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 various 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 organisms. They, in turn, feed on fish fry, small crustaceans.
In school, representatives of parasitic forms such as pinworms and roundworms are most often considered. They are able to live inside their host, 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 fungi and plants.
Building
The structure of roundworms suggests the presence of a cylindrical or spindle-shaped body. The cuticle covers itoutside. The primary cavity is located under the skin-muscle sac.
Food is delivered through the mouth into the throat. From here it goes into the digestive tube, consisting 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 respiratory and circulatory systems.
Universal ability to adapt 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-muscular sac serves as a kind of wall for him. The cuticle, located on the outside, acts as a skeleton.
The adaptive mechanisms of parasitic worms are such that this layer is not destroyed by the digestive juices of the host. He is also not afraid of chemical exposure in some cases.
Next is the hypodermis. This skin is made up of protoplasm. Under it are the longitudinal muscles. They are separated by peculiar ribbons.
Muscle cells are made up of twoparts:
- reducible;
- plasmic.
Representatives of roundworms have a mouth opening located in front of the body. It has 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 a reliable support for the muscle bag. It is also important in terms of metabolism.
The characteristic of the roundworm includes many important features. It is noteworthy that the organs of hematopoiesis and respiration in these creatures are absent. Their air exchange is carried out through the outer covers. Parasitic forms are completely capable of doing without oxygen.
Reproduction
In most cases, representatives of roundworms are dioecious organisms. Due to this, their descendants are genetically diverse. Some individuals are characterized by the so-called sexual dimorphism, that is, males do not look like females in their appearance.
Development is carried out indirectly. There is a larval stage. A change of owner is not required. Fertilization type - internal.
Sense organs and nervous system
Nervous system
Belongs to the ladder 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 are dorsal and abdominal. They are connected with jumpers.
Sense Organs
There are organs of touch and chemical sense, that is, worms are able to detect odors. Eyes in their most primitive form are present in free-living representatives.
There are several classes, but the most numerous are the nematodes. If your child is in 7th grade, they will study roundworms in the biology program. Traditional Representatives Considered at School:
- Ascaris;
- pinworms.
Ascarids. Features
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 arranged in several layers. There are larvae inside. Their viability sometimes lasts up to 10 years.
With insufficient hygiene, invasion occurs, that is, infection. In this case, eggs enter 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 to change hosts to develop.
After entering the intestines, the larvae emerge from the egg. They easily penetrate the mucous membrane and are introduced into the blood stream. After that, they enter the heart and then to 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 12days. All this time they grow and change their shell several times. After re-entering the small intestine, they continue to grow for three months. At the end of this period, the helminths become adults. Each of them lives for about 1 year.
These types of roundworms are dangerous because they cause poisoning in the body. Intoxication occurs under the influence of toxic substances, which are the result of the vital activity of parasites. In addition, after entering the organs and cavities, the ascaris causes mechanical damage to them.
Pinworm. Characteristics of roundworm
Another representative of the class - pinworm. It usually lives in the large intestine. 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 didn't wash your hands well after going to the restroom, these types of roundworms can easily enter your body. Be especially careful when in public places.
If pinworm eggs get under the nails, they can easily get into the mouth. After 6 hours, larvae will appear from them. Once in the small intestine, they move to its final sections. After another 14 days, the parasites will begin to multiply. Each individual lives no more than a month. But if re-infection occurs, the disease can be delayed. Sometimes flies and cockroaches also carry helminth eggs.
Meaning in human life and nature in general
Typerepresented not only by parasites, but also by predators. Plants are habitat for roundworms of the following species:
- onion;
- beet;
- wheat;
- potato.
Parasites have a depressing effect on the growth of crops. As a result, their yields are significantly reduced.
Detritophages can be found among these creatures. The source of food for them is organic residues, humus. Such worms are directly involved in the formation of the soil.
Where are nematodes found?
Finding them is not as difficult as it seems. If you suddenly find yourself out of town, go to the nearest river or lake. Pay attention to the sand on the shore. These creatures are often found in it. It also makes sense to look at 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 is digging in the sand and looking for bacteria, others are strenuously extracting the 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 the soil or vegetation containsnot enough moisture? They come to the aid of natural protection. As soon as the moss dries up, the nematodes fall into suspended animation. However, they remain alive. Such a state is necessary in order to successfully wait out hard times. The same can be said about parasites waiting for a new host. They will begin to show activity only when conditions are acceptable for life.
