Let's start the description with a little grimace worms... What can you do if there are such trump cards in the thick "deck" of the natural diversity of life forms.
I write “trump cards” not only because “ worms". The evolution of multicellularity from two-layered ones led to much more perfect forms of organisms with a three-layered body structure. And here nature had to tinker for a long time, creating not one, but whole.
Somehow it even becomes insulting for all mammals, which are only a separate class of organisms in the type of chordate animals. And here, "some worms" - and whole three types: flatworms, roundworms and annelids.
Well, let's start everything in order, so:
……………… Type Flatworms (three-layer)
…………………………………. K l ... a. with. with. NS
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.. Ciliated worms ……………………… .. Flukes ……………………… .. Tapeworms
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White planaria…. Liver fluke …… …………… Bovine tapeworm __________________________________________________________________________________
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More than 15 thousand species
Habitat : sea and fresh water bodies, moist soil, human and animal organisms.
……..
Structure: bilaterally symmetric
... For the first time in embryos, third
germ layer –
mesodermfrom which parenchymal cells and the muscular system develop. Body flattened.
………..
Body integuments and muscular system: musculocutaneous sac - from unilamellar epithelium (can to be with cilia) and three layers smooth muscles (annular, longitudinal and oblique).
Traffic: muscle contraction (flukes, tapeworms) or movement of cilia, andmuscles (ciliary worms).
Body cavity: absent , internal organs are located inparenchyma.
Digestive system:has two sections - anterior (mouth, pharynx) and middle (branches intestines). The gut is closed no anus and food debris is removed through the mouth... The tapedigestive system worms absent- absorption of food by all cells of the body. As you remember, this is one of the forms of biological progress -.
Excretory system: appears for the first time , formed by a system of tubules. One end begins in the parenchyma star cage with a bundle of cilia, and the other flows into excretory duct. Ducts are combined into one or two common channels ending in excretory pores. Elementary unit of the system areprotonephridia.
Nervous system:from supraopharyngeal ganglia(ganglia) and longitudinal nerve trunks, related cross bridges(ladder type).
Senses: touch and chemosensitive cells... Free living have organsvision and balance.…………..
Reproductive system: To As a rule, hermaphrodites.Mensreproductive system: testes, vas deferens, ejaculatory duct and copulatory organ... Womensreproductive system: ovary, oviduct, uterus, vitelline.
1. The appearance of the third germ layer -mesoderm.
2. The appearance of the excretory system - protonephridia.
3. The emergence of the nervous system ladder type.
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Structural features Bilaterally asymmetric - the only cavity of symmetry divides the body into left and right halves. Development occurs from three germ layers: ectoderm, endoderm and mesoderm. The third germ layer appears for the first time in the course of evolution and gives rise to the development of parenchymal cells that fill the gaps between the organs and the muscular system. Left half Right half
Structural features Body dimensions from 2-3 mm to 20 m. The body is elongated and flattened in the dorsal-abdominal direction; has a ribbon-like or leaf-like shape. The presence of developed organ systems is characteristic: muscular, digestive (absent in tape), excretory nervous and genital.
The integument of the body and the muscular system The cells of the epithelium and muscles are separate formations. The musculocutaneous sac consists of a single-layer epithelium (in aquatic forms, the epithelium has cilia) and three layers of smooth muscles: annular, longitudinal and oblique). Some representatives also have dorsal-abdominal muscles. Movement is provided by muscle contraction (flukes and tapeworms) or by cilia of the integumentary epithelium and muscle contraction (ciliary worms).
Digestive system Has two sections - front (mouth, pharynx) and middle (bowel branches). The intestine is closed blindly, the posterior part of the intestine and the anus are absent. Undigested food debris is removed by mouth. In tapeworms, the digestive system is absent (represented by individual digestive cells).
Excretory system Formed by a system of tubules, one end of which begins in the parenchyma with a stellate cell with a bundle of cilia, and the other flows into the excretory duct. The duct is united into one or two common channels, ending with excretory pores.
Nervous system. Sense organs. Consists of the supraopharyngeal ganglia and longitudinal nerve trunks that run along the body and are connected by transverse nerve bridges. Sense organs - touch and chemical sense. Free-living people have organs of touch and balance.
Hepatic flukes Hepatic flukes, usually 3 cm long and 1.3 cm wide. Hepatic flukes of the Opisthorchis order cause opisthorchiasis, symptoms of an early stage - enlargement of the liver, allergic reactions and gastrointestinal disorders; late stage symptoms - back pain, bilious colic, headaches and dizziness, insomnia. Treatment is carried out with anthelmintic, choleretic and enzyme preparations. High frequency electromagnetic radiation is also used.
Development cycle The life cycles of different genera differ. In species of the genus Fasciola, development occurs with one intermediate host (freshwater snail), and infection of the final host occurs when swallowed with water or eaten with coastal plants of the dormant stage - adolescaria. In the species of the genera Opisthorchis and Clonorchis, freshwater fish is the second intermediate host, and infection of the final host occurs when raw fish with invasive stages are eaten. In species of the genus Dicrocoelium, terrestrial lung snails and ants serve as intermediate hosts, and infection of the final host (usually a herbivore) occurs when an infected ant is eaten with grass.
Bovine tapeworm (tapeworm) It affects cattle and humans, causing teniarinhoses. Bovine tapeworm infection is especially common in equatorial Africa, Latin America, the Philippines and parts of Eastern Europe. An adult bovine tapeworm consists of more than 1000 segments and reaches 4-40 meters in length. The laying of the genital apparatus begins from about the 200th segment. The length of mature proglottids is mm, the width is 5-7 mm. The scolex (head section) is equipped with 4 suction cups without hooks (therefore unarmed). The life span of a bovine tapeworm in the human intestine, if no deworming measures are taken, is years. For a year, tapeworm produces ~ 600 million eggs, in a lifetime ~ 11 billion.
Development cycle Segments containing eggs are released from the human intestine (the main host). Together with the grass, they enter the cow's stomach (intermediate host). Six-hooked larvae emerge from the eggs, which penetrate into the blood vessels of the intestine and then into the muscles. In the muscles, the larva turns into Finns (a vial with a tapeworm head inside). When a person eats poorly processed phynose meat, the head of the tapeworm attaches to the intestinal wall and begins to produce segments.
Structural features Bilaterally asymmetric. Sizes from a few micrometers (soil) to several meters (sperm whale nematode). They have an unsegmented body with a dense cuticle. The ciliary cover is partially or completely reduced. The body is filiform, fusiform, non-segmented, round in cross section.
Digestive system Formed by the anterior, middle and posterior intestines. The anterior gut is differentiated into sections: the mouth with cuticular lips, the pharynx and the esophagus. The middle and hind gut are not divided into sections. The digestive tract ends with the anus.
Excretory system Presented by 1-2 cutaneous glands (modified protonephridia). These are large cells, from which two channels extend on the sides of the cell. At the posterior end of the body, the channels end blindly, and in the front they open into the external environment by the excretory pore.
Nervous system. Sensory organs Ladder-type nervous system. It is represented by the head nerve nodes (ganglia), the periopharyngeal nerve ring and several nerve trunks (dorsal and ventral), median transverse bridges. The sense organs are represented by the organs of touch and the chemical sense. Marine forms have light-sensitive receptors. Diagram of the ascaris nervous system: 1 - oral papillae with tactile endings and nerves innervating them, 2 - periopharyngeal nerve ring, 3 - lateral head ganglia, 4 - abdominal nerve trunk, 5 - lateral nerve trunks, 6 - circular nerves, 7 - posterior ganglion , 8 - sensitive papillae with corresponding nerves, 9 - anus, 10 - dorsal nerve trunk
Human Ascaris Ascaris are large round worms, their length can reach 40 centimeters. The organs of the gastrointestinal tract are most often affected, causing ascariasis. The preferred habitat for adults is the small intestine. Roundworm bisexual worms. Ascaris females can produce more than 200 thousand eggs per day. Fertilized eggs from the human intestine enter the soil. Larvae develop in them. Infection occurs when drinking water from open reservoirs, eating poorly washed vegetables, fruits, which have eggs with larvae. In the human body, the larva migrates: once in the intestine, it bores its walls and enters the bloodstream.
Structural features Bilateral symmetry of the body. Sizes from 0.5 mm to 3 m. The body is subdivided into the head lobe, trunk and anus. The polychaetae have a separate head with eyes, tentacles, and antennae. The body is segmented (external and internal segmentation). The body contains from 5 to 800 identical segments in the form of rings. The segments have the same external and internal structure (metamerism) and perform similar functions. The metameric structure determines a high degree of regeneration.
Body integument and muscular system The body wall is formed by the skin-muscle sac, consisting of a single-layer epithelium covered with a thin cuticle, two layers of smooth muscles (external annular and internal longitudinal) and a single-layer epithelium of the secondary body cavity. With the contraction of the annular muscles, the body of the worm becomes long and thin, with the contraction of the longitudinal muscles, it shortens and thickens.
Body cavity Secondary - whole (has epithelial vyzylka). In most, the body cavity is divided by transverse septa corresponding to the body segments. The cavity fluid is a hydroskeleton and an internal environment; it is involved in the transport of metabolic products, nutrients and reproductive products.
Digestive system Consists of three sections: anterior (mouth, muscular pharynx, esophagus, goiter), middle (tubular stomach, middle intestine) and posterior (hind intestine, anus). The glands of the esophagus and midgut secrete enzymes to digest food. Absorption occurs in the midgut.
Circulatory system Closed. There are two vessels: dorsal and abdominal, connected in each segment by annular vessels. Through the dorsal vessel, blood moves from the posterior end of the body to the anterior one, along the abdominal end from front to back. The movement of blood is carried out due to the rhythmic contractions of the walls of the dorsal vessel and the annular vessels ("heart") in the pharynx. Many have red blood.
Excretory system Metanephidial type. Metanephridia look like tubes with funnels, two in each segment. The funnel, surrounded by cilia, and the convoluted tubules are located in one segment, and the short tubule opening outward with an opening - excretory pore - is in the adjacent segment.
Nervous system. Sense organs. It is represented by the supraopharyngeal and subopharyngeal nerve nodes (ganglia), which are connected to the periopharyngeal nerve ring and the abdominal nerve chain, consisting of paired nerve nodes in each segment, connected by longitudinal and transverse nerve trunks. Polychaetae have organs of balance and vision (2-4 eyes). Most have only olfactory, tactile, and light-sensitive cells.
Reproduction and development Soil and freshwater forms are mainly hermaphodites. The sex glands only develop in certain segments. Internal insemination. The type of development is direct. Asexual reproduction is carried out by budding and fragmentation (due to regeneration). Marine representatives are dioecious. Development with metamorphosis, trochophore larva.
All worms can be divided into three types (flat, annelid, round), each of which has its own characteristic features. This type refers to invertebrates without a body cavity and exhibiting bilateral symmetry.
The main signs of the type of flatworms
- digestive;
- nervous;
- genital;
- excretory.
This type has several systems and even organ rudiments.
Circulatory system
Not available, but the function of the blood is performed by the parenchyma, which consists of connective cells. It is she who transports nutrients in the body.
Digestive system
Quite simplified, it consists of the pharynx and the intestine.
The pharynx is powerful, can:
- suck in;
- twist and wrap around your victim.
The intestine consists of two sections - anterior and middle, most often branched. It has a closed structure so that all undigested waste is expelled through the mouth. The mouth opening is located closer to the middle of the body of the worm.
Free worms are mostly predators and they even have a kind of prey capture device. This system is not observed in all classes; more primitive worms do not. For example, tapeworms feed on the entire surface.
Excretory system
The excretory system is quite large and consists of many tubules that join and lead to the excretory pores.
The parenchyma contains special cells that drive harmful substances into the tubules. For humans, these waste products are very dangerous and toxic, along with poison.
Muscular system
It is presented, which is formed by muscle fibers covered with epithelium. When these fibers contract, the worms can move.
Nervous system
In the upper part of the worm there are two head nodes, from which two nerve trunks descend. Longitudinal nerve trunks penetrate the body of the worm completely and are connected by transverse nerves, similar to a ladder.
With the help of cutaneous cilia, some worms can:
- feel the temperature;
- other external stimuli.
And among free worms there are representatives who have developed organs of vision (pigments that react to light) and balance.
Variety of species
There are three classes of this type:
- Suckers.
- Tape.
- Ciliary worms.
Flukes: representatives of the class and characteristics
Class representatives:
General characteristics of the fluke class:
Tapeworms: representatives of the class and characteristics
General characteristics of the class tapeworms:
Class representatives:
- is in stagnant water - ponds, ditches, very active. Covered with cilia, uses them to move on the water surface and attach to the bottom. The length is about 35 cm. The digestive system is developed, it feeds mainly on crustaceans and small invertebrates. Reproduction is sexual and asexual (it is divided in half, and then each half is completed). Wide habitat, found almost everywhere.
- Ehrenberg's mesostoma- a flat, leaf-shaped body, slightly convex, transparent and colorless, in old worms it is brown. Unlike planaria, the intestines are straight, not ramified. They live by attaching to aquatic plants. The mesostoma is predatory, hunts for crustaceans, worms, insects, and even freshwater hydras. It is able to withstand the drying out of reservoirs, live on flooded meadows, puddles, and after they are dried out, the eggs by the mesostome remain capable of development.
- Rhynchodemus land worm- soil worm, lives in humid places, most often under stones. Habitat Europe and North America. Can reach 12 mm, brown color with red longitudinal spots. The cilia are preserved on the abdominal side of the body; they move by muscle contraction. Predator eating insects.
General characteristics of ciliary worms:
"Features of the structure of the planaria" - The internal structure of the white planarian. White planaria or milky. White planaria. General characteristics of the type. The structure of the white planaria. Common signs. The excretory system of the planaria. Ciliary worms. Coelenterates. Variety of flatworms. Regeneration of the body of a planarian. White planaria. Various types of planaria. Bilateral and radial symmetry of the body. Planarian and Hydra body layers. The internal structure of the planaria.
"The structure of flatworms" - Movement. Digestive system of flukes. Nervous system. Sense organs. Ciliary worms. Turbellaria. Excretory system. The reproductive system. Life cycles of tapeworms. The reproductive system of flukes. Flukes are extremely fertile. Fluke class. Gas exchange and transport of substances. Ciliary digestive system. Type Flatworms. Tapeworms. Fluke development. The reproductive system is tape.
"Planarian structure" - Type Flatworms. Excretory system. The appearance of the third germ layer during development. The eggs are covered with dense shells. Milk planaria. Space between organs. Planarian movements. The reproductive system. Digestive system. Signs of flatworms. Planarian body. Type Ciliary worms. Flatworms. The internal structure of the planaria. Ring muscles. Unilamellar epithelium. Nervous system.
"The structure of the white planaria" - the integument of the body. Plathelminthes. Nephridia and kidney accumulation. A variety of flatworms. Composition of the group. Flatworms. The structure of the planaria. Structure. Grabbing food by white planaria. Muscle location. Nervous system and senses. Musculature. Pharynx and intestines. Food and movement. Complication of the body cavity. Turbellaria class. Ringed worms. The nervous system of the white planaria.
Worms are a fairly common species on earth. Roundworms differ from flat ones both in appearance and in the construction of internal vital systems. However, there are not only differences between these species. Worms of these classes do not have a circulatory and excretory system in the traditional sense, but their life cycle is the same. Adults become dangerous.
The differences between round worms and flat worms are not significant, but the harm to human health is significant.
General information on comparing flat and round worms
Flat individuals have a flattened body (often ribbon-like). They also differ in the presence of 3 muscle layers:
- annular;
- diagonal;
- longitudinal.
Round worms
- A cylindrical thin body, consisting of the so-called, outer cuticle, under which is the epithelial layer and muscles running along.
- The fluid fills the body (hydroskeleton).
- The structure of the digestive system is simple. It is a tube with mouth and excretory openings. It is conventionally divided into 3 parts - front, middle and back.
- The nervous system is represented by the periopharyngeal ganglion (a kind of brain). The nerve trunks branch off from the ganglion. Roundworms have a sense of touch and taste.
The main differences between roundworms within a species are their habitat. It should be noted that, unlike flat ones, round ones are bisexual. Both males and females are usually distinguishable. This type has more than 15 thousand species, living almost everywhere. Some can be seen under a microscope, but there are giants compared to them.
Flatworms
- ciliary;
- tape;
- flukes.
The structure of flatworms is somewhat different from round ones. Namely:
Flat representatives, with rare exceptions, are unisexual. Their breeding system is quite complex. In addition to the present symbiosis of male and female genital organs, this includes additional appendages and formations that fully ensure the process of fertilization and development of the embryo, by providing it with all the necessary substances.
What is the difference?
What common?
Any worms that have entered the human body pose a danger to him, especially if they are not noticed in time and adequate treatment is not applied. Helminths can cause many diseases, including: ulcers, colitis, intestinal obstruction, cysts, damage to the central nervous system, meningitis. Among the most dangerous species are flukes, paragonims and schistosomes, echinococci, roundworms, hookworms, trichinella.
The causative agent of opisthorchiasis: what it looks like, structure, habitat
The first case of the appearance of opisthorchis was recorded in 1884, when a helminth, previously unknown to science, was found in a cat in the northern part of Italy. S. Rivolta called the helminth a feline fluke.
7 years after the first case, the feline fluke was found already in the human body in Russian Siberia. In 1891, professor - pathologist K. N. Vinogradov carried out studies of the liver and found in it a leaf worm, which he gave the name of the Siberian fluke. Further studies have shown that the Siberian fluke is nothing more than a cat fluke that came across earlier. Subsequently, the helminth was given the name opisthorchis, and the disease was referred to as opisthorchiasis.
The structure and appearance of the helminth
Unlike other representatives of its class, opisthorchis is much smaller. This is what a helminth looks like: the body of a feline fluke is shaped like an oblong flat leaf or lancet, its length rarely exceeds 18 millimeters, and its width varies from 1.5 to 2 millimeters.
On the body of the helminth there are two suckers, one is abdominal and the other is oral, with the help of them the opisthorchis is attached to the mucous membranes of the damaging organs and sucks out nutrients. The mouth sucker of the helminth serves as the beginning of its digestive tract. At the rear end of the little body there is a special channel through which the processed waste products of the worm are released.
The reproductive system of the causative agent of opisthorchiasis is based on the hermaphroditic principle. Helminth has two pairs of genitals. Reproduction of opisthorchis occurs by the release of eggs. One individual of the worm in the body of its final host is capable of producing 900-1000 eggs daily.
Opisthorchis eggs are pale yellow in color, have a double-contoured delicate shell, at one pole of the eggs there is a special cap, and the other pole is slightly thickened. The sizes of helminth eggs vary from 0.011 to 0.019 in width and from 0.023 to 0.034 in length.
Habitat and endemic foci
The habitat of opisthorchis eggs are freshwater reservoirs, in such conditions they are able to maintain their vital activity for one year. It should be noted that opisthorchis develop with the participation of three carriers - one final host and two intermediate ones.
Considering that helminth develops in freshwater reservoirs, special endemic foci are distinguished, where the likelihood of infection with opisthorchiasis is high. These endemic foci include:
- Yamalo-Nenets Auth. Okrug, Khanty-Mansi auth. district, regions of Siberia, Altai Republic. Endemic foci in Russia are also confined to the basins of the Irtysh, Ob, Volga, Northern Dvina, Kama, Don, Dnieper, Biryusa.
- Ukraine and Kazakhstan.
- Italy, France, Holland.
- India, Thailand, other countries of Southeast Asia, where fishing predominates.
- Canada and the Northern Regions of the United States.
Development of the causative agent of opisthorchiasis
The causative agent of opisthorchiasis belongs to biohelminths, which means that a change of owners is necessary for its successful life. In this case, as mentioned above, the trematode has one final and two intermediate hosts, in their organisms it goes through a full life cycle.
The cycle of opisthorchis begins in the body of the final host, which is a person, as well as some mammals (cats, dogs, pigs, foxes, and others). Sexually mature individuals lay eggs, together with the excrements of the host, they go out into the environment, in the presence of favorable conditions, they continue their development.
Once in water bodies, the eggs of the opisthorchis settle at the bottom, where freshwater mollusks eat them. In their organisms, the larvae of opisthorchis - miracidia - emerge from the eggs. Miracidia have special cilia, penetrating into the intestinal wall of the mollusk, they lose them and turn into the maternal sporocyst. The sporocyst gives rise to redia, and these, in turn, are transformed into cercariae. Tailed cercariae leave the body of mollusks through the cover or mouth opening and begin to hunt for a second intermediate host.
The second intermediate host of the causative agent of opisthorchiasis is the fish of the cyprinid family. The fish swallows them through the mouth opening, and cercariae can also enter its body through the lateral lines and integument. In the organisms of cyprinids, cercariae are localized in the muscles and subcutaneous tissue, turning into metacercariae. The larvae of the metacercariae have a slightly oval shape, their dimensions are 0.34 mm in length and 0.24 mm in width. Metacercariae develop in the body of a fish for one and a half months, during which time they become invasive to humans.
How does the final host become infected? The causative agent of opisthorchiasis enters the human (animal) body when eating raw or insufficiently thermally processed fish. In the human body, metacercariae reach their sexual maturity by 10-14 days. The main centers of impact are the liver, its ducts, gallbladder and pancreas. Typical symptoms appear two to three weeks after the onset of the invasion.
Opisthorchiasis proceeds in two stages, this is due to the peculiarities of the life cycle of the helminth. Hence, the difference in the clinical picture for the period of invasion and the later period follows. Getting into the human body at the stage of metacercaria, the helminth develops to the stage of puberty, and then for many years lives in its usual places of localization.
In the early stages, the causative agent of opisthorchiasis provokes the development of an allergic reaction, which is very pronounced. A similar reaction of the human body is due to the fact that the helminth secretes enzymes and metabolic products that have a toxic effect.
- In the lymphatic system, inflammatory processes occur, the same phenomena are observed in the spleen.
- Purulent-inflammatory reactions can be found in the mucous membranes of the gastrointestinal tract and respiratory system.
- There is a violation of blood microcirculation in the internal organs, first of all, the part of the circulatory system located in the liver suffers.
- Hypoxic signs develop, gas exchange is disrupted.
- Dystrophic changes are observed in the liver, heart and other organs.
The rate of development of pathological changes in the human body directly depends on the degree of invasion intensity.
The chronic stage of opisthorchiasis is characterized by mechanical, allergic and neuro-reflex harmful effects of helminths. There is a secondary influence of the microbial flora, as well as the influence of the decay products of its own cells and tissues, most of all the cells of the gallbladder. Without timely diagnosis and treatment, the development of chronic cholangitis, pericholangitis, hepatitis, liver cirrhosis is likely.
Exposure to neuro-reflex is fraught with disturbances in the tone of the gallbladder and biliary tract, secretory dysfunction, impaired motor function of the stomach and intestines.
Symptoms of opisthorchiasis, as a rule, include the clinical picture of a disease such as chronic gastroduodenitis. The peculiarity is associated with pathological changes in the functions of the pancreas and adrenal glands, as well as with the development of inflammatory processes of the mucous membranes of organs. The causative agent of opisthorchiasis also provokes hormonal instability.
Treatment of opisthorchiasis should be immediate and mandatory, neglected cases of the disease lead to the development of liver cancer. Prevention of opisthorchiasis consists in the correct and sufficient processing of freshwater fish before eating it.
a source
Tapeworms (cestodes)
The oldest traces of cestodes are found in the remains of sharks living 270 million years ago.
Human infection
People can become infected with several types of tapeworms in different ways. When eating undercooked meat: pork (pork tapeworm), beef (bovine tapeworm) and fish (broad tapeworm). Or when living and eating in conditions of poor hygiene - dwarf and rat tapeworms, echinococcus.
Treatment
Now for the treatment of tapeworms, the main drugs are Praziquantel and Albendazole. Praziquantel is an effective drug that is preferred over the outdated Niclosamide. Cestodiasis can also be treated with some types of antibiotics. Doctors after a course of drugs can give enemas to patients in order to completely remove the worms from the intestines.
Structure
The main common elements of the body of the cestode. Others may be different (presence of a hook with hooks, types of suction cups may be slit-like, etc.)
Larvae, on the other hand, show a wide range of habitat preferences and can be found in almost any organ, both vertebrate and invertebrate hosts. Although most larval species prefer a specific organ.
The absence of a gastrointestinal tract markedly separates cestodes from nematodes and trematodes. The outer tegument (special epithelium) of the body serves not only as a protective covering, but also as a metabolically active layer through which nutrients are absorbed, along with secretions and waste transported from the body. To facilitate this process, the entire body surface is covered with microscopic wrinkles or ridges, which significantly increase the surface area available for nutrient absorption.
The worms do not need to move inside the host's body, so they do not have any organs of the musculoskeletal system and external bristles.
They also lack circulatory and respiratory systems.
The excretory and nervous systems of cestodes are similar to the systems of other representatives of flatworms.
Proglottid
The body of helminths of this class consists of a chain of segments (proglottids), which can be immature and mature, the last of which are at the end of the body and contain a fully formed uterus filled with eggs.
The collection of all proglottids (from two to several thousand) is called strobila. It is thin and resembles a strip of tape. Hence the common name "tape".
New segments grow from the neck, containing an independent digestive and reproductive system. By the time the segment reaches the end of the worm's tail, only the reproductive organs remain. In fact, such segments are already just bags of eggs. The segment is then detached from the body, carrying the tapeworm eggs out of the final host along with the feces.
Thus, each cestode consists of a series of segments with a full set of reproductive organs in a progressive degree of puberty, which bud off from the body on the side of the tail.
Scolex
Life cycle
The life cycle of cestodes includes an intermediate and final host (with the exception of the Dwarf tapeworm, which can develop in the same organism). It consists of several stages.
At the first stage, sexually mature tapeworms are in the body of the final host (vertebrates and humans), multiply and produce eggs, which are subsequently excreted into the environment along with feces.
At the second stage (depending on the type of cestodes), a larva (embryo) is formed in the eggs on land or in water.
At the third stage, the larvae enter the organism of the intermediate host (vertebrates and invertebrates), where they form the Finns. Finna is a spherical bladder (less often a worm-shaped) filled with liquid, inside which there are one or more heads. Depending on the number of heads, as well as on the presence of daughter bubbles inside, 5 forms of Finn are distinguished:
- cysticercus;
- cysticercoid;
- tsenur;
- echinococcus;
- plerocercoid.
At the fourth stage, the Finns enter the body of the final owner, their shell falls off, and segments begin to grow from the heads attached to the intestinal walls. Thus, at this stage, the growth and development of adults occurs.
The most common representatives
Pork and bovine tapeworms (tapeworms)
Infections caused by the ingestion of larvae of representatives of the Tsepni genus, in humans or animals, are called teniidosis. The presence of an adult worm in the body (teniasis and teniarinchiasis) rarely causes symptoms other than minor intestinal disturbances (diarrhea, constipation, or indigestion).
Bovine tapeworm does not cause human cysticercosis.
Dwarf tapeworm
The dwarf tapeworm (Hymenolepis nana) is the smallest member of the Tsepni genus that infects humans. This cestode belongs to a large family known as the Hymenolepis. Diagnostic signs of this family: scolex contains 24-30 hooks; an adult has one to three large testes and a saccular uterus.
The dwarf tapeworm is a cosmopolitan, i.e. widely distributed throughout the world. The infection is more common in children, although adults can also be infected (with the development of the disease hymenolepiasis). The disease may not cause any symptoms even with significant infection. However, some cases of anxiety, irritability, lack of appetite, abdominal pain and diarrhea have been reported in hymenolepiasis.
The life cycle of Hymenolepis nana does not necessarily require an intermediate host; full development occurs within the intestine of a single host (“direct” life cycle). It can also use insects as an intermediate host.
Wide ribbon
As a rule, they have a scolex, which is characterized by two shallow elongated bothria (slits), one located dorsally (on the back) and the other ventrally (on the ventral side). Proglottids are smoothed dorsoventrally, i.e. from the dorsal to the ventral.
