Flatworms are ciliated. Features of the structure of ciliary worms, their significance in nature and human life

This class includes free-living marine and freshwater, rarely terrestrial worms, the entire body of which is covered with ciliated epithelium. The movement of the worms is provided by the work of the cilia and the contraction of the muscles. Many species are characterized by regeneration.

A typical representative of ciliary worms - milky white p alan aria- lives in fresh stagnant water bodies on underwater objects and plants (Fig. 11.4). Its flat body is elongated, at the front end of which two small tactile tentacle-like outgrowths and two eyes are visible.

Planaria is a predatory animal. Her mouth is located on the ventral side, almost in the middle of the body. With the help of a muscular pharynx protruding outward, the planaria penetrates into the prey and sucks out its contents. In the branching middle section of the intestine, food is digested and absorbed.

excretory organs- protonephridia. They are represented by two branching canals, at one end opening outwards excretory openings, and at the other - by stellate cells scattered in the parenchyma. The stellate part of the cell passes into a canal, inside which a bundle of cilia is located. Liquid metabolic products seep into the pear-shaped extension of the initial section of the canal. Protonephridia are located on the sides of the body.

General characteristics of the type

The characteristic features of the type are as follows:

Body flat, its shape is leaf-shaped (in ciliaries and flukes) or tape-shaped (in tapeworms).

For the first time in the animal kingdom, representatives of this type developed bilateral (bilateral) symmetry of the body, i.e., only one longitudinal plane of symmetry can be drawn through the body, dividing it into two mirror-like parts.

In addition to the ectoderm and endoderm, they also have an average germ layer - mesoderm. Therefore, they are considered the first three-layer animals. The presence of three germ layers provides the basis for the development of various organ systems.

Forms the body wall knee muscle bag- a set of outer single-layer epithelium and several layers of muscles located under it - annular, longitudinal, oblique and dorsal-abdominal. Therefore, the body of flatworms is capable of performing complex and varied movements.

body cavity missing, since the space between the wall of the body and internal organs filled with loose mass of cells parenchyma. It performs a supporting function and serves as a depot of reserve nutrients.

The digestive system consists of two sections: the ectodermal foregut, represented by a mouth and a muscular pharynx, capable of turning outward in predatory ciliary worms, penetrating the victim and sucking out its contents, and blindly closed endodermal midgut. In many species, many blind branches extend from the main sections of the midgut, penetrating into all parts of the body and delivering them dissolved nutrients. Undigested remains of food are thrown out through the mouth.

excretory system protonephridial type. Excess water and metabolic end products (mainly urea) are excreted through the excretory pores.

The nervous system is more concentrated and is presented in pairs. head ganglion and extending from it longitudinal nerve trunks, connected by ring bridges. Nerve trunks are formed by bodies located along its entire length nerve cells and their offshoots. This type of organization nervous system called stem. All flatworms have developed organs of touch, chemical sense, balance, and free-living ones have vision.

All worms can be divided into three types (flat, ringed, round), each of which has its own characteristic features. This type refers to invertebrates lacking a body cavity and possessing bilateral symmetry.

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The main signs of the type of flatworms

• digestive;
• nervous;
• sexual;
• excretory.

This type has the presence of several systems and even the rudiments of organs

Circulatory system

Not available, but the function of the blood is performed by the parenchyma, consisting of connective cells. It is she who transports nutrients in the body.

Digestive system

Rather simplified, it consists of a pharynx and intestines.

The pharynx is powerful, can:

• suck;
• twist and wrap around your prey.

The intestine consists of two sections - anterior and middle, most often branched. It has a closed structure, so that all undigested waste exits through the mouth. The mouth opening is located closer to the middle of the body of the worm.

Free worms are mostly predators and they even have a kind of adaptation for capturing prey. This system is not observed in all classes; more primitive worms do not have it. For example, tapeworms feed on the entire surface.

excretory system

The excretory system is quite large and consists of many tubules that combine and lead to the excretory pores.

The parenchyma contains special cells that drive harmful substances into the tubules. For humans, these excretory products are very dangerous and toxic along with poison.

Representatives of the world of the simplest microorganisms a large number of. These include ciliary worms, of which there are about 3,500 types in nature.

Some of the striped worms are completely safe, while others can be dangerous to human life and health. Their size depends on the place of the environment where they live.

To view some of them, you need a microscope, and there are individuals that reach 40 cm in length. They can live freely in the environment, but they are predatory.

The habitat is mainly in the vicinity of water bodies, or on its shore, on the ground, under stones.

They also thrive in moist soil. Distinctive class planarians are considered, as they have the most diverse colors.

These individuals are called ciliated for a reason, their entire body is covered with them. Cilia are essential for locomotion. Ciliated individuals move in space like snakes, they can crawl or swim.

The structure and shape of ciliary worms are oval, slightly flattened, but individuals of an elongated type are found. All representatives of these worms have a bilateral symmetrical structure, in front they have an oral cavity, which is located on the belly.

They also have sensory organs in the front of the body.

Flatworms have their own characteristics structures of the ciliary cover, and have a ciliated epithelium. There are two types - these are sticky and separate cilia. However, not all representatives of this class have them.

The worm moves with the help of a secret fluid, which is produced by the secretion glands. Its secretion occurs in the front of the body of the individual, and it helps to maintain balance and move freely around the object on which it is located. Along the edges, the ciliary glands have unicellular origin.

The mucus they secrete is somewhat toxic. In nature, they need it to protect themselves from representatives of larger microorganisms. With age, the worms begin to lose their cilia, and outwardly it resembles a molt, like a cat or dog.

The internal structure of ciliated individuals completely coincides with the flat type of microorganisms. Their skin-muscular sac is formed with the help of a muscular organ.

It consists of 3 main fibers.

The first- this is an annular layer, it is located with outside individuals.

Second- diagonal, it is at a slight angle, and last- This is a longitudinal layer that forms in the lower part of the body.

With the contraction of muscle tissue, the process of movement is accelerated, and large ciliated individuals increase the speed of sliding.

Digestive and excretory system

Digestive system ciliary worms has a complex internal structure, consisting of numerous organs. Through them, useful substances required for vital activity enter.

There are ciliary individuals that do not have a full-fledged digestive system, they are called non-intestinal. Individuals with a well-formed intestinal tract are divided into two types, these are branched intestinal and rectal.

Depending on this, there are deviations in the structure; in branched worms, the oral cavity is located near the back of the body.

And in individuals with a rectal type of structure, the mouth is located in front, it is adjacent to the pharynx, which has blind branches intestinal tract. On the body of the worms there are glands that provide external digestion of food, and they are called pharyngeal.

Microorganisms have external digestion, so they can get useful nutrients for themselves by attaching their mouth to the victim.

In the process, he secretes a secret that is able to digest food from the outside, and then absorbs it into his body. They feed mainly on small microorganisms that do not have vertebrae, such as crustaceans.

They don't have a simple excretory system, it consists of a significant number of pores through which processed substances leave the body. The numerous branches that make up the excretory system connect to one or two main channels attached to the intestinal tract.

When it is absent, the accumulation of unnecessary substances occurs on the upper surface of the trunk in some cells. After a sufficient amount of excretions have accumulated, they themselves eventually detach from the worm.

Nervous system and sense organs

Eyelash worms differ in the structure of the nervous system.

Some representatives of this class have several nerve endings that are located only in the front of the body. And there are flatworms that have a significant number of neurons that connect to the main trunks, there can be up to 8 of them.

It is inherent in ciliated beings to have a sensory system. On their body there are cilia that do not have mobility. There are representatives of this class who know how to feel balance, since they have statocysts. This organ is vesicles or pits, the difference is the type of individual.

They react to the environment with the help of sensilla, these are motionless cilia that are distributed throughout the body. In the presence of an organ of a staticist, the presence of an orthogon is possible.

That is, flatworms have a brain system consisting of many channels, which belongs to the lattice type.

The characteristic of the structure of the olfactory organs is very interesting. Due to the fact that there is a developed sense of smell, Turbellaria can find food for itself. On the body of a predator there are special pits into which a signal is received from environment, and it is transmitted to the brain system.

Despite the fact that there are several eyes on the body near the brain ganglia, they do not have vision. Some scientists argue that large flatworms can still distinguish between surrounding objects. According to the research, it turned out that they have a lens that helps to see.

Ciliated individuals differ from flat ones in that they can breathe. Flatworms live in an anoxic environment where they reproduce. Ciliates need oxygen, as they live in a different environment. A predator breathes with the help of its body, that is, there are pores on its surface that absorb oxygen.

Reproductive system and method of reproduction

Ciliary worms simultaneously have female and male genital organs, that is, they are hemophradites. They have male organs in their testicles and female organs in their ovaries.

The seminal fluid for fertilization passes through special channels and enters the egg. Then it enters the oviduct, and forms a cloaca. Reproduction of the class is carried out by the cross method.

Individuals alternately fertilize each other, they spray the sperm liquid into the opening of the cloaca. The seeds form eggs that are covered with a shell. After they lay eggs, and subsequently a new individual hatches from them. By appearance they are like adult worms.

Reproduction of turbularia is somewhat different from other representatives of the class. Their egg hatches into a small larva, which is already growing in the habitat.

Ciliary worms can reproduce asexually.

A constriction appears on the body, which after a while divides the body into two separate parts. And gradually they acquire all the vital organs.

The ciliary worms are essential for maintaining balance in the invertebrate population. Predators eat them, and thus do not allow them to grow in large numbers.

Most Turbellaria are carnivores feeding on various small animals. The digestive system consists of the anterior and middle intestines, closed blindly. The mouth serves not only to swallow food, but also to throw out undigested solid residues. The mouth is usually placed on the ventral side of the body: a short distance from the anterior end of the body, in the middle of the ventral side, or closer to the posterior pole. The mouth leads to the ectodermal pharynx, which in turn passes into the midgut. In some large turbellarians (in freshwater planarians of the Tricladida order and in marine turbellarians of the Polycladida order), the oral opening does not open into the pharynx, but into a special deep protrusion of the outer integument called the pharyngeal pocket (Fig. 124, Fig. 135). A muscular pharynx protrudes from the bottom of the pocket into its cavity. It has the appearance of a tube that can be strongly extended and protrude outward through the mouth, serving to capture prey.

The endodermal midgut is arranged differently in many forms of Turbellaria. In small turbellarians (Rhabdocoela, Macrostomida, etc.) it looks like a simple bag or a blindly closed tube (Fig. 134). In large forms, the intestines, as a rule, are branched. So, in polycladida, the pharynx leads to the stomach, from which branching canals extend in all directions to the edges of the body, blindly closed at the ends (Fig. 135). In three-branched (Tricladida) from the pharynx, located near the middle of the body, three main branches of the intestine depart at once (Fig. 123, Fig. 124): one goes straight forward, the other two bend and go back along the sides of the pharynx; each of the branches gives side blind branches.

This structure of the intestine is not accidental. In small turbellarians, the size of which does not exceed a few millimeters, the products of digestion are easily distributed throughout the body through loose parenchymal tissue. In large tricladids and polycladids, sometimes reaching 1-3 and even 30 cm, this process is extremely difficult. In such turbellarians, the function of distributing the products of digestion throughout the body of the animal is performed by the branches of the intestine, penetrating the parenchyma in all directions and directly in contact with all tissues and organs.

In the process of digestion of food in turbellarians, as well as in coelenterates, great place occupies intracellular digestion. Food particles, previously processed by the secretion of the pharyngeal glands, enter the intestine and are captured by intestinal epithelial cells, in which numerous digestive vacuoles are formed. In the order of intestinalless turbellarians, a pronounced midgut is generally absent (

General characteristics. In most cases, free-living aquatic environment or soil flatworms with an unsegmented body covered with ciliated epithelium. There are usually several primitive ocelli on the dorsal side of the anterior end of the body. The mouth is located in most species in the middle of the ventral surface of the body.

Structure and life functions. The shape of the body of ciliary worms is different (Fig. 70). Some have folds in the form of a fringe on the sides of the body. The body length ranges from 0.2 mm to 35 cm or more (in terrestrial ones).

The integument is formed by ciliated (ciliated) single-layer epithelium. Its cells carry small cilia on their surface, the movement of which contributes to the swimming of the worm. Inside the epithelial cells are included the smallest shiny bodies - rhabdites, performing protective function, sometimes used to obtain food. They are periodically thrown out and, dissolving in water, dress the animal with a loose adhesive shell. In the integument of ciliary worms, many glandular cells are laid. Some of them secrete mucus, others - special poisonous protein substances. So, in dairy planarians, there are a lot of poisonous glands on the ventral side of the body. Having found any small animal, the worm covers it with its flat body and kills it with poison.

The nervous system of ciliary worms varies in degree of complexity. In some primitive forms it is diffuse. In others, several nerve cords run along the body, giving branches to various organs. Still others have (usually in the head part of the body) clusters of nerve cells - ganglia, from which longitudinal nerve cords extend (Fig. 71). But, as studies have shown, the integrating role of these head ganglia in ciliary worms is small.

The sense organs are represented by primitive eyes, the organs of balance - statocytes - tactile cells scattered in the integument. The number of eyes and their structure vary.

The digestive organs have a very diverse structure. In most species, the mouth is located in the middle part of the ventral side of the body. It leads into a voluminous pharynx, capable of protruding outward in many species, sticking to the prey and sucking it out. The intestine departs from the pharynx, sometimes straight, but more often branching into two, three or many branches. The anus is absent, and the remnants of food are thrown out through the mouth. Some ciliary worms are devoid of intestines, and food entering through the mouth enters the loose mass of parenchyma cells, which absorb and digest it. In forms with intestines, food is digested both in its lumen and by wall cells that capture food pieces. Therefore, ciliary worms are characterized by both extracellular and intracellular digestion.

Rice. 70. Types of wei:

/-milk planarpi; 2 - - polyhead to a

Rice. 71. Digestive and primary systems of lactic nlaia:

/ - mouth; 2 - pharynx; 3 --- anterior branch of the intestine; 4, 5 ...... posterior branches of the intestines; b--- head ganglion; 7 - lateral nerve cord; 8 - peephole

Intracellular digestion in ciliary worms was first described by the outstanding Russian scientist I. I. Mechnikov in 1865. Later, he established that intracellular digestion of food is widespread among multicellular animals. He discovered that a wide variety of animals have special cells - phagocytes, capable of capturing and digesting various microorganisms (including pathogens) that have entered their bodies. On the basis of these data, I. I. Mechnikov created a phagocytic theory of the struggle of organisms with pathogens, which has great importance for medicine and veterinary medicine.

Respiratory organs are absent. Gas exchange occurs through the integument of the entire surface of the body.

The organs of excretion in most species of ciliary worms are represented by protonephridia. Many marine species there are no special excretory organs or they are poorly developed and the residual metabolic products are removed from the body through the integument and walls of the intestine.

The reproductive organs of ciliary worms have a different structure. Most of these animals are hermaphrodites, but self-fertilization is eliminated by the maturation of eggs and spermatozoa at different times. Fertilization is internal.

The development of ciliary worms occurs in marine forms usually with transformation, while in freshwater forms it does not.

Ciliary worms have an exceptional ability to regenerate. No wonder they were called immortal under the surgeon's knife. In some species of these animals, when they were divided into 1500 parts, it was possible to obtain a new individual from each part.

After the discovery by A. O. Kovalevsky in the Red Sea of ​​peculiar crawling ctenophores (Coeloplana), which have a flattened body, ciliary covers and a number of other features characteristic of ciliary worms, the phylogenetic proximity of the latter to ctenophores, and through them to intestinal cavities, seems likely.