Representative ciliated ciliates. Ciliate class. Reproduction of ciliates. Conjugation process

The type includes more than 7 thousand species. Representatives are characterized by organelles of movement - cilia (at least at some stages of development), located on the surface of the cell in a certain order, as well as a unique nuclear apparatus consisting of two nuclei - a small generative micronucleus and a large vegetative macronucleus (Fig. 10). Asexual reproduction occurs by transverse division and sexual reproduction by conjugation.

Rice. 10. Slipper ciliate (Paramecium caudatum):

1 - eyelashes; 2 - digestive vacuoles; 3 - large nucleus (macronucleus); 4 - small nucleus (micronucleus); 5 - mouth opening and pharynx; 6 - undigested food remains; 7 - trichocysts; 8 - contractile vacuole

These are the most complexly differentiated unicellular organisms with permanent cytoplasmic structures. The cell walls of ciliates have an “alveolar structure” with four membranes and cavities - “alveoli” - in the middle. In addition, the wall contains trichocysts. This protective devices in the form of rods located under the pellicle. When the animal is irritated, the trichocysts shoot out.

The sexual process is accompanied by a restructuring of the nuclear apparatus. During conjugation in the partners' cells, the macronucleus disintegrates and the micronucleus undergoes reduction division. Four nuclei are obtained, three of them die. The remaining nucleus is divided into two pronuclei - male and female. An exchange occurs between individuals: one nucleus goes into the neighboring cell, the other comes from it. These haploid nuclei fuse to form a diploid nucleus, a synkaryon. Then the partners separate, and the synkaryons in each of them create a new nuclear apparatus by fission. The sexual process with the same restructuring of the nuclear apparatus can occur without a partner. The fusion of pronuclei in this case is self-fertilization and is called autogamy.

Rice. 11. Life cycle of Ichthyophthirius multifiliis:

Currently, several options for classifying ciliates have been proposed. According to traditional system The type is divided into two classes: ciliated ciliates and sucking ciliates. Representatives of the first of them have cilia throughout their lives, they have a strictly localized place of food intake - the cellular mouth. Sucking ciliates are sessile forms; as adults they do not have a mouth, but are equipped with tentacles used for catching prey and eating food. Like ciliated fish, they have two nuclei (micro- and macronucleus), and the sexual process follows the type of conjugation. Only the stages of asexual reproduction - “vagrants” - are provided with cilia, which bud from the parent individual and swim away. After some time, the “vagrants” sit on the substrate, lose their cilia and form sucking tentacles. It has been proven that sucking ciliates come from ciliated ciliates.

At the end of the section devoted to protozoa, we provide a description of the most important diseases caused by single-celled animals in Russia (Table 8).

Table 8.

Protozoal diseases of humans in Russia

Table 9.

Comparative characteristics of some taxonomic groups such as ciliates

The ciliate slipper is the simplest single-celled organism measuring about 0.1 mm. It is found in the same bodies of water as euglena and protozoan amoeba. It feeds mainly on bacteria and microscopic algae. Serves as food for larvae, small fish, and crustaceans.

Appearance of the ciliate slipper

Due to its resemblance to the sole of women's shoes, this type of ciliate acquired a second name - “shoe”. The shape of this single-celled organism is constant and does not change with growth or other factors. The entire body is covered with tiny cilia, similar to the flagella of euglena. Surprisingly, there are about 10 thousand of these cilia on each individual! With their help, the cell moves in water and captures food.

The ciliate slipper, the structure of which is so familiar from biology textbooks, is not visible to the naked eye. Ciliates are the smallest single-celled organisms, but at large cluster they can be seen without magnifying devices. IN muddy water they will appear as elongated white dots that are in constant motion.

The structure of the ciliate slipper

The structural features of the shoe ciliate lie not only in its external resemblance to the sole of a shoe. Internal organization This seemingly simplest organism has always been of great interest to science. A single cell is covered with a dense membrane containing cytoplasm. This gelatinous liquid contains two nuclei, large and small. The large one is responsible for cell nutrition and secretions, the small one is responsible for reproduction.

The hole that acts as the mouth is located on the wide side of the cage. It leads into the pharynx, at the end of which digestive vacuoles form.

The body structure of the slipper ciliates is also very different interesting feature- presence of trichocysts. These are special organs, or rather, organelles that serve the cell for nutrition and protection. Having noticed food, the ciliate releases trichocysts and retains the prey with them. She puts them out when she wants to protect herself from predators.

Nutrition of ciliates slippers

Single-celled organisms feed on bacteria that live in large quantities in polluted, muddy water. The ciliate slipper is no exception, the structure of its mouth allows it to capture bacteria floating by and quickly send them into the digestive vacuole. The mouth of the ciliate is surrounded by cilia, which are longer in this place than in other parts of the body. They form a perioral funnel, allowing them to capture as much food as possible. Vacuoles are formed in the cytoplasm as needed. At the same time, food can be digested in several vacuoles at once. Digestion time is about one hour.

Ciliates feed almost continuously if the water temperature is above 15 degrees. Feeding stops before reproduction begins.

Breathing and excretion of ciliates slippers

As for breathing, the ciliate slipper has a structure similar to other protozoa. Breathing is carried out over the entire surface of the body. Two contractile vacuoles ensure this process. The waste gas passes through special channels and is released through one of the contractile vacuoles. The release of excess fluid, which is the result of vital activity, occurs every 20-25 seconds, also through contraction. Under unfavorable conditions, the ciliate stops feeding, and the contractile movements of the vacuoles slow down significantly.

Reproduction of ciliates slippers

The ciliate slipper reproduces by division. About once a day, the nuclei, large and small, diverge in different directions, stretch and split in two. In each new individual, one nucleus and one contractile vacuole remain. The second one forms after a few hours. Each ciliate shoe has a structure identical to its parent.

In ciliates that have undergone multiple divisions, a phenomenon called sexual reproduction is observed. Two individuals connect with each other. Inside the resulting large cell, nuclear division and chromosome exchange occur. After completing such a complex chemical process, the ciliates are separated. The number of individuals does not increase from this, but they become more viable in changing external conditions.

The structure and vital activity of the slipper ciliate depends little on external factors. All shoes look the same, have the same shape and size, regardless of the conditions. Life activity also follows one scenario. Only temperature and light factors matter. Ciliates are very sensitive to changes in light. You can conduct a small experiment: darken the vessel in which the ciliates live, leaving a small bright window. In just a couple of hours, all the individuals will be drawn to this hole. Ciliates also perceive temperature changes. When it drops to 15 o C, the shoes stop feeding and reproducing, falling into a kind of suspended animation.

Type Ciliates structure photo protozoa animals cell nucleus drawing vacuole organelles

Latin name Ciliophora or Infusoria

Type of ciliate- highly organized unicellular organisms with the most complex system of organelles. They are characterized by the presence of motor organelles - cilia, nuclear dualism and a special form of the sexual process - conjugation.

Ciliates

general characteristics

Type of ciliate unites a large number of species (over 6000) of the most highly organized protozoa.
They are characterized by the presence of cilia, which are usually present in large numbers. Cilia serve as organelles of movement; they can stick together to form more complex organelles. Some sucking ciliates have cilia only on early stages life cycle. All ciliates are characterized by nuclear dualism, i.e. duality. This means that they have at least two nuclei that differ in both size and function. One of the nuclei, much larger, is called a macronucleus, and the second, small one, is called a micronucleus. Some types of ciliates have several micro- and macronuclei. The micronucleus serves as the sexual, or generative, nucleus, playing a major role in the sexual process. Macronucleus is a somatic, or vegetative, nucleus that regulates all life processes, except the sexual process.
Asexual reproduction of ciliates occurs by transverse division. The sexual process in ciliates occurs in a unique way, in the form of conjugation, which is not observed in protozoa of other classes. Conjugation consists of the temporary bringing together of two individuals and the mutual exchange of parts of their micronuclei.
Ciliates are inhabitants of mainly fresh water bodies, but are also found in brackish water and in the seas; some species have adapted to existence in moist soil. Among the ciliates there are many parasites (about 1000 species) of invertebrate and vertebrate animals.
The class is divided into two classes:

• Ciliated ciliates (Ciliata)
• Sucking ciliates (Suctoria).

Type of ciliates Class ciliated

Latin name Ciliatas

A - common slipper (Paramecium caudatum); 1- eyelashes; 2 - macronucleus; 3- micronucleus; 4- peristome; 5 - mouth; 6 - pharynx; 7 - formation of digestive vacuoles; 8 - digestive vacuoles; 9 - defecation; 10 - contractile vaccum reservoir; 11, 12 - afferent channels of contractile vacuoles; 13 - trichocysts; B - belly of Stylonichia mytilus; 1 - adoral membranella; 2, 3, 4 and 5 groups of frontal, abdominal, anal and caudal cirrhus; 6 - row of marginal cirrhs; 7 - dorsal setae; 8 - edge of the peristome; 9 - ireoral cilia; 10 - wavy membrane; 11 - peristome; 12 - adductor channel of the contractile vacuole; 13 - contractile vacuole reservoir; 14 - micronucleus; 15 - macronucleus; 16 - digestive vacuole; B - creeping stylonnchia; 1 - adoral membranella; 2, 3, 4 and 5 - frontal, abdominal, anal and XBOCI tumors; 6 - marginal cirri; 7 - dorsal setae; 8 - adducting channels; 9 - Contractile vacuole.

Ciliates have quite various shapes bodies. However, in many species, due to their adaptation to a swimming lifestyle, the body shape is elongated and streamlined. An example is the common slipper (Paramecium caudatum) (Fig. 2, A). The sizes are also different, some species reach quite large sizes, up to 2 mm in length (Spirostomum).
The body is covered with a thin but durable shell - the pellicle, which has a rather complex structure. The pellicle is flexible and elastic, so it does not serve as an obstacle to some changes in body shape. Many ciliates can bend it and squeeze it between various objects. The large ciliate “trumpeter” (Stentor) (Fig. 43, A) has an elongated body in the form of a gramophone pipe, but it can be strongly compressed and take on a spherical shape.
(P*cilia are the organelles of movement of ciliates. They are very thin and short numerous plasmatic hairs. The ultra-thin structure of cilia and flagella, studied using* an electron microscope, showed their striking similarity.

In some ciliates, cilia evenly cover the entire body. For example, a shoe has about 10,000-15,000 eyelashes arranged in regular rows. In others, the cilia are concentrated in certain places on the body. "The cilia's oscillations are essentially rowing movements, consisting of a backward stroke, in which the cilium moves quickly in one motion, and a return to its original position, when the cilium slowly moves forward, smoothly describing a semicircle. At room temperature, the lashes make about 30 strokes per second. The movements of the cilia occur in concert, resulting in regular wave-like vibrations of all rows of cilia. The shoe moves at a speed of up to 2.5 mm/sec, i.e. it passes in a second a distance 10-15 times the length of her body.

In addition to simple cilia, they have larger structures, usually surrounding the oral cavity or located on other parts of the body. These are the so-called membranellas (Fig. 2, B). Each membranella is a row of cilia stuck together into one plate, often having a triangular shape (Fig. 3, B); if a longer row of cilia sticks together, a wavy membrane or membrane is formed. Many people have such membranes in the mouth or throat. The structure of the ciliary apparatus and the location of various ciliary formations serve as important systematic features.
The cytoplasm of ciliated cells is clearly divided into outer, lighter and dense layer- ectoplasm and a more liquid and granular inner layer - endoplasm (Fig. 2).

Ectoplasm has a complex structure, forming a large number of organelles. It secretes on its surface the previously mentioned elastic pellicle. The pellicle of the shoe has a complex sculpture: it is formed by regular hexagons, in the center of which the cilia are placed. Apparently, such a structure increases the strength of the outer shell. Ectoplasm also contains cilia and membranellae along with basal bodies. In the ectoplasm of many ciliates there are large numbers of so-called trichocysts (Fig. 4). These are elongated rod-shaped bodies that strongly refract light. When irritated, the trichocysts are thrown out through special tubules in the form of a thin stream of liquid, solidifying in water as a thin elastic thread. Trichocysts are organelles of attack and defense. Predators use trichocysts to paralyze prey; “peaceful” - defend themselves from attacks by predators. By origin, trichocysts are a modification of motor organelles and are formed from basal bodies.

In I.'s ectoplasm, with appropriate processing, one can detect a network of the finest fibers lying near the basal bodies and trichocysts (Fig. 3, A). It is believed that these fibers - neurofans - conduct stimulation and determine the coordinated operation of the ciliary apparatus. However, in many cases such fibers have supporting value. It was stated above that many of them can change the shape of the body. This is due to the fact that special contractile filaments, or myonemes, are located in the ectoplasm. Thus, in the trumpeter (Stentor) and some others, the system of contractile myonemes consists of many longitudinally located fibers running along the body and lining the perioral recess (Fig. 5 A). The myoneme system of Caloscolex from the stomach of ruminants, described by Prof. V. A. Dogel (Fig. 5, B). The sessile ciliates Suwoek have a rather complex stalk, inside which myonemes also pass. When the twigs are irritated, their stalk curls into a spiral (Fig. 45).

A certain body shape, sometimes quite bizarre, is due to the presence of dense skeletal formations in the ectoplasm. Most often this is a whole system of supporting fibers (Fig. 5, B).

The digestive organelles of ciliates begin with a mouth, or cytostome, which is an opening in the pellicle. For many, the mouth is placed at the bottom of a special depression - the perioral cavity, or peristome (Fig. 2, A). In many animals that feed on small organisms (bacteria), the peristome is surrounded by a spirally arranged corolla of membranellae (hyperciliated and oriformed). A wavy membrane may be located in the peristome (Fig. 2 and 3, B).

The flickering movements of cilia and membranella cause water currents that carry food particles (bacteria, etc.) to the mouth. Many predators do not have a peristome, and they swallow food with a strongly stretched mouth (Fig. 40, B).

The mouth leads into the “pharynx,” or cytopharynx, which is a short canal sometimes also lined with cilia. A bubble forms at the inner edge of the pharynx, consisting of a droplet of liquid secreted by the endoplasm, into which food particles accumulating at the bottom of the pharynx enter. This is how a digestive vacuole is formed (Fig. 2, A).

In the shoe, when there is an abundance of food, a new digestive vacuole is formed approximately every minute. The food-containing vacuoles break away from the pharynx and move through the endoplasm of the ciliate, completing a certain path. Thus, in the slipper, each digestive vacuole first describes a small circle in the posterior half of the body, and then big circle, reaching the anterior end of the body.

The process of ingestion, the formation of digestive vacuoles and their movement in the endoplasm can be easily observed by adding ground carcass or carmine to a drop of water with ciliates. During movement in the vacuole, food is digested and the digested food is absorbed into the endoplasm. The endoplasm secretes enzymes into the digestive vacuoles.

It has been established that at different stages of digestion the acidity of the contents of the vacuole is different. Initially, the contents of the vacuole are acidic, then alkaline.

Vacuoles containing undigested food debris approach the surface of the ectoplasm. In many ciliates, at a certain place on the body, closer to the posterior end, in the pellicle there is a special opening - the cytoproct, through which defecation occurs (Fig. 2, A). The process of defecation occurs much less frequently than the formation of digestive vacuoles (after 7-10 minutes), since before defecation several vacuoles with undigested food residues merge into one. The entire process of digestion in the slipper, from the formation of vacuoles to defecation, lasts, depending on the temperature, from 1 to 3 hours.

As mentioned above, among ciliates there are many predators that feed on others (Fig. 6). For example, the large predatory Bursaria swallows slippers and others, forcing them into the throat with the movement of membranellas. In other predators, ingestion occurs differently. Their mouth is very stretchable, and they swallow and draw in quite large ciliates. Some carnivores can eat ciliates that are significantly larger than their own size. Thus, relatively small Didinium (Fig. 40, D) attack shoes, kill them with a special proboscis, then gradually suck them in and digest them.

Their excretory organelles are represented by one, two or several contractile vacuoles located in certain parts of the body (Fig. 2). Contractile vacuoles often have a rather complex structure (Fig. 7). In addition to the vacuole itself, which periodically contracts (systole) and expands (diastole), adductor channels located in the endoplasm lead to it. Due to this, the released substances enter the contractile vacuole from various parts ciliate bodies. An excretory duct leads from the vacuole to the pellicle, opening with a special opening to the outside (Fig. 7).

If there are two vacuoles (for example, in a shoe), they contract alternately. At 16°C, each vacuole contracts in 20-25 seconds (at the shoe).

Ciliates, like other protozoa, are able to respond to a variety of external stimuli. Unlike many flagellated ciliates, they do not have light-sensitive organelles. The role of sensitive organelles is played mainly by cilia and membranelles. In some, the cilia retain their motor function; in others, for example in stilonychia, the dorsal cilia serve only as tactile organelles.

The reaction to irritation is expressed in slowing down or accelerating, as well as in changing the direction of movement (shoes), in the curling of the peristome and compression of the body (stentors, suvoyki), in the contraction of the stalk
(suvoyki), etc. Ciliates are very sensitive to the slightest touch of foreign objects. They are very sensitive to change chemical composition environment, and different substances act on them differently, causing either a positive or negative reaction. Ability to respond differently to different chemical substances It has great importance in the life of ciliates when they find the food they need and the most favorable living conditions. For respiration, onias need a sufficient amount of oxygen dissolved in water. They,
like other protozoa, they breathe over the entire surface of the body. Therefore, ciliates react positively when an air bubble enters a droplet of water, gathering near it. Ciliates react positively or negatively to changes in environmental temperature, and each species is characterized by adaptability to a certain optimal temperature for it.

The nuclear apparatus of ciliated ciliates, as already mentioned, consists of one or several macronuclei having different shape(Fig. 2 and 43), and one or more micronuclei. The structure of the nuclear apparatus varies greatly in detail. Thus, the common slipper (Paramecium caudatum) has one large macronucleus and one micronucleus, located in the recess of the macronucleus. Another species of the same genus, P. aurelia, has two micronuclei. In the suvoek, the macronucleus has a horseshoe shape, and in the trumpeter, in addition to the very elongated, bead-shaped macronucleus, there are several micronuclei (Fig. 43). Differentiation of the nuclear apparatus into a vegetative nucleus - macronucleus and into a sexual, or generative, nucleus - micronucleus is characteristic of all ciliated ciliates.

A micronucleus differs from a macronucleus not only in size, but also in the number of chromosomes. While the micronucleus has a diploid set of chromosomes, the macronucleus is polyploid, that is, the set of chromosomes is repeated many times. Thus, in the slipper Paramecium caudatum the macronucleus is 80-ploid (according to other sources, 160-ploid), and in the closely related species P. aurelia it is 1000-ploid. In some, the ploidy level can reach 10-15 thousand.

Thus, ciliated ciliates have a very complex structure compared to other protozoa. It gets complicated in two ways. We have seen that ciliates have a large number of different organelles, often forming entire systems, for example, a system of digestive, excretory organelles, etc. On the other hand, ciliates are characterized by the multiplication, or polymerization, of many organelles. Undoubtedly, cilia with basal bodies correspond in origin to the flagellar apparatus of flagellates. But compared to the polymerization of locomotor organelles in polyflagellates, in ciliates polymerization goes much further. Developing a complex system an organelle consisting of a huge number of cilia, some of which turn into membranella, cirri, etc. Moreover, the complexity of the organization is expressed in the coordinated functioning of the entire motor apparatus. Ciliates are also characterized by an increase in the number of nuclei. They have at least two cores. However, unlike multiflagellates, this process is further complicated by differentiation of the nuclei.

Suctoria sucking ciliates

The class of Ciliates includes about 6 thousand species. These animals are the most highly organized among the protozoa.

With morphological and biological features Let's get acquainted with the structure of ciliates using the example of a typical representative - the slipper ciliate.

The structure of the ciliate slipper

External and internal structure of the ciliate slipper

The slipper ciliate has a size of about 0.1-0.3 mm. The body shape resembles a shoe, which is why it got its name.

This animal has permanent form body, since the ectoplasm is compacted on the outside and forms pellicle. The body of ciliates is covered with cilia. There are about 10-15 thousand of them.

A characteristic feature of the structure of ciliates is the presence of two nuclei: large (macronucleus) and small (micronucleus). The transmission is associated with the small nucleus hereditary information, and more importantly, the regulation of vital functions. The slipper ciliate moves with the help of cilia, with the anterior (blunt) end forward and at the same time rotates to the right along the axis of its body. High speed The movement of the ciliates depends on the paddle-like movement of the cilia.

The ectoplasm of the slipper contains formations called trichocysts. They perform a protective function. When the slipper ciliates are irritated, the trichocysts “shoot” out and turn into thin long threads that infect the predator. After using some trichocysts, new ones develop in their place in the ectoplasm of the protozoan.

Nutrition and excretory organs

The nutritional organelles of the slipper ciliate are: the preoral cavity, the cellular mouth and the cellular pharynx. Bacteria and other particles suspended in water, along with water, are driven by perioral cilia through the mouth into the pharynx and enter the digestive vacuole.

Having filled with food, the vacuole breaks away from the pharynx and is carried away by the current of the cytoplasm. As the vacuole moves, the food in it is digested by digestive enzymes and absorbed into the endoplasm. Then the digestive vacuole approaches the powder and undigested food remains are thrown out. Ciliates stop feeding only during the breeding season.

The organelles of osmoregulation and excretion in the slipper are two contractile, or pulsating, vacuoles with actuator canaliculi.

Thus, ciliates, in comparison with other protozoa, have a more complex structure:

• Constant body shape;
• the presence of a cellular mouth;
• presence of a cellular pharynx;
• powder;
• complex nuclear apparatus.

Reproduction of ciliates. Conjugation process

Ciliates reproduce by transverse division, in which nuclear division first occurs. The macronucleus divides amitotically, and the micronucleus divides mitotically.

From time to time they have sexual intercourse, or conjugation. During this, two ciliates come closer and closely attach to each other mouth openings. At room temperature in this form they float for about 12 hours. Large nuclei are destroyed and dissolved in the cytoplasm.

As a result of meiotic division, migrating and stationary nuclei are formed from small nuclei. Each of these nuclei contains a haploid set of chromosomes. The migrating nucleus actively moves through the cytoplasmic bridge from one individual to another and merges with its stationary nucleus, that is, the process of fertilization occurs. At this stage, each shoe forms one complex nucleus, or synkaryon, containing a diploid set of chromosomes. Then the ciliates disperse, their normal nuclear apparatus is restored again, and they subsequently multiply intensively by fission.

The process of conjugation contributes to the fact that the hereditary principles of different individuals are combined in one organism. This leads to increased hereditary variability and greater resilience of organisms. In addition, the development of a new nucleus and the destruction of the old one is of great importance in the life of ciliates. This is due to the fact that the basic life processes and protein synthesis in the body of ciliates are controlled by a large nucleus.

For a long time asexual reproduction in ciliates, the metabolism and rate of division decreases. After conjugation, the level of metabolism and the rate of division are restored.

The importance of ciliates in nature and human life

It has been established that ciliates play a significant role in the cycle of substances in nature. Various species of larger animals (fish fry) feed on ciliates.

They serve as population regulators unicellular algae and bacteria, thereby cleaning water bodies.

Ciliates can serve as indicators of the degree of contamination of surface waters - water supply sources.

Ciliates living in the soil improve its fertility.

Man breeds ciliates in aquariums to feed fish and their fry.

In a number of countries, human and animal diseases caused by ciliates are widespread. Particularly dangerous is the ciliate balantidium, which lives in the intestines of pigs and is transmitted to humans from the animal.