The structure, vital activity of a variety of ciliates. Infusoria shoe: external and internal structure, nutrition, reproduction, significance in nature and human life
Infusoria shoe - the simplest living moving cell. Life on Earth is distinguished by the diversity of living organisms that live on it, sometimes having the most complex structure and a whole set of physiology and life features that help them survive in this world full of dangers.
But among organic beings there are also such unique creations of nature, the structure of which is extremely primitive, but it was they who once upon a time, billions of years ago, gave impetus to the development of life and more complex organisms in all their diversity originated from them.
The primitive forms of organic life that now exist on earth include infusoria slipper, belonging to unicellular creatures from the group of alveolates.
It owes its original name to the shape of its spindle-shaped body, vaguely resembling the sole of an ordinary shoe with wide, blunt and narrower ends.
Such microorganisms are considered by scientists to be highly organized protozoa of class of ciliates, shoes are the most typical variety.
The shoe owes its name to the infusoria due to the structure of its body in the shape of a foot.
Slippers are usually bred in abundance in shallow fresh water with calm stagnant water, provided that this environment has an abundance of organic decomposing compounds: aquatic plants, dead living organisms, ordinary silt.
Even a home aquarium can become an environment suitable for their life activity, only it is possible to detect and carefully examine such living creatures only under a microscope, taking silt-rich water as a prototype.
Infusoria shoes – protozoa living organisms, called differently: tailed paramecia, are indeed extremely small, and their size is only from 1 to 5 tenths of a millimeter.
In fact, they are separate, colorless in color, biological cells, the main internal organelles of which are two nuclei, called: large and small.
As seen on the enlarged photo of infusoria shoes, on the outer surface of such microscopic organisms there are, located in longitudinal rows, the smallest formations called cilia, which serve as organs of movement for shoes.
The number of such small legs is huge and ranges from 10 to 15 thousand, at the base of each of them there is an attached basal body, and in the immediate vicinity of the parasonal sac, drawn in by a protective membrane.
The structure of the shoe infusoria, despite its apparent simplicity at a superficial examination, it has enough complexities. Outside, such a walking cell is protected by the thinnest elastic shell, which helps its body to maintain a constant shape. As well as protective supporting fibers located in a layer of dense cytoplasm adjacent to the membrane.
Its cytoskeleton, in addition to all of the above, consists of: microtubules, alveolar cisterns; basal bodies with cilia and nearby, without them; fibrils and filaments, as well as other organelles. Thanks to the cytoskeleton, and unlike another representative of the protozoa - amoeba, infusoria slipper unable to change the shape of the body.
The nature and lifestyle of ciliates shoes
These microscopic creatures are usually in constant undulating motion, picking up a speed of about two and a half millimeters per second, which for such negligible creatures is 5-10 times their body length.
The movement of ciliates shoes carried out by blunt ends forward, while it tends to rotate around the axis of its own body.
The shoe, sharply waving its cilia-legs and smoothly returning them to their place, works with such organs of movement like oars in a boat. Moreover, the number of such strokes has a frequency of about three dozen times per second.
As for the internal organelles of the shoe, the large ciliate nucleus is involved in metabolism, movement, respiration and nutrition, and the small one is responsible for the reproduction process.
The breathing of these simplest creatures is carried out as follows: oxygen enters the cytoplasm through the integument of the body, where, with the help of this chemical element organic matter is oxidized and converted into carbon dioxide, water and other compounds.
And as a result of these reactions, energy is generated that is used by the microorganism for its life activity. After all, harmful carbon dioxide is removed from the cell through its surface.
Feature of ciliates shoes, as a microscopic living cell, consists in the ability of these tiny organisms to respond to the external environment: mechanical and chemical influences, moisture, heat and light.
On the one hand, they tend to move to accumulations of bacteria to carry out their life and nutrition, but on the other hand, the harmful secretions of these microorganisms make the ciliates swim away from them.
Shoes also react to salt water, from which they are in a hurry to move away, but they willingly move towards heat and light, but unlike euglena, infusoria slipper so primitive that it does not have a light-sensitive eye.
Feeding ciliates slippers
Plant cells and a variety of bacteria, found in abundance in the aquatic environment, form the basis food infusoria shoes. And she carries out this process with the help of a small cellular recess, which is a kind of mouth that sucks in food, which then enters the cellular pharynx.
And from it into the digestive vacuole - an organelle in which organic food is digested. Substances that have entered inside are subjected to hourly processing when exposed first to an acidic and then to an alkaline environment.
After that, the nutrient substance is transferred by currents of the cytoplasm to all parts of the body of the ciliate. And the waste is brought out through a kind of formation - powder, which is placed behind the mouth opening.
In ciliates, excess water entering the body is removed through contractile vacuoles located in front and behind this organic formation. They collect not only water, but also waste substances. When their number reaches the limit value, they pour out.
Reproduction and lifespan
The process of reproduction of such primitive living organisms occurs both sexually and asexually, and the small nucleus is directly and actively involved in the process of reproduction in both cases.
The asexual form of reproduction is extremely primitive and occurs through the most common division of the organism into two parts that are similar to each other in everything. At the very beginning of the process, two nuclei are formed inside the body of the ciliate.
Then there is a division into a pair of daughter cells, each of which receives its part organelles ciliates shoes, and what is missing in each of the new organisms are formed anew, which makes it possible for these protozoa to carry out their vital activity in the future.
Sexually, these microscopic creatures usually begin to multiply only in exceptional cases. This can happen when there is a sudden onset of life-threatening conditions, such as a sudden cold snap or lack of nutrition.
And after the implementation of the described process, in some cases, both microorganisms participating in the contact can turn into a cyst, plunging into a state of complete suspended animation, which makes it possible for the body to exist in adverse conditions for a sufficiently long period, lasting up to ten years. But under normal conditions, the age of ciliates is short, and, as a rule, they are not able to live for more than a day.
During sexual reproduction, two microorganisms join together for a while, which leads to a redistribution of genetic material, resulting in an increase in the vitality of both individuals.
Such a state is called conjugation by scientists and lasts for about half a day. During this redistribution, the number of cells does not increase, but only the exchange of hereditary information between them takes place.
During the connection of two microorganisms, the protective shell between them dissolves and disappears, and a connecting bridge appears instead. Then the large nuclei of two cells disappear, and the small ones divide twice.
Thus, four new nuclei are created. Further, all of them, except for one, are destroyed, and the latter is again divided in two. The exchange of the remaining nuclei occurs along the cytoplasmic bridge, and from the resulting material, newly born nuclei, both large and small, arise. After that, the ciliates diverge from each other.
The simplest living organisms perform their functions in the general cycle of life. functions, ciliates shoes destroy many types of bacteria and themselves serve as food for small invertebrate animal organisms. Sometimes these protozoa are specially bred as food for the fry of some aquarium fish.
Questions:
1. On the basis of what signs can it be argued that the amoeba cell is an independent organism?
2. Describe the processes of nutrition and excretion in the amoeba.
3. Explain what is the role of protozoa in nature.
4. Establish a connection between the habitat and the types of nutrition of green euglena.
5. Compare the breeding methods of the amoeba proteus and green euglena.
6. Give justification for the statement about the intermediate position of green euglena between the two kingdoms of wildlife.
7. What is the complication of the organization of colonial forms of flagellates? Explain your answer with examples.
8. Prove with specific examples that ciliates have more complex structure than sarcodes and flagellates.
9. Establish a connection between the complication of the structure of ciliates-shoes and the processes of nutrition and excretion.
10. Describe the features of the reproduction process of ciliates-shoes.
11. Explain why the sexual process is not sexual reproduction. What is its biological significance?
12. Explain what functions the protozoan cell performs.
13. Name the measures that prevent the disease of amoebic dysentery and malaria.
14. Formulate a conclusion about the role of protozoa in nature and their impact on humans.
15. Explain why the protozoan cell is an independent organism.
16. Describe the habitats of unicellular organisms. What condition is necessary for their existence?
17. Explain what are the functions of vacuoles in the body of unicellular organisms.
18. Establish the relationship between the structure and methods of movement of unicellular organisms.
19. What are the features of the adaptation of protozoa to adverse conditions.
20. Describe the role in nature of two or three representatives of protozoa living in the aquatic environment.
21. What are the measures to prevent diseases caused by protozoa.
22. What is the name of the scientist who first described the group of protozoa.
23. What is common in the structure of protozoa?
24. Why do scientists claim that animals and plants had common ancestors?
25. Explain the sense in which doctors often use the expression "dirty hand disease." Give examples of diseases to which it refers.
26. Complete the sentences by entering the necessary words.
If a jar of .... hold for several days in a dark cabinet, then the color will disappear from it. ... will become light, but will not die, because in the dark they feed like ... . In the light... again.... and start eating like... .
27. Fill in the missing letters. Give definitions of concepts.
S..mb..oz - ...
K..lonia - ...
Cancer..guilt - ...
Ts..sta - ...
28. Explain how the way of eating and the way of life of the simplest are interconnected.
29. Is the statement true: "The school chalk, the walls of the palace and the walls of the pyramid have one source, one basis? Prove your point of view.
Which statements are true?
1. The cell of the simplest performs the role of an independent organism.
2. Reproduction in amoeba is asexual, and in ciliates-shoes - both asexual and sexual.
3. The organelles of the movement of ciliates-shoes are pseudopods.
4. Euglena green is a transitional form from plants to animals: it has chlorophyll, like in plants, but it feeds heterotrophically and moves like animals.
5. Amoeba has two types of nuclei in the body.
6. The small nucleus in ciliates is involved in sexual reproduction, and the large nucleus is responsible for vital activity.
7. Dysentery amoeba is carried by mosquitoes.
Infusoria class (Infusoria, or Ciliata)
Compared with other groups of protozoa, ciliates have the most complex structure, which is associated with the diversity and complexity of their functions.
Infusoria slipper (Paramecium caudatum)
To get acquainted with the structure and way of life of these interesting unicellular organisms, let us first turn to one characteristic example. Let us take shoe ciliates (species of the genus Paramecium), which are widespread in shallow freshwater reservoirs. These ciliates are very easy to breed in small aquariums, if you fill the pond with ordinary meadow hay. In such tinctures, many different types of protozoa develop, and shoe ciliates almost always develop. With the help of an ordinary educational microscope, you can see much of what will be discussed further.
Among the simplest ciliates shoes are fairly large organisms. Their body length is about 1/6 - 1/5 mm.
Where did the name "infusoria slipper" come from? You will not be surprised if you look under a microscope at a live ciliate, or even at its image (Fig. 85).
Indeed, the shape of the body of this ciliate resembles an elegant lady's shoe.
The infusoria shoe is in continuous rather fast movement. Its speed (at room temperature) about 2.0-2.5 mm/sec. That's a lot of speed for such a small animal! After all, this means that in a second the shoe runs a distance exceeding the length of its body by 10-15 times. The trajectory of the shoe is rather complicated. It moves with its front end straight ahead and at the same time rotates to the right along the longitudinal axis of the body.
Such an active movement of the shoe depends on the work of a large number of the finest hair-like appendages - cilia that cover the entire body of the ciliate. The number of cilia in one individual of the shoe ciliates is 10-15 thousand!
Each cilium makes very frequent paddle-like movements - at room temperature up to 30 beats per second. During the blow back, the cilium is held in a straightened position. When it returns to its original position (when moving down), it moves 3-5 times slower and describes a semicircle.
When a shoe swims, the movements of numerous cilia covering its body are summed up. The actions of individual cilia are coordinated, resulting in the correct wave-like vibrations of all cilia. The oscillation wave starts at the front end of the body and propagates backward. At the same time, 2-3 waves of contraction pass along the body of the shoe. Thus, the entire ciliary apparatus of the ciliate is, as it were, a single functional physiological whole, the actions of the individual structural units of which (cilia) are closely connected (coordinated) with each other.
The structure of each individual shoe cilium, as shown by electron microscopic studies, is very complex.
The direction and speed of movement of the shoe are not constant and unchanging quantities. The shoe, like all living organisms (we have already seen this with the example of the amoeba), reacts to a change in the external environment by changing the direction of movement.
A change in the direction of movement of protozoa under the influence of various stimuli is called taxis. In ciliates, it is easy to observe various taxis. If in a drop where shoes float, place any substance adversely affecting them (for example, a crystal table salt), then the shoes float away (as if running away) from this factor unfavorable for them (Fig. 86).
Before us is an example of a negative taxis on a chemical effect (negative chemotaxis). You can observe the shoe and positive chemotaxis. If, for example, a drop of water in which ciliates swim is covered with a cover glass and a bubble of carbon dioxide (CO 2) is let under it, then most of the ciliates will go to this bubble and settle down around it in a ring.
The phenomenon of taxis is very clearly manifested in shoes under the influence of an electric current. If a weak electric current is passed through the liquid in which the shoes are floating, then the following picture can be observed: all ciliates orient their longitudinal axis parallel to the current line, and then, as if on command, move towards the cathode, in the area of \u200b\u200bwhich they form a dense cluster. The movement of ciliates, determined by the direction of the electric current, is called galvanotaxis. Various taxises in ciliates can be detected under the influence of a wide variety of environmental factors.
The entire cytoplasmic body of the ciliate is clearly divided into 2 layers: the outer one is lighter (ectoplasm) and the inner one is darker and granular (endoplasm). The most superficial layer of ectoplasm forms an outer very thin and at the same time strong and elastic shell - the pellicle, which plays an important role in maintaining the constancy of the shape of the body of the ciliate.
In the outer layer (in the ectoplasm) of the body of a living shoe, numerous short sticks are clearly visible, located perpendicular to the surface (see Fig. 85.7). These formations are called trichocysts. Their function is very interesting and is connected with the protection of the simplest. With mechanical, chemical or some other strong irritation, trichocysts are thrown out with force, turning into thin long threads that hit a predator attacking the shoe. Trichocysts are a powerful defense. They are arranged regularly between the cilia, so that the number of trichocysts approximately corresponds to the number of cilia. In place of the used ("shot") trichocysts, new ones develop in the ectoplasm of the shoe.
On one side, approximately in the middle of the body (see Fig. 85.5), the shoe has a rather deep depression. This is oral cavity, or peristome. Cilia are located along the walls of the peristome, as well as along the surface of the body. They are developed here much more powerfully than on the rest of the surface of the body. These closely spaced cilia are arranged in two groups. The function of these highly differentiated cilia is associated not with movement, but with nutrition (Fig. 87).
How and what do shoes eat, how do they digest?
Shoes are among the ciliates, the main food of which is bacteria. Along with bacteria, they can also swallow any other particles suspended in water, regardless of their nutritional value. The perioral cilia create a continuous flow of water with suspended particles in the direction of the oral opening, which is located deep in the peristome. Small food particles (most often bacteria) penetrate through the mouth into a small tubular pharynx and accumulate at the bottom of it, on the border with the endoplasm. The mouth opening is always open. Perhaps it will not be a mistake to say that the ciliate shoe is one of the most voracious animals: it feeds continuously. This process is interrupted only at certain moments of life associated with reproduction and the sexual process.
The food lump accumulated at the bottom of the pharynx then breaks off from the bottom of the pharynx and, together with a small amount of liquid, enters the endoplasm, forming digestive vacuole. The latter does not remain at the site of its formation, but, falling into the currents of the endoplasm, makes a rather complex and regular path in the body of the shoe, called the cyclosis of the digestive vacuole (Fig. 88). During this rather long (at room temperature, taking about an hour) journey of the digestive vacuole, a number of changes occur inside it associated with the digestion of the food in it.
Here, just like amoeba and some flagellates, typical intracellular digestion occurs. From the endoplasm surrounding the digestive vacuole, digestive enzymes enter it, which act on food particles. The products of food digestion are absorbed through the machine of the digestive vacuole into the endoplasm.
In the course of cyclosis of the digestive vacuole, several phases of digestion are replaced in it. In the first moments after the formation of a vacuole, the liquid filling it differs little from the liquid of the environment. Soon, digestive enzymes begin to enter the vacuole from the endoplasm, and the reaction of the environment inside it becomes sharply acidic. This is easy to detect by adding some indicator to food, the color of which changes depending on the reaction (acidic, neutral or alkaline) of the environment. In this acidic environment, the first phases of digestion take place. Then the picture changes and the reaction inside the digestive vacuoles becomes slightly alkaline. Under these conditions, there are next steps intracellular digestion. The acid phase is usually shorter than the alkali phase; it lasts approximately 1/6 - 1/4 of the entire stay of the digestive vacuole in the body of the ciliate. However, the ratio of acidic and alkaline phases can vary within fairly wide limits, depending on the nature of the food.
The path of the digestive vacuole in the endoplasm ends with the fact that it approaches the surface of the body and through the pellicle its contents, consisting of liquid and undigested food residues, are thrown out - defecation occurs. This process, in contrast to amoebas, in which defecation can occur anywhere, in shoes, as in other ciliates, it is strictly confined to a specific area of the body located on the ventral side (abdominal is conventionally called the surface of the animal on which the perioral recess is placed ), approximately midway between the peristome and the posterior end of the body.
Thus, intracellular digestion is a complex process consisting of several phases successively replacing each other.
Calculations show that in about 30-45 minutes, a volume of fluid equal to the volume of the ciliate body is excreted from the shoe through the contractile vacuoles. Thus, due to the activity of contractile vacuoles, a continuous flow of water is carried out through the body of the ciliate, which enters from the outside through the mouth opening (together with digestive vacuoles), as well as osmotically directly through the pellicle. Contractile vacuoles play an important role in regulating the flow of water passing through the body of the ciliate and in regulating osmotic pressure. This process proceeds here in principle in the same way as in amoebas, only the structure of the contractile vacuole is much more complicated.
For many years, among scientists studying protozoa, there was a dispute over the question of whether there are any structures in the cytoplasm associated with the appearance of a contractile vacuole, or whether it is formed every time anew. On a living ciliate, no special structures that would have preceded its formation can be observed. After the contraction of the vacuole - systole - occurs, absolutely no structures are visible in the cytoplasm at the site of the former vacuole. Then a transparent bubble or adductor channels reappear, which begin to increase in size. However, no connection between the newly emerging vacuole and the previously existing vacuole is found. It seems that there is no continuity between successive cycles of the contractile vacuole and any new contractile vacuole is formed anew in the cytoplasm. However, special research methods have shown that this is not actually the case. The use of electron microscopy, which gives a very high magnification (up to 100 thousand times), convincingly showed that the ciliate has a particularly differentiated cytoplasm in the area where contractile vacuoles are formed, consisting of an interweaving of the thinnest tubes. Thus, it turned out that the contractile vacuole does not arise in the cytoplasm on " empty place", but on the basis of the previous special cell organoid, the function of which is the formation of a contractile vacuole.
Like all protozoa, ciliates have a cell nucleus. However, in terms of the structure of the nuclear apparatus, ciliates differ sharply from all other groups of protozoa.
nuclear apparatus ciliates are characterized by their dualism. This means that ciliates have two different types nuclei - large kernels, or macronuclei, and small nuclei, or micronuclei. Let's see what structure the nuclear apparatus has in the ciliates of the shoe (see Fig. 85).
In the center of the body of the ciliate (at the level of the peristome), a large massive nucleus of an ovoid or bean-shaped shape is placed. This is the macronucleus. In close proximity to it, there is a second nucleus many times smaller, usually quite closely adjacent to the macronucleus. This is a micronucleus. The difference between these two nuclei is not only in size, it is more significant, deeply affecting their structure.
The macronucleus, compared with the micronucleus, is much richer in a special nuclear substance (chromatin, or, more precisely, deoxyribonucleic acid, abbreviated DNA), which is part of the chromosomes.
Recent studies have shown that the macronucleus has several tens (and in some ciliates hundreds) times more chromosomes than micronuclei. The macronucleus is a very peculiar type of multichromosomal (polyploid) nuclei. Thus, the difference between micro- and macronuclei affects their chromosomal composition, which determines the greater or lesser richness of their nuclear substance - chromatin.
In one of the most common types of ciliates - shoes(Paramecium caudatum) - has one macronucleus (abbreviated Ma) and one micronucleus (abbreviated Mi). This structure of the nuclear apparatus is characteristic of many ciliates. Others may have several Ma and Mi. But a characteristic feature of all ciliates is the differentiation of nuclei into two qualitatively different groups, into Ma and Mi, or, in other words, the phenomenon of nuclear dualism *.
* (There is, perhaps, one exception to this rule - no nuclear dualism has been found in marine ciliates of the genus Stephanopogon. This case requires further research.)
how multiply ciliates? Let us turn as an example again to the infusoria shoe. If you plant a single copy of the shoe in a small vessel (microaquarium), then in a day there will be two, and often four ciliates. How does this happen? After a certain period of active swimming and feeding, the ciliate is somewhat stretched in length. Then, exactly in the middle of the body, an ever-deepening transverse constriction appears (Fig. 90). In the end, the ciliates, as it were, are laced in half, and two individuals are obtained from one individual, initially somewhat smaller than the parent individual. The entire fission process takes about an hour at room temperature. The study of internal processes shows that even before the transverse constriction appears, the process of fission of the nuclear apparatus begins. Mi is shared first, and only after it is Ma. We will not dwell here on a detailed consideration of the processes of nuclear fission and will only note that Mi is divided by mitosis, while the division of Ma in appearance resembles direct nuclear fission - amitosis. This asexual reproduction process of the shoe ciliates, as we see, is similar to the asexual reproduction of amoebas and flagellates. In contrast, ciliates in the process of asexual reproduction always divide across, while in flagellates, the division plane is parallel to the longitudinal axis of the body.
During division, a deep internal restructuring of the ciliate body occurs. Two new peristomes, two pharynxes and two mouth openings are formed. By the same time, the division of the basal nuclei of cilia is timed, due to which new cilia are formed. If the number of cilia did not increase during reproduction, then as a result of each division, the daughter individuals would receive approximately half the number of cilia of the mother individual, which would lead to complete "baldness" of the ciliates. Actually this does not happen.
From time to time, most ciliates, including shoes, have a special and extremely peculiar shape. sexual process, which was named conjugations. We will not analyze here in detail all the complex nuclear changes that accompany this process, but note only the most important. Conjugation proceeds as follows (Fig. 91), Two ciliates approach each other, are closely applied to each other by the ventral sides, and in this form they swim quite long time together (at the shoe for about 12 hours at room temperature). The conjugants then separate. What happens in the body of ciliates during conjugation? The essence of these processes is as follows (Fig. 91). The large nucleus (macronucleus) collapses and gradually dissolves in the cytoplasm. Micronuclei first divide, some of the nuclei formed as a result of fission are destroyed (see Fig. 91). Each of the conjugants retains two nuclei. One of these nuclei remains in place in the individual in which it was formed ( stationary core), while the other actively moves into the conjugation partner ( migrating nucleus) and merges with its stationary core. Thus, in each of the conjugants at this stage there is one nucleus formed as a result of the fusion of the stationary and migrating nuclei. This complex nucleus is called syncarion. The formation of a synkaryon is nothing more than a process of fertilization. And in multicellular organisms, the essential moment of fertilization is the fusion of the nuclei of germ cells. In ciliates, germ cells are not formed, there are only sex nuclei, which merge with each other. Thus, mutual cross-fertilization occurs.
Shortly after the formation of the synkaryon, the conjugants separate. According to the structure of their nuclear apparatus, at this stage they still differ very significantly from the usual so-called neutral (non-conjugating) ciliates, since they have only one nucleus each. In the future, due to the synkarion, the normal nuclear apparatus is restored. The synkaryon is divided (one or more times). Part of the products of this division, through complex transformations associated with an increase in the number of chromosomes and enrichment in chromatin, turns into macronuclei. Others retain the structure characteristic of micronuclei. In this way, the nuclear apparatus characteristic and typical of ciliates is restored, after which the ciliates begin asexual reproduction by fission.
Thus, the process of conjugation includes two essential biological moments: fertilization and restoration of a new macronucleus due to synkaryon.
What is the biological significance of conjugation, what role does it play in the life of ciliates? We cannot call it reproduction, because there is no increase in the number of individuals. The above questions have served as material for numerous experimental studies carried out in many countries. The main result of these studies is as follows. Firstly, conjugation, like any other sexual process, in which two hereditary principles (paternal and maternal) unite in one organism, leads to an increase in hereditary variability, hereditary diversity. An increase in hereditary variability increases the adaptive capabilities of the organism to environmental conditions. The second biologically important side of conjugation is the development of a new macronucleus due to the fission products of the synkaryon and, at the same time, the destruction of the old one. Experimental data show that it is the macronucleus that plays an extremely important role in the life of ciliates. They control all major life processes and the most important of them is determined - the formation (synthesis) of a protein that constitutes the main part of the protoplasm of a living cell. With prolonged asexual reproduction by division, a peculiar process of "aging" of the macronucleus, and at the same time of the entire cell, occurs: the activity of the metabolic process decreases, the rate of division decreases. After conjugation (during which, as we have seen, the old macronucleus is destroyed), the metabolic rate and the rate of division are restored. Since the process of fertilization occurs during conjugation, which in most other organisms is associated with reproduction and the appearance of a new generation, in ciliates, the individual formed after conjugation can also be considered as a new sexual generation, which arises here, as it were, due to the "rejuvenation" of the old.
On the example of ciliate shoes, we met with a typical representative of an extensive class of ciliates . However, this class is characterized by an extraordinary variety of species, both in structure and in lifestyle. Let's take a closer look at some of the most characteristic and interesting forms.
In ciliates, the cilia of the shoe evenly cover the entire surface of the body. This is a characteristic feature of the structure (Holotricha). Many ciliates are characterized by a different nature of the development of the ciliary cover. The fact is that the cilia of ciliates are capable, when combined together, to form more complex complexes. For example, it is often observed that cilia located in one or two rows close to each other join (stick together) together, forming a plate, which, like cilia, is capable of beating. Such lamellar contractile formations are called membranell(if they are short) or membranes(if they are long). In other cases, cilia are joined together, located in a tight bundle. These formations are cirres- resemble a brush, the individual hairs of which are stuck together. different kind complex ciliary formations are characteristic of many ciliates. Very often, the ciliary cover does not develop evenly, but only in some parts of the body.
Infusoria trumpeter (Stentor polymorphic)
In fresh waters, species of large beautiful ciliates belonging to kind of trumpeters (Stentor). This name is quite consistent with the shape of the body of these animals, which really resembles a pipe (Fig. 92), widely opened at one end. At the first acquaintance with live trumpeters, one can notice one feature that is not characteristic of a shoe. At the slightest irritation, including mechanical (for example, tapping with a pencil on glass, where there is a drop of water with trumpeters), their body contracts sharply and very quickly (in a fraction of a second), taking on an almost regular spherical shape. Then, rather slowly (time is measured in seconds), the trumpeter straightens out, taking on his characteristic shape. This ability of the trumpeter to contract quickly is due to the presence of special muscle fibers located along the body and in the ectoplasm. Thus, a muscular system can also develop in a unicellular organism.
in the genus trumpeter there are species, some of which are characterized by a rather bright color. Very common in fresh waters blue trumpeter(Stentor coeruleus), which is bright blue. This coloration of the trumpeter is due to the fact that the smallest grains of blue pigment are located in its ectoplasm.
Another species of trumpeter (Stentor polymorphus) is often colored green. The reason for this coloration is quite different. The green color is due to the fact that small unicellular green algae live and multiply in the endoplasm of the ciliate, which give the body of the trumpeter a characteristic color. Stentor polymorphus is a typical example of mutually beneficial cohabitation - symbiosis. The trumpeter and algae are in a mutually symbiotic relationship: the trumpeter protects the algae living in its body and supplies them with carbon dioxide formed as a result of respiration; for their part, the algae provide the trumpeter with oxygen, released in the process of photosynthesis. Apparently, part of the algae is digested by ciliates, being food for the trumpeter.
Trumpeters swim slowly in the water with the wide end forward. But they can also be temporarily attached to the substrate by the posterior narrow end of the body, on which a small sucker is formed.
In the body of the trumpeter, one can distinguish the trunk section expanding from back to front and almost perpendicular to it
located wide perioral ( peristomal) field. This field resembles an asymmetric flat funnel, on one edge of which there is a recess - a pharynx leading to the endoplasm of the ciliate. The body of the trumpeter is covered with longitudinal rows of short cilia. Along the edge of the peristomal field, a powerfully developed perioral ( adoral) membranella zone (see Fig. 92). This zone consists of a large number of individual ciliated plates, each of which, in turn, is composed of many cilia stuck together with each other, located in two closely spaced rows.
In the region of the oral opening, the perioral membranes are wrapped towards the pharynx, forming a left-handed spiral. The flow of water, caused by the oscillation of the perioral membranella, is directed towards the mouth opening (into the depth of the funnel formed by the anterior end of the body). Along with water, food particles suspended in water also enter the pharynx. The food objects of the trumpeter are more diverse than those of the slipper. Along with bacteria, it eats small protozoa (for example, flagellates), unicellular algae, etc.
The trumpeter has a well-developed contractile vacuole, which has a peculiar structure. The central reservoir is located in the anterior third of the body, slightly below the mouth opening. Two long adducting channels depart from it. One of them goes from the reservoir to the posterior end of the body, the second is located in the region of the peristomal field parallel to the perioral zone of the membranella.
The trumpeter's nuclear apparatus is arranged in a very peculiar way. The macronucleus here is divided into rosaries (there are about 10 of them), connected to each other by thin bridges. Several micronuclei. They are very small and usually adhere closely to the macronucleus rosary.
The infusoria trumpeter is a favorite object for experimental research on regeneration. Numerous experiments have proven the high regenerative capacity of trumpeters. A ciliate with a thin scalpel can be cut into many parts, and each of them through a short time(several hours, sometimes a day or more) will turn into a proportionally built, but small trumpeter, which then, as a result of energetic feeding, reaches the size typical for this species. To complete the recovery processes, the regenerating piece must contain at least one segment of a beaded macronucleus.
The trumpeter, as we have seen, has different cilia: on the one hand, they are short, covering the entire body, and on the other, there is a near-oral zone of membranella. In accordance with this characteristic feature of the structure, the detachment of ciliates, to which the trumpeter belongs, was named differently. ciliary ciliates(Heterotricha).
Ciliates Bursaria (Bursaria truncatella)
The second interesting representative of ciliary ciliates is often found in fresh waters bursaria(Bursaria truncatella, Fig. 93). This is a giant among ciliates: its dimensions can reach 2 mm, the most common sizes are 0.5-1.0 mm. Bursaria is clearly visible to the naked eye. In accordance with its name, the bursaria has the shape of a bag, wide open at the front end (bursa is a Latin word, translated into Russian means "purse", "bag") and somewhat expanded at the rear end. The entire body of the ciliate is covered with longitudinal rows of short cilia. Their beating causes a rather slow forward movement of the animal. The bursaria swims as if "rolling over" from side to side.
From the anterior end deep into the body (approximately 2/3 of its length) a perioral depression protrudes - a peristome. On the ventral side, it communicates with the external environment through a narrow slit; on the dorsal side, the peristome cavity does not communicate with the external environment. If you look at the cross section of the upper third of the body of the bursaria (Fig. 93, B), you can see that the peristome cavity occupies most of the body, while the cytoplasm surrounds it in the form of a rim. At the anterior end of the body, on the left, a very powerfully developed perioral zone ( adoral) membranella (Fig. 93, 4). It descends into the depth of the peristome cavity, turning to the left. The adoral zone extends to the deepest part of the peristome. There are no other ciliary formations in the peristomal cavity apart from the perioral membranes, except for the ciliary strip running along the ventral side of the peristome cavity (Fig. 93, 10). On the inside back wall the peristomal cavity has a narrow slit along almost its entire length (Fig. 93, 7), the edges of which usually closely adjoin each other. This is oral slot. Its edges move apart only at the time of eating.
Bursaria do not have a narrow food specialization, but they are mainly predators. When moving forward, they encounter various small animals. Thanks to the work of the membranelles of the near-oral zone, the prey is drawn with force into the vast peristomal cavity, from where it can no longer swim out. Food objects are pressed against the dorsal wall of the peristomal cavity and penetrate the endoplasm through the expanding oral fissure. Bursaria are very voracious, they can swallow rather large objects: for example, their favorite food is shoe ciliates. Bursaria is able to swallow 6-7 shoes in a row. As a result, very large digestive vacuoles are formed in the endoplasm of the bursaria.
nuclear apparatus bursaria is quite complicated. They have one long sausage-shaped macronucleus and a large (up to about 30) number of small micronuclei randomly scattered in the endoplasm of the ciliate.
Bursaria are among the few species of freshwater ciliates that lack a contractile vacuole. How osmoregulation is carried out in this large ciliate is still not entirely clear. Under the ectoplasm of the bursaria in different parts of the body, fluid bubbles of various shapes and sizes can be observed - vacuoles that change their volume. Apparently these irregular shape vacuoles and correspond in their function to the contractile vacuoles of other ciliates.
It is interesting to watch the successive stages asexual reproduction bursaria. At the initial stages of division, there is a complete reduction of the entire cavity of the peristome and the near-oral zone of the membranella (Fig. 94). Only the outer cilium is preserved. The infusoria takes the form of an egg. After that, the body is laced with a transverse groove into two halves. In each of the resulting daughter ciliates, through rather complex transformations, a typical peristome and perioral zone of membranella develop. The whole process of dividing the bursaria proceeds quickly and takes a little more than an hour.
It is very easy to observe another important life process in bursaria, the onset of which is associated with conditions unfavorable for ciliates, the process of cyst formation ( encystation). This phenomenon is characteristic, for example, of amoeba. But it turns out that even such complexly organized protozoa as ciliates are capable of passing into an inactive state. If the culture where the bursaria live is not fed or cooled down in time, then mass encystation will begin in a few hours. This process proceeds as follows. Bursarids, as well as before division, lose the peristome and perioral zone of membranells. Then they become completely spherical, after which they distinguish a double shell of a characteristic shape (see Fig. 94, D).
In the state of cysts, bursaria can be for months. When favorable conditions occur, the cyst shell bursts, the bursaria come out of it, develop a peristome and move on to an active life.
Stilonychia (Stylonichia mytilus)
A very complex and diversely differentiated ciliary apparatus has ciliates related to detachment of gastrointestinal (Hypotricha), numerous species of which live in both fresh and sea water. One of the most common, frequently encountered representatives of this interesting group can be called stilonychia(Stylonichia mytilus). This is a rather large ciliate (up to 0.3 mm long), living at the bottom of freshwater reservoirs, on aquatic vegetation (Fig. 95). Unlike the slipper, trumpeter, and bursaria, stylonychia lacks a continuous ciliary cover, and the entire ciliary apparatus is represented by a limited number of strictly defined ciliary formations.
The body of Stilonychia (like most other ventral ciliates) is strongly flattened in the dorso-abdominal direction, and its dorsal and ventral sides, anterior and posterior ends are clearly distinguishable. The body is somewhat widened anteriorly, narrowed posteriorly. When examining the animal from the ventral side, it is clearly seen that in the anterior third on the left there is a complexly arranged pinnate and oral opening.
On the dorsal side, cilia are quite rarely located, which are not capable of beating. They can rather be called thin elastic bristles. They are motionless and have nothing to do with the function of movement. These cilia are usually assigned a tactile, sensitive function.
All ciliary formations associated with movement and food capture are concentrated on the ventral side of the animal (Fig. 95). There is a small number of thick finger-like formations located in several groups. This is abdominal cirrhosis. Each of them is a complex ciliary formation, the result of a close connection (sticking together) of many dozens of individual cilia. Thus, the cirres are like brushes, the individual hairs of which are closely brought together and connected to each other.
With the help of cirrhos, the animal moves quite quickly, "runs" along the substrate. In addition to "crawling" and "running" on the substrate, stilonychia is capable of producing rather sharp and strong jumps, immediately breaking away from the substrate. These sharp movements are carried out with the help of two powerful tail cirres (see Fig. 95), which do not take part in the usual "crawling".
Along the edge of the body on the right and left are two rows of marginal ( marginal) cirrh. From the right edge of the animal, they run along the entire body, while from the left edge they reach only the region of the peristome. These ciliary formations serve to propel the animal when it is detached from the substrate and swims freely in the water.
We see, therefore, that the diverse and specialized ciliary apparatus of stylonychia allows it to make very diverse movements, in contrast, for example, to simple sliding in water, like a shoe or a trumpeter.
The ciliary apparatus associated with the function of nutrition is also complex. We have already seen that the perioral depression ( peristome), at the bottom of which the mouth opening leading to the pharynx is located, is located in the anterior half of the animal on the left. Along the left edge, starting from the most anterior end of the body, there is a strongly developed zone of perioral ( adoral) membranella. With their beating, they direct the flow of water towards the mouth opening. In addition, in the region of the peristomal recess, there are three more contractile membranes (membranes), which extend into the pharynx with their inner ends, and a number of special perioral cilia (Fig. 95). This whole complex apparatus serves to capture and direct food into the mouth opening.
Stilonychia is one of the protozoa with a very wide range of food objects. It can rightfully be called an omnivore. She can eat, like a shoe, bacteria. Among its food objects are flagellates, unicellular algae (often diatoms). Finally, Stilonychia can also be a predator, attacking other, smaller species of ciliates and devouring them.
Stilonychia has a contractile vacuole. It consists of a central reservoir located at the left posterior end of the peristome and one adductor canal directed backwards.
The nuclear apparatus, as always in ciliates, consists of a macronucleus and a micronucleus.
The macronucleus is composed of two halves connected by a thin constriction; there are two micronuclei, they are located directly near both halves of Ma.
Stilonychia, partly bursaria, trumpeter - these are all ciliates with a wide range of food items. The ability to absorb various foods is characteristic of most ciliates. However, among them one can also find such species that are strictly specialized in relation to the nature of food.
Ciliates-predators
Among the ciliates there are predators that are very "picky" about their prey. A good example is infusoria. didynia(Didinium nasutum). Didinium is a relatively small ciliate, with an average length of about 0.1-0.15 mm. The front end is elongated in the form of a proboscis, at the end of which the mouth opening is placed. The ciliary apparatus is represented by two corollas of cilia (Fig. 96). Didinius swims quickly in the water, often changing direction. The preferred food of the didinia is shoe ciliates. In this case, the predator is smaller than its prey. Didinius penetrates into the prey with a trunk, and then, gradually expanding the mouth opening more and more, swallows the shoe whole! In the proboscis there is a special, so-called rod, apparatus. It consists of a number of elastic strong sticks located in the cytoplasm along the periphery of the proboscis. It is believed that this apparatus increases the strength of the walls of the proboscis, which does not burst when swallowing such a huge prey as compared to didinium, like a shoe. Didinius is an example of an extreme case of predation among protozoa. If we compare didinium swallowing its prey - shoes - with predation in higher animals, then it is difficult to find similar examples.
Didinius, swallowing paramecia, of course, swells very much. The digestion process is very fast, at room temperature it takes only about two hours. Then the undigested remains are thrown out and the didinium begins to hunt for another victim. Special studies have found that the daily "diet" of didinium is 12 shoes - a truly colossal appetite! It must be borne in mind that in the intervals between the next "hunts" didinia sometimes divide. With a lack of food, didinia are very easily enccoted and just as easily come out of the cysts again.
Herbivorous ciliates
Much less often than predation, "pure vegetarianism" is found among ciliates - eating exclusively plant foods. One of the few examples of ciliates-"vegetarians" can serve as representatives kind of nassula (Nassula). Their food object is filamentous blue-green algae (Fig. 97). They penetrate into the endoplasm through the mouth, located on the side, and then are twisted by the infusoria into a tight spiral, which is gradually digested. Algae pigments partially enter the cytoplasm of the ciliates and stain it in a bright dark green color.
Suvoyka (Vorticella nebulifera)
An interesting and rather large group of ciliates in terms of the number of species are sessile forms attached to the substrate, forming detachment of round-mouthed (Peritricha). Suvoyki (species of the genus Vorticella) are widespread representatives of this group.
Suvoys remind graceful flower like a bell or lily of the valley, sitting on a long stalk, which is attached to the substrate with its end. The suvoyka spends most of its life in a state attached to the substrate.
Consider the structure of the body of ciliates. In different species, their sizes vary over a fairly wide range (up to about 150 microns). The oral disc (Fig. 98) is located on an expanded anterior part of the body, which is completely devoid of cilia. The ciliary apparatus is located only along the edge of the mouth ( peristomal) disk (Fig. 98) in a special groove, outside of which a roller (peristomal lip) is formed. Three ciliated membranes run along the edge of the roller, two of which are located vertically, one (outer) is horizontal. They form somewhat more than one full turn of the helix. These membranes are in constant flickering motion, directing the flow of water to the mouth opening. The oral apparatus begins rather deeply with a funnel at the edge of the peristomal field (Fig. 98), in the depth of which there is an oral opening leading to a short pharynx. Suvoys, like shoes, feed on bacteria. Their mouth opening is constantly open, and there is a continuous flow of water towards the mouth.
One contractile vacuole without adductor canals is located near the mouth opening. The macronucleus has a ribbon-like or sausage-like shape, closely adjacent to it is a single small micronucleus.
Suvoyka is able to sharply shorten the stalk, which in a fraction of a second is twisted with a corkscrew. At the same time, the body of the ciliate also contracts: the peristomal disc and membranes are drawn inward and the entire anterior end closes.
The question naturally arises: since the suvoys are attached to the substrate, in what way is their settlement in the reservoir carried out? This occurs through the formation of a free-floating stage - a vagrant. At the posterior end of the ciliate body, a corolla of cilia appears (Fig. 99). At the same time, the peristomal disc retracts inward and the ciliate separates from the stalk. The resulting tramp is able to swim for several hours. The events are then played out in reverse order: the ciliate attaches to the substrate with its posterior end, the stalk grows, the posterior corolla of cilia is reduced, the peristomal disc straightens at the anterior end, and the adoral membranes begin to work. The formation of vagrants in suvoyka is often associated with the process of asexual reproduction. The infusoria on the stalk divides, and one of the daughter individuals (and sometimes both) becomes a tramp and swims away.
Many types of suwoks are capable of encysting under adverse conditions.
Among the sessile ciliates belonging to the group of round-ciliated, only relatively few species, like the suwoks discussed above, are solitary living forms. Most of the species included here are colonial organisms.
Usually coloniality occurs as a result of incomplete asexual or vegetative reproduction. The individuals formed as a result of reproduction, to a greater or lesser extent, retain connection with each other and together form an organic individuality of a higher order, uniting large quantities individual individuals, which gets the name of the colony (we have already met with examples of colonial organisms in class of flagellates .).
Colonies of round-ciliated ciliates are formed as a result of the fact that separated individuals do not turn into vagrants, but keep in touch with each other with the help of stalks (Fig. 100). At the same time, the main stem of the colony, as well as its first branches, cannot be attributed to any of the individuals, but belongs to the entire colony as a whole. Sometimes the colony consists of only a small number of individuals, while in other species of ciliates, the number of individual individuals of the colony can reach several hundred. However, the growth of any colony is not unlimited. Upon reaching the dimensions characteristic of this species, the colony ceases to increase and the individuals formed as a result of division develop a corolla of cilia, become vagrants and swim away, giving rise to new colonies.
Colonies of round-ciliated ciliates are of two types. In some, the stalk of the colony is irreducible: when irritated, only individual individuals of the colony contract, drawing in the pinnate, but the entire colony as a whole does not undergo changes (this type of colony includes, for example, the genera Epistylis, Opercularia). In others (for example, the genus Carchesium), the stalk of the entire colony is able to contract, since the cytoplasm passes through all the branches and thus connects all the individuals of the colony to each other. When such colonies are irritated, they shrink entirely. The whole colony in this case reacts as a whole, as an organic individuality.
Among all colonial ciliated ciliates, zootamnia (Zoothamnium arbuscula) is of particular interest. The colonies of this ciliate are distinguished by a special regularity of the structure. In addition, an interesting biological phenomenon of polymorphism is outlined here within the colony.
The zootamnia colony looks like an umbrella. On one, main, stalk of the colony are secondary branches (Fig. 101). The size of an adult colony is 2-3 mm, so they are clearly visible with the naked eye. Zootamnii live in small ponds with clean water. Their colonies are usually found on underwater plants, most often on elodea (water plague).
The stalks of the zootamnia colony are contractile, since the contractile cytoplasm passes through all the branches of the colony, with the exception of the basal part of the main stalk. With a reduction that occurs very quickly and abruptly, the entire colony gathers into a lump.
Zootamnia is characterized by a strictly regular arrangement of branches. One main stem is attached to the substrate. Nine main branches of the colony depart from its upper part in a plane perpendicular to the stalk, strictly regularly located relative to each other (Fig. 102, 6). Secondary branches extend from these branches, on which individual individuals of the colony sit. Each secondary branch can have up to 50 ciliates. The total number of individuals in the colony reaches 2-3 thousand individuals.
Most of the individuals of the colony in their structure resemble small single suvoiks, 40-60 microns in size. But in addition to small individuals, which are called microzoids, on adult colonies, approximately in the middle of the main branches, individuals of a completely different type and size develop (Fig. 102, 5). These are large spherical individuals with a diameter of 200-250 microns, exceeding the volume of the microzoid by a hundred or more times in mass. Large individuals are called macrozoids.
In their structure, they differ significantly from small individuals of the colony. Their peristome is not expressed: it is drawn inward and does not function. From the very beginning of its development from a microzoid, a macrozoan ceases to take food on its own. It lacks digestive vacuoles. The growth of the macrozoid is apparently carried out at the expense of substances that enter through the cytoplasmic bridges connecting all the individuals of the colony to each other. In the part of the body of the macrozoid, with which it is attached to the stalk, there is an accumulation of special grains (granules), which, as we will see, play a significant role in its further fate. What are these large spherical macrozoids, what is their biological role in the life of a zootamnia colony? Observation shows that macrozoids are future vagrants from which new colonies develop. Reaching size limit, the macrozoid develops a corolla of cilia, separates from the colony, and swims away. At the same time, its shape changes somewhat, from spherical it becomes conical. After some time, the tramp is always attached to the substrate with the side on which the granularity is located. The formation and growth of the stalk immediately begins, and granules are spent on the construction of the stalk, which are localized at the posterior end of the vagrant. As the stem grows, the graininess disappears. After the stalk reaches the final length characteristic of zootamnia, a series of rapidly successive divisions begins, leading to the formation of a colony. These divisions are made in a strictly defined sequence (Fig. 102). We will not dwell on the details of this process. Let us only pay attention to the following interesting phenomenon. During the first divisions of zootamnia tramps, during the development of a colony in the forming individuals, the pinnate and mouth do not function. Feeding begins later, when the young colony already consists of 12-16 individuals. Thus, all the first stages of colony development are carried out exclusively at the expense of those reserves that were formed in the body of the macrozoid during its growth and development on the mother colony. There is an undeniable similarity between the development of zootamnia vagrant and the development of the egg in multicellular animals. This similarity is expressed in the fact that development in both cases is carried out at the expense of previously accumulated reserves, without the perception of food from the external environment.
When studying sessile ciliary ciliates, the question arises: how is the form of the sexual process characteristic of ciliates carried out in them - conjugation? It turns out that in connection with a sedentary lifestyle, it undergoes some significant changes. By the beginning of the sexual process, special, very small vagrants are formed on the colony. Actively moving with the help of a corolla of cilia, they crawl for some time along the colony, and then come into conjugation with large normal sedentary individuals of the colony. Thus, the differentiation of conjugants into two groups of individuals occurs here: small, mobile (microconjugants) and larger, immobile (macroconjugants). This differentiation of conjugants into two categories, of which one (microconjugants) is mobile, was necessary fixture to a sedentary lifestyle. Without this, the normal course of the sexual process (conjugation) could obviously not be ensured.
Sucking ciliates (Suctoria)
A very peculiar group in terms of the way they eat is represented by sucking ciliates(Suctoria). These organisms, like suvoyka and other ciliated ciliates, are sessile. The number of species belonging to this order is measured by several dozen. The body shape of sucking ciliates is very diverse. Some of their characteristic species are shown in Figure 103. Some sit on the substrate on more or less long stalks, others do not have stalks, in some the body branches quite strongly, etc. However, despite the variety of forms, all sucking ciliates are characterized by the following two features : 1) the complete absence (in adult forms) of the ciliary apparatus, 2) the presence of special appendages - tentacles that serve to suck out prey.
In different types of sucking ciliates, the number of tentacles is not the same. Often they are gathered in groups. With a high magnification of the microscope, it can be seen that at the end of the tentacle is equipped with a small club-shaped thickening.
How do tentacles function? It is not difficult to answer this question by observing sucking ciliates for some time. If some small protozoan (flagellate, ciliate) touches the tentacle of the suk-torii, then it will instantly stick to it. All attempts by the victim to break away are usually in vain. If you continue to observe the prey stuck to the tentacles, you can see that it gradually begins to decrease in size. Its contents through the tentacles are gradually "pumped" into the endoplasm of the sucking ciliate until only one pellicle remains from the victim, which is discarded. Thus, the tentacles of sucking ciliates are completely unique, nowhere else in the animal world are organs for trapping and at the same time sucking food (Fig. 103).
Sucking ciliates are motionless predators that do not chase prey, but instantly catch it, if only careless prey touches them itself.
Why do we refer these peculiar organisms to the class of ciliates? At first glance, they have nothing to do with them. The following facts speak about the belonging of suctoria to ciliates. Firstly, they have a nuclear apparatus typical of ciliates, consisting of a macronucleus and a micronucleus. Secondly, during reproduction, they develop cilia that are absent in "adult" individuals. Asexual reproduction and, at the same time, the resettlement of sucking ciliates is carried out by the formation of vagrants, equipped with several annular corollas of cilia. The formation of vagrants in suctoria can occur in different ways. Sometimes they are formed as a result of not quite uniform division (budding), in which each kidney that separates outwards receives a macronucleus segment and one micronucleus (Fig. 104, L). On one maternal individual, several daughter buds can form at once (Fig. 104, B). In other species (Fig. 104, D, E), a very peculiar method of "internal budding" is observed. At the same time, a cavity is formed inside the body of the mother suctory, in which the tramp kidney is formed. It comes out through special openings, through which it "squeezes" with known difficulty.
This development of the embryo inside the mother's body, and then the act of childbearing, is an interesting analogy of the simplest with what happens in higher multicellular organisms.
On the previous pages, several typical free-living representatives of the ciliate class have been considered, differently adapted to different conditions environment. It is interesting to approach the issue of adapting ciliates to living conditions and, on the other hand, to see what are the characteristic common features of ciliates living in certain, sharply defined environmental conditions.
As an example, let's take two very sharply different habitats: life in the composition of plankton and life on the bottom in the thickness of the sand.
Planktonic ciliates
In the composition of both marine and freshwater plankton, quite big number types of ciliates.
The features of adaptations to life in the water column are especially pronounced in radiolarian. The main line of adaptation to the planktonic way of life is reduced to the development of such structural features that contribute to the soaring of the organism in the water column.
A typical planktonic, moreover, almost exclusively marine family of ciliates is tintinnids(Tintinnidae, Fig. 105.5). The total number of species known so far tintinnid about 300. These are small forms, characterized by the fact that the protoplasmic body of the ciliate is placed in a transparent, light and at the same time strong house, consisting of organic matter. A disc protrudes from the house, carrying a corolla of cilia, which are in constant flickering motion. In the state of hovering infusoria in the water column, it is mainly supported by the constant active work of the ciliary apparatus. The house, obviously, performs the function of protecting the lower body of the ciliate. Only 2 species of tintinnids live in fresh water (not counting 7 species characteristic only of Lake Baikal).
Freshwater ciliates have some other adaptations to life in plankton. In many of them, the cytoplasm is very strongly vacuolated (Loxodes, Condylostoma, Trachelius), so that it resembles foam. This leads to a significant reduction in specific gravity. All of the listed ciliates, in addition, have a ciliary cover, thanks to which the body of the ciliate, in terms of specific gravity only slightly exceeding the specific gravity of water, is easily maintained in a state of "floating". In some species, the shape of the body contributes to an increase in the specific surface area and facilitates soaring in the water. For example, some planktonic ciliates of Lake Baikal resemble an umbrella or a parachute in shape (Liliomorpha, Fig. 105.1). There is one planktonic sucking ciliate in Lake Baikal (Mucophrya pelagica, Fig. 105.4), which differs sharply from its sessile relatives. This species is devoid of a stem. Its protoplasmic body is surrounded by a wide slimy sheath, an adaptation leading to weight reduction. Long thin tentacles stick out, which, along with their direct function, probably also perform another one - an increase in the specific surface area, which contributes to soaring in water.
Finally, it is necessary to mention one more, so to speak, indirect form of adaptation of ciliates to life in plankton. This is the attachment of small ciliates to other organisms that lead a planktonic lifestyle. Yes, among circumciliated ciliates(Peritricha) there are fairly numerous species that attach themselves to planktonic copepods. This is a normal and normal way of life for these types of ciliates.
Along with round-ciliated ciliates and among sucking (Suctoria) there are species that settle on planktonic organisms.
ciliates living in the sand
Sandy beaches and shoals represent an extremely peculiar habitat. Along the coast of the seas, they occupy vast spaces and are characterized by a peculiar fauna.
Carried out for last years Numerous studies in various countries have shown that many sea sands are very rich in diverse microscopic or microscopic fauna. Between the sand particles there are numerous small and tiny spaces filled with water. It turns out that these spaces are richly populated by organisms belonging to the most diverse groups of the animal world. Dozens of species of crustaceans, annelids, roundworms, especially numerous flatworms, some mollusks, coelenterates live here. AT in large numbers here there are also protozoa, mainly ciliates. According to modern data, the fauna of ciliates inhabiting the thickness of sea sands includes approximately 250-300 species. If we keep in mind not only ciliates, but also other groups of organisms inhabiting the thickness of the sand, then the total number of their species will be very large. The whole set of animals that inhabit the thickness of the sand, living in the smallest gaps between the grains of sand, is called psammophilic fauna.
The richness and species composition of the psammophilic fauna is determined by many factors. Among them, the particle size of the sand is of particular importance. Coarse-grained sands have poor fauna. The fauna of very fine-grained silty sands (with a particle diameter of less than 0.1 mm) is also poor, where, obviously, the gaps between the particles are too small for animals to live in them. The sands richest in life are medium- and fine-grained.
The second factor that plays an important role in the development of the psammophilic fauna is the richness of sand in organic remains and decomposing organic matter (the so-called degree of saprobity). Sands devoid of organic matter are poor in life. On the other hand, sands are also almost lifeless and are very rich in organic matter, since the decay of organic matter leads to oxygen depletion. Often, anaerobic hydrogen sulfide fermentation is added to this.
The presence of free hydrogen sulfide is an extremely negative factor affecting the development of fauna.
A fairly rich flora of unicellular algae (diatoms, peridiniums) sometimes develops in the surface layers of sand. This is a factor that favors the development of psammophilic fauna, since many small animals (including ciliates) feed on algae.
Finally, a factor that has a very negative effect on the psammophilic fauna is the surf. This is quite understandable, since the surf, washing over the upper layers of sand, kills all living things here. The psammophilic fauna is the richest in sheltered, well-heated coves. Ebb and flow do not prevent the development of psammophilic fauna. When the water temporarily leaves at low tide, exposing the sand, then in the thickness of the sand, in the intervals between the grains of sand, it remains, and this does not prevent the existence of animals.
In ciliates, which are part of the psammophilous fauna and belong to various systematic groups (orders, families), many common features are developed in the process of evolution, which are adaptations to the peculiar conditions of existence between sand particles.
Figure 106 shows some species of the psammophilic fauna of ciliates belonging to different orders and families. There are many similarities between them. The body of most of them is more or less strongly elongated in length, worm-like. This makes it easy to "squeeze" into the smallest holes between the grains of sand. In very many species (Fig. 106) the elongation of the body is combined with its flattening. The ciliary apparatus is always well developed, which allows active, with a certain force, to move in narrow gaps. Quite often, cilia develop on one side of the worm-like flattened body, the opposite side is bare. This feature is probably associated with the ability, which is pronounced in most psammophilous species, to stick (attach) to the substrate very closely and very firmly through the ciliary apparatus (a phenomenon called thigmotaxis). This property allows animals to remain in place when currents of water arise in the narrow gaps where they live. In this case, it is probably more advantageous for the side opposite to that on which the animal attached itself to the substrate to be smooth.
What do psammophilic ciliates eat? A significant part of the "diet" in many species is algae, especially diatoms. Bacteria serve them to a lesser extent as food. It also depends to a large extent on the fact that there are few bacteria in sands that are not heavily polluted. Finally, especially among the largest psammophilous ciliates, there are a considerable number of predatory forms that eat other ciliates belonging to smaller species. Psammophilic ciliates are apparently widespread everywhere.
Ciliates apostomata
ciliates spirophria(Spirophrya subparasitica) in an encysted state can often be found sitting on a small stalk on small planktonic marine crustaceans (especially often on crustaceans of the genus Idia). While the crustacean actively swims in sea water, the spirophria sitting on it do not undergo any changes. For further development ciliates, it is necessary that the crustacean be eaten by a marine hydroid polyp, which happens often (Fig. 107). As soon as the cysts of spirophria, together with the crustacean, enter the digestive cavity, small ciliates immediately come out of them, which begin to vigorously feed on the food slurry formed as a result of the digestion of the swallowed crustacean. Within an hour, the size of the infusoria increases by 3-4 times. However, reproduction does not occur at this stage. Before us is a typical growth stage of ciliates, which is called a trophont. After some time, together with undigested food residues, the trophont is thrown out by the polyp into the sea water. Here, actively swimming, it descends along the body of the polyp to its sole, where it attaches itself, being surrounded by a cyst. This stage of an encysted, large ciliate sitting on a polyp is called a tomont. This is the breeding phase. Tomont does not feed, but quickly divides several times in succession (Fig. 107, 7). The result is a whole group of very small ciliates. Their number depends on the size of the tomont, which in turn is determined by the size of the trophont that gave it its origin. Small ciliates formed as a result of the division of the tomont (they are called tomites or tramps), represent the stage of settling. They come out of the cyst, swim quickly (without eating at the same time, but using the reserves they have in the cytoplasm). If they are "lucky" to come across a copepod, they immediately attach themselves to it and become encysted. This is the stage from which we began our consideration of the cycle.
In the life cycle of spirophria we have considered, a sharp delineation of stages that have different biological significance attracts attention. Trophon is the growth stage. It only grows, accumulates a large amount of cytoplasm and all kinds of reserve substances due to energetic and fast food. The trophont is not capable of reproduction. The reverse phenomenon is observed in the tomont - inability to feed and vigorous rapid reproduction. After each division, there is no growth, and therefore the reproduction of the tomont is reduced to a rapid decay into many vagrants. Finally, vagrants perform their special and only characteristic function: they are individuals - settlers and distributors of the species. They are unable to eat or reproduce.
Life cycle of ichthyophthirius
By the end of the growth period, ichthyophthirius, compared with vagrants, reaches a very large size: 0.5-1 mm in diameter. Upon reaching the limit value, the ciliates actively move out of the tissues of the fish into the water and slowly swim for some time with the help of the ciliary apparatus covering their entire body. Soon, large ichthyophthirius settle on some underwater object and secrete a cyst. Immediately after encysting, successive divisions of the ciliates begin: first in half, then each daughter individual is divided again into two, and so on up to 10-11 times. As a result, up to 2000 small, almost rounded individuals covered with cilia are formed inside the cyst. Inside the cyst, vagrants are actively moving. They pierce the shell and come out. Actively swimming vagrants infect new fish.
The rate of division of ichthyophthirius in cysts, as well as the rate of its growth in fish tissues, depends to a large extent on temperature. According to studies by various authors, the following figures are given: at 26-27°C, the development of vagrants in a cyst takes 10-12 hours, at 15-16°C it takes 28-30 hours, at 4-5°C it lasts for 6 -7 days.
The fight against ichthyophthirius presents significant difficulties. Of primary importance here are preventive measures aimed at preventing free-swimming vagrants from penetrating the tissues of the fish. To do this, it is useful to carry out frequent transplantation of sick fish into new reservoirs or aquariums, to create flow conditions, which is especially effective in the fight against ichthyophthirius.
ciliates trichodina
The whole system of adaptations of trichodins to life on the surface of the host is aimed at not breaking away from the host's body (which is almost always tantamount to death), while maintaining mobility. These devices are very perfect. The body of most trichodinas is in the form of a rather flat disk, sometimes a cap. The side facing the body of the host is slightly concave, it forms an attachment sucker. Along the outer edge of the sucker there is a corolla of well-developed cilia, with the help of which the movement (crawling) of the ciliates mainly occurs on the surface of the body of the fish. This corolla corresponds to the corolla found in vagrants of the sessile round-ciliated ciliates discussed above. Thus, trichodina can be compared with a tramp. On the abdominal surface (on the sucker), trichodins have a very complex supporting and attachment apparatus, which helps to keep the ciliates on the host. Without going into the details of its structure, we note that its basis is a ring of complex configuration, consisting of separate segments bearing external and internal teeth (see Fig. 109, B). This ring forms an elastic and at the same time strong basis of the abdominal surface, which acts as a sucker. Different types of trichodin differ from each other in the number of segments that form the ring, and in the configuration of the outer and inner hooks.
On the side of the body of trichodina opposite from the disk, there is a pinnate and oral apparatus. Its structure is more or less typical of circumciliated ciliates. Clockwise-twisted adoral membranes lead to a recess at the bottom of which is the mouth. The nuclear apparatus of trichodin is typically arranged for ciliates: one ribbon-like macronucleus and one micronucleus located next to it. There is one contractile vacuole.
Trichodins are widely distributed in reservoirs of all types. Especially often they are found on fry of different species of fish. With mass reproduction, trichodins are applied great harm fish, especially if the masses cover the gills. This disrupts the normal breathing of the fish.
In order to clean fish from trichodins, it is recommended to do therapeutic baths from a 2% solution of sodium chloride or a 0.01% solution of potassium permanganate (for fry - within 10-20 minutes).
ciliates intestinal tract ungulates
From the scar through the mesh, food is burped into the oral cavity, where it is additionally chewed (chewing gum). The chewed food mass swallowed again through a special tube formed by the folds of the esophagus no longer goes to the scar, but to the book and from there to the abomasum, where it is exposed to the digestive juices of the ruminant. In the rennet, under conditions of an acidic reaction and the presence of digestive enzymes, ciliates die. Getting there with chewing gum, they are digested.
The number of protozoa in the rumen (as well as in the net) can reach colossal values. If you take a drop of the contents of the scar and examine it under a microscope (when heated, since ciliates stop at room temperature), then ciliates literally swarm in the field of view. It is difficult even in culture to obtain such a mass of ciliates. The number of ciliates in 1 cm 3 of the contents of the scar reaches a million, and often more. In terms of the entire volume of the scar, this gives truly astronomical figures! The richness of the contents of the rumen with ciliates depends to a large extent on the nature of the food of the ruminant. If the food is rich in fiber and poor in carbohydrates and proteins (grass, straw), then there are relatively few ciliates in the rumen. When carbohydrates and proteins (bran) are added to the diet, the number of ciliates increases dramatically and reaches huge numbers. It must be borne in mind that there is a constant outflow of ciliates. Getting together with the chewing gum into the abomasum, they die. A high level of the number of ciliates is maintained by their vigorous reproduction.
Odd-toed ungulates (horse, donkey, zebra) also have a large number of ciliates in the alimentary tract, but their localization in the host is different. Odd-toed ungulates do not have a complex stomach, due to which the possibility of developing protozoa in the anterior sections of the alimentary tract is absent. But in equids, the large and caecum are very well developed, which are usually clogged with food masses and play an essential role in digestion. In this section of the intestine, just as in the rumen and mesh of ruminants, a very rich fauna of protozoa develops, mainly ciliates, most of which also belong to the order of endodiniomorphs. However, in terms of species composition, the fauna of the rumen of ruminants and the fauna of the large intestine of equids do not coincide"
Infusoria of the intestinal tract of ruminants
Of greatest interest are ciliates ofrioscolecid family (Ophryoscolecidae), related to order endodiniomorph . A characteristic feature of this detachment is the absence of a continuous ciliary cover. Complex ciliary formations - cirres - are located at the front end of the body of ciliates in the region of the mouth opening. To these basic elements of the ciliary apparatus, additional groups of cirrhae can be added, located either at the anterior or posterior end of the body. The total number of species of ciliates of the ofrioscolecid family is about 120.
Figure 110 shows some of the most typical representatives ofrioscolecid from the rumen of ruminants. The ciliates of the genus Entodinium (Entodinium, Fig. 110, A) are most simply arranged. At the anterior end of their body there is one perioral zone of cirrhus. The front end of the bodies, on which the mouth opening is located, can be drawn inward. Ectoplasm and endoplasm are sharply demarcated. The anal tube is clearly visible at the posterior end, which serves to remove undigested food residues. Somewhat more complex structure anoplodynia(Anoplodinium, Fig. 110, B). They have two zones of the ciliary apparatus - perioral cirrhi and dorsal cirrhi. Both are located at the front end. At the posterior end of the body of the species shown in the figure, there are long sharp outgrowths - this is quite typical for many species of ofrioscolecids. It has been suggested that these outgrowths contribute to the "pushing" of ciliates between plant particles that fill the scar.
Kinds Genus Eudiplodynia (Eudip-lodinium, Fig. 110, B) are similar to anoplodynia, but, unlike them, have a skeletal base plate located along the right edge along the pharynx. This skeletal plate consists of a substance similar in chemical nature to fiber, that is, to the substance that makes up the shells of plant cells.
At genus polyplastron (Polyplastron, Fig. 110, D, E) there is a further complication of the skeleton. The structure of these ciliates is close to eudiplodynia. The differences boil down primarily to the fact that instead of one skeletal plate, these ciliates have five. Two of them, the largest, are located on the right side, and three, smaller ones, are on the left side of the ciliate. The second feature of the polyplastron is an increase in the number of contractile vacuoles. Entodynia has one contractile vacuole, anoplodynia and eudiplodynia have two contractile vacuoles, and polyplastron has about a dozen of them.
At epidinium(Epidinium, Fig. 110), which have a well-developed carbohydrate skeleton located on the right side of the body, the dorsal zone of the cirrhus shifts from the anterior end to the dorsal side. Spines often develop at the posterior end of ciliates of this genus.
The most complex structure reveals genus Ofrioscolex (Ophryoscolex), after which the whole family of ciliates is named (Fig. 110, E). They have a well-developed dorsal zone of cirrhus, covering about 2/3 of the circumference of the body and skeletal plates. Numerous spines are formed at the posterior end, of which one is usually especially long.
Acquaintance with some typical representatives ofrioscolecid shows that within this family there has been a significant complication of organization (from entodynia to ofrioscolex).
In addition to ciliates ofrioscolecid family , in the rumen of ruminants, representatives of the already known to us are found in small quantities. detachment of isociliary ciliates . They are represented by a small number of species. Their body is evenly covered with longitudinal rows of cilia, skeletal elements are absent. In the total mass of the ciliate population of the rumen, they do not play a significant role, and therefore we will not dwell on them here.
What and how do ciliates ofrioscolecides eat? This issue has been studied in detail by many scientists, especially in detail by Professor V. A. Dogel.
Ofrioscolecid food is quite diverse, and a certain specialization is observed in different species. The smallest species of the genus Entodynia feed on bacteria, starch grains, fungi and other small particles. Very many medium and large ofrioscolecids absorb particles of plant tissues, which make up the bulk of the contents of the rumen. The endoplasm of some species is literally clogged with plant particles. You can see how ciliates pounce on scraps of plant tissues, literally tear them into pieces and then swallow them, often twisting them into a spiral in their body (Fig. 111, 4). Sometimes it is necessary to observe such pictures (Fig. 111, 2), when the body of the ciliate itself is deformed due to swallowed large particles.
In ofrioscolecid, predation is sometimes observed. Larger species devour smaller ones. Predation (Fig. 112) is combined with the ability of the same species to feed on plant particles.
How do ciliates enter the rumen of a ruminant? What are the routes of infection with ofrioscolecides? It turns out that newborn ruminants do not yet have ciliates in the rumen. They are also absent while the animal is feeding on milk. But as soon as the ruminant switches to plant food, ciliates immediately appear in the scar and mesh, the number of which is growing rapidly. Where do they come from? Long time It was assumed that ciliates of the rumen form some kind of resting stages (most likely, cysts), which are widely dispersed in nature and, when swallowed, give rise to active stages of ciliates. Further studies have shown that ruminant ciliates do not have any resting stages. It was possible to prove that infection occurs with active mobile ciliates that penetrate the oral cavity when burping the cud. If you examine a chewing gum taken from the oral cavity under a microscope, then it always contains a large number of actively floating ciliates. These active forms can easily penetrate into the mouth and further into the rumen of other ruminants from a common vessel for drinking, along with grass, hay (which may contain saliva with ciliates), etc. This route of infection has been proven experimentally.
If the resting stages are absent in ofrioscolecids, then it is obviously easy to obtain "infusor-free" animals by isolating them while they are still feeding on milk. If direct contact is not allowed between growing young and ruminants with ciliates, then young animals may be left without ciliates in the rumen. Such experiments were carried out by several scientists in different countries. The result was clear. In the absence of contact between young animals (milk taken from their mother during the period of feeding) and ruminants with ciliates in the rumen, animals grow up sterile in relation to ciliates. However, even short-term contact with animals with ciliates (a common feeder, a common bucket for drinking, a common pasture) is enough for ciliates to appear in the rumen of sterile animals.
Above were the results of experiments on the content of ruminants, completely devoid of ciliates in the rumen and net. This is achieved, as we have seen, by early isolation of the young. Experiments were carried out on sheep and goats.
In this way, it was possible to observe animals "without ciliates" for a considerable period of time (over a year). How does the absence of ciliates in the rumen affect the life of the host? Does the absence of ciliates affect the host negatively or positively? To answer this question, the following experiments were carried out on goats. Twin kids (of the same litter and same sex) were taken in order to have more similar material. Then one of the twins of this pair was brought up without ciliates in the rumen (early isolation), while the other from the very beginning of feeding on plant foods was abundantly infected with many types of ciliates. Both received exactly the same diet and were brought up in the same conditions. The only difference between them was the presence or absence of ciliates. On several pairs of kids studied in this way, no differences were found in the course of development of both members of each pair ("infusor" and "without infusor"). Thus, it can be argued that ciliates living in the rumen and the net do not have any sharp effect on the vital functions of the host animal.
The above results of the experiments do not allow, however, to assert that the ciliates of the rumen are completely indifferent to the owner. These experiments were carried out with a normal diet of the host. It is possible that under other conditions, with a different diet (for example, with insufficient feeding), it will be possible to reveal the effect on the host of the fauna of the protozoa inhabiting the rumen.
Various suggestions have been made in the literature about the possible positive influence of the protozoan fauna of the rumen on the digestive processes of the host. It was pointed out that many millions of ciliates, actively swimming in the rumen and crushing plant tissues, contribute to the fermentation and digestion of food masses located in the anterior sections of the digestive tract. A significant number of ciliates, which enter the abomasum along with the chewing gum, are digested, and the protein, which makes up a significant part of the body of the ciliates, is absorbed. Infusoria, therefore, can be an additional source of protein for the host. It has also been suggested that ciliates contribute to the digestion of fiber, which makes up the bulk of the food of ruminants, and its transfer to a more digestible state.
All of these assumptions are not proven, and objections have been raised against some of them. It was pointed out, for example, that ciliates build the protoplasm of their body from proteins that enter the rumen with the food of the host. By ingesting vegetable protein, they convert it into the animal protein of their body, which is then digested in the abomasum. Whether this provides any benefit to the host remains unclear. All these questions are of great practical interest, since we are talking on the digestion of ruminants - the main objects of animal husbandry. Further research on the role of rumen ciliates in ruminant digestion is highly desirable.
Ofrioscolecides of ruminants have, as a rule, a wide specificity. In terms of species, the population of the scar and net of cattle, sheep, and goats is very close to each other. If we compare the species composition of the rumen of African antelopes with cattle, then here, too, about 40% of total number species will be common. However, there are many species of ofrioscolecid that are found only in antelopes or only in deer. Thus, against the background of the general broad specificity of ofrioscolecides, one can speak of separate, more narrowly specific types of them.
Infusoria of the intestines of equids
Let us now turn to a brief acquaintance with the ciliates inhabiting the large and caecum of equids.
In terms of species, this fauna, like the fauna of the rumen of ruminants, is also very diverse. Currently, about 100 species of ciliates living in the large intestine of animals have been described. horse family . The ciliates found here in the sense of their belonging to different systematic groups are more diverse than the ciliates of the rumen of ruminants.
In the intestines of horses, there are quite a few species of ciliates belonging to the order of isociliary, i.e., ciliates in which the ciliary apparatus does not form membranella or cirrhosis near the oral zone (Fig. 113, 1).
Order entodyniomorph (Entodiniomorpha) is also richly represented in the intestines of the horse. While only one family of endodiniomorphs (ofrioscolecid family) is found in the rumen of ruminants, representatives of three families live in the intestines of a horse, but we will not dwell on the characteristics of which here, limiting ourselves to only a few drawings of typical horse species (Fig. 113) .
Detailed studies by A. Strelkov showed that different types of ciliates are far from evenly distributed along the horse's large intestine. There are two different groups of species, two faunas, as it were. One of them inhabits the caecum and the abdominal section of the large colon (the initial sections of the large intestine), and the other - the dorsal section of the large colon and the small colon. These two complexes of species are rather sharply demarcated. There are few species common to these two sections - less than a dozen.
It is interesting to note that among the numerous species of ciliates inhabiting the large intestine of equids, there are representatives of one genus related to sucking ciliates. As we saw above, sucking ciliates(Suctoria) are typical free-living sessile organisms with a very special way of feeding with the help of tentacles (see Fig. 103). One of the genera of suctoria has adapted to such a seemingly unusual habitat as the large intestine of a horse, for example, several species allantosis(Allantosoma). These very peculiar animals (Fig. 114) do not have a stalk, cilia are absent, club-shaped tentacles thickened at the ends are well developed.
With the help of tentacles, allantosomes stick to different types of ciliates and suck them out. Often, the prey is many times greater than the predator.
The question of the nature of the relationship between the ciliates of the large intestine of equids and their hosts is still unclear. The number of ciliates can be as high, and sometimes even more, than in the rumen of ruminants. There is data showing that the number of ciliates in the large intestines of a horse can reach 3 million in 1 cm 3. The symbiotic significance suggested by some scientists is even less likely than for rumen ciliates.
The most likely opinion is that they cause some harm to the host, absorbing a significant amount of food. Part of the ciliates is taken out - out with fecal masses, and thus the organic substances (including protein) that make up their body remain unused by the owner.
Balantidia captures a variety of food particles from the contents of the large intestine. Especially willingly, he feeds on starch grains. If balantidia lives in the lumen of the human colon, then it feeds on the contents of the intestine and does not exert any harmful influence. This is a typical "carriage", which we met already when considering dysenteric amoeba. However, balantidia is less likely than the dysenteric amoeba to remain such a "harmless tenant."
At present, specialists have well developed various methods, allowing the cultivation of balantidia in an artificial environment - outside the host organism.
As can be seen from the figure, troglodytella is one of the complex endodiniomorphs. She, in addition to the perioral zone of cirrhosis (at the anterior end of the body), has three more zones of well-developed cirrhi, annularly covering the body of the ciliate. Trogloditells have a well-developed skeletal apparatus consisting of carbohydrates, covering almost the entire anterior end of the body. The sizes of these peculiar ciliates are quite significant. In length, they reach 200-280 microns.
Supporting skeletal formations develop mainly at the anterior end of the body, which has to experience mechanical stress and overcome obstacles, pushing through the intestinal lumen between food particles. Species genus radiophria (Radiophrya) at the anterior end on one side of the body (which is conventionally considered the abdominal side) there are very strong elastic ribs (spicules) lying in the surface layer of the ectoplasm (Fig. 117, C, D, E). Species Genus Menilella (Mesnilella) there are also supporting rays (spicules), which for most of their length lie in the deeper layers of the cytoplasm (in the endoplasm, Fig. 117, A). Similarly arranged supporting formations are also developed in species of some other genera Astomat.
asexual reproduction in some ciliates, astomat proceeds in a peculiar way. Instead of the transverse division in two, which is characteristic of most ciliates, many astomats have an uneven division ( budding). At the same time, the kidneys that separate at the posterior end remain associated with the mother individual for some time (Fig. 117, B). As a result, chains are obtained, consisting of an anterior large and posterior smaller individuals ( kidney). In the future, the kidneys gradually separate from the chain and move on to independent existence. This peculiar form of reproduction is widespread, for example, in radiophria already known to us. The chains of some astomats resulting from budding resemble in appearance the chains of tapeworms. Here again we encounter the phenomenon of convergence.
The nuclear apparatus of the astomat has a structure characteristic of ciliates: a macronucleus, most often of a ribbon-like shape (Fig. 117), and one micronucleus. Contractile vacuoles are usually well developed. Most species have several (sometimes over a dozen) contractile vacuoles arranged in one longitudinal row.
A study of the distribution of Astomat species by different types of hosts shows that most of the Astomat species are confined to strictly defined host species. Most astomats are characterized by a narrow specificity: only one species of animal can serve as a host for them.
Despite the large number of studies devoted to the study of astomat ciliates, one very important aspect of their biology remains completely unclear: how does the transmission of these ciliates from one host individual to another occur? It has never been possible to observe the formation of cysts in these ciliates. Therefore, it is suggested that infection occurs actively - mobile stages.
intestinal ciliates sea urchins
Sea urchins are very numerous in the coastal zone of our northern (Barents) and Far Eastern seas (the Sea of Japan, the Pacific coast of the Kuril Islands). Most sea urchins feed on plant foods, mainly algae, which they scrape from underwater objects with special sharp "teeth" surrounding the mouth opening. In the intestines of these herbivorous hedgehogs there is a rich fauna of ciliates. Often they develop here in mass quantities, and the contents of the intestines of the sea urchin under the microscope are almost as "teeming" with infusoria as the contents of the rumen of ruminants. It must be said that, in addition to deep differences in the living conditions of the ciliates of the intestines of the sea urchin and the rumen of the ruminant, there are some similarities. They lie in the fact that both here and there ciliates live in an environment very rich in plant remains. Currently, over 50 species of ciliates are known to live in the intestines of sea urchins, which are found only in the coastal zone, where urchins feed on algae. At great depths, where algae no longer grow, there are no ciliates in sea urchins.
According to the way of life and the nature of nutrition, most ciliates of the intestines of sea urchins are herbivorous. They feed on algae, which in large quantities fill the intestines of the host. Some species are quite "finicky" in their choice of food. For example, strobilidium (Strobilidium, Fig. 118, A) feeds almost exclusively on large diatoms. There are also predators that eat representatives of other, smaller species of ciliates.
In ciliates from the intestines of sea urchins, unlike astomat, there is no strict confinement to certain types of hosts. They live in a wide variety of algae-eating sea urchins.
Ways of infection of sea urchins with ciliates have not been studied. However, here with a high degree of probability it can be assumed that it occurs in active free-floating forms. The fact is that ciliates from the intestines of sea urchins can live for a long time (many hours) in sea water. However, they have already adapted so much to life in the intestines of hedgehogs that outside their body, in sea water, sooner or later they die.
Finishing acquaintance with ciliates, it should be emphasized once again that they represent a rich in species, an extensive and prosperous group (class) of the animal world. Remaining at the level of cellular organization, infusoria have reached, in comparison with other classes of protozoa, the greatest complexity of structure and functions. A particularly significant role in this progressive development (evolution) was probably played by the transformation of the nuclear apparatus and the emergence of nuclear dualism (qualitative non-equivalence of nuclei). The richness of the macronucleus in nucleic substances is associated with active processes metabolism, with vigorous processes of protein synthesis of the cytoplasm and nuclei.
Conclusion
We have come to the end of our review of the structure and way of life of a vast type of animal world - protozoa. Their characteristic feature, as has been repeatedly emphasized above, is unicellularity. In terms of their structure, protozoa are cells. However, they are incomparable with the cells that make up the body of multicellular organisms, because they themselves are organisms. Thus, protozoa are organisms at the cellular level of organization. Some highly organized protozoa, possessing many nuclei, already seem to go beyond the morphological limits of the cell structure, which gives reason to some scientists to call such protozoa "supracellular". This changes little the essence of the matter, because a unicellular organization is still typical of Protozoa.
Within the limits of unicellularity, protozoa have come a long way of evolutionary development and have given a huge variety of forms adapted to the most diverse conditions of life. At the heart of the pedigree stem of the protozoa are two classes: sarcodes and flagellates. The question of which of these classes is more primitive is still being debated in science. On the one hand, the lower representatives of the Sarcodidae (ameba) have the most primitive structure. But flagellates show the greatest plasticity of the type of metabolism and stand, as it were, on the border between the animal and plant worlds. In the life cycle of some sarcodes (for example, foraminifera) there are flagellar stages (gametes), which indicates their relationship with flagellates. It is obvious that neither modern sarcods nor modern flagellates can be the initial group of evolution of the animal world, because they themselves have gone a long way in historical development and have developed numerous adaptations to modern living conditions on Earth. Probably, both of these classes of modern protozoa should be considered as two trunks in evolution, originating from ancient forms that have not survived to this day, which lived at the dawn of the development of life on our planet.
In the further evolution of protozoa, changes of a different nature occurred. Some of them led to a general increase in the level of organization, an increase in activity, and the intensity of life processes. Such phylogenetic (evolutionary) transformations include, for example, the development of organelles of movement and food capture, which has reached a high level of perfection in the class of ciliates. It is indisputable that cilia are organelles corresponding (homologous) to flagella. While in flagellates, with a few exceptions, the number of flagella is small, in ciliates the number of cilia has reached many thousands. The development of the ciliary apparatus sharply increased the activity of protozoa, made it more diverse and complex shapes their relationship with the environment, forms of reactions to external stimuli. The presence of a differentiated ciliary apparatus, undoubtedly, was one of the main reasons for the progressive evolution in the class of ciliates, where a wide variety of forms adapted to different habitats arose.
The development of the ciliary apparatus of ciliates is an example of this kind of evolutionary change, which was named by Acad. Severtsov aromorphoses. Aromorphoses are characterized by a general increase in organization, the development of adaptations of wide significance. An increase in organization is understood as changes that cause an increase in the vital activity of the organism; they are associated with the functional differentiation of its parts, leading to more diverse forms of communication between the organism and the environment. The development of the ciliary apparatus of ciliates refers precisely to this kind of structural transformations in the process of evolution. This is a typical aromorphosis.
At protozoa, as was emphasized by V. A. Dogel, changes in the type of aromorphoses are usually associated with an increase in the number of organelles. Polymerization of organelles occurs. The development of the ciliary apparatus in ciliates is a typical example of such changes. The second example of aromorphosis in the evolution of ciliates is their nuclear apparatus. We examined above the structural features of the core of ciliates. The nuclear dualism of ciliates (the presence of a micronucleus and a macronucleus) was accompanied by an increase in the number of chromosomes in the macronucleus (the phenomenon of polyploidy). Since chromosomes are associated with the main synthetic processes in the cell, primarily with the synthesis of proteins, this process led to a general increase in the intensity of the main vital functions. Here, too, polymerization took place, affecting the chromosome complexes of the nucleus.
ciliates- one of the most numerous and progressive groups of protozoa, comes from flagellates. This is evidenced by the complete morphological similarity of their organoids of movement. This stage of evolution was associated with two large aromorphoses: one of them affected the organelles of movement, the second - the nuclear apparatus. Both of these types of changes are interconnected, since both lead to an increase in vital activity and complication of the forms of interrelations with the external environment.
Along with aromorphoses, there is another type of evolutionary change, expressed in the development of adaptations (adaptation) to certain, sharply defined conditions of existence. This type of evolutionary change was also called dioadaptation by Severtsov. In the evolution of protozoa, this type of change played a very important role. Above, when considering different classes protozoa, numerous examples of idioadaptive changes are given. adaptations for a planktonic lifestyle different groups protozoans, adaptations to life in the sand in ciliates, the formation of protective shells of oocysts in coccidia, and much more - all these are idioadaptations that played a large role in the emergence and development of individual groups, but were not associated with general progressive changes in organization.
Adaptations to various specific habitats in protozoa are very diverse. They ensured the wide distribution of this type in a wide variety of habitats, which was discussed in detail above, when describing individual classes.
Infusoria-shoe - a representative of the type of Infusoria. It has the most complex organization. The habitats of ciliates are reservoirs with polluted stagnant water. The length of her body is 0.1-0.3 mm. The infusoria has a permanent body shape in the form of a human footprint. outer layer ectoplasm forms a strong elastic pellicle. The organelles of movement are cilia - short plasma outgrowths covering the body of the protozoan; their number reaches 10-15 thousand. In the cytoplasm between the cilia there are special protective formations - trichocysts. With mechanical or chemical irritation of ciliates, trichocysts shoot out a long thin thread, which is introduced into the body of an enemy or victim and injects a poisonous substance that has a paralyzing effect.
The structure of the shoe infusoria:
1 - Cilia, 2 - Digestive vacuoles, 3 - Macronucleus, 4 - Micronucleus, 5 - Contractile vacuole, 6 - Cell mouth, 7 - Powder
The infusoria-shoe reproduces asexually - by transverse division into two parts. Reproduction begins with nuclear fission. The micronucleus undergoes mitotic division, and the macronucleus is divided in half by ligation, but beforehand, the amount of DNA is doubled in it. The last step in the process of asexual reproduction is the division of the cytoplasm by a transverse constriction. In addition, the ciliates are characterized by a sexual process - conjugation, during which genetic information is exchanged. The sexual process is accompanied by a restructuring of the nuclear apparatus. The macronucleus breaks down and the micronucleus divides meiotically to form four nuclei. Three of them die, and the remaining nucleus divides again by mitosis and forms the female and male haploid nuclei. Two ciliates are temporarily connected by cytoplasmic bridges in the region of the mouth openings. The male nucleus passes into the partner's cell and merges with the female nucleus there. After that, the macronucleus is restored and the ciliates diverge. Thus, during conjugation, genetic information is updated, new features and properties appear without an increase in the number of individuals, so conjugation cannot be called reproduction. In the life cycle of ciliates-shoes, conjugation alternates with asexual reproduction.
1. Variety of sarcodes.
2. Variety of flagella.
Representatives of the second subtype move with the help of flagella, which is reflected in the name of this group.
- Flagellates. Euglena green is a typical representative of this group. This protozoan has a fusiform shape, covered with a dense elastic membrane. At the anterior end of the body there is a flagellum, near the base of which there is a light-sensitive eye - a stigma and a contractile vacuole. Closer to the posterior end, in the thickness of the cytoplasm, there is a nucleus that controls all the vital processes of the body. The green color of Euglena is due to numerous chloroplasts. In the light, this flagellate photosynthesizes, but being in unlit areas of the reservoir for a long time, it switches to feeding on the decay products of complex organic substances, extracting them from the environment. Thus, green euglena can combine both an autotrophic type of metabolism and a heterotrophic one. The existence of organisms with such a mixed type of nutrition indicates the relationship of the animal and flora. Most of the flagella
3. Variety of sporozoans and ciliates.
The Ciliates type includes protozoa, which are distinguished by the most complex organization among unicellular animals. A typical representative of this group is the infusoria-shoe - a common inhabitant of fresh water. Her body is covered with a dense shell - pellicle and therefore has a relatively constant shape. A characteristic feature of the structure is the presence of cilia, evenly covering the entire body of the shoe. The movements of the cilia are coordinated due to the network of contractile fibers located in the surface layer of the cytoplasm. The second characteristic feature is the presence of two nuclei, large (macronucleus) and small (micronucleus). The nuclei also differ functionally: a large one regulates metabolism, and a small one participates in the sexual process (conjugation). The infusoria-shoe feeds on bacteria, unicellular algae, which are adjusted by cilia to the cellular mouth, which lies at the bottom of the pre-oral cavity. After passing through the cell pharynx, which ends in the cytoplasm, food particles are enclosed in digestive vacuoles, where they are broken down by the action of enzymes. Undigested residues are thrown out through the powder. In the body of the shoe there are two alternately pulsating complex contractile vacuoles. Shoes reproduce asexually, by dividing in half. Multiple asexual reproduction is replaced in the shoe by the sexual process - conjugation, during which two shoes come together and exchange genetic material. After that, the shoes diverge and soon begin asexual reproduction again. The biological significance of conjugation lies in the combination in one organism of the hereditary properties of two individuals. This increases its viability, which is expressed in better adaptability to environmental conditions.
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On this page, material on the topics:
- briefly about flagellates, pseudopods, sporozoans and ciliates
- sarcodes and sporozoans
- variety of flagella
- infusoria slipper report summary
- what is the difference between ciliates and sarcode species
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