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pijawka) formed from the verb *pjati, multiple verb from *piti"drink". At the same time, in Russian the form would be expected *leech(cf. Ukrainian p᾽yavka), and and in this case explain by a secondary rapprochement with the verb "drink" according to folk etymology.
In Latin hirūdō find the same suffix as in testūdō"tortoise", however, the etymologization of the root causes difficulties. As possible relatives are called hīra"small intestine" and haruspex"haruspex".
Structure
The body length of different representatives varies from a few millimeters to tens of centimeters. The largest representative Haementeria ghilianii(up to 45 cm).
The anterior and posterior ends of the body of leeches bear suckers. At the bottom of the anterior there is a mouth opening leading to the pharynx. Proboscis leeches (detachment Rhynchobdellida) the pharynx is able to move outward. In jaw leeches (for example, medicinal leeches), the oral cavity is armed with three movable chitinous jaws that serve to cut through the skin.
Food
Biology of the body
The body is elongated or oval, more or less flattened in the dorsal-abdominal direction, clearly divided into small rings, which in number 3-5 correspond to one segment of the body; numerous glands in the skin that secrete mucus; at the posterior end of the body there is usually a large sucker, often at the anterior end there is a well-developed sucker, in the center of which the mouth is placed; more often, the mouth is used for suction. At the anterior end of the body there are 1-5 pairs of eyes arranged in an arc or in pairs one after the other. Powder on the dorsal side above the rear suction cup. Nervous system consists of a two-lobed supraesophageal ganglion, or brain, connected to it by short commissures of the subpharyngeal node (derived from several merged nodes of the abdominal chain) and the abdominal chain itself, located in the abdominal blood sinus and having about 20 nodes. The head node innervates the sense organs and the pharynx, and 2 pairs of nerves depart from each node of the abdominal chain, innervating the body segments corresponding to them; the lower wall of the intestine is equipped with a special longitudinal nerve that gives branches to the blind sacs of the intestine. The digestive organs begin with a mouth armed with either three chitinous toothed plates (maxillary P. - Gnathobdellidae), which serve to cut through the skin when sucking blood in animals, or a proboscis capable of protruding (in proboscis P. - Rhynchobdellidae); numerous salivary glands open into the oral cavity, sometimes secreting a poisonous secret; the pharynx, which plays the role of a pump during sucking, is followed by an extensive, highly extensible stomach, equipped with lateral sacs (up to 11 pairs), of which the posterior ones are the longest; the hindgut is thin and short. The circulatory system consists partly of real, pulsating vessels, partly of cavities - sinuses, representing the remainder of the cavity (secondary) of the body and interconnected by annular channels; blood in proboscis P. is colorless, in jawed - red due to hemoglobin dissolved in the lymph. Special respiratory organs are available only in the river. Branchellion, in the form of leaf-like appendages on the sides of the body. The excretory organs are arranged according to the type of metanephridia, or segmental organs of annelids, and most P. have a pair of them in each of the middle segments of the body. P. - hermaphrodites: the male genital organs consist of most of the vesicles (testes), a pair in 6-12 middle segments of the body, connected on each side of the body by a common excretory duct; these ducts open outwards with one opening lying on the ventral side of one of the anterior rings of the body; the female genital opening lies one segment behind the male and leads into two separate oviducts with saccular ovaries. Two individuals copulate, each simultaneously playing the role of a female and a male. P. during laying of eggs allocates with glands lying in the genital area, thick mucus surrounding the middle part of P.'s body in the form of a cover; eggs are laid in this sheath, after which P. crawls out of it, and the edges of its holes come together, stick together and thus form a capsule with eggs inside, usually attached to the lower surface of the algae leaf; the embryos, leaving the facial membrane, sometimes (Clepsine) keep for some time on the underside of the mother's body. All P. are predators, feeding on the blood of mostly warm-blooded animals or mollusks, worms, etc.; they live mainly in fresh water or in wet grass, but there are also marine forms (Pontobdella), just like terrestrial forms (in Ceylon). Hirudo medicinalis - medical P. up to 10 cm long and 2 cm wide, black-brown, black-green, with a longitudinal patterned reddish pattern on the back; the belly is light grey, with 5 pairs of eyes on the 3rd, 5th and 8th rings and strong jaws; distributed in the swamps of the South. Europe, South. Russia and the Caucasus. In Mexico, Haementaria officinalis is used in medicine; another species, H. mexicana, is poisonous; in tropical Asia, Hirudo ceylonica and other related species living in humid forests and in the grass are common, causing painful bleeding bites to humans and animals. Aulostomum gul o - horse P., black-green in color, with a lighter bottom, has a weaker armament of the mouth and therefore unsuitable for therapeutic purposes; the most common species in the north. and central Russia. Nephelis vulgaris is a small P. with a thin narrow body, gray in color, sometimes with a brown pattern on the back; equipped with 8 eyes located in an arc at the head end of the body; related to her original Archaeobdella Esmonti, Pink colour, without rear suction cup; lives on the silt bottom in the Caspian and Azov seas. Clepsine tessel ata - Tatar P., with a wide oval body, greenish-brown in color, with several rows of warts on the back and 6 pairs of triangular eyes, located one after the other; lives in the Caucasus and Crimea, where it is used by the Tatars for medicinal purposes; the transitional place to the order of bristle-legged (Chaetopoda Oligochaeta) worms is occupied by Acanthobdella peledina, found in Lake Onega.
History of medical use
Medical leech ( Hirudo officinalis) - found in the north of Russia, so especially in the south, in the Caucasus and Transcaucasia, in Poti, Lankaran. In the 19th century, leeches were a profitable export item: Greeks, Turks, Italians, and others came to the Caucasus for them. In addition, artificial breeding of leeches was carried out in special pools or parks according to the Sale system in Moscow, St. Petersburg, Pyatigorsk and Nizhny Tagil. Based on the laws in force, catching leeches during their breeding season - in May, June and July - is prohibited; when fishing, only those suitable for medical use should be selected, that is, not less than 1 1/2 inches in length; leeches are small, as well as too thick, should be thrown back into the water when catching. To supervise the observance of these rules, the provincial medical departments are entrusted with the duty to testify the stocks of leeches from barbers and other merchants who trade them. Since medicine expelled leeches from use, the leech trade has fallen completely.
Notes
Sources
- Ruppert E.E., Fox R.S., Barnes R.D. Invertebrate zoology. Vol. 2: Lower coelomic animals. M., "Academy", 2008.
Wikimedia Foundation. 2010 .
- Semipalatinsk region
- Kunduz
See what "Leech" is in other dictionaries:
leeches- (Hirudinea), a class of annelids. Length from several mm up to 15 cm, rarely more. Descended from small-bristle worms. The body is usually flattened, rarely cylindrical, with two suckers (oral and posterior); consists of a head blade, 33 rings ... ... Biological encyclopedic dictionary
leeches- LEECHES, a class of worms. Length 0.5-20 cm. Body usually flattened, with 2 suckers. About 400 species live in fresh and marine waters. Most leeches are bloodsuckers, the salivary glands of which secrete the protein substance hirudin, which prevents ... ... Modern Encyclopedia
leeches- class of annelids. Length 0.5-20 cm. They have front and back suction cups. 400 species. In fresh and marine waters. Most leeches are bloodsuckers whose salivary glands secrete hirudin, which prevents blood clotting. Medical leech ... ... Big Encyclopedic Dictionary
leeches- (Hirudinei) detachment of the class of annelids. The body is elongated or oval, more or less flattened in the dorsal-abdominal direction, clearly divided into small rings, which in number 3 5 correspond to one segment of the body; Numerous glands in the skin... Encyclopedia of Brockhaus and Efron
But for treatment, only a medical leech is used. Among medical leeches, there are two subspecies:
Medicinal leech (Hirudina medicinalic)
Apothecary leech (Hirudina officinalic)
Color. May vary from black to reddish-brown. Abdomen motley. The sides are green with an olive tint.
The size. About 3 - 15 cm - length, about 1 cm - width.
Lifespan. Up to 20 years.
Habitat. They are found mainly in Africa, Central and Southern Europe, as well as Asia Minor. In Russia, they are not so numerous, they mainly spread to the south of the European part of the country. Although there is evidence that individual individuals of the species were found in the southern and eastern parts of Siberia.
They love fresh clean water- lakes, ponds, quiet rivers, as well as damp places near the water - clay shores, wet moss. Leeches live in stagnant water - running water is unfavorable for them.
Lifestyle and behavior. Most of the time, the medicinal leech spends hiding in thickets of algae, hiding under snags or stones. This is both a cover and an ambush.
Leeches love warm sunny weather and even tolerate heat quite well, it is in these conditions that they are most active. They are also not afraid of drought - they either crawl away from a drying up reservoir, or dig deeper into the coastal silt. Leeches are able to stay on land for a long time in hot and humid weather.
With the deterioration of conditions (lower air temperature, windy weather), medical leeches become lethargic and passive. Leeches overwinter by burrowing into coastal silt or bottom soil. Frosts are detrimental to them.
The body of the leech is greatly flattened and elongated when swimming, and the posterior sucker acts as a fin. With wave-like movements, the leech moves in the water.
For medical leeches, an instant reaction to external stimuli is quite characteristic: smell, temperature, splash.
A hungry leech can be recognized by the characteristic position of the body - it sticks to a plant or stone with its back suction cup, while the front one makes circular movements.
Enemies: Desman, water rat, shrews, bugs, dragonfly larvae.
Food. As food, medicinal leeches use the blood of worms, molluscs and vertebrates, and in their absence they can eat insect larvae, ciliates, and mucus of aquatic plants. The leech bites through the skin of the victim and sucks out a small amount of blood, about 10-15 ml. Having satiated, the leech can remain without food for quite a long time - an average of six months, since the blood in its body is digested slowly. However, a record fasting period was observed, which amounted to 1.5 years.
Reproduction. The medicinal leech is a hermaphrodite. Leeches begin to lay eggs during the warm period, approximately two weeks before the end of August or in mid-September. With unfavorable weather conditions this period comes earlier or is delayed.
In the process of reproduction, the leech crawls out onto land, digs a small depression in the silt, then a special department of medical leeches, buy medical leeches, buy leeches in Perm, buy leeches in Perm, the cover of a leech - a girdle - secretes a foamy cocoon in which eggs are laid. This cocoon contains albumin, a protein that serves as food for embryos. The egg incubation period is about two months.
Newborn medicinal leeches are transparent and resemble adults, they still spend some time in a cocoon, feeding on albumin, but soon crawl out. Small leeches that have not reached puberty attack tadpoles, snails, frogs.
If a leech does not drink the blood of a mammal within three years from the moment it emerges from the cocoon, it will never reach puberty.
- the mention of it in many causes unpleasant associations. And the truth is appearance in leeches, it is unattractive, one might even say repulsive. But this creature brings great benefits to a person, helping to get rid of many diseases.
Types of leeches
Medical leeches belong to the type of annelids, class girdle worms, subclass of leeches, proboscis detachment, family Hirudinidae (jaw leeches). Its name in Latin is Hirudo medicinalis. The medical type is successfully used in the treatment of patients in Europe, Russia, Ukraine. Asia, Africa, America use other types of leeches.
AT wild nature there are up to 500 varieties of leeches. With such a variety of bloodsuckers, only three main types are used in treatment:
Other types of leeches not only do not benefit, but can also harm humans and animals.
Equine (Limnatis nilotica). Also known as Egyptian or Nile. Habitat - Transcaucasia, Central Asia, Mediterranean. This species cannot bite through the skin, so they stick to the mucous membranes. May enter the oral cavity. The animal, increasing in size when sucking blood, can cause suffocation of a person and lead to death.
Surveyor Leech (Piscicola geometra). It has a large rear suction cup, despite the fact that it itself is no more than 5 cm in length. It feeds on the blood of fish. Sensing the fish, it begins to move towards it and firmly attaches itself to it. Fish sometimes die due to blood loss. Can be harmful to fisheries if leeches breed in large numbers.
Common or false horse (Haemopis sanguisuga). This is a predatory species, reaches 10 cm in length. Lives in rivers, ditches, ponds, crawls ashore. It can swallow the victim whole, or bite off pieces. It attacks those animals with which it can easily cope. Doesn't suck blood. Habitat - Ukraine, Russia, Moldova, Belarus.
Eight-eyed (Herpobdella octoculata). Flat, about 6 cm long. It lives in reservoirs with stagnant water, survives even in very dirty environments. It feeds on both living and dead larvae of insects and small animals.
Pond (Helobdella stagnalis). The smallest representative It grows no more than 1 cm. It is common in almost all reservoirs. The main color is brown, but green is also found. Attaches to worms, larvae, snails.
Habitat
The wild animal is very common in Europe, but its numbers are constantly declining due to the constant catch. And also the draining of swamps and the unfavorable ecological state of the water contribute to the decrease in the species. It is widely distributed in the north, right up to Scandinavia, and in the south it is also found near Algeria.
Medical species most often live in the Transcaucasus and Azerbaijan. But the area of \u200b\u200bdistribution of pharmacies is Stavropol and the Krasnodar Territory.
Animals can perfectly be both in water and on land. Can only live in fresh water. Salt water bodies are unsuitable for them. When migrating from one habitat to another, they can travel quite long distances on a hard surface.
They settle in ponds and reservoirs, where the bottom is silted and reeds grow. However, the water must be clean. Gets along well with frogs. The favorite habitat of leeches is stones and snags. Under them, she hides, sometimes protruding not completely out of the water.
What does it look like
The body of a medical leech is round, slightly flattened, divided into 33 annular segments. In turn, each of the segments is divided into 3 or 5 parts. In each of the segments there is a central ring in which sensitive papillae are located. They act as a sensor. There are suction cups on the back and front. The anterior sucker functions as a mouth. The bloodsucker has 270 teeth. The rear suction cup is much larger, as it is used to attach the leech to the surface.
The medical appearance is dark brown in color, almost black. The back is darker, stripes are clearly visible along it. Body without bristles, covered with cuticle. Her bloodsucker periodically resets as the animal grows. As a rule, this happens every 2-3 days.
The animal moves without any problems and quite quickly. Able to move both on water and on solid surfaces. The leech uses suckers as a means of movement on the ground, and also helps itself by contracting the body. Once in the water, the animal makes oscillatory movements and swims in waves. It is so strong that one end of the torso can stick to the surface and raise its body to a vertical position. This way she can search for what she needs.
The principle of operation of a leech
The choice of the bite site remains with the leech. Having decided on the site of attachment, it makes a bite with a depth of no more than 2 mm and is saturated with blood. The total volume of sucked blood at a time does not exceed 15 ml. After detachment of the bloodsucker, the wound will bleed from 4 to 20 hours. Everything will depend on individual features organism, and also because how much enzyme the leech will release. It is called hirudin and prevents blood from clotting. It is not necessary to stop the blood, as this achieves a therapeutic effect.
From the moment the skin is bitten and the saliva of the medical leech enters the human blood, the healing effect begins. Useful components within 15-20 minutes are carried throughout the body with blood flow.
How a leech sucks blood - a person does not feel it. A slight discomfort may occur at the moment of biting the skin. After that, the blood by gravity already enters the mouth, and then into the stomach of the bloodsucker. She doesn't roll there. As it saturates, the animal increases in size. When the limit of filling her stomach comes, it falls off by itself.
In anticipation of food, leeches are attached to the surface with two suckers. As soon as they feel that a potential victim is approaching, they begin to move towards it. Having reached the goal, the leech is attached with its rear end to the body, and the front end is looking for the most suitable place to bite. This will be either an area with thin skin, or where the vessels are located closest to the surface.
Once attached, the leech does not let go of the victim until it is completely satiated. The animal may not eat for a long time. Therefore, the amount of blood drunk will depend on how long the bloodsucker has been starving. For example, if a leech has not received nutrition for about six months, then its saturation time can take up to 1.5 hours.
The reproduction of leeches in nature occurs once a year, when the animals reach sexual maturity. It comes at the age of four. To breed offspring, leeches choose the summer period. The mating process in leeches is called copulation. Mating occurs by entwining one individual with another, as if they are glued. When fertilization has occurred, after mating, the female lays cocoons. Usually their number does not exceed 5 pieces.
Leech embryos feed on the protein mass that is inside the cocoon. The cocoon itself is covered with dense protective shell. After about two weeks, small leeches hatch, which can already drink blood. The number of babies ranges from 20 to 40 pieces.
The benefits of leeches
Medicinal leeches are successfully used in the treatment of many diseases. They can, if not completely cure, then significantly improve the patient's condition. The use of leeches in complex treatment accelerates the recovery of the patient.
Treatment with a medical leech is called hirudotherapy. The highest effect is achieved due to several actions of hirudotherapy:
- hirudin- a hormone that prevents blood clotting and thrombosis;
- eglins - substances that prevent joint damage, cure existing diseases;
- hyaluronidase - an enzyme that promotes the process of fertilization is used in the treatment of infertility.
Salivary secret contains painkillers and antibacterial substances.
The main diseases in which the use of a medicinal leech is indicated are.
For hirudotherapy, medical leeches grown artificially should be used. It is strictly forbidden to use for the treatment of leeches caught in open water. Wild animals are carriers of dangerous diseases, diseases accumulate on their jaws when bitten by infected animals.
Contraindications to hirudotherapy
Despite the enormous benefits and positive results in the treatment of diseases with medical leeches, there are a number of contraindications:
- poor blood clotting;
- oncology;
- hemolysis;
- individual intolerance to enzymes;
- allergic reactions;
- anemia;
- tuberculosis of various forms.
Treatment with a medicinal leech will undoubtedly bring great benefits. However, hirudotherapy should be carried out by a qualified specialist so as not to harm the human body.
The body is flattened in the dorsal-abdominal direction, bears two suckers. The anterior or oral sucker is formed as a result of the fusion of four segments; at its bottom there is a mouth opening. The posterior sucker is formed by the fusion of seven segments. The total number of body segments is 30-33, including segments that form suckers. Parapodia are absent. True leeches lack bristles, bristle-bearing ones have. Leeches living in water swim, bending their body in waves, land leeches "walk" on the ground or leaves, alternately sticking to the substrate with either the front or the back suction cup.
rice. one. Diagram of the structure of the front
end of the body of a medical leech:
1 - ganglion, 2 - longitudinal muscles,
3 - pharynx, 4 - muscles of the pharynx,
5 - jaws, 6 - wall
front sucker.
The composition of the skin-muscle sac includes a dense cuticle, a single-layer epithelium, annular and longitudinal muscles. The epithelium contains pigment and glandular cells. The cuticle is divided into small rings; the outer segmentation does not correspond to the larger inner segmentation.
In general, in bristle-bearing leeches it is preserved, in real leeches it is reduced to one degree or another. In most species of true leeches, the secondary cavity is filled with parenchyma, and longitudinal lacunar canals remain from the coelom.
rice. 2. Structure diagram
medicinal leech:
1 - head ganglia,
2 - oral sucker,
3 - pockets of the stomach,
4 - midgut,
5 - hindgut,
6 - anus,
7 - rear suction cup,
8 - abdominal nervous
chain, 9 - metanephridia,
10 - testes, 11 - egg
bag, 12 - vagina,
13 - copulatory organ.
A real closed-type circulatory system, similar to that of oligochaetes or polychaetes, is found only in some species of leeches (bristle-bearing leeches). In jawed leeches, the circulatory system is reduced, and its role is played by lacunae of coelomic origin: dorsal, ventral, and two lateral.
Gas exchange occurs through the integument of the body, some sea leeches have gills.
Excretory organs - metanephridia.
The nervous system is represented by the ventral nerve chain, which is characterized by a partial fusion of the ganglia. The subpharyngeal ganglion consists of four pairs of merged ganglia, the last ganglion of seven pairs. The sense organs of leeches are goblet organs and eyes. Goblet organs - chemoreception organs - are located in transverse rows on each segment, with their help, leeches learn about the approach of the victim, identify each other. The eyes are transformed goblet organs of the anterior segments, they have only a photosensitive value. The number of eyes different types- from one to five pairs.
Leeches are hermaphrodites. Fertilization is usually internal. The eggs are laid in cocoons. Postembryonic development is direct.
The Leech class is subdivided into subclasses: 1) Ancient, or Bristle-bearing leeches (Archihirudinea), 2) True leeches (Euhiridinea). The subclass Real leeches is divided into two orders: 1) Proboscis (Rhynchobdellea), 2) Proboscis (Arhynchobdellea).
rice. 3. Appearance
medicinal leech
Detachment Beskhobotnye (Arhynchobdellea)
Medical leech (Hirudo medicinalis)(Fig. 3) is bred in the laboratory for medical purposes. The body length is on average 120 mm, width 10 mm, the maximum values can be much higher. Each of the three jaws has 70-100 sharp "teeth". After a leech bite, a trace in the form of an equilateral triangle remains on the skin.
Under laboratory conditions, they reach sexual maturity in 12-18 months and breed at any time of the year. The reproductive system consists of nine pairs of testes and one pair of ovaries enclosed in egg sacs. The vas deferens merge into the ejaculatory canal, which ends with the copulatory organ. The oviducts leave the ovaries, which flow into the convoluted uterus, which opens into the vagina. Fertilization is internal. Cocoons are oval in shape and reddish-gray in color, average length 20 mm, width 16 mm. In one cocoon from 15 to 20 eggs. The egg diameter is about 100 microns. After 30-45 days, small leeches, 7-8 mm long, emerge from the cocoons. In laboratory conditions, they are fed on blood clots of mammals.
Adult leeches are used for hypertension, strokes, for resorption of subcutaneous hemorrhages. Hirudin, contained in the saliva of leeches, prevents the development of blood clots that clog blood vessels.
In nature, medicinal leeches live in small fresh water bodies and feed on mammals and amphibians.
rice. four. Big
false horse leech
Large false horse leech (Haemopis sanguisuga)(Fig. 4) lives in fresh water bodies. It leads a predatory lifestyle, feeds on invertebrates and small vertebrates, swallowing them whole or in part. The mouth and pharynx can be greatly stretched. The number of blunt "teeth" on each jaw is 7-18. Stomach - with one pair of pockets.
The false horse leech is often confused with the medical one, although they are quite easily distinguished by the color of the dorsal side of the body. The dorsal surface of the body of the false horse leech is black, uniform, sometimes with randomly scattered dark spots. On the dorsal side of the body of a medical leech there is a characteristic pattern in the form of longitudinal stripes. False horse leeches should not be kept together with medical ones, as they eat them.
External structure
Medical leechThe body of leeches is noticeably flattened in the dosoventral direction. At the anterior end there is a muscular anterior sucker, in the center, which fits the mouth opening. At the posterior end there is a second, very strongly developed posterior sucker, above which the anus opens on the dorsal side.
Leeches do not have any appendages or parapodia. The bristles are preserved only in a primitive species - the bristle leech. It has four pairs of setae on five anterior segments.
leeches very mobile, crawling and floating animals . Attached by the posterior oral sucker, the leech pulls the body forward, then attaches with the oral sucker, while the posterior sucker is pulled away from the substrate and the body is pulled to the head end, bending into a loop. Then the leech is sucked again by the back sucker, etc. Thus, the leeches make "walking" movements. Leeches swim, producing wave-like movements with their whole body, in which their body bends in a dorsoventral direction.
The external ringing of leeches is false, secondary, it does not coincide with the true internal segmentation. Each real segment in different leeches corresponds to 3 to 5 outer rings. The external ringing of leeches is an adaptive trait that provides body flexibility with a powerful development of the skin-muscle sac.
The body of leeches is formed by 33 segments (with the exception of the bristle leech, which has 30 segments), of which a weakly separated head lobe - the prostomium - and four head segments are part of the anterior sucker. trunk department represented by 22 segments. The posterior sucker is formed by the fusion of the last seven segments.
Skin-muscular sac
The skin-muscular sac of leeches is formed by a single-layer epithelium, which secretes a dense layered cuticle, and powerfully developed muscles. The skin of leeches is rich in glandular cells that secrete mucus and is permeated with a network of lacunar capillaries. Under the epithelium there are numerous pigment cells that cause a peculiar pattern of leeches.
Leeches are characterized by the presence of three continuous layers of musculature of the skin-muscular sac, like in flatworms: the outer annular, diagonal, and the most powerful longitudinal. The dorsoventral muscles, which are not part of the skin-muscular sac, are also strongly developed.
Body cavity and circulatory system
In almost all leeches, the entire space between the organs is filled with parenchyma, like in flatworms. Only in leeches does the parenchyma fill the secondary body cavity, while in flatworms it fills the primary.
In another order - proboscis leeches (Rhynchobdellida) - a stronger growth of the parenchyma is observed. This leads to a partial reduction of the coelom. However, the coelomic cavity is preserved as a whole system of lacunae. Four main coelomic lacunae run along the entire body: two on the sides, one above the intestine, surrounding the dorsal blood vessel, and one below the intestine, it contains the ventral blood vessel and the ventral nerve cord. These gaps communicate with each other, forming a network of smaller gaps. Thus, proboscis leeches have both a circulatory system and a lacunar system, which is a modified coelom.
In the third order, the higher jawed leeches (Gnathobdellida), which include the medical leech and many other freshwater leeches, the development of the parenchyma goes as far as in the proboscis leeches. The blood vessels lying inside coelomic lacunae in proboscis leeches are reduced in jaw leeches. The function of the circulatory system is performed by the lacunar system, which originates from the coelom. Such a process of functional replacement of one organ by another, different in origin, is called substitution or replacement of organs.
excretory system
The excretory organs of leeches are represented by segmental organs of metanephridial origin. However, the number of pairs of pephrindia does not correspond to the number of segments. The medicinal leech has only 17 pairs. In connection with the transformation of the coelom into a system of lacunae, the structure of the metanephridia of leeches also changed. The funnels of the metanephridia open into the ventral lacuna (coelom), but not directly into the nephridial canal. They are separated from the nephridial canal by a septum, so the secreted substances diffuse from the funnel into the nephridium.
Such a structure of the metanephridia of leeches (separation of the infundibulum from the nephridial canal) is explained by the functional transformation of the lacunae into the main circulatory system, replacing the circulatory one. The metanephridia of leeches are characterized by the presence of a special expansion - the bladder.
Digestive system
The mouth is placed on the bottom of the front sucker. It leads to the front digestive system lined with ectoderm and consisting of an oral cavity and a muscular pharynx. The structure of the oral cavity and pharynx in proboscis and jaw leeches is different.
In proboscis leeches, the oral cavity, growing back, surrounds the pharynx in the form of a vagina. A very muscular pharynx turns into a proboscis, protruding and retracting with the help of special muscles. The proboscis can penetrate into the thin covers of various animals (for example, mollusks), and in this way the leech sucks out blood.
In jawed leeches (medical leeches, etc.) in the oral cavity there are three longitudinal muscular ridges that form jaws directed with their crests towards each other. Muscular rollers are covered with chitin, serrated along the edge. With these jaws, leeches incise the skin of an animal or person. In the throat of blood-sucking jaw leeches, glands open that secrete a special substance - hirudin, which prevents blood clotting.
Next, food enters the endodermic midgut, which consists of the stomach and posterior midgut. The stomach forms paired lateral protrusions, of which the last pair is usually especially developed, extending to the posterior end of the body. The stomach serves as a reservoir for long-term storage of blood. The blood that fills his pockets does not clot for weeks and months.
The posterior part of the midgut is represented by a relatively short straight tube in which the final digestion and absorption of food takes place. It passes into a short, often enlarged posterior ectodermic gut, which opens with an anus above the posterior sucker.
Nervous system and sense organs
The nervous system of leeches consists of a paired supraesophageal ganglion connected by circumpharyngeal connections with the subpharyngeal ganglionic mass. The latter is formed by the fusion of the first four pairs of ganglia of the abdominal nerve chain. This is followed by 21 ganglia of the ventral nerve chain and a ganglionic mass (of eight pairs of ganglia) that innervates the posterior sucker.
The sensory organs of leeches are represented by sensitive kidneys, or goblet organs. Each such organ consists of a bundle of spindle-shaped cells located under the epithelium. The outer end of sensitive cells forms a sensitive hair. Nerves from the ventral nerve cord approach the inner ends of these cells.
Some of the goblet organs perform the functions of chemical sense organs, others - tactile. The eyes of leeches have a similar structure to the goblet organs described above. There may be several pairs. The eye consists of vesicle-shaped photosensitive cells with large vacuoles inside, to which the nerves that make up the axial part of the eye approach. The eye is surrounded by dark pigment.
Reproductive system, reproduction and development
According to the structure of the genital organs and the method of reproduction, leeches have much in common with oligochaetal rings. They are hermaphrodites, and their genitals are concentrated mainly in the region of the 10th and 12th body segments. Leeches have a girdle section, which, unlike oligochaetes, coincides in position with the penis. The girdle becomes noticeable only during the breeding season.
The male reproductive apparatus consists of several pairs (4-12 or more) of the testes. The medicinal leech has 9 pairs of testes located inside the seed sacs. Short vas deferens depart from them, opening into longitudinal paired vas deferens. The latter in the area of the 10th segment form dense balls - appendages of the testes, in which sperm accumulates. Then they pass into the ejaculatory (paired) canals that open in the copulatory organ, which can protrude forward through the unpaired male genital opening on the 10th segment. Not everyone has a copulatory organ. In many leeches, spermatozoa are enclosed in spermatophores. Spermatophores are either introduced into the female genital opening or stuck into the skin, and the spermatozoa penetrate the body of the leech and make their way to the female reproductive tract.
The female reproductive apparatus consists of a pair of ovaries located in egg sacs. They pass into short and wide uterus, which are interconnected and form an unpaired oviduct, which flows into a wide vagina, which opens on the 11th segment with the female genital opening.
Fertilized eggs are laid in a cocoon secreted by a girdle. The cocoon is either attached to aquatic plants, or is located at the bottom of the reservoir. Some leeches lay single eggs.
The development of leeches is not direct, since larvae emerge from the eggs, remaining, however, in a cocoon. The larvae have cilia and protonephridia. In the cocoon, the transformation of larvae takes place, and already formed leeches emerge from the cocoon into the water. The laying of eggs in relatively strong cocoons, which protect eggs and larvae well, causes a small number of eggs. It is measured in various leeches in units, in extreme cases, in tens.
Classification
The class of leeches is divided into three orders: 1. Bristle-bearing (Acanthobdellida); 2. Proboscis (Rhynchobdellida); 3. Jaw (Gnathobdellida).
Order Bristle-bearing leeches (Acanthobdellida)
A very primitive relic form bearing four pairs of sharp, curved setae on five anterior segments. The anterior sucker is absent, only the posterior one is present. The parenchyma is poorly developed, there is a coelomic cavity and a circulatory system.
Squad Proboscis leeches (Rhynchobdellida)
Proboscis leeches are remarkable for breeding and caring for offspring. The leech lays eggs that remain attached to the ventral side of its body. At this time, the leech is not very mobile: it sits, attached with suckers, on some plant and makes oscillatory body movements. When the juveniles hatch from the eggs, the leech does not change its position and the young leeches remain attached to the ventral side of the mother with their suckers, usually for several days, and then spread and begin to lead an independent existence.
Squad Jawed leeches (Gnathobdellida)
Most jaw leeches in the oral cavity have the jaw apparatus described above.
In addition to the medicinal leech (Hirudo medicinalis), common in the southern part of Russia, this order includes the ubiquitous false horse leech (Haemopis sanguisuga). This is a large dark-colored leech, has weak jaws and is not able to bite through the skin of humans and mammals. It feeds on worms, mollusks and other invertebrates. The cocoons of the false-horse leech are buried in the coastal strip, above the water level.
Some jawed leeches (especially those found in southern latitudes) can be human parasites, for example, from the genus Limnatis. One of them, L. turkestanica, is found in Central Asia. When drinking raw water from a reservoir, it can enter the human nasopharynx, where it settles and sucks blood. In addition to severe irritation, it causes bleeding. In the jungles of Sri Lanka, India, Indonesia, land animals from the genus Haemadipsa live. They hide in damp places, in grass and under foliage, and attack animals and humans, causing very sensitive bites.
