Order of Foraminifera (Foraminifera). Protozoa. Sponges. Coelenterates. Flatworms. Foraminifera roundworms move by means of
foraminifera- inhabitants of the sea. In some seas, for example, in the Laptev Sea, the East Siberian Sea, as Professor Yuri Ivanovich Polyansky writes, foraminifera 2-3 cm in size cover the bottom in an almost continuous layer.
Foraminifera are also enclosed in shells of various, sometimes very bizarre shapes. The severity of these shells makes them settle at the bottom, although some swim in the water column. Such foraminifers are easy to recognize: their shells are strewn with long needles. This helps the protozoa "soar" in the water column.
Foraminifera shells are usually multichambered. Like a prudent homeowner, the simplest builds more and more new “rooms” to its “house” during its life. It is not surprising that "giants" 2-3 cm in size, which we have already mentioned, are so often found among foraminifers. But now comes the time of reproduction, the time to leave the carefully built "apartment building". The body of the protozoan breaks down into a hundred, or even more, tiny amoebas. They come out of the parental shell and each begin to rebuild their own "house". The empty parent shell sinks to the bottom. According to Professor Valentin Alexandrovich Dogel, "one gram of finely sifted sand in the places richest in these shells contains up to 50 thousand shells."
Shells of sea rhizomes cover about a third of the ocean floor and account for three-quarters of all ocean sediments. They formed thick layers of limestone and chalk. From limestone, consisting of these shells (once settled on the bottom of the sea, which was on the site of the modern Sahara desert), the pyramids of the Egyptian pharaohs were built.
Now about 1 thousand species of foraminiferal rhizomes are known and almost 30 times more fossil species of these protozoa are known.
RAY EVIKI (RADIOLARIANS)
Looking at them, it seems that these lacy plexuses are not part of living beings, but the finest
jewelry designed to decorate the outfits of sea princesses, ”wrote about
radiolarians P. E. Vasilkovsky.
It is no coincidence that the German zoologist XIX in. Ernst Haeckel, who was also a talented artist, in
in his atlas of drawings "The Beauty of Forms in Nature" he assigned a significant place to radiolarians. Many years
Haeckel devoted his life to the study of these protozoa.
If the life of most foraminifera takes place on the seabed, then radiolarians spend it in
"hovering" in the thickness of sea water and are ideally adapted to this. It is for this "soaring"
serve as needles of their skeleton, increasing the area of the body.
Radiolarians are able, like a kind of "umbrella", to straighten their body on skeletal needles, and
They can also squeeze it a little. The larger their body area, the lower the specific gravity. changing
body area, radiolarians can float up, or they can go into the depths of the ocean. During heavy rains
being afraid of fresh water, radiolarians thus “run away” into the depths. They do the same when
storms during the winter season. By the way, radiolarians do not like cold, and therefore in the northern seas they
few. And in total, about 8 thousand species of these protozoa are known to science.
Radiolarians catch their prey with numerous thin threads - pseudopods, diverging
from the center of their body in all directions.
The reproduction of radiolarians resembles the reproduction of foraminifers. The body of the parent is divided
for many newborns -
Among the huge army of living organisms that inhabit our planet, there are foraminifers. This name seems a little unusual to some people. The creatures that wear it also differ in many ways from the creatures we are accustomed to. Who are they? Where do they live? What do they eat? What is their life cycle? What niche did they occupy in the animal classification system? In our article, we will cover all these issues in detail.
Group Description
Foraminifera are representatives of a group of protists, unicellular organisms with a shell. Before proceeding to the study of foraminifers, let's get acquainted directly with the group to which they belong.
Protists are a set of organisms that are part of a paraphyletic group, which includes all eukaryotes that were not part of the plants, fungi and animals familiar to us. He introduced this name in 1866, but it acquired a modern understanding only when it was mentioned in 1969 by Robert Whittaker, in the author's work on the system of five kingdoms. The term "protists" comes from the Greek "proti", which means "first". These are the organisms from which, one might say, life began on our planet. By traditional standards, protists branch into three branches: algae, fungi, and protists. All of them have a polyphyletic nature and cannot assume the role of a taxon.
Protists are not isolated according to the presence of positive characteristics. Most often, protists are a common set of unicellular organisms, but at the same time, many of their varieties are able to build the structure of a colony. Some of the representatives may be multicellular.
General phenotypic data
The simplest foraminifera have an external skeleton in the form of a shell. Their predominant number is limestone and chitinoid structures. Only occasionally do we come across creatures with a shell of foreign particles glued together through the activity of the cell.
The cavity located inside the shell, through numerous pores, communicates with the environment present around the body. There is also a mouth - a hole leading into the cavity of the shell. Through the pores, the thinnest, outer and branching pseudopods germinate, which form a connection with each other with the help of reticulopodia. They are necessary to move the cell along the surface or in the water column, as well as to obtain food. Such pseudopods form a special mesh, the diameter of which extends far beyond the shell itself. Particles begin to stick to such a network, which in the future will serve as food for foraminifers.
Lifestyle
Foraminifera are protists, mainly of the marine type. There are forms inhabiting brackish and fresh waters. You can also meet representatives of species that live at great depths or in a loose silty bottom.
Foraminifera are divided into planktonic and benthic. In plankton, the shell is considered the most widespread "organ" of their biogenic activity, which takes the form of sediments on the bottom of the oceans. However, after the mark of 4 thousand meters, they are not observed, which is due to the rapid process of their dissolution in the water column. Silt from these organisms covers about a quarter of the total territory of the planet.
The data obtained through the study of fossil foraminifera allow us to determine the age of deposits formed in the distant past. Modern species are very small, from 0.1 to 1 mm, while extinct representatives could reach up to 20 cm. Most shells are sandy fractions, up to 61 µm. Maximum concentration of foraminifera in sea water. There are a lot of them in the water area near the equator and waters of high latitudes. They were also found in the Mariana Trench. It is important to know that the diversity of species and the complexity of their shell structure is typical only for the equatorial region. In some places, the concentration indicator can reach one hundred thousand copies in the thickness of one cubic meter of water.
The concept of benthic protists
Benthos is a collection of animal species that inhabit the strata of ordinary soils and those at the bottom of reservoirs. Oceanology considers benthos - as organisms that live on the sea and ocean floor. Researchers of the hydrobiology of fresh water bodies describe them as inhabitants of the continental type of water bodies. Benthos are divided into animals - zoobenthos and plants - phytobenthos. Among this variety of organisms, a large number of foraminifera is observed.
In the zoobenthos, animals are distinguished by their habitat, mobility, penetration into the soil or the method of attachment to it. In accordance with the way of feeding, they are divided into predators, herbivores and organisms that feed on particles of organic nature.
The concept of planktonic protists
Species of planktonic foraminifera are the smallest organisms that drift in the water column and cannot resist the current (swim where they want). Such specimens include some types of bacteria, diatoms, protozoa, molluscs, crustaceans, fish larvae, eggs, etc. Plankton serves as food for a large number of animals that inhabit the waters of rivers, seas, lakes and oceans.
The word "plankton" was introduced into speech by the German oceanologist W. Hensen in the last years of the 1880s.
Features of the sink device
Foraminifera are animals whose shells are classified according to the way they are formed. There are two forms - secretory and agglutinated.
The first type is characterized by the fact that the formation of the shell occurs through the combination of mineral and organic substances that the animal itself secretes.
The second (agglutinated) type of shells is formed by capturing a number of fragments from the skeletons of other organisms and sand particles. Bonding is carried out by a substance secreted by a unicellular organism.
School chalk contains a large percentage of foraminiferal shells, which are its main element.
Based on the composition, the following types of protists are distinguished:
- Organic foraminifers are the most ancient form, occurring at the beginning of the Paleozoic.
- Agglutinated - consisting of a variety of particles, up to carbonate cement.
- Secretion calcareous - composed of calcite.
Foraminifera shells in the structure differ in the number of chambers. The "house" of an organism can consist of one chamber or many. Multi-chamber sinks are divided according to the linear or spiral method of the device. The winding of roundings in them can occur in a ball-shaped and planospiral, as well as in a trochoid way. There were foraminifers with an oritoid type of shell. In almost all organisms, the first chamber is the smallest, and the largest is the last. Secretion-type shells often have "stiffening ribs" that increase the mechanical strength index.
Life cycles
The foraminifera class is characterized by a haplo-diplophase life cycle. In a generalized scheme, it looks like this: representatives of haploid generations undergo as a result of which a single-type series of gametes with two flagella appears. These cells merge in pairs and form the integral structure of the zygote. An adult individual belonging to the agamont generation will develop from it in the future.
The fact that a doubling of the chromosome set occurs during fusion leads to the formation of a diploid generation. Inside the agamont, the process of nuclear division takes place, which proceeds already due to meiosis. The space around the haploid nucleus, which has become so due to the reduction division, is separated by the cytoplasm and forms the shell. This leads to the formation of agamonts, which are similar in purpose to spores.
The simplest in nature
Consider the role and importance of foraminifera in nature and human life.
Feeding on bacterial organisms and the remains of organic nature, the protozoa do a great job of keeping pollution away.
Protozoa, among which there are many foraminifera, have a high fertility rate under certain environmental conditions. They act as food for the fry.
Euglena, in addition to being food for other inhabitants of water bodies and cleaning them, carry out photosynthesis processes, reducing the concentration of CO2 and increasing the content of O2 in the waters.
The degree of pollution can be determined by analyzing the amount of euglena and ciliates in the water column. If the reservoir contains a huge amount of organic compounds, then there will be an increased indicator of the number of euglena. Amoebas are most often concentrated where the content of organic substances is low.
"Houses" of protozoa participated in the formation of limestone and chalk fossils. Therefore, they play an important role in industry, as they formed substances that are widely used by man.
Taxonomy data
In our time, about ten thousand species of foraminifera are known, and the number of known fossils exceeds forty thousand. The most famous examples are the amoeba foraminifera, myliolids, globigerins, etc. In the hierarchical table of taxonomic elements of wildlife, they were given the title of a class, which is also called the type of the simplest eukaryotic organisms. Previously, this domain consisted of five suborders and was included in the single order Foraminiferida Eichwald. A little later, the researchers decided to raise the status of foraminifera to a whole class. The classification distinguishes in them the presence of 15 subclasses and 39 detachments.
Results
Based on the material of the article, it can be understood that foraminifers are representatives of protists, unicellular organisms that are part of the superkingdom of eukaryotes. They have shells, which are formed from two basic materials, namely, from grains of sand and from minerals, as well as from substances that secrete them. Foraminifera occupy an important place in the food chain. They had a huge impact on the formation of the modern picture of the soils of the planet.
Foraminifera is the most extensive order of protozoan animals of the subclass of rhizopods, which are included in the class of sarcodidae of the sarcomastigophora type. This order includes more than 4 thousand species of these animals. All foraminifera are marine single-celled organisms involved in the formation of benthos in the bottom layers. Planktonic organisms are representatives of only two families of foraminifers; they live in the water column.
Representatives of this order of animals are widespread in the oceans and seas everywhere. They are found in all latitudes and at any depth. But in the polar regions, the number of foraminifers per unit volume of water is almost a hundred times less than in the equatorial zone. The greatest diversity of foraminiferal species is observed in subsoil salt waters and wells with salt water in Central Asia. Scientists regard them as the remains of marine fauna.
A distinctive feature of foraminifera is the presence of a shell - a protective formation that surrounds the animal's body from the outside. This is the external skeleton, its structure is complex, and the shape is diverse in different species. The shell of most foraminifera is calcareous, sometimes chitinoid, less often consists of grains of sand adhering to the mucus covering the body of the animal. Shells can be single-chamber, multi-chamber, in some cases branching. The shell has an internal cavity that communicates with the surrounding space through many pores and a large opening - the mouth. Through the pores and mouth, thin pseudopods (rhizopodia) emerge from the shell, which serve to move and catch food. These rhizopodia are interconnected, forming a network, the size of which exceeds the size of the shell itself. This is a device for hunting numerous unicellular organisms - food for foraminifers. According to the way of feeding, foraminifers are divided into filter feeders, predators and herbivores.
The cell sizes of foraminifera range from 0.1 to 1 mm, extinct species reached a diameter of 20 cm. In the cell of an individual of this order, there may be one or more nuclei that perform various functions, like in ciliates. In planktonic forms of foraminifera, to increase buoyancy in the cytoplasm, there are inclusions of gas bubbles, drops of fat and fresh water.
The life cycle of foraminifera is an alternation of haploid and diploid generations. The zygote gives rise to the diploid generation. After repeated division of the nucleus, the individual becomes multinucleated and breaks up into many gametes, from which the haploid generation develops. Later, the gametes copulate, again forming diploid zygotes.
Fossil foraminifera have been known since the Cambrian period, although scientists believe that these organisms appeared on Earth as early as the Precambrian. The heyday of foraminifers was in the Carboniferous and Permian geological periods. At that time, the shells after the death of these organisms formed significant layers of sedimentary rocks - chalk and limestone. As a result of mountain-building processes, the bottom of the seas with deposits of these rocks rose and turned into land. This is how the mountain ranges were formed: the Himalayas, the Alps, the Pyrenees, consisting mainly of foraminiferal limestones, which people have long used as a building material and to produce lime. Fossil foraminifera play an important role in the stratigraphy of Paleozoic, Mesozoic and Cenozoic deposits, that is, determining the age of rocks.
The most extensive detachment among the rhizopods are the inhabitants of the sea - foraminifera(Foraminifera). More than 1000 species of foraminifera are known in the modern marine fauna. A small number of species, probably remnants of the marine fauna, inhabit the subsoil salt waters and brackish wells of Central Asia.
Foraminifera are ubiquitous in the oceans and seas. They are found in all latitudes and at all depths, from the coastal littoral zone to the deepest abyssal depressions. Nevertheless, the greatest diversity of foraminiferal species occurs at depths of up to 200-300 m. The vast majority of foraminiferal species are inhabitants of the bottom layers and are part of the benthos. Only very few species live in the sea water column, are planktonic organisms.
Let's get acquainted with some of the most characteristic forms of the foraminifera skeleton (Fig. 32).
Among the huge variety of structure of foraminiferal shells, two types can be distinguished by their composition. Some of them consist of particles foreign to the body of the rhizomes - grains of sand. Just as we have seen in diffusion(Fig. 30), foraminifers with such agglutinated shells ingest these foreign particles and then excrete them on the surface of the body, where they are fixed in a thin outer leathery layer of the cytoplasm. Representatives of the genera Hyperammina, Astrorhiza (Fig. 32, 3-7) and others have this type of shell structure. For example, in some areas of our northern seas (the Laptev Sea, the East Siberian Sea), these large foraminifers, reaching lengths, almost a continuous layer cover the bottom.
The number of foraminifera species with agglutinated shells is relatively small (although the number of individuals of these species can be huge). Most of them have calcareous shells, consisting of calcium carbonate (CaCO3).
These shells are secreted by the cytoplasm of the rhizopods, which have the remarkable property of concentrating in their body calcium contained in sea water in small quantities (calcium salts in sea water are a little over 0.1%). The sizes of calcareous shells of different species of foraminifera can be very different. They range from 20 microns to 5-6 cm. This is about the same size ratio as between an elephant and a cockroach. The largest of the foraminifers, whose shell is 5-6 cm in diameter, can no longer be called microscopic organisms. The largest (genera Cornuspira and others) live at great depths.
Among the calcareous shells of foraminifera, in turn, two groups can be distinguished.
Single-chamber foraminifera have a single cavity inside the shell, which communicates with the external environment by the mouth. The shape of single-chamber shells is varied. In some (for example, Lagena), the shell resembles a bottle with a long neck, sometimes equipped with ribs (Fig. 32, 2).
Very often there is a spiral twisting of the shell, and then its inner cavity becomes a long and thin canal (for example, Ammodiscus, fig. 32, 8, 9).
Most calcareous shells of rhizopods are not single-chambered, but multi-chambered. The internal cavity of the shell is divided by partitions into a number of chambers, the number of which can reach several tens or hundreds. The partitions between the chambers are not continuous, they have holes, due to which the protoplasmic body of the rhizopod is not divided into parts, but is a single whole. The walls of the shells are not in all, but in many foraminifera, they are pierced with tiny pores, which serve to exit the pseudopodia. This will be discussed in more detail below.
The number, shape, and mutual arrangement of chambers in the shell can be very different, which creates a huge variety of foraminifera (Fig. 32). In some species, the chambers are arranged in one straight row (for example, Nodosaria, fig. 32, 12), sometimes their arrangement is two-row (Textularia, fig. 32, 22). The spiral shape of the shell is widespread, when individual chambers are arranged in a spiral, and as they approach the chamber carrying the mouth, their dimensions increase. The reasons for this gradual increase in the size of the chambers will become clear when we consider the course of their development.
, 
The spiral shells of foraminifera have several whorls of the spiral. The outer (larger) whorls can be located next to the inner whorls (Fig. 32, 17, 18) so that all chambers are visible from the outside. This is an evolute type of shell. In other forms, the outer (larger) chambers completely or partially cover the inner chambers (Fig. 33, 1). This is an involute type of shell. We find a special form of shell structure in foraminifera myliolid(family Miliolidae, fig. 32, 19). Here, the chambers are strongly elongated parallel to the longitudinal axis of the shell and are located in several intersecting planes. The whole shell as a whole turns out to be oblong and somewhat reminiscent of a gourd seed in shape. The mouth is located on one of the poles and is usually equipped with a tooth.
, 
The shells belonging to the cyclic type are distinguished by a great complexity of structure (the genera Archiacina, Orbitolites, etc., Fig. 33, 2, 34). The number of chambers here is very large, and the inner chambers are arranged in a spiral, while the outer ones are arranged in concentric rings.
What is the biological significance of such a complex structure of multichamber shells of rhizopods? A special study of this issue showed that multi-chamber shells are much more durable than single-chamber shells. The main biological significance of the shell is the protection of the soft protoplasmic body of the rhizopod. With the multi-chamber structure of the shell, this function is carried out quite perfectly.
How is the soft protoplasmic body of foraminifera arranged?
The inner cavity of the shell is filled with cytoplasm. A nuclear apparatus is also placed inside the shell. Depending on the stage of reproduction (which will be discussed below), the nucleus may be one or several. Numerous very long and thin pseudopodia protrude from the shell through the aperture, branching and anastomosing with each other. These special false legs characteristic of foraminifera are called rhizopodia. The latter form a fine mesh around the shell, the total diameter of which usually considerably exceeds that of the shell (Fig. 34). In those species of foraminifera that have pores, the rhizopodia protrude out through the pores.
The function of the rhizopodia is twofold. They are organelles of movement and food capture. Various small food particles “stick” to the rhizopodia, very often these are unicellular algae. Digestion can take place in two ways. If the particle is small, it gradually “slides” along the surface of the rhizopodia and is drawn through the mouth into the shell, where digestion takes place. If the food particle is large and cannot be drawn into the shell through a narrow mouth, then digestion occurs outside the shell. At the same time, the cytoplasm gathers around the food and a local, sometimes quite significant thickening of the rhizopodia is formed, where digestion processes are carried out.
Studies carried out in recent years with the use of time-lapse filming have shown that the cytoplasm, which is part of the rhizopodia, is in continuous motion. Along the rhizopodia in the centripetal (towards the shell) and centrifugal (away from the shell) directions, currents of the cytoplasm flow rather quickly. On the two sides of the thin rhizopodia, the cytoplasm seems to flow in opposite directions. The mechanism of this movement is still not clear.
Reproduction of foraminifera is quite complex and in most species is associated with the alternation of two different forms of reproduction and two generations. One of them is asexual, the second is sexual. At present, these processes have been studied in many species of foraminifera. Without going into details, let's look at them using a specific example.
Figure 35 depicts the life cycle of the foraminifera Elphidium crispa. This species is a typical multichambered foraminifera with a spirally twisted shell. Let us begin our consideration of the cycle with a multichambered rhizopod with a small germ chamber in the center of the spiral (microspherical generation).
In the cytoplasm of the rhizopod, there is initially one nucleus. Asexual reproduction begins with the fact that the nucleus successively divides several times, resulting in the formation of many small nuclei (usually several tens, sometimes over a hundred). Then, a section of the cytoplasm separates around each nucleus and the entire protoplasmic body of the rhizopod breaks up into many (according to the number of nuclei) mononuclear amoeba-like embryos that go out through the mouth. Immediately around the amoeboid embryo, a thin calcareous shell stands out, which will be the first (embryonic) chamber of the future multi-chamber shell. Thus, during asexual reproduction at the first stages of its development, the rhizopod is single-chambered. However, very soon the following ones start to be added to this first chamber. It happens like this: a certain amount of cytoplasm immediately protrudes from the mouth, which immediately releases the shell. Then there comes a pause, during which the protozoan intensively feeds and the mass of its protoplasm increases inside the shell. Then again a part of the cytoplasm protrudes from the mouth and another calcareous chamber is formed around it. This process is repeated several times: more and more new chambers appear until the shell reaches the dimensions characteristic of this species. Thus, the development and growth of the shell is of a stepwise nature. The dimensions and mutual position of the chambers are determined by how much protoplasm protrudes from the mouth and how this protoplasm is located in relation to the previous chambers.
We began our consideration of the life cycle of Elphidium with a shell that had a very small embryonic chamber. As a result of asexual reproduction, a shell is obtained, the embryonic chamber of which is much larger than that of the individual that started asexual reproduction. As a result of asexual reproduction, individuals of the macrospherical generation are obtained, which differ significantly from the microspherical generation that gives rise to them. In this case, the offspring is not quite similar to the parents.
In what way do individuals of the microspherical generation arise?
They develop as a result of sexual reproduction of the macrospherical generation. It happens in the following way. As with asexual reproduction, the sexual process begins with nuclear fission. The number of nuclei formed in this case is much greater than during asexual reproduction. A small area of cytoplasm separates around each nucleus, and in this way a huge number (thousands) of single-nuclear cells is formed. Each of them is equipped with two flagella, thanks to the movement of which the cells actively and quickly swim. These cells are sex cells (gametes). They merge with each other in pairs, and the fusion affects not only the cytoplasm, but also the nuclei. This process of fusion of gametes is the sexual process. The cell formed as a result of the fusion of gametes (fertilization) is called a zygote. It gives rise to a new microspherical generation of foraminifera. Immediately after its formation, a calcareous shell stands out around the zygote - the first (embryonic) chamber. Then the process of development and growth of the shell, accompanied by an increase in the number of chambers, is carried out according to the same type as in asexual reproduction. The shell turns out to be microspherical because the size of the zygote that secretes the embryonic chamber is many times smaller than the mononuclear amoeboid embryos formed during asexual reproduction. In the future, the microspherical generation will begin asexual reproduction and again give rise to macrospherical forms.
On the example of the life cycle of foraminifera, we meet with an interesting biological phenomenon of the regular alternation of two forms of reproduction - asexual and sexual, accompanied by the alternation of two generations - microspherical (develops from a zygote as a result of fertilization) and macrospherical (develops from mononuclear amoeboid embryos as a result of asexual reproduction).
Let us note one more interesting feature of the sexual process of foraminifers. It is known that in most animal organisms, germ cells (gametes) are of two categories. On the one hand, these are large, immobile egg (female) cells, rich in protoplasm and reserve nutrients, and on the other hand, small mobile spermatozoa (male sex cells). Sperm motility is usually associated with the presence of an actively moving filamentous caudal region. In foraminifera, as we have seen, there are no morphological (structural) differences between germ cells. In their structure, they are all the same and, due to the presence of flagella, they have mobility. There are still no structural differences that would make it possible to distinguish between male and female gametes. This form of the sexual process is the original, primitive.
As already mentioned, the vast majority of modern species of foraminifera are demersal (benthic) organisms found in seas of all latitudes from the coastal zone down to the deepest depths of the oceans. A study of the distribution of rhizopods in the ocean showed that it depends on a number of environmental factors - temperature, depth, and salinity. Each zone has its own species of foraminifera. The species composition of foraminifera can serve as a good indicator of habitat conditions.
Among foraminifera there are a few species that lead a planktonic lifestyle. They constantly "soar" in the thickness of the water mass. Typical example of planktonic foraminifera - different species globigerin(Globigerina, Fig. 36). The structure of their shells differs sharply from the structure of the shells of benthic rhizopods. The shells of globigerins are thinner-walled, and most importantly, they have numerous appendages diverging in all directions - the thinnest long needles. This is one of the adaptations for life in plankton. Due to the presence of needles, the surface of the body, namely the ratio of surface to mass - a value called specific surface area, increases. This increases friction when immersed in water and promotes "floating" in the water.
Foraminifers, which are widespread in modern seas and oceans, were also richly represented in previous geological periods, starting from the most ancient Cambrian deposits. Lime shells after reproduction or death of the rhizomes sink to the bottom of the reservoir, where they are part of the silt deposited on the bottom. This process takes tens and hundreds of millions of years; as a result, powerful deposits are formed on the ocean floor, which include a myriad of rhizopod shells. During mountain-building processes that have taken place and are taking place in the earth's crust, as is known, some areas of the ocean floor rise and become land, the land sinks and becomes the ocean floor. Most of the modern land in various geological periods was the bottom of the ocean. This also fully applies to the territory of the Soviet Union (with the exception of a few northern regions of our country: the Kola Peninsula, most of Karelia, and some others). Sea bottom sediments on land turn into sedimentary rocks. All marine sedimentary rocks contain rhizopod shells. Some deposits, such as Cretaceous ones, mostly consist of rhizopod shells. Such a wide distribution of foraminifera in marine sedimentary rocks is of great importance for geological work, and in particular for geological exploration. Foraminifera, like all organisms, did not remain unchanged. In the course of the geological history of our planet, the evolution of the organic world has taken place. Foraminifers also changed. Different geological periods of the Earth's history are characterized by their own species, genera and families of foraminifera. It is known that the geological age of these rocks can be determined from the remains of organisms in rocks (fossils, imprints, etc.). Foraminifera can also be used for this purpose. As fossils, due to their microscopic size, they offer very great advantages, since they can be found in very small amounts of rock. In geological exploration of minerals (especially in oil exploration), the drilling method is widely used. This results in a small-diameter rock column covering all the layers through which the drill has passed. If these layers are marine sedimentary rocks, then microscopic analysis always reveals foraminifera in them. In view of the great practical importance, the question of the association of certain species of foraminifera with certain sedimentary rocks of calcareous age has been developed with a high degree of accuracy.
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Foraminifera are sarcodes with thin, complexly branched pseudopods or pseudopodia. The body of foraminifera consists of protoplasm with one or more nuclei and is enclosed in a shell that communicates with the external environment through a special opening - mouth(Fig. 2). In addition to the mouth, there are holes in the walls of the shell - foramen, which perform the same function as the mouth. The protoplasm of foraminifera consists of an outer layer - ectoplasm and inner layer endoplasm. The endoplasm fills (lines) the internal cavity of the shell.
It has a heterogeneous composition, contains various inclusions. Ectoplasm is more homogeneous.
Pseudopodia or pseudopodia are movable thin outgrowths ectoplasm. They are organelles for food capture, partial digestion, and eruption. The pseudopods also perform respiratory functions. The length of the pseudopodia can be 100 times the thickness and several times the diameter of the cell.
Foraminifera locomotion occurs by stretching and shortening of the prolegs. Foraminifera feed on microscopic (algae, larvae, protozoa) organisms and detritus.
Skeleton structure. Most foraminifera have a shell. It can be secretory (of organic and mineral composition) or agglutinated (from Latin agglutinare - to stick).
The organic shell is made up of tectin. It is not preserved in a fossil state.
The agglutinated or “sandy” shell consists of quartz grains, sponge spicules, shells of other foraminifera, and other materials cemented with ferruginous, calcareous, and, less commonly, siliceous cement.
Most foraminifera form a secretion-calcareous shell. The shell is secreted by protoplasm.
The shell walls have a different structure: granular, fibrous, thin-layered. Holes (foramanes) are often visible on the surface. These are the openings of the pore channels. The wall without pore channels looks porcelain-like and is called unperforated. The porous (perforated) wall looks vitreous.
In fusulinids, the shell wall reaches great complexity and is differentiated into several layers.
The shell of foraminifers is single-chambered, two-chambered or multi-chambered and has a variety of shapes.
With continuous growth, a single-chamber shell is formed in the form of a cone, ball or tube.
A two-chamber shell consists of an oval initial chamber and a second long, tubular, separated from the initial by a partition. The second chamber is straight, spirally coiled or branched.
The multichamber shell develops as a result of discontinuous growth. When growth slows down, constrictions form on the shell, separating one chamber from another. The newly formed chambers inside the shell are separated by partitions or septa.
Septa on the outer surface of the shell correspond to septal sutures.
Multi-chamber shells reach the greatest variety of forms.
Several types of structure of foraminiferal shells are distinguished (Fig. 3).
Types of shell structure. The type of shell structure is understood as a regularity in the relative spatial arrangement of its parts, with which the shape of the shell is associated.
The following types are distinguished: irregular, uniaxial, spiral (spiral-planar and spiral-conical), milioline (Fig. 3).
Wrong the type of structure is the most primitive. The shell is radiant, branched, irregularly ball-shaped. In radiant and branched shells, the shell is usually single-chambered, in irregularly ball-shaped ones, it is two-chambered.
The second chamber looks like a wrapped tube.
With uniaxial type chamber structures follow each other along a straight axis. The sink is single-chamber or multi-chamber. The end of the shell where growth begins is called proximal, the opposite end of the shell, on which the mouth is located, is called distal.
Uniaxial shells are typical of benthic foraminifers. They lie freely or crawl along the bottom. Sometimes such forms pass to an attached way of life and then the shell becomes irregular, creeping along the substrate.
The spiral-planar type is characterized by a spiral axis lying in one plane - the plane of symmetry. Therefore, the shells are bilaterally symmetrical. The imaginary straight line around which the shell winds up is called winding axis or shell axis. It is perpendicular to the spiral axis and is used to measure the thickness of the shell.
Sinks can be two-chamber and multi-chamber. The first chamber is initial, spherical, the second is tubular, spirally wrapped (Fig. 3).
Multi-chamber shells have a variety of shapes, which depend on the ratio of diameter and thickness.
The diameter lies in the plane of symmetry, it is perpendicular to the winding axis.
If d > thickness and significant, the shell has a disk-shaped or lenticular shape, if d » thickness, the shell acquires spherical shape, if the thickness > d (significantly!), appears fusiform the form.
In the shell distinguish turns. Each revolution describes a full circle. The lines of contact between adjacent whorls are called spiral seams. If all whorls are visible from the side, the shell is called evolutionary(non-embracing) - fig. 3, 4. In many forms, only the last whorl is visible from the outside, which closes all the previous ones. This sink is called involute(embracing). Many shells show navel- conical recess on each side. In the evolute forms, the umbilicus is wide and more or less deep; involute- narrow. Sometimes the navel is filled with the substance of an additional skeleton.
Spiral-conical the type of structure differs from the spiral-planar one by the location of the spiral axis not in one plane, but along an imaginary spiral surface. In these shells (Fig. 3, 4), height and diameter are distinguished. Depending on the ratio of height to diameter, spiral-conical shells are divided into trochoid and spiral-helical.
Trochoid- the ratio of height and diameter is different, but the height does not exceed the diameter.
At spiral screw height is greater than diameter. Shells are mostly multi-chambered. In individual whorls, the number of chambers is 2, 3, 4, 5, depending on which two-row, three-row, four-row and five-row shells are distinguished. Separate cameras are located to each other at a certain angle. Spiral conical sinks can be heteromorphic, i.e. a three-row can go to a two-row or other type of structure.
In spiral-conical shells, the side on which all the turns of the spiral are visible is called dorsal or dorsal. The side on which fewer revolutions or one last one is visible is called ventral or abdominal.
Properly glomerular or miliolinic the type of structure is a separate group of spiral-planar shells. The chambers are located in several mutually intersecting planes or in one plane, forming a tangle.
Cyclic shells are a variety of spiral-planar shells, they are relatively rare (numulitids). Chambers in the early stages are arranged in a spiral, and in the future - in concentric circles.
Additional skeleton represents secondary deposits of skeletal substance on the outer surface of the shell or inside it. The external additional skeleton is represented by ribs, spines, tubercles. Sometimes these are umbilical discs that fill the navel area. Internal skeletal formations are found in the orders fusulinids, endothyrids, and nummulitids.
Reproduction. In the process of reproduction of foraminifera, alternation of generations is observed - asexual and sexual. Both processes are based on cell division. In multichambered foraminifera, the same species produces 2 types of shells: megaspherical with a large initial chamber and a small number of subsequent chambers and microspherical with a small initial chamber and numerous subsequent chambers. The microspherical shell is larger than the megaspherical one. It contains many nuclei, which are scattered in disorder in the protoplasm. A megaspherical individual has one nucleus. It is formed in the process of sexual reproduction, and microspherical - in the process of asexual reproduction. The presence of two types of shells in one species is called dimorphism.
Ecology and Taphonomy of Foraminifera.
Modern foraminifera make up a significant part of the plankton of the tropical and subtropical zones, beyond which they are carried by currents. They also inhabit the bottom of the sublittoral. Continental sublittoral foraminifera live between grains of soil in capillary spaces filled with water. The waters are either slightly salty or fresh.
The development of marine foraminifera is affected by light and food (unicellular algae and some bacteria).
Once in the sediment after the death of an animal, foraminifera shells bring calcium carbonate, magnesium, iron oxides, and other waste products into it.
In modern sediments of warm-water basins, benthic foraminifera are not numerous and are, as it were, an admixture to the main part of the sediment.
In the reef deposits of modern seas, foraminifers are rock-forming (along with corals, calcareous algae, and other organisms).
The benthic foraminifera of the bathyal region are of less importance. In the abyssal area at the bottom, agglutinated foraminiferal shells accumulate (up to 20% of the sediment).
In the geological past, foraminifera were repeatedly rock-forming. Carbonate rocks of the Middle Carboniferous on the Russian platform and on the western slope of the Urals (Perm region, Bashkiria and Orenburg region) are almost entirely composed of fusulinids.
In the Late Carboniferous and Early Permian, along the western slope of the Urals in a shallow warm sea, dome-shaped reefs were formed, largely consisting of fusulinic and other organogenic limestones.
The benthic foraminifers of the Late Permian (Urals, Tien Shan, Pamir) and the entire Cretaceous were also rock-forming. The chalk strata consist of shells of benthic and planktonic foraminifers. The rock-forming role of benthic foraminifers (nummulitids) in the Paleogene deposits of the European part of Russia, Central and Central Asia, and Western Europe is great.