Guinea worm

There are worms that live in human blood. These include schistosomes. Their main habitat is blood vessels. However, they are able to penetrate various organs, causing symptoms of damage to the genitourinary system, liver, and kidneys.

The blood may contain larvae of some helminths. For example, in tapeworms this is how they spread throughout the body of the intermediate host. With the blood flow, the larvae migrate to various organs, where they attach and form cysts containing the heads of adult worms. When the latter enter the digestive tract of the final host, they attach to the intestinal wall, giving rise to a sexually mature individual.

Flatworms: general characteristics

The body of flatworms is capable of complex and varied movements.

All flatworms have common structural features:

• The outer cover is represented by the cuticle. In free-living individuals, it is covered with cilia; the surface of the body of worms is usually smooth.
• Under the outer covering there are several layers of muscle fibers.
• There is no body cavity.
• The digestive system has only one opening - the mouth. The intestine ends blindly. Some worms lack digestive organs altogether. Thus, tapeworms, which absorb nutrients throughout the body from the lumen of the host’s intestine, do not need them.
• There is no circulatory system or blood, as well as respiratory organs.
• The excretory system is represented by a network of tubes that penetrate the entire body.
• The nervous system is primitive. Near the pharynx there are several ganglia from which nerve trunks connected by jumpers extend. Sense organs are formed only in free-living individuals and some worms at the larval stages of development.

The system that is really well developed is the sexual system. Flatworms are hermaphrodites. Reproduction is possible with the participation of 2 individuals or by self-fertilization.

Flukes

The development cycle of trematodes is one of the most complex. Miracidia emerge from eggs released into the external environment. The latter feel comfortable in water and exist for some time as free-living organisms. The next stage is the introduction of miracidia into the first intermediate host. The larva does this using a special cutting apparatus on the head. The host is usually a mollusk.

Their life cycle can take place in several hosts and is accompanied by regular alternation

Here the miracidium turns into a sporocyst, which gives rise to the next stage of the development cycle - redia. Those, in turn, are the predecessors of cercariae, which leave the intermediate host and again enter the aquatic environment. Next, the development cycle follows one of two options. Cercariae transform into cysts directly in the external environment (attached to algae) or in the body of a second intermediate host (mollusk, fish, amphibian).

These are the longest worms with a transparent shell

Infection of the definitive host occurs when it eats infected organs of the intermediate host. The development cycle ends with the attachment of the head from the cyst to the intestinal wall and the development of the adult worm. The latter can reach significant sizes (for example, the wide tapeworm grows up to 10 m long).

For flukes, humans are the final host, but for tapeworms they can also be an intermediate host.

What symptoms occur when a person is infected with a helminth? The clinical picture of the disease is determined, first of all, by which organ is affected. Sexually mature worms usually live in the intestines, so the overall picture of the disease is dominated by symptoms characteristic of digestive disorders: nausea, gas formation, bowel problems, abdominal pain.

Helminths secrete waste products that, when released into the blood, cause poisoning and symptoms of intoxication (fever, fatigue, etc.). In addition, they are perceived by the immune system as an allergen. Therefore, helminthiases are often accompanied by symptoms of an allergic reaction (skin rashes, itching).

Brief description

Habitat and appearance	Dimensions 10-15 mm, leaf-shaped, live in ponds and low-flowing reservoirs
Body cover and skin-muscle bag	The body is covered with single-layer (ciliated) epithelium. The superficial muscle layer is circular, the inner layer is longitudinal and diagonal. There are dorso-abdominal muscles
Body cavity	There is no body cavity. Inside there is spongy tissue - parenchyma
Digestive system	Consists of the anterior section (pharynx) and the middle section, which looks like highly branched trunks ending blindly
excretorysystem	Protonephridia
Nervous system	The cerebral ganglion and the nerve trunks coming from it
Sense organs	Tactile cells. One or more pairs of eyes. Some species have balance organs
Respiratory organs	No. Oxygen is supplied through the entire surface of the body
Reproduction	Hermaphrodites. Fertilization is internal, but cross-fertilization - two individuals are needed

Typical representatives of eyelash worms are planarians(Fig. 1).

Rice. 1.Morphology of flatworms using the example of milk planaria. A - appearance of planaria; B, C - internal organs (diagrams); D - part of a cross section through the body of a milk planaria; D - terminal cell of the protonephridial excretory system: 1 - oral opening; 2 - pharynx; 3 - intestines; 4 - protonephridia; 5 - left lateral nerve trunk; 6 - head nerve ganglion; 7 - peephole; 8 - ciliated epithelium; 9 - circular muscles; 10 - oblique muscles; 11 - longitudinal muscles; 12 - dorsoventral muscles; 13 - parenchyma cells; 14 - cells forming rhabdites; 15 - rhabdites; 16 - unicellular gland; 17 - a bunch of eyelashes (flickering flame); 18 - cell nucleus

General characteristics

Appearance and covers . The body of ciliated worms is elongated, leaf-shaped. Dimensions vary from a few millimeters to several centimeters. The body is colorless or white. Most often, eyelash worms are colored grains in different colors pigment, embedded in the skin.

Body covered single-layer ciliated epithelium. In the integument there are skin glands, scattered throughout the body or collected in complexes. Of interest are the types of skin glands - rhabditis cells, which contain light-refracting rods Rhabdites. They lie perpendicular to the surface of the body. When the animal is irritated, the rhabdites are thrown out and swell greatly. As a result, mucus forms on the surface of the worm, possibly playing a protective role.

Skin-muscle bag . Under the epithelium is basement membrane, which serves to give the body a certain shape and to attach muscles. The combination of muscles and epithelium forms a single complex - skin-muscle sac. The muscular system consists of several layers smooth muscle fibers. Most superficially located circular muscles, somewhat deeper - longitudinal and the deepest - diagonal muscle fibers. In addition to the listed types of muscle fibers, ciliary worms are characterized by dorso-abdominal, or dorsoventral, muscles. These are bundles of fibers running from the dorsal side of the body to the ventral side.

The movement is carried out due to the beating of the cilia (in small forms) or the contraction of the skin-muscular sac (in large representatives).

Clearly expressed body cavities ciliated worms do not. All spaces between organs are filled parenchyma- loose connective tissue. The small spaces between the parenchyma cells are filled with aqueous fluid, which allows the transfer of products from the intestines to the internal organs and the transfer of metabolic products to the excretory system. In addition, parenchyma can be considered as supporting tissue.

Digestive system eyelash worms blind. Mouth also serves for swallowing food, and for throwing away undigested food debris. The mouth is usually located on the ventral side of the body and leads into throat. In some large ciliated worms, such as the freshwater planaria, the mouth opening opens into pharyngeal pocket, in which it is located muscular throat, capable of stretching and protruding out through the mouth. Midgut in small forms of ciliated worms it is canals branching in all directions, and in large forms the intestine is represented three branches: one front, going to the front end of the body, and two rear, running along the sides to the rear end of the body.

Main feature nervous system ciliated worms compared to coelenterates is concentration of nerve elements at the anterior end of the body with the formation of a double node - the cerebral ganglion which becomes coordinating center of the whole body. They depart from the ganglion longitudinal nerve trunks, connected by transverse ring jumpers.

Sense organs in ciliated worms they are relatively well developed. Organ of touch All skin serves. In some species, the function of touch is performed by small paired tentacles at the anterior end of the body. Balance sense organs represented by closed sacs - statocysts, with hearing stones inside. Organs of vision are almost always available. There may be one pair of eyes or more.

Excretory system for the first time appears as separate system. She is presented two or several channels, each of which one end opens outwards, A the other is heavily branched, forming a network of channels of various diameters. The thinnest tubules or capillaries at their ends are closed by special cells - star-shaped(see Fig. 1, D). From these cells, they extend into the lumen of the tubules bunches of eyelashes. Thanks to their constant work, there is no stagnation of fluid in the body of the worm; it enters the tubules and is subsequently excreted. The excretory system in the form of branched canals closed at the ends by stellate cells is called protonephridia.

Reproductive system quite diverse in structure. It can be noted that, in comparison with coelenterates, ciliated worms special excretory ducts appear For

excretion of germ cells. Eyelash worms hermaphrodites. Fertilization - internal.

Reproduction. In most cases sexually. Most worms direct development, but in some marine species development occurs with metamorphosis. However, some eyelash worms can reproduce and asexually through transverse division. In this case, in each half of the body there is regeneration missing organs.

Integument of the body The outside of the body is covered with single-layer epithelium. In ciliated worms, or turbellarians, the epithelium consists of cells bearing cilia. Flukes, monogeneans, cestodes and tapeworms lack ciliated epithelium for most of their lives (although ciliated cells may be present in larval forms); their integument is represented by the so-called tegument, which in some groups carries microvilli or chitinous hooks. Flatworms that have a tegument are classified as Neodermata. Flatworms can regenerate 6/7 of their body.

Musculature Under the epithelium is a muscular sac, consisting of several layers of muscle cells that are not differentiated into individual muscles (certain differentiation is observed only in the area of ​​the pharynx and genitals). The cells of the outer muscle layer are oriented transversely, while the cells of the inner layer are oriented along the anterior-posterior axis of the body. The outer layer is called the circular muscle layer, and the inner layer is called the longitudinal muscle layer.

Nervous system and sensory organs The nervous system is represented by nerve ganglia located in the front part of the worm's body, cerebral ganglia and nerve columns extending from them, connected by jumpers. The sense organs are usually represented by individual skin cilia - processes of sensory nerve cells. Some free-living representatives of the type, in the process of adaptation to living conditions, acquired light-sensitive pigmented eyes - primitive organs of vision and organs of balance.

Structure The body is bilaterally symmetrical, with clearly defined head and caudal ends, somewhat flattened in the dorsoventral direction, in large representatives it is strongly flattened. The body cavity is not developed (except for some phases of the life cycle of tapeworms and flukes). Gases are exchanged across the entire surface of the body; respiratory organs and blood vessels are absent.

Questions: How many flatworms live in Russia? What body coverings do flatworms have? What muscles? What sense organs? Briefly describe the structure of the body. How do flatheads eat? How do they breathe? How do they reproduce?

Interesting facts 1. Flatworms are able to “learn” through digestion. A team of scientists has made an unusual discovery about the abilities of flatworms. It turns out that if planar worms are first trained to go through a maze, then ground into a puree and given to other worms to eat, then they will be able to go through this maze the first time.

Interesting facts 2. A heterosexual species of worms - schistosomes are inseparable throughout their lives. The female lives in the male's pocket all her life.

Interesting facts 3. Almost all types of flatworms can turn inside out. 4. Here are some more interesting facts about flatworms. For example, flatworms are truly almost immortal. If you cut off a very small piece of the worm, about 1/100 the size of the whole worm, it is still able to regenerate into a whole organism.

Interesting facts 5. On the skin of some planarians living in fresh water, scientists have discovered nettle cells, which are very similar to the stinging cells found in coelenterates. It turns out that these cells actually previously belonged to coelenterates, which were subsequently eaten by ciliated worms. Stinging cells are not digested by worms. They enter their skin and serve both defensive and offensive functions.

L I

summary of other presentations

“Structural Features of Planaria” - Internal structure of white planaria. White planaria or milky planaria. White planaria. General characteristics of the type. The structure of a white planaria. General signs. Excretory system of planaria. Eyelash worms. Coelenterates. Variety of flatworms. Regeneration of the planarian body. White planaria. Various types of planarians. Bilateral and radial symmetry of the body. Layers of the body of planaria and hydra. Internal structure of planaria.

“The structure of flatworms” - Movement. Digestive system of flukes. Nervous system. Sense organs. Eyelash worms. Turbellaria. Excretory system. Reproductive system. Life cycles of tapeworms. Reproductive system of flukes. Flukes are extremely fertile. Class Flukes. Gas exchange and transport of substances. Digestive system of ciliates. Type Flatworms. Tapeworms. Development of flukes. The reproductive system is tape.

“Structure of planaria” - 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. Reproductive system. Digestive system. Signs of flatworms. The body of a planaria. Type: Ciliated worms. Flatworms. Internal structure of planaria. Circular muscles. Single layer epithelium. Nervous system.

“Structure of a white planaria” - Body coverings. Plathelminthes. Nephridia and accumulation buds. Variety of flatworms. Group composition. Flatworms. The structure of planaria. Structure. Capture of food by a white planaria. Muscle location. Nervous system and sensory organs. Musculature. Throat and gut. Food and movement. Complication of the body cavity. Class Turbellaria. Annelids. Nervous system of a white planaria.

Structural features Bilaterally symmetrical - a single symmetry cavity 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 during evolution and gives rise to the development of parenchymal cells that fill the gaps between 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-ventral direction; has a ribbon-like or leaf-shaped form. It is characterized by the presence of developed organ systems: muscular, digestive (absent in ribbon-like), excretory, nervous and reproductive.

Integument of the body and the muscular system Epithelial and muscle cells are separate formations. The skin-muscle sac consists of a single-layer epithelium (in aquatic forms the epithelium has cilia) and three layers of smooth muscles: circular, longitudinal and oblique). Some representatives also have dorso-abdominal muscles. Movement is provided by muscle contraction (flukes and tapeworms) or by cilia of the integumentary epithelium and muscle contraction (ciliated worms).

The digestive system has two sections - the anterior (mouth, pharynx) and middle (branches of the intestine). The intestine is closed blindly, the hind intestine and anus are absent. Undigested food remains are removed through the mouth. Tapeworms do not have a digestive system (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 bunch of cilia, and the other ends into the excretory duct. The duct is united into one or two common channels, ending with excretory pores.

Nervous system. Sense organs. It consists of suprapharyngeal nerve ganglia (ganglia) and longitudinal nerve trunks running along the body and connected by transverse nerve bridges. Sense organs - touch and chemical sense. Free-living animals have organs of touch and balance.

Liver fluke Liver flukes usually reach 3 cm in length and 1.3 cm in width. Liver flukes of the order Opisthorchis cause opisthorchiasis, early stage symptoms are liver enlargement, allergic reactions and gastrointestinal disorders; symptoms of the late stage - pain radiating to the back, biliary colic, headaches and dizziness, insomnia. Treatment is 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 (a freshwater snail), and infection of the final host occurs when ingested with water or eaten with coastal plants of the dormant stage - Adolescaria. In species of the genera Opisthorchis and Clonorchis, the second intermediate host is freshwater fish, and infection of the definitive host occurs when eating raw fish with invasive stages. In species of the genus Dicrocoelium, land pulmonate snails and ants serve as intermediate hosts, and infection of the final host (usually a herbivore) occurs when an infected ant eats grass.

Bovine tapeworm (tapeworm) Affects cattle and humans, causing teniahrynchiasis. Bovine tapeworm infestation is particularly common in equatorial Africa, Latin America, the Philippines and parts of Eastern Europe. An adult tapeworm consists of more than 1000 segments and reaches 4-40 meters in length. The formation of the reproductive apparatus begins approximately from the 200th segment. The length of mature proglottids is mm, width is 5-7 mm. The scolex (head section) is equipped with 4 suckers without hooks (therefore unarmed). The lifespan of a bovine tapeworm in the human intestine, if no deworming measures are taken, is years. The tapeworm produces ~600 million eggs per year, and ~11 billion over its lifetime.

Development cycle Segments containing eggs are released from the human intestine (the main host). Together with the grass, they enter the stomach of the cow (intermediate host). The eggs hatch into six-hooked larvae that penetrate the blood vessels of the intestine and then into the muscles. In the muscles, the larva turns into finn (a vesicle with the head of the tapeworm inside). When a person consumes poorly processed fino meat, the head of the tapeworm attaches to the intestinal wall and begins to produce segments.

Structural features Bilaterally symmetrical. Sizes from several micrometers (soil) to several meters (sperm whale nematode). They have a non-segmented body with a dense cuticle. The ciliary cover is partially or completely reduced. The body is filiform, fusiform, unsegmented, round in cross section.

The digestive system is formed by the foregut, middle and hindgut. The foregut is differentiated into sections: the mouth with cuticular lips, the pharynx and the esophagus. The midgut and hindgut are not divided into sections. The digestive tract ends with the anus.

Excretory system Represented by 1-2 skin 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 canals end blindly, and at the front they open into the external environment with an excretory pore.

Nervous system. Sense organs Nervous system of the ladder type. It is represented by the head nerve ganglia (ganglia), the peripharyngeal nerve ring and several nerve trunks (dorsal and ventral), and median transverse bridges. The sense organs are represented by the organs of touch and chemical sense. Marine forms have photosensitive receptors. Diagram of the roundworm nervous system: 1 - oral papillae with tactile endings and the nerves innervating them, 2 - peripharyngeal nerve ring, 3 - lateral cephalic ganglia, 4 - abdominal nerve trunk, 5 - lateral nerve trunks, 6 - ring nerves, 7 - posterior ganglion , 8 - sensitive papillae with corresponding nerves, 9 - anus, 10 - dorsal nerve trunk

Human roundworm Roundworms are large roundworms, their length can reach 40 centimeters. Most often they affect the gastrointestinal tract and cause ascariasis. The favorite habitat of adults is the small intestine. Roundworms are bisexual worms. Female roundworms can produce more than 200 thousand eggs per day. Fertilized eggs from the human intestine enter the soil. Larvae develop in them. Infection occurs by drinking water from open reservoirs, eating poorly washed vegetables and fruits that contain eggs with larvae. In the human body, the larva migrates: once in the intestine, it drills through its walls and enters the bloodstream.

Structural features Bilateral symmetry of the body. Dimensions from 0.5 mm to 3 m. The body is divided into the head lobe, trunk and anus. Polychaetes 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 ring-shaped segments. 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 a skin-muscular sac, consisting of a single-layer epithelium covered with a thin cuticle, two layers of smooth muscle (external circular and internal longitudinal) and single-layer epithelium of the secondary body cavity. When the circular muscles contract, the body of the worm becomes long and thin; when the longitudinal muscles contract, it shortens and thickens.

Body cavity Secondary - coelom (has epithelial lining). In most, the body cavity is divided by transverse partitions corresponding to body segments. Cavity fluid is a hydroskeleton and internal environment; it is involved in the transport of metabolic products, nutrients and reproductive products.

The digestive system consists of three sections: anterior (mouth, muscular pharynx, esophagus, crop), middle (tubular stomach, midgut) and posterior (hindgut, anus). The glands of the esophagus and midgut secrete enzymes to digest food. Absorption occurs in the midgut.

Circulatory system is closed. There are two vessels: dorsal and abdominal, connected in each segment by ring vessels. Blood moves through the dorsal vessel from the rear end of the body to the front, and through the abdominal vessel from front to back. The movement of blood is carried out thanks to the rhythmic contractions of the walls of the spinal vessel and the annular vessels (“heart”) in the pharynx. Many people have red blood.

Excretory system of Metanefidial type. Metanephridia look like tubes with funnels, two in each segment. A funnel surrounded by cilia and convoluted tubules are located in one segment, and a short tubule opening outward with an opening, the excretory pore, is in the adjacent segment.

Nervous system. Sense organs. It is represented by suprapharyngeal and subpharyngeal nerve ganglia (ganglia), which are connected into a peripharyngeal nerve ring and an abdominal nerve chain, consisting of paired nerve ganglia in each segment, connected by longitudinal and transverse nerve trunks. Polychaetes 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 hermaphoditic. The gonads develop only in certain segments. Insemination is internal. Type of development - direct. Asexual reproduction is carried out by budding and fragmentation (due to regeneration). Marine representatives are dioecious. Development with metamorphosis, larva-trochophore.