In total, there are more than 20 thousand.species of these creatures. But at school they study only one of them. Depending on their biological characteristics, they can live in different conditions. Soil, fresh water and the sea - this is the habitat of roundworms. Also, there are some representatives leading a parasitic lifestyle.
general characteristics
These are non-segmented animals.The primary body cavity is filled with fluid. They are capable of active movement. Food for free-living species are bacteria, algae and single-celled. They, in turn, feed on fish fry, small crustaceans.
The school most often consider suchrepresentatives of parasitic forms like pinworms and roundworms. They are able to live inside their owner, whose role is played by animals and even humans. In humans, they lead to a deterioration of health, whereas in birds, fish and insects, there are sometimes cases of mass mortality. Some species are parasitic on mushrooms and plants.
Structure
The structure of roundworms suggests the presence of a cylindrical or spindle-shaped body. The cuticle covers it outside. The primary cavity is located under the skin-muscular bag.
Food is ingested through the mouth in the throat.From here it goes to the digestive tube consisting of the anterior, middle and posterior intestines. It ends with the anus. Modified skin glands are part of the excretory system.
These creatures are dioecious. They lack systems such as respiratory and circulatory.
Universal possibilities in terms of adaptation to environmental conditions can be explained by the presence of a dense outer layer (cuticle).
The habitat of roundworms in some cases includes moss. They are able to penetrate various parts of plants: stems, roots, tubers and leaves.
The distribution area of these creatures is wide.
Differences from other types
The structure of roundworms is somewhat different fromanatomical features of their flat counterparts. The cross section shows that the body has the shape of a circle. It is symmetrical and elongated. The skin-muscular bag serves as a kind of wall for it. The cuticle located outside plays the role of a skeleton.
Adaptive mechanisms of parasitic worms are such that this layer is not destroyed under the influence of the digestive juices of the host. Also, he is not afraid in some cases of chemical exposure.
Next is the hypodermis. This skin is made up of protoplasm. Under it are the longitudinal muscles. They are separated by a kind of ribbons.
Muscle cells consist of two parts:
- contractible;
- plasmatic.
Representatives of roundworms have mouthhole located in the front of the body. There is no epithelium lining. In addition to the internal organs, there is also a cavity fluid. In some species, it may have toxic properties. The great pressure created by it provides reliable support for the muscular bag. It is also important in terms of metabolism.
The characteristic of the roundworm includesmany important features. It is noteworthy that these creatures lack blood and blood formation organs. Air exchange at them is made through external integuments. Parasitic forms are able to do without oxygen.
Reproduction
In most cases, representatives of roundworms are dioecious organisms. Due to this, their descendants are distinguished by genetic diversity. For individuals, the so-called sexual dimorphism is characteristic, that is, males do not look like females in appearance.
Development is carried out indirectly. The larval stage takes place. A change of owner is not required. The type of fertilization is internal.
Sense organs and nervous system
Nervous system
It refers to the ladder type.It is otherwise called "orthogon." The throat is surrounded by a particular nerve ring. There are 6 nerve trunks that move back and forth. Among them, the most developed are spinal and ventral. They are connected with jumpers.
Sense organs
There are organs of touch and chemical feeling, that is, worms are able to catch odors. The eyes in the most primitive of their appearance are present in free-living representatives.
There are several classes, but the mostnumerous are nematodes. If your child goes to the 7th grade, roundworms will be studied in the biology program. Traditional representatives considered in school:
- roundworm;
- pinworms
Roundworm. Character traits
The first type of worms is a parasitic imagelife and lives in the small intestine. Helminth reaches a length of 40 centimeters. The female is able to lay over 200 thousand eggs per day. Their development without oxygen is impossible. They are covered with protective shells, arranged in several layers. Inside are the larvae. Their viability sometimes lasts up to 10 years.
При недостаточном соблюдении гигиены происходит invasion, that is, infection. In this case, the eggs fall into the oral cavity from the surface of unwashed vegetables and fruits, as well as hands. All this is indicated in the subject "biology". Roundworms do not need a change of hosts for development.
After entering the intestine, the larvae emerge fromthe eggs. They easily penetrate the mucous membrane and are introduced into the bloodstream. After that, they enter the heart and further into the lungs. From here they go to the bronchi and trachea. During this period, a person has a cough.
Перемещение личинок может продолжаться до 12 days. All this time they grow and change the shell several times. After re-entering the small intestine, they continue to grow for three months. At the end of this period, the worms become adult individuals. Each of them lives about 1 year.
These types of roundworms are dangerous becausecause poisoning in the body. Intoxication occurs under the influence of toxic substances that are the result of the activity of the parasites. In addition, after getting into the organs and cavities ascaris causes them mechanical damage.
Pinworm. Characteristic roundworm
Еще один представитель класса - острица.She usually lives in the large intestine. It is characterized by small size. Females are larger than males and reach 12 mm. Infection is carried out in the same way as in the case of ascaris.
The main cause of the invasion is insufficienthygiene. If you have washed your hands badly after visiting the toilet room, these types of roundworms can easily enter your body. Particular care should be exercised while in public places.
If pinworm eggs get under their nails, theycan easily get into the mouth. After 6 hours, the larvae will appear from them. Once in the small intestine, they will move to its end sections. After another 14 days, the parasites will begin to multiply. Each individual lives no more than a month. But if re-self-infection occurs, the disease can be delayed. Sometimes flies and cockroaches also carry helminth eggs.
Value in human life and nature in general
The type is represented not only by parasites, but also by predators. Plants are habitats for roundworms of the following species:
- onion;
- beet;
- wheat;
- potato
Parasites have a dampening effect on crop growth. As a result, their yield is significantly reduced.
Among these creatures can detect detritofagov. The source of food for them are organic residues, humus. Such worms are directly involved in soil formation.
Where do nematodes meet?
Finding them is not as difficult as it seems.If you suddenly find yourself out of town, head to the nearest river or lake. Pay attention to the sand, located on the shore. These creatures are often found in it. It also makes sense to look for growths on trees and old snags. This is also the habitat of roundworms.
Some species live in algae.Thus, they can be found almost everywhere. Each of them has its own power source. Despite this, they do not have to starve. Someone rummaging in the sand and looking for bacteria, others are actively pulling juices from plants.
Roundworms also live in the forest.To discover them, you should come here in rainy weather. If desired, you can simply take a piece of moss or lichen and drop it into the water. Surely you will find in it representatives of this type.
But how do they survive if in the soil orDoes vegetation contain enough moisture? They come to the aid of natural protection. As soon as the moss dries out, the nematodes fall into anabiosis. At the same time they remain alive. This condition is necessary in order to successfully wait out the best of times. The same can be said about the parasites that are awaiting a new host. They will become active only when conditions are acceptable for life.
