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. There are also individual 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 unicellular. They, in turn, feed on fish fry, small crustaceans.
At school, representatives of parasitic forms such as pinworms and roundworms are most often considered. They are able to live inside their master, whose role is played by animals and even humans. In humans, they lead to a deterioration in well-being, while in birds, fish and insects, cases of mass death are sometimes noted. Some species parasitize on fungi 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-muscle bag.
The intake of food is carried out through the mouth into the throat. From here, it goes into the digestive tube, which consists of the anterior, middle, and posterior intestines. It ends with an 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 invade various parts of plants: stems, roots, tubers and leaves.
The distribution range of these creatures is wide.
Differences from other species
The structure of roundworms is somewhat different from the anatomical 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-muscle bag serves as a kind of wall for it. The cuticle located outside performs the role of a skeleton.
The adaptive mechanisms of parasitic worms are such that this layer does not collapse 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 consists of protoplasm. Under it are the longitudinal muscles. They are separated by peculiar ribbons.
Muscle cells are made up of two parts:
Representatives of roundworms have a mouth opening located in front of the body. There is no lining of the epithelium in it. In addition to 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 muscle bag. It is also important in terms of metabolism.
The characteristic of a roundworm includes many important features. It is noteworthy that the organs of hematopoiesis and respiration in these creatures are absent. They exchange air through the outer covers. Parasitic forms are completely capable of doing without oxygen.
Breeding
In most cases, representatives of roundworms are dioecious organisms. Due to this, their descendants are distinguished by genetic diversity. For individual individuals, the so-called sexual dimorphism is characteristic, that is, males are not similar to females in their appearance.
Development is carried out indirectly. There is a larval stage. A change of owner is not required. The type of fertilization is internal.
Sense organs and nervous system
Nervous system
Belongs to the staircase type. It is otherwise called "orthogon". The pharynx is surrounded by a special nerve ring. There are 6 nerve trunks that extend back and forth. Among them, the most developed ones are dorsal and abdominal. They are connected using jumpers.
Sensory organs
There are organs of touch and chemical sensation, that is, worms are able to pick up odors. Eyes in their most primitive appearance are present in free-living representatives.
There are several classes, but the most numerous are nematodes. If your child goes to grade 7, roundworms will be studied in the biology program. Traditional representatives considered at school:
Roundworm. Specific traits
The first type of worms leads a parasitic lifestyle and lives in the small intestine. Helminth reaches a length of up to 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 located in several layers. Inside are larvae. Their viability sometimes persists until 10 years.
With insufficient hygiene, invasion, that is, infection, occurs. In this case, the eggs enter the oral cavity from the surface of unwashed vegetables and fruits, as well as hands. All this is indicated in the subject of "biology". Roundworms do not need to change hosts for development.
After entering the intestines, the larvae exit the egg. They easily pierce the mucous membrane and invade the bloodstream. After that, they enter the heart and then into the lungs. From here they pass into the bronchi and trachea. During this period, a person has a cough.
The movement of larvae can last up to 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, helminths become adults. Each of them lives about 1 year.
These types of roundworms are dangerous in that they cause poisoning in the body. Intoxication occurs under the influence of toxic substances that are the result of the life of parasites. In addition, after getting into the organs and cavities of the roundworm, it inflicts mechanical damage to them.
Pinworm. Roundworm Characteristics
Another representative of the class is pinworm. Usually she 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 roundworm.
The main cause of invasion is poor hygiene. If you wash your hands poorly after visiting the toilet room, these types of roundworms can easily enter your body. Particular care should be taken while in public places.
If pinworm eggs fall under the nails, they can easily get into the mouth. After 6 hours, larvae will appear from them. Once in the small intestine, they will move to its final sections. After another 14 days, the parasites will begin to multiply. Each individual lives no more than a month. But in case repeated self-infection occurs, the disease can drag on. Sometimes flies and cockroaches also carry helminth eggs.
Significance in human life and nature in general
The type is represented not only by parasites, but also by predators. Plants - the habitat of roundworms of the following species:
- onion;
- beetroot;
- wheat;
- potato.
Parasites have a depressing effect on crop growth. As a result, their productivity is significantly reduced.
Among these creatures, detritophages can be found. The source of food for them are organic residues, humus. Such worms are directly involved in soil formation.
Where do nematodes occur?
Finding them is not as difficult as it seems. If you suddenly find yourself in the countryside, go to the nearest river or lake. Pay attention to the sand located on the shore. These creatures are often found in him. It also makes sense to look at growths on trees and old driftwood. 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 digs in the sand and looks for bacteria, while others intensively pull juices from plants.
Roundworms also live in the forest. To find them, you should come here in rainy weather. If desired, you can simply take a piece of moss or lichen and lower it into the water. Surely you will find representatives of this type in it.
But how do they survive if there is not enough moisture in the soil or vegetation? Natural protection comes to their aid. As soon as the moss dries up, the nematodes fall into suspended animation. However, they remain alive. This condition is necessary in order to successfully wait out the bad times. The same can be said of parasites awaiting a new host. They will begin to show activity only when the conditions are acceptable for life.