The variety of species included in the type Roundworms is huge, a person is constantly confronted with them. Their habitat is vast, there is no place where they live. The name comes from the shape - the cross section is round.
The sizes of individuals are very small. They can distinguish between light and dark, and are often predators. The latter settle in the organs of humans, birds and animals. Reach quite large sizes - up to 8 meters long.
The most famous and numerous representatives of the Class Proper Roundworms (or nematodes) are given a general description in terms of their importance as a source of infection for adults and children. It is often carried out on the example of ascaris and pinworms, as the most important from the standpoint of medicine.
Body structure and physiology
The characteristics of individuals of the Type Roundworms in the context of the location of the organs will not be voluminous due to the scarcity of them.
Functioning systems: nervous, as well as excretory, sexual. In the future, it is logical to carry out the description on the example of nematodes due to the high prevalence of species.
The shape of the body with pointed ends and the nature of the movements helped them adapt to living in various environments. From the outside, the nematodes are covered with several layers of cuticle, which protects against external influences. Below it is the hypodermis, followed by a layer of muscles, which is made up of longitudinal fibers, divided into 4 ribbons that help with crawling. The muscles of the back, as well as the abdominal muscles, contract, work in opposition to each other, which explains the movement of the worms on its side.
The digestive system is straight, resembling a tube. The mouth is surrounded by lips (the bulk of them have 3), in some predatory worms - by teeth. It is a tool for pinching the intestinal mucosa of the host. Organisms living on plants have a developed piercing-sucking organ - a stylet that extends from the oral cavity.
How individuals reproduce
The most important characteristic of Roundworms is the way they reproduce. It is advisable to consider the structure of the reproductive system using the example of roundworms.
In the female (which is larger than the male) it is paired and tubular. The vagina at one end goes into the opening on the abdomen, on the other hand it bifurcates into the uterus. Each, gradually narrowing, continues with the oviduct, which flows into the ovary. The tubes contain germ cells at various stages of development.
The reproductive organs of the male are unpaired:
- testis;
- spermaduct;
- ejaculatory canal;
- copulatory bag, from where cuticular needles come out - organs involved in copulation.
The seminal fluid passes through the vagina into the uterus, where fertilization takes place.
The general characteristic of the type in the context of the development of each species is more clearly seen in the example of roundworms and pinworms, which cause great harm to health and are rapidly spreading.
The eggs are very resistant, even to different temperatures, after leaving the intestines they mature to larvae. The process takes place in a humid environment for a month.
Infection follows after ingestion of eggs and larvae through food, which then seep into the veins and are carried by the blood to the lungs. Then gradually pass into the bronchi, windpipe and mouth. From there, with the help of saliva, they move a second time to the intestines, where they grow and become ready for reproduction.
Children's pinworm is very widespread. It lives most often in the intestines of children, has a length of 5-10 mm. Leads to the development of enterobiasis.
Fertilized females move to the anus, where they can live for quite a long time due to comfortable conditions, causing itching and laying eggs there. The embryos emerge from the shell, once again entering the intestine with food. Pregnant women can also become infected.
Pathogenic value
Individual representatives of nematodes can be characterized as life-threatening.
Svainik is the causative agent of a disease that causes severe anemia.
Whipworm is very common, causing trichuriasis. Its eggs are not visible to the eye due to their microscopic size. The risk of infection is high for those involved in agriculture. The disease in severe form leads to prolapse of the rectum.
Pathogen Control Measures
Avoid entry into organs. To this end, you need to observe personal hygiene, carefully choose ponds for swimming, children's playgrounds. When working in the ground, it is important to use a protective suit. Exclude fertilization of land with human and infected animal excrement.
body integuments
The body is formed by a skin-muscular sac covered with a cuticle. The cuticle cannot be stretched, so roundworms periodically shed it and increase in size.
muscles
Roundworms have 3 types of muscles: dorsal, abdominal and longitudinal, providing bending of the worm in different directions.
Digestive system
In the digestive system of worms, evolutionary changes have occurred, characterized by the appearance of the hindgut and anus. As part of their digestive system, there are 3 sections - anterior, middle and posterior. The anterior section contains the mouth, pharynx, and esophagus. Digestive processes take place in the middle section.
Respiratory system
Roundworms do not have a respiratory system. The entire surface of the body is used for gas exchange.
Circulatory system
There is no circulatory system. Transport of substances is carried out by hemolymph.
excretory system
The organs of excretion are protonephridia or skin glands, called cervical. Some roundworms do not have excretory organs.
Nervous system
The nervous system has a ladder type. It consists of a near-pharyngeal nerve ring with six nerve trunks, which are connected by jumpers.
sense organs
Roundworms are endowed with organs of touch and smell. Free-living representatives have primitive eyes.
Regeneration
Roundworms are not capable of regeneration.
reproduction
Reproduction is sexual with internal fertilization. Most representatives of the type Roundworms are dioecious. Some have sexual dimorphism. The development of roundworms is indirect, there is a larval stage.
Classification
Type Roundworms are divided into 5 classes:
Gastrociliary.
Actually roundworms, or nematodes.
Hairy.
Rotifers.
Scrapers.
How are roundworms different from flatworms?
The difference between these types:
1. Flatworms have a flat body shape. Roundworms have a round body shape.
2. The digestive system of flatworms is non-permeable: there is no anus. Roundworms developed an anus, and consequently their herbal system became permeable.
3. Roundworms reproduce only through the sexual process, while flatworms reproduce both sexually and asexually.
4. All representatives of roundworms are dioecious. Flatworms are hermaphrodites.
5. Flatworms are capable of regeneration, but roundworms are not.
The systematization of roundworms is still open. Initially, all worms (round, flat, annelids) were combined into one type - worms. In this taxonomy, the class of roundworms was subdivided into two subclasses :
- Adenophorea (Adenophorea) ;
- Secernents (Secernentea) .
The difference between subclasses consisted in the presence or absence of phasmid - tactile organs. After combining roundworms into a separate type group, a classification was proposed that distinguishes six grades :
- Nematodes (Nematoda) ;
- Gastrociliary (Gastrotricha) ;
- Kinorinchi (Kinorinchi) ;
- Hairy (Gorciiacea) ;
- Rotifers (Rotatoria) ;
- Acanthocephala (Acanthocephala) .
Subsequently, gastro-ciliated, rotifers, hairy, acanthocephalans were separated into separate types, and kinorhynchus became a class of the clade Cycloneiralia. The class Nematodes or, in fact, Roundworms has also been revised. Modern taxonomy (2011) highlights three classes of roundworms :
- Chromadoria (Chromadorea) ;
- Oenoplia (Enoplea) ;
- Dorylaimea (Dorylaimea) .
Rice. 1. The human roundworm is a representative of chromadoria.
Some experts consider the class Dorylaimea to be a subclass of Enoplea.
The classes include 31 orders, more than 200 families, and about 3000 genera. Currently, about 30 thousand species have been described, but the diversity of nematodes suggests about a million species.
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Main Representatives
Rice. 2. Potato nematode.
|
species name |
Peculiarities |
Diseases caused |
|
Ascaris |
The size of the female is 40 cm, the male is 20 cm. The eggs are resistant to chemical attack (to the acidic environment of the gastrointestinal tract), but die at high temperatures. The female lays 240 thousand eggs per day. In the environment, eggs remain viable for 6 years. Infection occurs through dirty fruits, vegetables and hands. |
Ascariasis |
|
Enterobiasis |
||
|
Vlasoglav |
It has a filamentous shape. The anterior end is much narrower than the posterior. The size of an adult does not exceed 5 cm. It is localized in the small intestine and upper colon. Infection occurs through dirty food and water. |
Trichuriasis |
|
Trichinella |
The size of the female is 3.5 mm, the male is 1.5 mm. Adult individuals are localized in the small intestine, from where the larvae through the capillaries enter the striated muscles. Infection through meat. |
Trichinosis |
Rice. 3. Pinworm.
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- the body has a primary cavity;
- the helminth has an anus and a back part of the intestine;
- type annelids are dioecious individuals.
The main signs of roundworms:
- They have a non-segmented, rounded body in cross section. Its surface is three-layered and consists of meso-, endo- and ectoderm. The worm has a skin-muscular sac.
- All types of annelids have a pseudo-target - this is the primary cavity of the body, filled with liquid. It gives the body additional elasticity and performs the functions of a hydroskeleton. This fluid is also responsible for metabolic processes. It is here that all the internal organs that form the digestive, nervous, excretory, muscular and reproductive systems are located.
- The structure of roundworms is such that they lack a respiratory and circulatory system.
- Features of roundworms also consist in the fact that their digestive system is represented by a through tube that begins with a mouth opening. The mouth is surrounded by cuticular lips. At the end of the digestive tube is the anus. The whole tube is divided into three sections. Pinworms have a special extension of the esophagus called the bulbus.
- As for the nervous system, it consists of the peripharyngeal ring, head ganglia and nerve trunks (abdominal, spinal and two lateral trunks). The most developed abdominal and dorsal rods. They are connected by special jumpers.
- No matter how many species of roundworms, all of them have poorly developed sense organs. As a rule, they consist of tactile tubercles and special organs of chemical sensation.
- The excretory system of the roundworm consists of a small number of excretory phagocytic cells. They accumulate metabolic products and foreign substances that enter the cavity of the body.
- Nematodes are roundworms that have a tubular structure of the genitals. The number of genital organs of the female, as a rule, is paired. The male, on the contrary, has unpaired genitals. His genital apparatus incorporates the testis and the vas deferens, which passes into the ejaculatory canal and opens into the back of the intestine. The body structure of the female is somewhat different. Her reproductive apparatus consists of paired ovaries, from which come two tubular oviducts and a paired uterus. It unites into a common vagina.
We have listed the common features characteristic of representatives of the roundworm type. However, the external structure of individual individuals may vary slightly. So, if you describe a group of roundworms, the representatives of this class are as follows:
- roundworm;
- whipworm;
- pinworms;
- hookworm;
- trichinella;
- guinea worm.
Roundworm
This is a rather large helminth, the female of which can grow up to 40 cm, the males - about 20 centimeters. Ascaris has a cylindrical body narrowed towards the ends. The body of the male from the rear end is twisted in a spiral towards the abdomen.
Important! Infection of people occurs when eating unwashed fruits and herbs.
The life cycle of roundworm in the human body is as follows:
- After the egg is in the intestine, its shell is dissolved by digestive juices, and the larva emerges from it.
- It enters the bloodstream through the intestinal walls. Then it migrates through the liver to the right atrium, ventricle and lungs.
- From there, through the pulmonary capillaries, the larva enters the bronchi and trachea, provoking a cough.
- During coughing, it is swallowed again and again ends up in the intestines. Here she reaches the state of a sexually mature individual, lives and breeds for up to a year.
Pinworms
Important! Eggs become infectious a couple of hours after they are laid. If, during combing this area, the eggs fall under the nails of the patient, he re-infects himself if hygiene is not observed.
Since the life expectancy of a sexually mature pinworm reaches 58 days, the patient may self-heal if there is no re-infection. As for males, they die immediately after mating with females and leave the body naturally (with feces).
The anterior filiformly elongated part of the body of the worm is thinner than the posterior one. It contains the esophagus. The posterior end of the male is thickened and spirally twisted. Here is the intestines and the reproductive system. The eggs of this worm outwardly very much resemble a barrel with caps in the form of corks at the ends. They are light transparent and reach 50 microns in length.
Trichinella
This worm is a biohelminth. Its life cycle is as follows:
The worm lives in the small intestine, where it can live up to five years. It is referred to as geohelminths. Hookworm migrates in the human body like roundworms. Eggs with feces enter the external environment, where a day later they hatch into larvae that feed on feces. After they reach the filarial stage, the larvae become infective.
Sometimes infection occurs by the oral route, but more often filariae penetrate the skin. From the intestines, the larvae migrate to the blood vessels and lungs. Then they rise through the bronchi to the trachea, from where, during the cough reflex, they are thrown into the mouth and swallowed. After that, they settle in the duodenum.
The characteristic features of the type organization are as follows:
- The body is thin, cylindrical, elongated and pointed at the ends. On a transverse section, it is round (which gave the name to the type).
- The skin-muscle sac consists of an outer multilayer without a cellular structure cuticles, below it single layer epithelium and layer longitudinal muscle fibers thanks to the contractions of which the body can bend serpentine.
- body cavity — primary, filled with liquid under greater than atmospheric pressure. The cavity fluid gives the body elasticity and, due to this, plays the role hydroskeleton. It also provides transport of nutrients and waste products.
- For the first time in the animal world, the digestive system is represented by a through digestive tube, divided into three sections - the anterior, middle and hindgut. Anterior section begins with a mouth opening leading to the oral cavity and pharynx, capable of working as a pump. The pharynx is separated from the midgut by a valve. IN midgut food is digested and absorbed. The midgut is followed by the ectodermal hindgut opening on the ventral side of the body , anus.
- The excretory system is represented by a pair of lateral longitudinal canals that merge under the pharynx into one duct and open on the ventral side of the body as an excretory opening. The end products of vital activity accumulate in the cavity fluid, and from it they enter the excretory canals.
- The nervous system is represented annular parapharyngeal ganglion and several longitudinal ones extending from it nerve trunks, interconnected by semicircular nerve bridges. There are organs of taste, touch, and free-living roundworms have light-sensitive eyes.
- Roundworms - dioecious animals that reproduce only sexually. In roundworm, males and females are outwardly distinguishable (sexual dimorphism). The reproductive system has a tubular structure: in the female - paired ovaries, oviducts, uterus and unpaired vagina, in the male - unpaired testis, vas deferens, ejaculatory canal, copulatory apparatus. Fertilization is internal, development usually proceeds with incomplete transformation (with the larval stage).
Figure 11.6. Appearance (a) and internal structure (b) roundworm: 1 - mouth opening; 2 — pharynx; 3 — intestines; 4 - vagina; 5 — uterus; 6 —oviduct; 7—ovary; 8 - ejaculatory canal; 9 — testis; 10 — vas deferens.
The development cycle is complex, associated with the release of eggs into the external environment and the migration of larvae in the human body. Fertilized eggs, covered with dense protective shells, from the human intestine enter the soil. In the presence of oxygen and a sufficiently high temperature, a larva develops in them for about a month. The egg becomes contagious (invasive). With contaminated water and food, eggs enter the human small intestine. Here the larvae are released from the shell, pierce the intestinal mucosa with their elastic body and penetrate into the blood vessels. With the blood flow through the portal and inferior vena cava, they enter the right atrium, right ventricle and lungs (through the pulmonary arteries). From the lung tissue penetrate into the bronchi, from them into the trachea, and then into the pharynx. During migration, the larvae develop in the presence of oxygen. From the pharynx, they enter the intestines, where they complete their development cycle. Life expectancy is about a year.
Roundworms have a ubiquitous distribution and a high number of individuals, which indicates the biological progress of this group of animals. Their ancestors are considered ancient ciliary worms.
