Ringworms are practically the largest species of higher animals that live freely in soil, sea and fresh water. This type of worm has a more complex organization than round worms or flat ones.
In ring-shaped worms, a secondary cavity, a highly organized blood supply system, and the nervous system first appear.
Earthworm: structure
In cross section, the body is almost round. The average length is about 30 cm. It is divided into 150-180 segments, or segments. The belt located in the anterior third of the body performs its function during the period of sexual activity (earthworm - hermaphrodite). Four rigid, well-developed small setae are located on the sides of the segments. They contribute to the movement of the body of the worm in the soil.
The body color is reddish brown, and on the abdomen is slightly lighter than on the back.
Natural necessity
The circulatory system is present in all animals, starting with the secondary cavity annelids. It was formed due to an increase in vital activity (compared, for example, with flatworms). Living in constant motion requires stable, energetic muscle work, which, in turn, necessitates an increase in the cells of the incoming oxygen and nutrients that only blood can deliver.
What is the circulatory system of the earthworm? The two main arteries are the dorsal and the abdominal cavity. In each segment between the arteries are looped vessels. Of these, several are slightly thickened and covered with muscle tissue. In these vessels performing the work of the heart, the muscles, contracting, push blood into the abdominal artery. The ring "hearts" at the exit to the spinal artery have special valves that prevent the blood flow from going in the wrong direction. All vessels are divided into a large network of the thinnest capillaries. Oxygen in them comes from the air, and nutrients are absorbed from the intestines. Capillaries located in muscle tissue give off carbon dioxide and decay products.
The circulatory system of the earthworm is closed, since it does not mix with the fluid of the cavity during the entire movement. This makes it possible to significantly increase the rate of metabolism. In animals that do not have a blood pumping system, heat transfer is two times lower.
Earthworm Circulatory System
The nutrients absorbed by the intestines during the movement of the worm are distributed through a well-formed circulatory system.
Her scheme is quite complicated for this type of animal. Above and below the intestine, blood vessels run along the entire body. The vessel passing in the back is equipped with muscles. She, contracting and stretching, wave-like pushes blood from the back to the front of the body. In the anterior segments (in some types of worms it is 7-11, in others - 7-13), the vessel running along the back communicates with several pairs of vessels extending transversely to the main one (usually 5-7). The circulatory system of the earthworm with these vessels imitates the hearts. Their muscles are developed much stronger than the others, therefore they are the main ones in the whole system.
Functional Features
The functions of the circulatory system of the earthworm are similar to the functions of the hemodynamics of vertebrates. Blood flowing out of the hearts enters a vessel located in the abdominal cavity. In it there is a movement to the posterior end of the body of the worm. On its way, this blood carries nutrients to smaller vessels located in the walls of the body. During puberty, blood also flows to the genitals.
The structure of the circulatory system of the earthworm is such that the vessels in each organ pass into the smallest capillaries. Blood from them flows into the vessels located across the main, from which blood flows into the spinal artery. Musculature is present in all blood vessels, even the smallest. This allows the blood to not stagnate, especially in the peripheral part of the circulatory system of this type of annular.
Intestines
In this part of the body of the worm is a particularly dense plexus of capillaries. They seem to entangle the intestines. Part of the capillaries brings nutrients, another part carries them throughout the body. The muscles of the vessels surrounding the intestines of this ringed species are not as strong as the spinal vessel or heart.
Blood composition
The circulatory system of the earthworm in the lumen is red. This is because the blood contains substances that are close in their chemical structure to hemoglobin, which is part of the blood composition of vertebrates. The difference lies in the fact that these substances are in plasma (the liquid part of the blood composition) in dissolved form, and not in the blood cells. The blood of the earthworm itself is cells without color, of several types. They are similar in structure to the colorless cells that make up the blood of vertebrates.
Oxygen cell transport
Oxygen cells in vertebrates from the respiratory system carry hemoglobin. In the blood of earthworms, a substance similar in composition also brings oxygen to all cells of the body. The only difference is that the worms have no respiratory organs. They “inhale” and “exhale” the surface of the body.
A thin protective film (cuticle) and worm skin epithelium together with a large capillary network of the skin guarantee good absorption of oxygen from the air. The capillary web is so large that it is even in the epithelium. From here, blood moves through the wall vessels of the body and transverse vessels into the main trunk channels, so that the whole body is enriched with oxygen. It is the large capillary network of the walls that gives the reddish tint to the body of this ringed species.
Here it must be taken into account that the thinnest film covering the body of the earthworm (cuticle) is very easily moistened. Therefore, first, oxygen dissolves in drops of water, which are retained by skin epithelium. From this it follows that the skin must always be moisturized. Thus, it becomes clear that environmental humidity is one of the important conditions for the life of these animals.
Even the slightest drying of the skin stops breathing. For the circulatory system of the earthworm does not bring oxygen cells. Not very long, he can hold out in such conditions, using internal water supplies. Glands located in the skin help out. When the situation becomes really acute, the earthworm begins to utilize the cavity fluid, sprinkling it in parts from the pores located on the back.
Digestive and nervous systems
The digestive system of earthworms consists of the anterior intestine, middle and posterior. Due to the need to live more actively, the digestive system of earthworms has gone through several stages of improvement. The digestive apparatus appeared departments, each of which has a specific function.
The main organ of this system is the intestinal tube. It is divided into the oral cavity, pharynx, esophagus, stomach (muscular body), middle and hind intestines, anus.
The ducts of the glands enter the esophagus and pharynx, which affect the pushing of food. In the middle intestine, food is chemically processed, and digestion products are absorbed into the blood. Residues exit through the anus.
Along the entire length of the body of the worm, from the side of the peritoneum, the neural chain runs. Thus, each segment has its own developed nerve lumps. In the front of the neural chain there is a ring bridge, consisting of two connected nodes. It is called the periopharyngeal nerve ring. From it diverges a network of nerve endings throughout the body.
The digestive, circulatory and nervous system of the earthworm is significantly complicated, due to the progress of the entire species of annulus. Therefore, in comparison with other types of worms, they have a very high organization.