007_053_p,:1.5; BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.2)
Glandular thickening of the integument. During reproduction, girdle cells secrete a cocoon substance into which fertilized eggs are placed. Pay attention to the thinnest layer of cuticle, secreted by the skin epithelium and covering the entire body.
2. Pay attention to the skin of the worm. Determine whether it is dry or wet?
3. Gently touch the worm's skin with a piece of filter paper(bio_2007_053_p,:1.6).
The skin epithelium of earthworms is rich in mucous glands. Therefore, their skin is constantly hydrated. This is of great importance in respiration, which occurs through the integument of the body when moving in the soil
4. Gently run your finger along the ventral or side of the worm's body from the back to the front end(you will feel the touch of the bristles). Using a magnifying glass, examine the location of the bristles on the body of the worm (BIOLOG_2.5.4.1.1p20_1_dozhd_chyerv_1_u.:5.3).
Each segment of the body, except for the head lobe, bears 8 pairs of setae close together, so that 4 double rows of setae stretch along the body. An earthworm moves by contracting its body. When moving in the soil, an important role is played by the alternating stretching and expansion of the front end of the body, causing the soil particles to move apart. The bristles with which the worm clings to the substrate also play a significant role in the process of movement.
5. What do you think is the significance of such skin and such bristles for the life of a worm in the soil?
6. Watch a worm crawling on paper(listen to see if it rustles with bristles) (bio_2007_053_p,:2.1).
As the worm moves along rough paper, the rustling of the bristles on the paper can be heard. The worm clings to the substrate with its bristles.
7. Watch a worm crawling on glass moistened with water. How does he move(bio_2007_053_p,:2.2)?
When moving on glass (smooth surface), the rustling of the bristles is not heard: the worm does not cling to the smooth substrate with the bristles. The body of the worm is greatly elongated, and alternating muscle contractions are observed along the entire length of the body.
8. Touch different parts of the earthworm's body with the tip of a pencil. What are you observing?
9. Bring a piece of onion to the front end of the worm's body. What are you observing?
Irritability, protective reflex.
10. Draw a conclusion about the structural features and movement of the earthworm in connection with its habitat.
Oligochaete worms have an elongated, segmented body. The surface of the body is constantly moisturized due to the secretion of mucus by the glands of the skin epithelium. This is of great importance for breathing. The movement of oligochaetes occurs due to muscle contractions. But the bristles with which the worm clings to the substrate also play a significant role in the movement of oligochaetes. Well-developed nervous system: they have irritability and protective reflexes.
Homework assignment paragraph 13
Behind the mouth opening there is a strong muscular pharynx, which passes into a thin esophagus, and then into an extensive goiter. In the crop, food accumulates and is moistened. After this, it enters the muscular chewing stomach, which looks like a bag with thick hard walls. Here the food is ground, after which, by contraction of the muscular walls of the stomach, it moves into a thin tube - the intestine. Here, under the influence of digestive juices, food is digested, nutrients are absorbed through the intestinal wall into the body cavity and enter the blood. With the blood, nutrients are carried throughout the worm's body. Undigested food remains are thrown out through the anus.
Excretory organs
The excretory organs of the worm consist of the finest whitish convoluted tubes. They lie in pairs in almost every segment of the worm's body. Each tube opens at one end with a funnel-shaped expansion into the body cavity. The other end opens outward on the animal's ventral side with a very small opening. Through these tubes, unnecessary substances that accumulate there are released from the body cavity.
Nervous system
The nervous system of an earthworm is more complex than that of a hydra. It is located on the ventral side of the body and looks like a long chain - this is the so-called ventral nerve cord. Each segment of the body has one double nerve ganglion. All nodes are connected to each other by jumpers. At the anterior end of the body in the pharynx area, two jumpers extend from the nerve chain. They cover the pharynx on the right and left, forming a peripharyngeal nerve ring. There is a thickening in the peripharyngeal ring above. This is the suprapharyngeal ganglion. Many fine nerves extend from it to the front part of the worm’s body. This explains the great sensitivity of this part of the body. This structural feature of the earthworm has a protective value. Branching throughout the tissues and organs of the body, the nervous system of the earthworm and other animals regulates and unites the activities of all organs, connecting them into one whole - the animal’s body.
Body symmetry
Unlike Hydra and many other coelenterates, the body of the earthworm exhibits clearly defined bilateral symmetry of the body. In animals with this structure, the body is divided into two identical halves, right and left - the only plane of symmetry that can be drawn along the main axis of the body from the mouth to the anus. Bilateral symmetry is characteristic of worms and many other animals.
The transition of worms from the radial symmetry of the body, characteristic of their ancestors - coelenterates, to bilateral symmetry is explained by their transition from a swimming or sessile lifestyle to crawling, to a terrestrial lifestyle. Consequently, the development of different forms of symmetry in multicellular animals is associated with changes in the conditions of their existence.
Earthworms are one of the most ancient inhabitants of planet Earth. They live almost everywhere, with the exception of the permafrost of Antarctica. Thanks to this boneless creature, the soil becomes fertile. It is their vital activity that is the fundamental factor for the formation of the fertile layer.
General characteristics and living conditions
The earthworm's body shape, color, and size are the unique characteristics of an invertebrate. Let's take a closer look.
The body of the worm is made up of many ring-shaped segments. In some individuals their number reaches 320. The worms move with the help of short bristles located on these segments. Externally, the body of individuals resembles a long tube.
For their normal functioning, the humidity level must be at 75%. Worms die if the soil dries out and the humidity drops to 35% or lower. This is due to the fact that they breathe through their skin. Consequently, they simply cannot live in dry soil and water.
The most optimal temperature for their comfortable life is from 18 to 24 degrees above zero. If it starts to get colder, the worms begin to go deeper, where it is warmer and more humid. If the atmospheric temperature does not rise, they hibernate. If this indicator rises above 42 degrees, then the worms die. The same thing happens if the temperature is too low. And worms crawl out after rain due to lack of oxygen in the soil.
Interesting fact: it was the ability to fall into a state of suspended animation that allowed worms to survive during the Ice Age.
The benefits of worms
It is thanks to worms that the soil throughout the planet is in constant motion. The lower layers rise to the top and are saturated with carbon dioxide and humic acids. These invertebrates provide potassium and phosphorus.
Worms prepare the soil for plant growth better than any human hand or technique. Thanks to these creatures, even large stones and objects sink deep into the ground over time. And small pebbles are gradually ground in the stomach of the worms and turn into sand. However, the excessive use of chemicals by humans in agriculture inevitably leads to a reduction in their population. Today, there are already 11 species of earthworms in the Red Book of Russia.
Color
The color of an earthworm directly depends on skin pigments. But this characteristic is relevant only for living individuals.
If the worm lacks skin pigments, it will remain pink or red throughout its life. In the presence of this component, the color of the earthworm can be brown, blue, yellow or brown.
For example, the Allophora chlorotica worm is yellowish or greenish in color. A Lumbricus rubellus - earthworms are brown-red or purple in color with a pearlescent tint.
Body length
The average size of all individuals is from 5 to 20 centimeters, with a thickness from 2 to 12 mm. However, in tropical forests there are invertebrate individuals up to 3 meters long. Naturally, with such sizes there can be more than 3 thousand ring-shaped segments.
Types of worms
Invertebrate animals live in all layers of the soil, hence the species that feed on the surface of the earth are distinguished:
Surface Feeders | Soil feeders |
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Litter | Individuals under no circumstances fall below 10 centimeters into the ground | Living in deep soil layers |
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Soil-litter | They live at a depth of 10 to 20 centimeters | They constantly form new tunnels, but feed in the humus layer |
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They constantly make deep passages, but only the upper end of the body can come out for food consumption and mating. |
Littering and burrowing individuals are characteristic of waterlogged soils. In other words, they live near ponds, swamps and in regions with a humid subtropical climate.
The tundra is characterized by soil-litter and litter worms. In the steppes, only soil species can be found.
Worm nutrition and digestive organs
Regardless of the type and color of the earthworm, they are all omnivores. By ingesting huge amounts of soil, they consume half-rotten leaves. From this mixture they receive useful substances. They do not eat only leaves with an unpleasant odor, but they like fresh leaves.
Charles Darwin wrote about the omnivorous nature of worms. He conducted many experiments by hanging pieces of various foods, including the remains of dead worms, over a pot containing animals, and most of this food was eaten.
After digesting the soil, the worm rises out and throws it out. Excreta, soaked in intestinal secretions, is viscous and hardens when dried in air. There is no randomness in their actions; waste is first dumped on one side, then on the other. As a result, a characteristic turret-like entrance to the burrow is formed.
Worms not only feed on leaves, plant stems, and scraps of wool, they use them to plug the entrances to burrows.
In all earthworms, regardless of body shape and color, the mouth is located at the front end of the body. The swallowing process occurs due to the muscular pharynx. After this, food - earth with leaves - enters the intestines. If some part of the food has not been digested, it is thrown away along with the processed food. The release occurs through the anus, located at the posterior end of the body.
Reproductive system
All earthworms are hermaphrodites. Before laying eggs, two different individuals exchange seminal fluid by lightly touching them. After this, each worm secretes mucus from a “belt” located on the front of the body, into which eggs enter. After some time, the lump with them practically slides off the body and turns into a cocoon. After maturation, young individuals emerge from it.
and sense organs
Absolutely all individuals, regardless of the color of the earthworm, do not have sensory organs. Their tactile sense works best. Similar cells are located throughout the body, and even a slight vibration of the ground causes the worm to hide and sink into deeper layers of soil. These elements are also responsible for the perception of light. After all, such individuals do not have eyes. But if you shine a flashlight on them at night, they will quickly hide.
Researchers say worms have a nervous system. This is confirmed by the fact that they have elementary reflexes: when the body is touched, it instantly contracts, protecting the worm from touch.
Even Darwin noticed that such creatures are distinguished by their smell. If the worm does not like the aroma of food, then he will refuse such a meal.
Animal enemies
It doesn’t matter at all what body color an earthworm has, what type it is or where it lives, all individuals have natural enemies. The most terrible of them is the mole. This mammal not only eats worms, but also stores them for the future. The mole has a paralyzing substance in its saliva that acts specifically on invertebrates. This is how he catches worms.
Frogs and shrews will not disdain to taste them. Many birds eat earthworms - these are blackbirds, poultry, starlings and woodcocks. Many arthropods do not disdain worms - these are arachnids, various types of insects and centipedes.
Vermiculture
Recently, the topic of organic vegetable growing has become relevant. The question may arise as to what worms have to do with it. Everything is very simple. Vermiculture is based on the cultivation of earthworms. In this case, it does not matter at all what color the earthworm is, the most important thing is the production of vermicompost. Recent trends suggest that vermiculture will soon completely replace harmful chemical fertilizers from agriculture.
Earthworms, they are earthworms, this is far from being one species, but an entire suborder of the class Oligochaete worms, which belongs to the phylum Annelids. The earthworm is characterized by most of the structural features of its type and class.
Earthworms are ubiquitous. Our area is home to more than a dozen species similar to each other (European earthworms), whose body length is 10-20 cm, the number of segments is 100-180. At the same time, the Australian earthworm can reach a length of 3 meters.
During the day, earthworms crawl in the soil. At night and after rain they can come to the surface. With the onset of cold weather, they go underground, to a depth of 2 m. The back of the body is slightly flattened. When crawling out of the soil, the worm holds the edge of the hole with its rear end.
The body of an earthworm, as a representative of annelids, is divided into segments by ring constrictions. As in all oligochaetes, the parapodia are reduced, only tufts of bristles are preserved from them, which allow the worm to cling, rest against the ground and facilitate pushing the body forward. In other words, the bristles provide adhesion to the substrate.
The surface of the body is moist and covered with mucus, which facilitates movement in the soil and also facilitates the penetration of oxygen into the body.
The epithelium secretes a layer of transparent cuticle and also contains many mucous cells. Under the epithelium there are circular and longitudinal muscles. The body of an earthworm can contract and elongate. Circular muscles make the body of the worm thin and long, longitudinal muscles shorten and thicken. The longitudinal layer of muscles is more powerful. Alternate contraction of these muscles ensures movement. Each segment can change its shape separately.
The coelomic sacs of adjacent segments communicate with each other, thus the liquid in them mixes.
An earthworm often swallows soil, eating its way through. Nutrient particles are absorbed from the soil in the intestines. If the soil is soft, then it drills it with the front end. First, the front end is stretched and thinned, inserted between lumps of soil. Then the front end thickens, causing the soil to move apart. Next, the worm pulls up the back of the body.
They feed on rotting plant debris. In addition, they can drag fallen leaves from the surface. By dragging plant debris into the soil, worms contribute to their decomposition and the formation of fertile soil.
The digestive system consists of the mouth, pharynx, esophagus, crop, gizzard, midgut, hindgut, and anus. Swallowing food is done through the muscular pharynx. The stomach grinds food; in addition to the muscles of the walls, swallowed grains of sand are involved in this. On the dorsal side, the wall of the midgut forms an invagination, increasing the absorption surface. The midgut is lined with ciliated epithelium, in which there are many unicellular glands. Complex organic substances are broken down in it, and simpler substances are absorbed into the blood. In the walls of the earthworm's midgut there is a dense network of blood vessels. The hindgut is small and ends at the anus.
A special feature of earthworms are calcareous glands, whose ducts flow into the esophagus. The substances they release neutralize the acids contained in the soil.
Breathing occurs over the entire surface of the skin. In the superficial layers of the body wall there is a dense network of blood vessels. When it rains, earthworms crawl to the surface due to lack of air in the soil.
The circulatory, nervous and excretory systems are similar to polychaetes. However, in the circulatory system there are so-called “hearts” - annular vessels capable of muscular contraction. Located in segments 7-13. In a number of species, ring vessels are present only in the anterior part of the body.
There are no metanephridia (excretory organs of annelids) in the anterior three segments.
Sense organs are poorly developed. The skin contains sensitive cells - organs of touch. There are also cells in the skin that perceive the degree of illumination.
Earthworms are hermaphrodites. The reproductive system is located in several segments of the anterior part of the body. The testes are located in front of the ovaries.
Mutual cross fertilization. Each of the mating worms transfers sperm to the partner's seminal receptacle.
In the first third of the body of earthworms there is a special belt; its glandular cells secrete mucus, which, when dried, forms a muff. Unfertilized eggs are laid in it. After mating, spermatozoa enter from the seminal receptacles. Fertilization occurs. After this, the sleeve slides off the worm's body and turns into a cocoon. Small worms develop from the eggs.
Capable of regeneration. If a predator tears off part of the worm's body, the other half completes the missing part. If the worm is divided into two parts, the result is two individuals, which can be considered asexual reproduction. However, the earthworm itself does not reproduce this way.
The body of the earthworm is round in shape; the length of most representatives of this genus is no more than 15 centimeters, occasionally more than twenty, and the length of the largest is slightly more than thirty centimeters.
Consists of 100-180 segments. The segments have small, fairly elastic bristles that are practically invisible, but if you run your finger from the rear tip to the front, you can immediately feel it. The worm needs bristles so that it can cling to uneven ground surfaces while moving.
On the front of the worm's body there is a small thickening that serves as the place where the genital organs are located. The cells located in this thickening are activated during reproduction to lay eggs. If you look closely, you will notice that the belly of the earthworm is somewhat lighter than the rest of the parts. The worm has not only a circulatory system, but also a nervous, tactile and digestive system.
What environment do earthworms live in?
During the daytime, worms prefer to stay in the soil of the swarm, with passages in it. Light soil, the worm drills with its front tip. To do this, he first compresses the front part so that it becomes thinner, and tries to push it forward between the soil lumps. Subsequently, the front tip becomes thicker, the lumps move apart, and the worm pulls up the back part. In hard soil, raincoats make passages for themselves, passing them through the intestinal tract. Earthen heaps are often visible on the surface of the earth - these are traces of the night activity of worms. They emerge from their burrows after heavy rainfall (that’s why they are called rainfall). In the summer, worms prefer to stay in the upper layers of the soil, and in the winter, to escape the cold, they dig holes, the depth of which can be more than two meters.
As the temperature drops, they become less active and their circulatory system circulates more slowly.
Taking a worm in your hands, you will find that its skin is moist, and it itself is covered with mucus, which makes it easier to move in the ground. Apart from this, it is only through the moist skin that the oxygen required for respiration reaches his body. This is how the worm breathes.
Directly under the skin there are circular muscles fused with it, and underneath them are longitudinal muscles. Those. An earthworm is a kind of skin-muscular sac. Thanks to the circular muscles, the body of the worm becomes thinner and longer, and thanks to the longitudinal muscles, it shortens and thickens. Due to the alternate functioning of these data, the muscle and the worm move.
How does an earthworm work?
The structure of an earthworm, when compared with the organisms of other animals, is quite primitive, but it has quite interesting features. Under the skin-muscular pouch there is a fluid-filled cavity of the body, and it contains the internal organs. When compared with roundworms, the body cavity of a roundworm is divided by septa, the number of which is equal to the number of segments. They have their own separate walls and are located under the skin-muscular pouch.
Now let's take a closer look at all the available organs of the worm.
Digestive system
The earthworm's mouth is located at the front. The puffball prefers rotting vegetation, swallowing it with soil. Likewise, he often drags fallen leaves into his hole. Swallowing is accomplished through the pharynx. Next, the food ends up in the intestines. Food that has not had time to be digested comes out through the anus located at the back. This is how the digestive system works in almost all types of worms. The worm also needs its mouth in order to drag various small objects to which it simply sticks. As you can see, the digestive system is quite primitive and lacks the organs that higher beings have.
The earthworm has a closed circulatory system, but there are some peculiarities. It is based on two main vessels, the dorsal and the abdominal, which are connected to each other using ring vessels, in some ways very similar to arteries and veins. Depending on the species, the blood of worms can be colorless, red or even green.
Speaking about the circulatory system of the earthworm, the dorsal vessel, which pulsates blood throughout the body, deserves special attention.
Special vessels that cover the intestines and are located in all segments, distill blood into the cavity of the abdominal vessel, which cannot pulsate on its own. The worm's blood flow is from front to back. In addition to these blood flows, there are also vessels that carry blood from the dorsal to the parapodial vessels. In them, the blood oxidizes when it comes into contact with environmental oxygen.
The skin of an annelid worm also has its own vessels, which are connected to the general circulatory system. Those. The circulatory system of worms is quite complex, but it is thanks to it that worms survive in rather difficult conditions.
Nervous system
The nervous system of annelids consists of two nerve trunks. Nerve nodes are formed in the segments on them. those. a kind of nerve chain emerges. In front, two nodules are connected to each other by circular bridges - a perioral nerve ring is formed. Nerves go from the nodules to various organs.
Organs of touch
Worms do not have special organs of touch, but sensitive cells in the skin allow it to feel touch and distinguish when it is light and when it is dark.
Reproductive system
As you know, and we have already talked about this, worms are hermaphrodites, that is, they can do without mating. But most often, reproduction occurs after contact between two individuals and the exchange of sperm between them. Then they spread out, and mucus begins to secrete from a kind of coupling located in front. Into which the eggs subsequently arrive. Then the lump of mucus slides off the worm's body, forming a cocoon. From which small worms are subsequently obtained.
This video talks about the structural features of earthworms.