Type of roundworms - nematodes, very numerous and diverse. This type of living organisms unites almost 25 thousand species, united in 31 orders and 3 classes.

The sizes of roundworms differ in variety - from a few micrometers to several meters.

The most microscopic roundworms have a size of no more than 80 micrometers. Nematodes have a whole, unsegmented, filamentous, or spindle-shaped body. Some worms are barrel-shaped or lemon-shaped.

The body of roundworms is a developed muscular system, and in some species it is covered with a smooth, in others - annular nine-layer cuticle (skin). This gives them the opportunity to adapt to various living conditions: in water, in the ground, in the organisms of animals and humans.

Under the cuticle is the subcutaneous layer - the hypodermis, which forms 4 chords around the circumference of the body:

• Dorsal - on the back.
• Ventral - on the abdomen.
• 2 side.

The nervous system plays an important role in the activity of the internal organs of nematodes, so it is quite developed.

Inside the spinal and ventral chords are parallel nerve fibers connected by transverse bridges and assembled into single nerve trunks. The first such jumper is located in the throat of the worm. From them, nerve fibers depart to the muscles and other organs. On the sides are sensitive sensory nerves.

The sense organs in roundworms are poorly developed, and are represented by bristles in the abdominal part of the body. With these bristles, nematodes sense their surroundings, their location. Small dimples serve as organs of smell. Large, to some extent developed species of worms have the simplest organs of vision.

Digestive organs

The digestive system of roundworms is similar in structure to a through tube. It begins with the mouth, then follows the esophagus, which passes into the anterior, then the middle intestine and ends with the posterior intestine, which goes out on the abdomen from the tail end of the worm.

The main features of roundworms are that they have:

• The whole is a hollow space of the body, filled not with connective tissue, as in other worms, but with liquid. The coelom is called the primary body cavity.
• The caudal part of the intestine, ending with the anus.

The roundworm's mouth leads into an easily expanding pharynx, provided with lips. Along the edges of the mouth opening there are teeth with which the worm grinds food. The pharynx opens the entrance to the midgut and acts as a kind of pump.

In the process of contraction of the radial muscles, food is sucked into the intestine. The movement of food is also facilitated by intracavitary fluid, which forms pressure in the intestines.

Roundworms do not have hematopoiesis, and there is no respiratory system. But gas exchange still occurs. We can say that the worms "breathe" the cuticle, or integument of the body. The energy of the nematode is obtained from glycogen, which is broken down in the internal organs of the worm.

The decay products are excreted from the body by the primary cavity fluid. Nutrients after processing in the intestines also enter this fluid, and are delivered to other parts of the body.

The excretory system is represented by two closed ducts that lead to the abdomen of the nematode. The decomposition products formed in the body of the roundworm first enter the coelom fluid, from it into the ducts of the excretory system, from where they are excreted.

A feature of roundworms can be called their sexual division into male and female individuals. The genitals of both have an elongated tubular shape. In the paired genital organs of the female, represented by a double uterus, as well as two ovaries with oviducts, from several tens to several thousand eggs are formed after the sexually mature male introduces spermatozoa from the vas deferens into the female's genital slit with needles formed from the cuticle.

About 25,000 species are currently known.

Modern taxonomy

Groups previously considered classes in to the group Primary worms (or Roundworms in the broadest sense):

Gastrotrichous (Gastrotrichous)

Rotifers

hairies

kinorhynchus

priapulides
Currently they are separate types.
The group Primary worms was disbanded as a team (having no common evolutionary origin).

In modern systematics, nematodes belong to the Moulting (Ecdysozoa) group, along with arthropods, tardigrades and the above types, except for rotifers (they belong to Platyzoa).

General characteristics of the nematode class

Bilateral symmetry

Three-layer

There is a primary body cavity.

Primary body cavity (pseudocoel)- a body cavity that does not have its own epithelial lining.

In roundworms, the primary body cavity is the space between the muscles and intestines filled with pressurized fluid that performs the function hydroskeleton. All internal organs are located in the primary cavity.

Functions of the primary body cavity:

Maintaining the shape of the body;
- participation in muscle movement (in combination with muscles and hard cuticles). Since the fluid is incompressible, it transmits pressure well;
- transport of nutrients and metabolic products.

The body is thin (usually a few mm in diameter), cylindrical, non-segmented, elongated and pointed at the ends. On the transverse section, it is round, which gave the name to the type.

Cytological features

Characteristic of nematodeseuthelium- the constancy of the number of cells in the body. The development program is strictly genetically predetermined and specific to the species.
Mosaic development(hard deterministic, that is, the fate of each cell is strictly predetermined), there is no tendency to regulation.

Size of nematodes

Rice. The internal structure of roundworm

excretory system: 2 lateral blindly closed canals, merging under the pharynx into one duct, opening on the ventral side of the body with an excretory opening. The end products of vital activity accumulate in the cavity fluid, and from it they enter the excretory canals. There are no flame cells with cilia.
In addition, ammonia can be released from the nematode body by diffusion through the body wall.

circulatory system no. The transport of substances is carried out by the primary cavity of the body.

Nervous system: annular peripharyngeal ganglion, two longitudinal nerve trunks - dorsal and ventral, passing in ectoderm ridges and interconnected by semicircular nerve bridges. In addition, there are nerve fibers that run along the body.

sense organs represented by numerous sensilla and tactile tubercles at the mouth opening: mechano- and chemoreceptors. There are organs of taste, touch, and free-living roundworms have light-sensitive eyes.

reproductive system: most are dioecious. Often: sexual dimorphism.
♀: paired ovaries, oviducts, uterus and genital opening on the ventral side.
♂: unpaired filiform testis and vas deferens, which flows into the intestine in front of the anus (essentially a cloaca). There is a complex copulatory apparatus with devices for holding the female during copulation. Spermatozoa are amoeba.
Fertilization is internal, development proceeds with incomplete transformation (4 larval stages).

human roundworm

♀: 20 - 40 cm.

♂: 15 - 20 cm. The back end of the body is bent down.

Disease: ascariasis.

The development of roundworm occurs without a change of owners; the only owner is a human.

Due to the presence of a multi-layered strong cuticle and intracavitary pressure, the roundworm body is tense like a string. Relying on intestinal loops, it easily resists the movement of food masses.

Food: contents of the small intestine.

Life cycle of roundworm

The development cycle is complex, associated with the release of eggs into the external environment and the migration of larvae in the human body. In the development cycle, the roundworm goes through several larval stages.

Under favorable conditions, eggs can remain viable for up to 10 years.

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 within a month. After the first larval molt in the egg, the egg becomes infective ( invasive).

Rice. fertilized roundworm egg

With contaminated water and food, eggs are eaten by humans and enter the small intestine.

Here the larvae hatch, pierce the intestinal mucosa and enter the blood vessels. With the blood flow through the portal vein, liver and inferior vena cava, they enter the right atrium, right ventricle and through the pulmonary artery to the lungs.

The larvae successively pass from the blood into the pulmonary vesicles, bronchi, windpipe and into the oral cavity of the host, and from here, together with saliva, enter the intestine for the second time.

During migration, the larvae molt 2 times and increase in size up to 2.2 mm. Migration of roundworm larvae lasts about 2 weeks.

In the intestine, the larvae grow, molt again and reach sexual maturity in 2-2.5 months. The life expectancy of adult roundworms is about 1 year.

Eggs and larvae develop in the presence of oxygen, the adult form is a strict anaerobe.

Rice. Life cycle of roundworm

Pinworm (Enterobius vermicularis)

Rice. Pinworm structure. 1 - mouth; 2 - vesicle; 3 - esophagus; 4 - bulb of the esophagus; 5 - intestines; 6 - genital opening; 7 - uterus; 8 - ovary; 9 - anus.

Rice. Male and female pinworm

♀: up to 12 mm. The tail is styloid.

♂: up to 5mm. The tail is spiral.

Disease: enterobiasis.

It lives in the lower part of the small intestine and in the upper part of the large intestine, more often in the caecum.

Food: intestinal contents.

Rice. Self-infection with enterobiasis

At the anterior end of the body of pinworms there is a swelling that surrounds the mouth opening and is called the "vesicle". With its help, the pinworm is attached to the intestinal wall.

Pinworm life cycle

Mating of pinworms occurs in the human ileum, after which the male dies, and numerous eggs develop in the female. To lay them, the female crawls out of the anus through the rectum, after which she lays eggs on the perianal folds and dies.

The total life expectancy of pinworms in the human body does not exceed 1 month. Then comes self-healing.

Carriers: insects (flies, cockroaches, etc.). Infection occurs by eating food contaminated with eggs. Often there is a self-infection of the patient.

Prevention: ironing, food hygiene and personal hygiene (washing hands, vegetables, fruits).

Human whipworm (Trichocephalus trichiurus)

Vlasoglav - the causative agent of trichuriasis.

In Russia, this invasion ranks second after ascariasis.

Rice. Vlasoglav

The back of the body of the female is straight, widened. It contains all the main sections of the digestive tract; the female has a uterus. The rear end of the body of the male is wrapped in the form of a spiral.

Whipworm eggs are shaped like a barrel or a lemon with light "plugs" at the poles.

Whipworm life cycle

A person becomes infected with trichuriasis by swallowing whipworm eggs. The cycle of development passes without migration. Larvae emerge from the eggs, which move to the caecum, where they penetrate the mucous membrane with their narrow anterior end and remain there until the end of their lives. A month later, the helminths reach puberty and begin sexual reproduction.

The life expectancy of the whipworm is 5-6 years.

Trichinella spiral (Trichinella spiralis)

The causative agent of trichinosis natural focal zooanthroponosis.

Foci of trichinosis can be natural and synanthropic.

Rice. Adult Trichinella and its larva in the muscles

Sexually mature Trichinella reach 3-4 mm in length.

The females are viviparous.The larvae migrate to the striated muscles, supplied with a dense network of blood capillaries (muscles of the tongue, diaphragm, esophagus, eyes, etc.), and there they encapsulate, causing fever and various allergic manifestations.

life cycle of trichinella

Infection with trichinosis occurs by eating the meat of animals containing live encapsulated larvae of Trichinella. In the gastrointestinal tract, under the action of digestive enzymes, the capsule dissolves, the larvae enter the intestinal lumen, where, after several molts, they turn into sexually mature forms.

Then fertilization takes place. Fertilized females give birth to live larvae. The female lives for about 3-6 weeks, and during this time she hatches from 200 to 2000 larvae.

The larvae penetrate the lymphatic and circulatory systems and are carried throughout the host's body with the bloodstream. During migration, the larvae molt several times. Then, with the help of a drilling stylet and a secreted enzyme, the larvae actively penetrate from the capillaries into the fibers of the striated muscles.

In the muscles, the larvae coil up into a spiral. An inflammatory process develops around them, and a connective tissue capsule is formed. After about 1 year, the walls of the capsule calcify. The larva remains viable inside the capsule up to 20-25 years.

Rice. life cycle of trichinella

For the transformation of the larvae into a sexually mature form, they must enter the intestines of another host. This happens if the meat of an animal with trichinosis is eaten by an animal of the same or a different species: for example, the meat of one trichinosis rat is eaten by another. In the intestines of the second host, the capsules dissolve, releasing the larvae, which turn into sexually mature forms (males and females) within 2-3 days. After fertilization, the females give birth to a new generation of larvae.

Each organism infected with Trichinella first becomes the definitive host, and then an intermediate host for larvae hatched by fertilized females.

For the full development of one generation of helminths, a change of owners is necessary.

Rishta (Dracunculus medinensis;

The final owner is a man, sometimes animals (dogs, monkeys). Intermediate hosts are freshwater cyclops crustaceans.

Rishta (Dracunculus medinensis) enters the human body orally when drinking water in which there were copepods infected with guinea worm larvae. When it enters the human body, the guinea worm gnaws through the intestinal wall and enters the lymphatic vessels, and from there it penetrates into the body cavity, where it undergoes two successive molts and reaches puberty. After mating, the males die, and the females migrate into the subcutaneous fatty tissue. There, the females continue to grow and reach a length of 80 cm.

The larvae exit the female genital tract through the rupture of the uterus and the walls of the body of the helminth near its anterior end. They are excreted from the body of the final host through a hole formed on the skin under the action of the secretion of special glands located at the anterior end of the female helminth.

Upon contact with water, the bubble bursts, and the front end of the female emerges from it. The ejection of larvae from the body of the guinea worm occurs due to the contraction of its muscles upon contact with water, which may be due to the cooling of the anterior end of the helminth under the action of water. Within 2-3 weeks, the female spawns up to 3 million larvae into the water. After that, the females die. They dissolve or calcify.

To complete the cycle, the larvae must infect the cyclops.

The traditional method of treatment for a long time was to slowly wind the guinea worm on a stick so that the worm does not tear. This could go on for several days.

Rice. Life cycle of guinea worm

Filaria

The final owner is a human.

Intermediate hosts of filariae are blood-sucking insects, less often ticks, which receive larvae (microfilariae) by sucking the blood of the final host and then infecting other vertebrates.

Filariae are localized in the body cavity, subcutaneous tissue, lymphatic and blood vessels, and the heart. They can cause blockage of the lymphatic ducts, which leads to elephantiasis corresponding part of the body.

Rice. Elephantiasis

hookworm

Crooked head of the duodenum (Ancylostoma duodenale) is the causative agent of hookworm.

The length of the worm is up to 13 mm.

Rice. Hookworm. a - female; b - male; c - oral capsule of the hookworm.

The anterior end of the hookworm body is bent to the ventral side. The head end has an oral capsule with 6 cutting teeth and glands that secrete enzymes that prevent blood clotting.

Rice. Hookworm head capsule

Helminths feed on blood. In the place of attachment of helminths to the intestinal wall, ulcers up to 2 cm in diameter are formed, bleeding for a long time.

Sexual reproduction in the human intestine. The eggs are released into the environment. Free-living larvae hatch from the eggs in the soil. The larva is able to live in the soil for several months.

Human infection occurs when the larvae are swallowed along with food and water or brought into the mouth with dirty hands (oral route), or (rarely) when the larvae actively penetrate the skin.

When infected through the skin, the larvae migrate through the blood stream to the lungs, from there they rise through the airways into the pharynx, are swallowed and enter the small intestine. Migration lasts about 10 days.

When infected by the oral route, there is no migration. In the small intestine, the larvae molt twice, and 4-6 weeks after infection, the females begin to lay eggs. The life expectancy of hookworm is up to 5 years.

Task 1. Fill in the table.

Characteristics of the type Roundworms
Representatives of the type	General features of the structure	Specific features of the structure	Habitat and lifestyle
roundworm Task 2. Fill in the gaps in the text. Human roundworms have separate sexes. The reproductive organs of the female are paired ovaries, the male is the filiform testis. Every day the female lays about 100-200 thousand eggs. Large roundworm ensures the preservation of eggs in nature, since most of them do not enter the body and die. Eggs are covered with a strong and dense shell. From the human intestine, they enter the bloodstream, the lungs. After two or three weeks, the larva develops. A prerequisite for the development of roundworm eggs is the presence of a damp environment. If eggs with larvae enter the human body, then infection with ascariasis will occur. Task 3. Fill in the table. Comparative characteristics of bovine tapeworm and human roundworm Comparable feature View human roundworm Bull tapeworm Type of roundworms flatworms body integuments tight and elastic cuticle dense cuticle and epithelium body cavity primary body cavity primary body cavity Nutrition and digestion has a mouth, esophagus, stomach and anus there are no organs of nutrition, food is absorbed through all the integuments of the body Breath through all the integuments of the body do not use oxygen for breathing Selection through the excretory opening leftover food is expelled through the mouth Nervous system longitudinal nerve trunks underdeveloped, sensory organs absent Reproduction and development dioecious reproduction hermaphrodites Task 4. Write down the numbers of signs characteristic of the human roundworm. Signs of animals. 1. Free-living worm. 2. Body with bilateral symmetry. 3. Hermaphrodite. 4. The larva develops in the intermediate host. 5. The intestine ends with an anus. 6. The larva develops in the lungs, but with the blood enters the heart and liver. 7. Has a circulatory system. 8. Dioecious animal. 9. Reproduces in the human intestine. 10. Intermediate owner - cattle. 11. The body is covered with a dense cuticle that protects the worm from the digestive juices of the host. 12. The body is ribbon-like, jointed. 13. The female is larger than the male. 14. There is no mouth opening, food is absorbed by the whole body. 15. There is a digestive and nervous system. Signs of roundworm: 4, 3, 8, 9, 13, 15. Task 5. Fill in the table.

The body of roundworms has a cylindrical shape, it is elongated in length with points at the ends. The movement of roundworms occurs due to contractions of the muscle fibers that make up their body.

The digestive system of nematodes is represented by the primary cavity in which the process of digestion takes place. The alimentary canal is divided into three sections: the middle, anterior and hindgut.

The anterior intestine of roundworms begins with the oral cavity and passes into the pharynx. This is where food absorption takes place. The digestion of food occurs in the midgut, and the absorption of nutrients also occurs here. The hindgut ends with an anus.

The annular peripharyngeal ganglion, as well as the nerves extending from it, form the nervous system of roundworms. Nematodes have organs of touch and taste. Some types of free-living worms have photosensitive eyes.

Reproduction of roundworms

Roundworms belong to the species of dioecious animals. Reproduction occurs exclusively sexually. For some species of roundworms, sexual dimorphism is inherent - the external difference between the male and the female.

The reproductive system of the female is represented by the oviducts, uterus, unpaired vagina and paired ovaries, the male has a vas deferens, an unpaired testis, and a copulatory apparatus.

Roundworms are characterized by internal fertilization with incomplete transformation (including the larval stage).

Pinworms parasitize the human large intestine. Females lay their eggs around the anus, which often causes itching. If hygiene is not observed, the eggs enter the human body. Often pinworms do not exceed 1 cm in length.

Roundworms are three-layered undivided animals with bilateral (two-sided) symmetry, the body of which is covered with a skin-muscular sac, and the space between the internal organs is filled with liquid.

Systematics. Type Roundworms is divided into classes: Gastrotrichs, Nematodes, Hairy, Scabs, Rotifers. The most famous and important is the Nematode class, which will be mainly discussed.

Body shape. Most of the roundworms have a strongly elongated body, round in cross section. The ends of the body are usually pointed. However, spherical, lemon-shaped and bean-shaped forms come across. It is customary to distinguish between the esophagus, middle and tail of the body.

Skin-muscle bag. Outside, the body of the nematodes is covered with a dense multilayered cuticle. Most often it has a ringed structure. This layer has an important supporting and protective value.

Under the cuticle is the actual skin of nematodes - cellular or syncytial epithelium, which is called the hypodermis. The hypodermis forms longitudinal thickenings on the dorsal and ventral sides, as well as on the sides - hypodermal ridges. Large nerve trunks are located in the dorsal and ventral ridges, and channels of the excretory system are located in the lateral ridges. The hypodermis plays an important role in nematode respiration.

Musculature in nematodes is represented by a single layer of longitudinal muscle cells adjacent to the hypodermis. Most often, the muscle layer is divided into dorsal and ventral bands, which ensure the mobility of the body of the worms. There are also smaller muscle groups that ensure the mobility of internal organs - esophageal, intestinal, anal, vulvar, spicular, and some others. These muscles run from the body wall to the corresponding organs.

Traffic. In connection with the structure of the muscular system, the movements of nematodes are extremely imperfect. These animals can only very slightly lengthen or shorten the body if all the muscles act simultaneously; Curl up in an annular shape if only one muscle works and bend serpentine if the muscles work alternately. Some soil nematodes are capable of jumping several millimeters.

body cavity. Unlike flatworms, in which the space between the body wall and internal organs is filled with parenchyma, in roundworms this space forms a cavity filled with fluid. This cavity does not have its own walls and is limited to a layer of muscles and internal organs. Such a cavity is called primary (synonyms: protocoel, hemocoel, schisocoel). The primary cavity is filled with fluid under significant pressure (high cavitary turgor), which maintains the shape of the nematode (support function). Metabolic products accumulate in the liquid, which are subsequently excreted from the body (excretory function).

Digestive system nematodes is end-to-end and consists of three sections - the anterior, middle and hindgut.

The foregut begins with a mouth opening surrounded by lips. The mouth may contain teeth, a spear, or a stylet. The oral cavity is followed by the esophagus, the structure of which is quite diverse. It can be direct or divided into departments. In a number of species, there are swellings on the esophagus - metacorpal and cardiac bulbs. Inside the cardiac bulb, there is often a muscular crusher that homogenizes food. Between the bulbs there is a small isthmus - isthmus - which is surrounded by a nerve ring. The esophagus has a cuticular lining. Some groups have esophageal glands that secrete enzymes.

The midgut is a tube of single-layered epithelium. Digestion and absorption of food takes place in this section.

The posterior part of the intestine is lined from the inside with a cuticle and opens at the posterior end of the body in females with an anus, and in males - in the cavity of the cloaca.

excretory system. In the esophageal part of the body there are one or two large cells of the cervical gland. These cells form one or two excretory canals, which stretch in the lateral ridges of the hypodermis along the entire body. In the anterior part, the two canals join into an unpaired duct, which opens outward through the excretory pore. Many species have several so-called phagocytic cells that capture foreign substances from the cavity fluid. These cells are probably associated with excretory ducts.

Nervous system. The central part - the nerve ring - encircles the esophagus. The ring consists of nerve fibers and a few nerve cells. Six nerve trunks extend forward from the ring to the organs of the esophageal part of the body. Several trunks also stretch back. However, they are located in the hypodermis. Usually one or two nerve trunks are most developed. The close relationship between the nervous system and the skin-muscular sac allows some authors to speak of a skin-muscular-nervous sac in nematodes.

Sense organs. Nematodes have developed tangoreceptors (tactile), chemoreceptors (chemical sense) and photoreceptors. Tangoreceptors are represented by papillae (small elevations on the cuticle) and setae. These organs are located mainly at the head end, and in males and in the tail area. Chemoreceptors are represented by amphids - peculiar recesses in the cuticle, which have a different structure. Amphids are located on the lips and on the sides of the head. Free-living aquatic nematodes sometimes have paired pigment spots at the head end, equipped with a small lens. These are kind of photosensitive organs.

Sexual system. Nematodes are dioecious organisms, while males are easily distinguished from females (sexual dimorphism). Males are usually smaller; their tail is hooked to the ventral side.

The reproductive system of males and females has a tubular structure. In some species, the genital tube is unpaired ( monodelphic ), while others have a steam room ( didelphic ). In the latter case, both tubes have a common excretory duct.

In males usually a monodelphic reproductive system, it consists of a gland - testis, and excretory ducts - the vas deferens and ejaculatory canal. Amoeba-like spermatozoa are produced in the testes and enter the ducts. The ejaculatory canal, together with the posterior intestine, opens at the posterior end of the body into the cloaca. Males also have a copulatory apparatus. It consists of one or two chitinous spicule and knuckle. Curved spicules extend outward along the groove of the shank and are fixed in the genital opening of the female. In many species, males have paired wide outgrowths on the sides of the tail, forming genital bursa. During mating, the male clasps the body of the female with these outgrowths.

Reproductive system of females usually didelphic. Each of the two genital tubes consists of an ovary, an oviduct, and a uterus. Both uteruses lead to a common vagina, which opens with a genital opening - the vulva. The vulva is most often located in the front of the body.

A necessary condition for the manifestation of the vital activity of nematodes is the presence of drop-liquid moisture. Some species tolerate prolonged drying (10 years or more).

Meaning. Inhabiting almost all biocenoses, nematodes are of great importance. They decompose dead organisms and take part in soil formation. The high abundance of nematodes in soil and bottom silt determines their significant role in food chains.

Morphology the scraper is very peculiar. The most characteristic feature of all acanthocephalans is the presence of a proboscis at the anterior end of the body, armed with hooks and capable of being drawn into a special vagina. Under the cuticle is the hypodermis, which is a syncytium with a system of cavities - lacunae. Muscle cells also merge with each other. Special muscles move the proboscis and some parts of the reproductive system. There is a muscle ligament , which stretches from the proboscis sheath to the posterior end. The body cavity is primary. The nervous system consists of one ganglion and nerve trunks extending from it. The sense organs are extremely poorly developed and are represented only by small tactile papillae. Acanthocephalans have no intestines and absorption of food occurs through the integument.

Acanthocephalans are dioecious animals. The testes in males are paired, usually compact and connected with the ligament. The vas deferens depart from the glands, which merge into an unpaired ejaculatory canal. The ducts of the cement glands also open into this organ, the secretions of which clog the genital opening of the female during mating. The sex glands of females - the ovaries - are also paired and located inside the ligament. However, even in young females, the ovaries break up into lumps of eggs. The ligament in some species of acanthocephalans bursts, and the eggs fall into the body cavity. They are brought out through a special complex apparatus. A special uterine bell swallows the eggs; at the same time, mature ones are passed into the uterus and subsequently brought out, while immature ones are pushed back into the body cavity.

Development cycle scraping occurs with the change of owners. Some eggs ripen in water. Others are on dry land. For further development, the eggs of "aquatic" species must enter the body of an intermediate host - usually a crustacean; in "soil" species, insects serve as such a host. In arthropods, a larva is formed - acantor , which is encapsulated and converted into acanthella with a proboscis screwed in. When such an arthropod is eaten by the definitive host, the acanthella turns into an adult acanthocephalan. In the cycle of development of "aquatic" species of acanthocephalans, additional hosts are often present - fish that eat crustaceans and serve as food for the final hosts - predatory fish.