Ciliated worms white planaria. Basic information about white planaria. The internal structure is divided into a number of systems

Under stones in freshwater bodies of water at the very bottom you can find white flatworms. They belong to the class of ciliates and are primitive creatures. Scientists named this species of worm planaria. In Russia they can be found in the middle zone. Planarians are distributed almost all over the world. These worms are also popular among aquarists, since they do not cause much harm to either aquatic inhabitants or humans.

The simplest and most primitive inhabitant of the aquarium is the flatworm - planaria.

general characteristics

For example, under the coastal stones of Lake Baikal you can find individuals up to 30 centimeters.

Appearance

The body of the planaria is bipolar and covered with small cilia, thanks to which it moves. Its main color is white, but there are worms of green, gray, yellowish, brown, reddish and even lilac colors. Spotted planarians are found in some habitats.

Planaria come in a variety of colors, but most are white.

The muscle fibers under the ciliated skin can contract, allowing them to lengthen or shrink. They have a diamond-shaped head with two black eyes, which are able to detect the level of illumination. They have an organ of balance that helps them navigate where is up and where is down.

Organs of touch in the worm they are presented in the form of sensitive cells scattered throughout the body. They are developed quite well. The head part of the body has paired tentacles.

Internal structure

The digestive system of planaria has an interesting structure. Its swallowing apparatus is very unusual and is located under the abdomen.

The feeding process of planaria involves throwing out special threads that swell in water, with the help of which the freshwater predator captures prey. Then he presses his whole body against his prey, sucks it with his mouth and pulls it down his throat.

The internal structure includes:

• muscle bag;
• nervous system;
• excretory system;
• digestive system;
• sense organs.

The most interesting thing in the structure is the digestive system, especially the process preceding swallowing

As for the circulatory system, planaria does not have it. Nutrients are absorbed directly by the intestinal cells, and the influx of oxygen and removal of carbon dioxide occur through the skin. Due to the fact that their body is flat, worms have very good gas exchange. Their respiration is carried out due to oxygen dissolved in water. Since they do not have an anus, the worms get rid of food debris by throwing them back through the mouth. Digestion of food occurs due to digestive juices produced by intestinal cells.

Lifestyle and reproduction

Planaria leads a hidden lifestyle and is usually active at night, and during the day it hides under stones or snags at the bottom or in thickets of aquatic plants. It poses a danger to shellfish, which may die if they swallow it. It also has excellent vitality. This is due to good regeneration.

Since planaria is a hermaphrodite, then Reproduction occurs in two ways:

1. By fission, when the body of a flatworm stratifies at the very peak of sexual activity. After some time, each part transforms into a full-fledged individual. The spontaneous disintegration of the body usually occurs under unfavorable conditions - for example, an increase in temperature or lack of oxygen.
2. Using the sexual method, which involves laying eggs on any type of substrate. To do this, the worms must come into contact with each other for a few seconds. When the female and male cells unite, the zygote will head to the oviduct, where it will be saturated with nutrients and various trace elements. After this, a cocoon will form, which will subsequently become an egg. Within two weeks, it matures and, as a result, many small individuals appear.

White planaria is found in freshwater reservoirs or aquariums, a class of ciliated worms. These are microorganisms such as flatworms. In appearance it is similar to or. But unlike them, it does not pose any harm to the health of animals and humans.

The characteristics of the external structure are as follows. The white planaria has a symmetrical body up to 2 cm long and no more than 5 mm thick. The body is divided along its entire length by an axis, the right side repeats the structure of the left side. Color white or milky white. The front, head, part of the microorganism is slightly expanded, has two tentacles with black eyes. The back is pointed.

The lifestyle of the white planaria does not harm plants, aquatic animals and humans, but it does not bring any benefit either. In nature, milky white planaria can be found under stones and live at the bottom of reservoirs. It moves in the water with slow and smooth wave-like movements.

Planaria is a predator. Eats protein foods, e.g. eggs of crustaceans, small snails or the remains of digested food of large aquatic inhabitants. It can be added to the aquarium along with food, algae or snails. When a planaria enters an aquarium, it changes the biological diversity of the species in it. They can destroy crustaceans, shrimp and small fish.

A distinctive feature is that flatworms are not two-layered, but three-layered microorganisms. In addition to ectoderm and endoderm, there is mesoderm. Its significance is enormous. From it various internal organs and entire systems are formed.

The description of the outer cover is as follows. The body is covered with a skin-muscular sac, which is formed by longitudinal and transverse muscles. Beneath these layers of muscle fibers is a loose mass of cells called parenchyma. All internal organs, presented in a simplified form, are placed in a similar muscular sac.

Skin cells have cilia. Between the cells there are tubular glands that secrete bitter mucus, which ensures speed and smoothness of movements. Mucus is most often released during times of danger.

The development cycle is free, independent of the main and intermediate host. Seeing the victim, movement slows down even more. The worm almost crawls thanks to its cilia. The external skin sac also helps to move.

The structure of a microorganism from the inside

The structure and functions of the organ systems of flatworms can be studied and considered using the example of white planaria.

The digestive system begins with the oral cavity. It is located in the front part of the body - below. Passes into the pharynx and midgut. When the worm swallows food, the proboscis can be seen extending, representing the pharynx. Food moves into the final part of the pharynx, which is connected to the intestines. The intestine is represented by three branches. This allows them to feed on food larger than the planaria itself.

The digestive system has another feature. The white planaria has a closed intestine and no anus. Food is digested into molecular fragments with the help of produced enzymes, and then absorbed by the intestines into the cells. Remains of digested food are removed through the oral cavity.

The excretory system can be divided into two parts. The first part is represented by the organs of the digestive tract, and the second part is represented by the skin. The entire surface is made up of tubular holes that help suck in oxygen and release carbon dioxide.

Inside the body there are tubules that end in pores in the front of the body. The cells of the terminal section of the tubules absorb harmful, toxic substances or excess fluid from adjacent tissues.

There are no signs of the presence of respiratory organs. The respiratory function is performed by a skin-muscular sac, which absorbs oxygen dissolved in water.

The peculiarities are that the body is devoid of organs of the circulatory system. Since the body is small, the nutrients and oxygen necessary for development are distributed throughout the body without obstacles without the help of special organs.

The nervous system of the white planaria consists of a cluster of neurons and nerve trunks that branch from them. The nerve trunks are connected to each other, due to which the nerve impulse passes from one part of the body to another. A distinctive feature is that all the nerve elements are not concentrated scattered throughout the body, but in the head.

Reproductive organs of a microorganism

The white planaria includes both female genital organs in the form of ovaries and oviduct, and male genital organs, represented by testes and vas deferens. But, despite this structure, it reproduces sexually and asexually.

Asexual reproduction occurs in the form of division of the worm into two unequal parts capable of existence. Gradually, after division, the missing organs are added to each part. And the planaria is ready for independent existence.

Most often, planarians reproduce sexually. The parenchyma contains a large accumulation of testes, which pass into the vas deferens. The ovary is located in the wide front part of the body and, with the help of the oviduct, connects with the spermatic receptacle, where fertilization occurs.

During sexual reproduction, two planarians touch their ventral sides for a few seconds. After this, the fertilized zygote moves through the oviducts. During movement, they absorb nutrients and become covered with a shell. Ultimately, the shell becomes dense, similar to a cocoon. In this form, the eggs are attached to aquatic plants. After 2-3 weeks, young individuals emerge. Planarians most often hide their laid eggs behind plant leaves or behind rocks.

Planaria is not dangerous to humans. But for pet fish lovers, you need to carefully monitor the aquarium. Avoid contamination and promptly get rid of unwanted residents.

Planarians differ from other worms in their very large size; they are distributed throughout the planet. The feeding hole is located in the abdominal cavity and leads to a retractable pharynx. In structure, planaria belongs to the coelenterate animals. These worms do not have respiratory organs; they receive oxygen through the work of the whole body. Many fish do not swim to the habitats of planarians, since the skin of the worms has poisonous glands. Sensing danger, the animal secretes skin mucus, which scares away other inhabitants of the deep sea.

There are 12 genera in the planarian family, each of them has its own specific characteristics, different habitats and reproduction. The body of predators is covered with small cilia, which allow them to move freely. The color of the animals typically ranges from green to brown, with unique pink and yellow species also found.

Milk planaria is the main representative of the entire family. It lives in both warm and cool places and can be found at the bottom of the pond and on the leaves of plants. Like all coelenterates, the milky white planaria distinguishes between top and bottom. Moving forward, the animal searches for a source of food, while at the same time releasing unnecessary substances through the mouth. The structure of the white planaria is no different from other species of this family; its body is covered with cilia and specks, with the help of which it can quickly move along the bottom of the lake.

The nervous system of the white planaria consists of a cluster of nerve cells and nodes that control the functioning of the entire body. There is no circulatory system; the necessary nutrients come directly from the intestines. Many processes (including gas exchange) occur through the skin.

The digestive system of the white planaria is represented by a small abdomen and a pharynx, which can extend when searching for food. It is worth noting that the digestive apparatus, disconnected from the body, is able to work for some time; it will try to swallow and digest food.

The black planaria is distinguished by a rounded head and the presence of a large number of eyes; in captivity it can feed on simple white bread. In the depths of the sea, black worms prefer to hunt small fish and do not refuse carrion.

By nature, planarians are hermaphrodites. The reproductive system consists of male and female cells, which can replace each other at the right time. It reproduces using holes in the abdominal cavity, two individuals come into contact and exchange information. The eggs increase in size and come out over time. After two weeks, new planaria are born.

In addition, this type of flatworm can reproduce by transverse division. From each half, a whole planaria is formed within a few days.

What are the symptoms of the disease? Before undergoing tests and clinical examination, the following signs can help determine the presence of a blastocyst in the body:

• sudden weight loss;
• constant abdominal pain, cramps;
• itching and liquid stool;
• refusal of food;
• fever and decreased immunity.

Treatment is prescribed to each patient individually. As a rule, in the initial stages it is recommended to take drugs and medications. In addition, there are methods of treatment using traditional recipes. Patients need to take a decoction of wormwood, a small amount of chili pepper, ginger and mustard.

The main methods of preventing the disease are thorough hand washing, fighting flies, and eating only clean foods. Playing sports and leading a healthy lifestyle are encouraged.

Video – White planaria

Planaria are small flat worms belonging to the class Turbellaria. They have an oblong leaf-shaped body and are usually differently colored: black, brown, greenish.

There are even spotted planarians. A characteristic feature of these representatives of the class is the cover of the finest cilia covering their body.

How do planarians move?

When observing a crawling planaria, it is very difficult to determine how it moves. The worm moves smoothly, slowly and evenly, as if swimming, without any visible effort. In fact, everything is explained simply. Planarians secrete abundant mucus that envelops the objects on which they sit. When moving, the cilia covering the body rest against this mucus, smoothly pushing the animal’s body forward. The movements of the cilia are invisible to humans, so sliding through the mucus seems smooth and uniform. Small planarians can swim in water by hitting the water with their cilia.

The mucus that abundantly covers the body of planaria helps them not only move, but is also a protective device. Predators attacking the worm literally stick together and, as a result, are unable to capture the prey. The mucus obviously contains some substances that are unpleasant for enemies, so planarians are very rarely attacked. In the skin of some planarians, stinging cells were found, similar in structure to those of coelenterates. The most interesting thing is that these cells most likely actually once belonged to a freshwater hydra, which worms readily eat. The hydra is digested in the body of the predator, and its formidable weapon continues to serve its next owner.

How do planarians feed?

Despite their small size and very delicate appearance, planarians are quite active predators. They hunt for various aquatic animals, the size of which, naturally, is comparable to the worm itself.

Planaria have a well-developed chemical sense (smell). Sensing prey, the worm heads towards it and, sticking out its throat, tears its victim with strong sucking movements. Worms can starve for a long time and lose a lot of weight, but retain their characteristic body shape.

Features of planaria

Turbellaria are the first animals in which, as we have already said, in the process of evolution the rudiments of the brain appeared in the form of a brain nerve ganglion. In this regard, scientists have always been interested in the behavior of these worms and the possibility of “training” them. Various researchers have made attempts to develop conditioned reflexes in planaria. Let us describe one of the simplest experiments. The bottom of the aquarium, where the planaria were kept, was divided into dark and light halves. First, scientists observed how much time the worms spent on one and the other half. Then, in one of the fields (light or dark), the worms began to receive a weak electric shock, which caused a sharp contraction of their body. If the time the planaria spent on this field was further reduced, we could talk about the animals becoming accustomed. The planarians stopped swimming to the field where they received the electric shock only after 70-80 combinations. Let's compare, for example, with ants, in which conditioned reflexes can be developed after 1-2 presentations of a signal. When the electric shocks stopped, the planarians very quickly “forgot” the acquired habit. Thus, the still extremely primitive nervous system of ciliated worms determines very unstable and difficult to develop conditioned reflexes.

During the process of evolution, these worms developed a very interesting adaptation to unfavorable conditions. When the water temperature increases, there is a lack of oxygen, etc. Planarians can disintegrate into pieces, from which whole animals regenerate when favorable conditions occur. This process is known as self-mutilation. Some species, even under normal conditions, are capable of dividing into parts, which can be considered as a special form of reproduction. Scientists, studying the ability of planaria to regenerate, found that even from 1/279 of the body part of this animal, a whole organism with all its inherent organs can be restored.

The high ability of planaria to regenerate is also associated with an unusual method of fertilization, which is observed in some lower ciliated worms. The lower turbellaria are bisexual organisms, with male organs already developed in them, while female organs in primitive species are not yet developed. During reproduction, each individual can play the role of both a male and a female. In this case, the male injects sperm anywhere in the female’s body, tearing the tissues of the female’s body with his copulatory organ, which has a stylet or spine. More recently, German scientists made absolutely stunning observations of the reproduction of marine turbellaria in captivity. It turned out that each individual strives to be a male. When encountered, turbellarians “rear up” and, swaying their bodies as if in a duel, strive to thrust their stiletto into the body of another individual. Each worm “wants” to be a male in order, on the one hand, to protect the body from punctures, and on the other hand, to save energy, which is spent in large quantities on the development of eggs. The pierced turbellaria assumes a “submission” pose and lowers the raised part of the body. More advanced species of planaria develop a female reproductive apparatus.

Reproduction of planarians

Planarians lay eggs enclosed in a dense shell. Sometimes they lie in capsules sitting on a thin stalk, or in cocoons that the worms place in secluded protected places. The eggs hatch into small whitish forms that immediately begin an independent life.

All planaria are aquatic animals that live in various standing reservoirs, clear mountain rivers, underground lakes, forest puddles, etc. In northern and central Russia, the most common species is the milky-white planaria (Dendrocoelum lacteum), so named for its color. This is one of the largest planarians, reaching 3 centimeters in length, with a completely white body, through which the branched dark intestine is clearly visible. The planaria has 2 black eyes, with the help of which it navigates during its travels. It is interesting that one cave species of planaria, which lives in the dark, has no eyes.

The much smaller brown planaria (Planaria torva) is also often found in stagnant bodies of water. In accordance with its name, this brown worm has a rounded head and a pair of eyes. The mourning planaria (Planaria lugubris), which lives in flowing waters, is also dark in color, but has a characteristic head shape that looks like a triangle. The black planaria (Polycelis nigra) has a series of ocelli along the edge of its head.

The Baikal planarians are distinguished by their extraordinary richness of shapes, colors, and various adaptations. Some of them are real giants among turbellaria, reaching 30 centimeters in length. They inhabit the lake from coastal rocks to depths of over 1,100 meters, some of them have even adapted to life in the fast, stormy Angara.

To catch planaria, you need to try to catch more aquatic plants in the net and carefully examine them. Most often, these turbellaria can be found on the underside of water lily leaves floating on the surface of the water. However, it is initially difficult for inexperienced researchers to notice the small, brownish, very slowly moving worms. Only the milky white planaria catches the eye due to its size and color.

Reading time: 5 min

White planaria lives in small lakes, ponds and other freshwater bodies. This is a predator of flatworms belonging to the class of ciliated worms. Flatworms, which include the white planaria, have a more complex development than coelenterates.

General information

The worm has a translucent body that is milky white or crystal white. The black eyes are located on top and stand out sharply against the light body. With their help, the planaria can distinguish the level of illumination. The white planaria is able to distinguish between the bottom and the top. Under the body - from below, there are sources of food, prey. There are various dangers on top of the body.

White planaria is widespread. In natural freshwater bodies of water, the worm likes to hide under small pebbles and accumulations of silt. Forms of existence - attached and mobile. The milk planaria that lives in natural reservoirs, sensing danger, begins to secrete slippery bitter mucus, which can be poisonous and dangerous for some small animals.

The flatworm in question is a tenacious and very hardy organism. In some cases, with mechanical damage, even 1/3 of the body of an adult is enough for regeneration and the formation of a full-fledged white planaria.

Body shape and structural features

The milky white planaria (Dendrocoelum lacteum) has an elongated thin body, flattened in the dorso-ventral direction. The length of the body does not exceed 2 cm. Compared to the total volume of the body, the area of ​​its outer surface is noticeably increased due to flattening. The anterior part of the worm is widened. It contains tactile organs in the form of small processes. The back of the worm is pointed. The body shape is mirror-symmetrical in the longitudinal direction. This form is characteristic of the bodies of a large number of multicellular organisms that have a tendency to actively move.

The milk planaria, like other flatworms, has a three-layer structure. Therefore she has:

• ectoderm;
• mesoderm;
• endoderm.

The formation of these layers of the body occurs during the development of the embryo. In this case, the mutual modulation of the layers is important. The development of the embryo begins with the formation of the ectoderm. Based on the cells of this layer, the nervous and digestive systems are subsequently partially formed.

Mesoderm partially ensures the formation of connective tissues and internal systems of the white planaria body. For example, the reproductive and muscular systems. Subsequently, the mesoderm protects the internal organs, providing them with support. The endoderm is the inner layer of the white planarian embryo. As the endoderm develops, the midgut and its accessory glands are formed.

The planarian body consists of the following tissues:

• integumentary (epithelial);
• muscular;
• connecting;
• nervous.

The presence of these types of tissues has been recorded in multicellular animals, a class higher than flatworms. In the spaces between the epithelial cells there are glands that secrete protective mucus.

Milk planaria is a type of ciliated worm. The body of an adult is covered with columnar epithelial cells. They contain cilia necessary for motor activity.

The white planaria lacks:

• anus;
• circulatory system;
• body cavity;
• brain.

Reproduction of planarians

Clinical picture

Doctor of Medical Sciences, Professor Gandelman G. Sh.:

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The flatworm in question is a hermaphrodite, so adult reproduction occurs in both asexual and sexual ways. During asexual reproduction, the body of an adult is torn into two parts. The break line runs across the body behind the mouth opening. After regeneration of the missing half of the body, 2 adults are obtained from each half. Asexual reproduction is usually carried out by adult white planaria in the absence of a normal habitat.

Sexual reproduction is a more complex process. The testes, in which sperm maturation occurs, are scattered in large numbers throughout the body of an adult. There are only 2 ovaries in which the development of eggs occurs. They have an elliptical shape and are located in the head of the body. For copulation (copulation), adult individuals need to touch their bodies on the ventral side. At this moment, the partner’s copulatory organ is inserted into the copulatory bursa of 1 individual. Through it there is a mutual outpouring of sperm. The sperm reaches the spermatic receptacles through the oviducts. Here, as a result of the interpenetration of male and female cells, a zygote is formed. This is a diploid cell with a double set of chromosomes.

Planaria eggs

The eggs obtained as a result of fertilization move along the oviducts to the reproductive cloaca. As they move, the eggs are gradually enveloped in a protective shell of yolk cells and absorb nutrients and microelements necessary for the further development of the embryo.

In the genital cloaca, several membrane-coated eggs unite. Planaria eggs are light brown in color. They form a cocoon the size of a pinhead. Planaria eggs remain viable when exposed to extreme temperatures (high and low), small amounts of dissolved oxygen, or the presence of strong chemical elements in the water.

The adult individual must choose a secluded and safe place at the bottom of the reservoir to place the cocoon. A small stalk is used to attach the cocoon to leaves, stones and other objects. Thanks to this, the cocoon is in limbo. There is no metabolism (metamorphosis) during ontogenesis (individual development). Hatching from the egg after 15 - 20 days, small planaria differ from adult individuals only in their smaller size. At the same time, they are fully adapted to independent existence.

Digestive system

White planaria is a heterotroph, i.e. a small predator. Therefore, it receives the nutrients necessary for life from exogenous substances produced by other organisms. In nature, its usual diet consists of:

• small crustaceans;
• worms;
• fish caviar

The partially white planaria is a saprotroph, meaning it can feed on carrion. In captivity, planaria can be fed white bread.

The digestive system of white planarians is of a closed type. The mouth opening of white planarians is located on the belly. Therefore, to capture food, the worm needs to position itself on top of the prey. Muscle contraction helps to press tightly to the object of the hunt. Next, a movable pharynx extends from the mouth opening, through which food is swallowed. Using a retractable pharynx, the milky white planaria can do more than just swallow food. The planaria first inserts its pharynx into the object of its hunt and sucks out particles of soft tissue.

The pharynx of the white planaria is also the foregut. It connects to the midgut. The midgut has 2 lateral processes extending from the pharynx to the ventral side of the body. The central section of the midgut bends towards the head of the body and ends with the pharynx and oral opening. Its complex shape with various branches makes it possible to digest large foods in the intestines.

The end of the intestine is the cecum without the anus. In the intestinal cavity, food is digested using digestive juices. They are secreted by glandular cells of the intestine. After digestion of protein and other necessary elements, food remains are regurgitated out through the mouth. Metabolism in the body of a white planaria occurs slowly, while metabolic processes occur twice as fast as in coelenterates.

Excretory system

The type of excretory system in white planaria is protonephridial. It consists of:

• pronephridia - stellate or flame cells;
• excretory tubule system;
• multiple excretory pores.

The excretory canals located along the body open on the dorsal surface of the body with several external openings - pores. From the inside, the channels have numerous processes and branches. At the end of each branch there is a cell with constantly moving cilia. Their vibration resembles the flame of a burning candle. That is why the cell is called “flame cell”.

The cilia, by their vibration, form a constant movement of fluid through the excretory tubules. This fluid consists of water and metabolic waste products secreted by body tissues. Reaching the excretory pores, the liquid pours out through them.

These pores are mostly located on the back. Since the white planaria does not have respiratory organs, they also form a respiratory system. Through them, oxygen enters the body and carbon dioxide is expelled. The relatively large plane of the body improves gas exchange during breathing.

Nervous system and sense of touch

The white planaria has a primitive nervous system consisting of organs such as:

• ganglion (nervous ganglion head) - 1 piece;
• longitudinal nerve column - 2 pcs;
• transverse inter-trunk jumpers;
• multiple small nerves.

Clusters of nerve cells are located on the surface of the skin. Tactile sensitivity is provided through special branches that approach the surface of the skin or vital organs. The brain is missing. The nervous system of the white planaria makes it capable of forming a fixed reaction to external stimuli. These reactions are produced under the influence of electric current and light. During asexual reproduction, acquired stereotypical reactions are preserved in both halves after the formation of whole individuals from them.

The circular muscles are located across the body directly under the ciliated (ciliated) epithelium. Their contraction allows not only to narrow, but also to elongate the body. Below are the oblique muscles. The longitudinal muscles make up the lower layer and connect the abdominal and dorsal regions of the body. Parenchyma fills the space between the internal organs; it is located under the transverse and longitudinal layers of muscles. A complex muscular system is necessary to perform various types of movements and give the body various shapes. White planarians envelop solid objects with mucus secreted. Resting against the layer of mucus with their body cilia, they push the body forward. White planaria can be quite an interesting object for studying the behavior of flatworms in their natural habitat.