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 appears 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. planaria can break up 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 turbellarians 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.

Planarian reproduction

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.

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 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

The milky planaria (so called for its characteristic coloring) becomes a real disaster when it gets into an aquarium, turning the latter into its hunting grounds. It eats fish fry, snails, crustaceans, and is also capable of attacking adults. Planaria clog the gills of fish, causing suffocation and death. This, however, is where the harm caused by this representative of the class of ciliated worms ends. Aquarists really dislike planaria, but it is of no interest to medicine.

Planaria is a free-living organism. It is dangerous exclusively for small inhabitants of ponds and aquariums. It poses no threat to humans.

Anatomy and physiology: body shape, integument

All flatworms have a similar structure. Their bodies are elongated and have bilateral symmetry. There is a pronounced head end, which carries sensory organs, thanks to which the worm is able to navigate in space, as well as choose the direction of movement.

Appearance of white planaria

The color of planaria is predominantly white. However, there are worms of other colors (black planaria, brown and others). Variations in coloration provide good camouflage.

Anatomy and physiology: internal organs

Planarians do not have a body cavity. The organs are separated from each other by parenchymal tissue. Planaria lack a circulatory system, as well as a respiratory system. It receives oxygen diffusely through the integument of the body, and nutrients enter the cells directly from the intestines.

The digestive system of planaria is not continuous, that is, it has one opening - the oral cavity. Through it food enters and waste products are eliminated. The excretory system is a network of tubes that pass through the entire body and open mainly on the back of the worm. Liquid wastes, including toxic compounds, are removed through them.

Internal structure of white planaria

Being a predator, the planaria has adaptations that allow it to detect and capture prey. Its digestive system is equipped with a retractable pharynx, and its senses help it navigate in space and detect movement.

Anatomy and Physiology: Reproduction

The latter reproduces not only sexually. There is another option, characteristic of primitive organisms with a simple body organization. The symmetrical structure makes reproduction by division possible.

Class Ciliated worms, or Turbellaria (Turbellaria)

There are more than 3,000 species of eyelash worms. The length of their body covered with cilia varies from 1 to 50 cm.

External structure and lifestyle white planiria . The length of the white planaria reaches 1-2 cm. At the front end of the flattened body there are eyes and tactile tentacles. The posterior end is pointed.

The white planaria is nocturnal. It feeds on small crustaceans, worms and the remains of large organisms.

Internal structure of planaria. Life processes occur in planaria thanks to the work of the corresponding systems of internal organs: movement, digestion, excretion, nervous and reproductive. Let's consider each of them separately.

System of movement organs. The movement of white planaria is carried out using skin-muscle bag which covers the body. Its outer layer is represented by cells with cilia (ciliated epithelium). Below it there are three types of muscle fibers (circular, longitudinal and dorso-abdominal).

Thanks to this variety of muscles, the white planaria (like all other flatworms) is capable of performing complex movements: contracting and extending the body, narrowing and expanding it, as well as twisting and undulating. Due to the cilia, it moves as if gliding.

Digestive system. On the ventral side in the middle of the body of the white planaria is located mouth , turning into throat . Unlike other animals, the planarian's pharynx is an absolutely remarkable adaptation! It has the ability... to stick out through its mouth and capture prey. Consequently, the pharynx of the white planaria also performs the function of a catching apparatus!

From the pharynx the captured prey enters the intestines , so that there, in its branches, it can be digested. (The substances necessary for this are secreted by single-celled glands located along the intestinal walls.) The nutrients then penetrate into all other cells of the body. Undigested food remains are expelled through the mouth.

Excretory organ system. The excretory system is represented by two longitudinal excretory canals , which branch repeatedly, penetrating the entire body.

With the help of the excretory system, the body removes excess water and other substances.

Breath. The planaria breathes oxygen dissolved in water, which enters the body through the entire surface of the body. There are no special respiratory organs.

Nervous system. If in Hydra the nerve cells are still “scattered” throughout the body, then in Planaria they are already “collected” into two longitudinal nerve trunk . And in the front part they are even combined into a special thickening - ganglion . Sensitive endings of nerve cells travel from the nerve ganglia to the sensory organs and other parts of the body.

In this form, the nervous system is capable of well coordinating the activities of all organs and systems of the white planaria.

Most eyelash worms have eyes (from one pair to several dozen), in the skin - tactile cells, and in some species - tentacles at the anterior end of the body. Various irritations and changes in the environment picked up by the senses are transmitted through sensory endings to the nerve nodes. And from there a signal is sent to the muscles. Thus, the nervous system responds to irritation - a reflex.

Reproductive system. On the sides of the body of the white planaria there are two oval bodies - ovaries . Numerous bubbles are scattered throughout the body - testes . Eggs develop in the ovaries. Sperm are produced in the testes, which travel through the vas deferens into the seminal sacs and are stored there.

Consequently, the same planaria produces both female and male reproductive cells. Such animals, as is known, are called bisexual, or hermaphrodites. The eggs travel through the oviducts to the spermatic receptacle, where fertilization occurs.

Reproduction and development of white planaria. Planarians exhibit both asexual and sexual reproduction. Asexually, it reproduces through transverse division in half, followed by regeneration of missing body parts. When reproducing sexually, planaria lay eggs in dense cocoons formed from frozen mucus. Whitish worms hatch from them, which immediately begin to hunt the smallest animals: ciliates, rotifers, etc.