The small pond snail serves as an intermediate host for. Liver fluke - Who is the intermediate host of the fluke

The small pond snail is similar to the common pond snail, only the shell size is smaller (see appendix fig. 25). The small pond snail lives in temporary reservoirs - puddles, ditches, in swampy meadows, sometimes even on wet soil near the water's edge. In a word, there are many places where a temporary resident is found.

It feeds, like its relative, on algae and microorganisms.

The small pond snail is distributed throughout Europe and North Asia, as well as common pond snail.

gastropods;

coil family;

horn coil.

Coils (Planorbis) belong to the class of gastropods (Gastropoda), to the order of pulmonary (Pulmonata), to the family of coils (Planorbidae).

The body of the coil, like that of pond snails, is divided into three parts: head, torso and leg (see appendix fig. 26). The leg is a muscular abdominal part of the body, leaning on which the mollusk slowly glides. At the coils, the turns of the shell are located in the same plane. Coils are not as mobile as pond snails, and cannot be suspended from the surface film.

Coils live on plants in stagnant and slow-flowing reservoirs, in the same place as an ordinary pond snail, but rises to the surface of the water much less frequently.

beauty family;

larva of a beauty girl.

On a sunny day, blue lights flash up and then go out over the river (see appendix fig. 27). It is flitted by graceful dragonflies. At some point, they resemble helicopters.

The body is bronze-green, the wings of females are light smoky, those of males are almost entirely blue.

All dragonflies, wherever they are, wherever they fly, need water. They lay their eggs in the water. And only in water can their larvae live. The larvae do not look like adult dragonflies. They just have the same eyes.

Special mention must be made of the eyes of dragonflies. Each eye is made up of thousands of small eyes. Both eyes are large and protruding. Thanks to this, dragonflies can look in all directions at the same time. This is very handy for hunting. After all, dragonflies are predators. And their larvae, living in the water, too.

Dragonflies hunt in the air - they grab insects on the fly. The larvae live in the water, and here they also get food for themselves. But they do not chase prey, but lie in wait for it. The larva sits motionless or crawls slowly along the bottom. And some tadpoles or some insects swim by. The larva does not seem to care about them, but how this tadpole or insect turns out to be close. Once! She instantly throws long arm and grabs prey, quickly pulling it to itself.

"But insects don't have arms," ​​you say. And you will be right. Yes, of course they don't have hands. But there is a very long lower lip with hooks at the end. The lip folds like a hand at the elbow when you press the brush to your shoulder. And while the larva watches for prey, the lip is not visible. And when the prey is close, the larva instantly throws out its lip to its full length - as if shooting it - and grabs a tadpole or an insect.

But there are moments when the larva needs to save itself. And here saves her speed. More precisely, the ability to move with lightning speed from place to place.

Some predator rushed at the larva. Another second - and the larva was gone. But where is she? Just been here, and now in a completely different place. How did she get there? Very simple. Activated your " jet engine".

It turns out that dragonfly larvae have a very interesting adaptation: a large muscular sac inside the body. The larva sucks water into it, and then throws it out with force. It turns out a water "shot". The water jet flies in one direction, and the larva itself in the opposite direction. Just like a rocket. This is how it turns out that the larva makes a lightning-fast jerk and slips out from under the very "nose" of the enemy.

After flying a few meters, the larva slows down, sinks to the bottom or clings to some plant. And again it sits almost motionless, waiting for the time when it will be possible to throw out the "hand" and grab the prey. And it will be necessary - it will re-launch its " rocket launcher True, not everyone has a "jet engine", but only the larvae of large dragonflies.

A year later, the larvae of some dragonflies, after three years, the larvae of others climb out of some plant sticking out of the water to the surface. And this is where it happens small miracle: the skin of the larva bursts and a dragonfly appears from it. The most real and not at all like a larva.

The dragonfly will shed its skin like a suit, and even pull out its legs, like out of stockings. He will sit for several hours, rest, spread his wings and go on his first flight.

Some dragonflies fly far from their birthplace. But the time will come, and they will definitely return. Because they cannot live without a river or a lake, a pond or a swamp - without water, in a word. And the river, the pond, the lake also cannot live without these friends of theirs.

Dragonfly eggs are laid in water or in the tissues of aquatic plants. The eggs hatch into larvae of an extremely characteristic shape, interesting in their biological features. These larvae play an important role among other living material in freshwater excursions.
Dragonfly larvae are found everywhere in stagnant and slowly flowing water. Most often they are on aquatic plants or at the bottom, where they sit motionless, sometimes move slowly. There are species that burrow into the silt.

The larvae move either by swimming or crawling. Larvae from the group of buttercups swim differently than others. Big role when moving, expanded gill plates located at the posterior end of the abdomen play, which serve as an excellent fin. Bending its long body, the larva beats the water with this fin and rapidly pushes forward, moving like a small fish.

Dragonfly larvae feed exclusively on live prey, which they watch motionless for hours, sitting on aquatic plants or at the bottom. Their main food is daphnia, which they eat in huge quantities especially by younger larvae. In addition to daphnia, dragonfly larvae willingly eat water donkeys. They are less willing to consume cyclops, perhaps due to the small size of the latter.
The favorite food of dragonfly larvae are also mayfly larvae and mosquito larvae from the families of culicids and chironomids.
They also eat larvae. water beetles, if only able to master them. However, they do not touch large larvae of swimmers, well-armed and no less predatory, even if they are planted in a common vessel with them.
Dragonfly larvae do not chase their prey, but sit motionless on aquatic plants or on the bottom and guard the prey. When a daphnia or other animal suitable for food approaches, the larva, without moving from its place, throws out its mask with lightning speed and grabs its prey.

For grasping prey, the larvae have a wonderful mouth apparatus, which is aptly called "masks". This is nothing more than a modified lower lip, which looks like grasping tongs, sitting on a long lever - a handle. The lever is equipped with a hinge joint, thanks to which the whole device can be folded and, in a calm state, covers the underside of the head like a mask (hence the name). Noticing the prey with its large bulging eyes, the larva, without moving, aims at it and with a lightning movement throws its mask far forward, grabbing the prey with remarkable speed and accuracy. Captured prey is immediately devoured with strong gnawing jaws while the mask brings the prey to the mouth and holds it like a hand while eating.

Luke-type larvae have the ability to discard gill plates if they are infringed. This is easy to verify by experience: put the larva in the water and squeeze the gill plate with the tip of tweezers. This phenomenon is called self-mutilation (autotomy) and is well known in many animals (spiders, lizards, etc.). For this reason, it is necessary to catch larvae from the water that lack 1 - 2, and sometimes all 3 tail plates. In the latter case, breathing takes place, in all likelihood, through a thin skin that covers the body. The torn off plate is restored again after some time, due to which it is possible to observe larvae with gill plates of unequal length. It should be noted that in Calopteryx one of the plates is always shorter than the other two, which is not an accidental circumstance, but a generic feature.

Dragonflies reproduce using eggs that the females lay in the water. The clutches of different species are very diverse. Dragonflies such as yoke and buttercups drill their eggs into the tissues of aquatic plants. In this regard, their eggs also have a characteristic oblong shape, and the stuck end is pointed. In the place where the egg is stuck, a trace remains on the surface of the plant, which then takes the form of a dark spot or scar.
Since the eggs different types dragonflies are placed on the plant in a certain order, then peculiar, sometimes very characteristic patterns are formed.

The suborder of dragonflies is homoptera;

Lutka family; sunflower-bride.

A very slender, elegant, graceful dragonfly (see appendix fig. 28). The body is green, metallic-shiny. In females, the sides, breasts are yellow, and in males with a bluish-gray bloom.

There are no significant differences between dragonflies, and all descriptions of dragonflies and their larvae are the same, so in the previous chapter you can find all descriptions of both larvae and adults.

Mayfly Squad;

Mayfly ordinary.

Quiet summer evenings when the sun's rays are no longer burning, some insects that look like butterflies, but with two or three long threads on their tails, swarm in the air near the banks of rivers, lakes and ponds (see appendix fig. 29). They either soar up, then freeze, stabilizing the fall with long tail threads, then, spreading their wide wings, slowly sink down. So they swirl over the shore, like a dense fog or cloud about ten meters high and about a hundred meters long. These swarms rush over the water like a storm. You will not see such an exceptional phenomenon every day, only in July-August it is repeated several times.

This is dancing, carrying out the mating flight, mayflies. Their wings and they themselves are so tender that it is simply amazing how they do not break during the flight. You involuntarily think that they will not live long. And this opinion is true: many mayflies live only one day. Therefore, they are called mayflies, and their scientific name comes from Greek word"ephemeron" - short-lived.

After the mating flight, the females lay their eggs in the water and die. With such a short life, they do not eat anything.

Mayfly larvae develop in water. The larvae live longer, two to three years. And unlike an adult, they eat very well. And they feed on algae, decaying organic matter, small invertebrates and molt up to twenty-five times during development. Many fish feed on the larvae of mayflies, and various birds eat adult mayflies.

On examination, the quick, sharp movements of the larvae are primarily striking. When disturbed, it takes off headlong and swims very briskly, with three feathery caudal filaments, richly pubescent with hairs (Cloon, Siphlurus), serving as fins. The legs serve mainly for attachment to aquatic plants. The quick movements of the mayflies probably serve as a defense against their many enemies, who actively hunt for these tender larvae. The color of the larvae, in general, greenish, matching the color of the aquatic plants among which they huddle, probably also plays a protective role.

The respiration of larvae is easy to observe during excursions. It is of great interest as good example tracheal-gill breathing. The gills look like thin delicate plates that are placed in rows on both sides of the abdomen (Cloeon, Siphlurus). These delicate tracheal leaves are constantly moving, which can be perfectly seen in a larva sitting in water even without the help of a magnifying glass. Most often, these movements are uneven, jerky: as if a wave runs through the leaves, which then remain motionless for some time until new wave. The physiological significance of this movement is quite clear: in this way, the flow of water washing the gill plates increases, and the exchange of gases accelerates. The larvae's need for oxygen is generally very high, therefore, in aquariums, the larvae die at the slightest damage to the water.
The food of the larvae is very diverse. The free-swimming, stagnant water forms most commonly encountered on excursions are peaceful herbivores, feeding on microscopic green algae (Cloeon, Siphlurus). Other species lead a predatory lifestyle and actively hunt for small aquatic animals. The food of many species of mayflies is still not well understood.

The phenomena of reproduction in mayflies are of great interest and have long attracted the attention of observers. Unfortunately, these phenomena on excursions have to be seen only by accident. As mentioned above, females drop their eggs into the water. The eggs hatch into larvae, which grow and molt many times (the Cloeon has more than 20 molts), and the rudiments of wings gradually form in them. When the larva completes its development, a winged insect hatches. At the same time, the larva floats to the surface of the reservoir, the covers on its back burst, and in a few seconds an adult mayfly emerges from the skin, which flies into the air. Since the process of hatching in larvae is often carried out simultaneously, the surface of those reservoirs where larvae are found in large numbers presents a wonderful sight during hatching, which has been described more than once in the literature: the surface of the water seems to boil from a multitude of hatching insects, and clouds of mayflies, like snow flakes hovering in the air. However, the winged insects that hatch from the larvae do not represent the final stage of development. They are called subimago and after a short period of time (from several hours to 1-2 days) they molt again, thus turning into imago ( the only case among moulting insects are winged). Sometimes on an excursion you can watch how a winged mayfly sits on some plant or even on a person and immediately sheds its skin.

Detachment ticks;

hydrachnida family;

The vast majority of ticks are very small animals, no more than one millimeter, only a few are larger, for example, our tick.

flatworms, trematodes migrate from one carrier to another until they find permanent habitats. To reach the final host, they have to go through a complex life cycle.

The variety of stages of development of the liver fluke is also amazing. From the period of the egg entering the external environment and to the stage of reproduction, which occurs by laying eggs by an adult hermaphroditic marita.

And if the mollusk can rightly be considered the first owner of the liver fluke, then any representative of the warm-blooded animal world or the person himself will be the final one.

The bright class of trematodes is, in fact, rather unusual. It has many species that have only some similarities with each other: cat fluke, lanceolate, giant liver fluke and even Chinese fluke. The average size provides for a length of up to 5 cm, but there are individuals that reach more than 7.5 cm.

Also of interest is the variety of methods of reproduction.

Depending on the consequences to which the final host of the liver fluke is exposed, representatives of the family Fasciolidae and the order Opisthorchis are distinguished.

They provoke the appearance in the human body of serious diseases, such as fascioliasis and opisthorchiasis, which affect the organs of the biliary system.

Life cycle of the liver fluke

How does the path of development of a trematode to a sexually mature adult individual, ready for growth and reproduction, take place? And who is intermediate host liver worm.

• mature marita. The result of cross-insemination inside the hermaphrodite is the process of fertilization. After that, about a million eggs appear every week. They get into the outer aquatic environment with secretions of animals, people. The final host of the liver worm suffers greatly, as marita infects the liver and its cells;
• miradium. It appears under the influence of light. The ciliary larva develops for about 17-18 days at a favorable temperature of no more than 29 ° C. For a day, she must find the carrier and penetrate into his body. Usually it becomes a small pond snail;
• sporocyst. Parthenogenetic form, which is formed inside the mollusk by ridding the larva of the ciliary cover. In the sporocyst, fertilization occurs internally. Gradually torn apart;
• redia or eggs fertilized by a sporocyst. They reproduce this way several times. But already in the liver of a mollusk. This process can take up to 2 months. After that, larvae with tails appear;
• cercariae. They leave the snail and head closer to the shore, where their further development. The larva sheds its tail and attaches itself to plants. Covered with a thick sheath. A cyst is formed;
• adolescaria can be in a state of cysts for several months. Then, together with water or plants, it enters the body and intestines of the final host;
• the hermaphrodite marita worm already has a leaf-shaped body. Length - 3 cm. The larva has an oral and abdominal cavity, it is able to remove the remnants of vital activity, and is equipped with a reproductive system.

Temporary intermediate host of the liver fluke

There are three types of it life cycle:

• at a temporary carrier;
• free larval stage;
• from the final owner.

At the stage of adolescaria, the final or temporary host of the liver fluke can be livestock, which is often found near water bodies or cats, dogs. Another definitive host of the liver fluke is also able to become infected at this stage - a person. Penetration pathways are water ingress into oral cavity or ears when swimming.

Definitive host of the liver fluke

How does the process of human infection occur:

1. non-observance of hygiene rules;
2. polluted poorly purified water;
3. fish living in freshwater reservoirs;
4. animal meat;
5. poorly processed products that fall on the table from the garden.

And here begins a new stage of the life cycle. First, the worms enter the intestines through the mouth and stomach, where they pass to the stage of a full-fledged larva. They migrate to the liver and bile ducts. Destroy the walls and tissues of the liver.

Sometimes they get into respiratory system but they quickly die. After 3 months, they reach the stage of a sexually mature individual and multiply.

Names: common pond snail, marsh pond snail, big pond snail, lake farmer.

Area: Europe Asia, North Africa, North America.

Description: pond snail, refers to lung molluscs. The largest of the pond snails living in Russia. In last years divided into two types - Limnaea stagnalis and Limnaea fragilis.The appearance of the pond snail is very variable: depending on the conditions of existence, the color, thickness, shape of the mouth and whorl of the shell, and dimensions vary. The body of the pond snail can be divided into three main parts: the body, head and leg. The body repeats the shape of the shell, closely adhering to it. The shell is thin spiral (twisted in 4-5 turns), strongly elongated, with a large last turn. The shell consists of lime, covered with a layer of greenish-brown horn-like substance. The head is large, with flat triangular tentacles and eyes set at the inner edge of their bases. The tentacles are filiform. The mouth of the pond snail leads to the pharynx. It contains a muscular tongue covered with teeth (grater). From the pharynx, food enters the stomach, then into the intestines. The liver aids in the digestion of food. The intestine opens with an anus into the mantle cavity. The leg is narrow and long, muscular, occupies the entire ventral side of the body. The breathing hole is protected by a prominent blade. The circulatory system is open. The heart pumps blood into the vessels. Large vessels branch into small ones, from which blood enters the spaces between the organs.

Color: the color of the legs and body is from blue-black to sandy-yellow. The shell of the pond snail is brown.

The size: shell height 35-45 mm, width 23-27 mm.

Lifespan: up to 2 years.

Habitat: stagnant water bodies (ponds, lakes, river backwaters, canals, swamps) with abundant vegetation. It can live in slightly brackish water. There is also a pond snail in drying up reservoirs.

Enemies: fish.

Food/food: the pond snail feeds on rotting remains of plants and animals. It deliberately swallows sand that remains in the stomach and helps grind hard food.

Behavior: the pond snail is almost always active. It crawls among thickets, scraping algae and small animals from the underside of leaves. Max speed crawling - 20 cm / min. Breathes air, the reserves of which renew, rising to the surface (6-9 times per hour). Pond snails, living in deep lakes at a considerable depth, breathe air dissolved in water, which is filled in the respiratory cavity. When the reservoir dries, it seals the mouth of the shell with a dense film. Can freeze into ice and then come to life when thawed.

Reproduction: the common pond snail is a hermaphrodite. Cross fertilization. It lays eggs enclosed in transparent slimy cords, which it attaches to underwater plants and objects. Lays 20-130 eggs.

Season/breeding period: during the whole year.

Incubation: about 20 days.

Offspring: development without a larval stage. Small pond snails with a thin shell emerge from the eggs.

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The common pond snail is the most common member of the family in Europe. It feeds on waste and carrion that other animals do not consume.

   Basic data:
DIMENSIONS
Shell length: 45-70 mm.
Shell Width: 20-30 mm.

BREEDING
Mating period: spring or summer when the water warms up.
breeding type: pond snails are hermaphrodites.
Number of eggs: 200-300 eggs in cords attached to underwater objects. Eggs hatch into miniature replicas of adults.

LIFESTYLE
Habits: keep alone in stagnant ponds and rivers with slow flow.
Food: organic waste and algae, sometimes carrion.
Lifespan: 3-4 years.

RELATED SPECIES
About 100 species belong to the family of pond snails, for example, eared, marsh and small pond snails.

   An ordinary pond snail lives in water, but breathes atmospheric air. That is why it can inhabit reservoirs with stagnant water, which contains a minimal amount of oxygen. In such swamps and lakes there are many rotten plant and animal remains - the main food of an ordinary pond snail.

BREEDING

LIFESTYLE

FOOD

• The shape of the common pond snail shell depends on the place of existence of a particular individual. These mollusks are extremely variable; not only their size, color, shape, but also the thickness of the shell vary.
• The small pond snail is one of the smallest representatives of the family. It lives not only in reservoirs, but also in water meadows and pastures. The small pond snail is an intermediate host of the liver fluke, which causes fascioliasis in sheep and cattle.
• The shells of all European species of pond snails are twisted to the right. Only as an exception are individuals with left-handed (leotropic) shells.

FEATURES OF THE ORDINARY POND