Among the huge army of living organisms that inhabit our planet, there are foraminifera. This name seems a little unusual to some people. The creatures that carry it are also very different from the creatures we are used 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 with the study of foraminifera, we will familiarize ourselves directly with the group to which they belong.
Protists are many organisms that are part of the paraphyletic group, which includes all eukaryotes that were not part of the usual plants, fungi, and animals. This name was introduced by Ernst Haeckel in 1866, however, it gained modern understanding only when it was mentioned in 1969 by Robert Whittaker, in the author's work on the system of the five kingdoms. The term "protists" comes from the Greek "proti", which means "first." These are the organisms with which, one might say, life began on our planet. In accordance with traditional standards, protists branch into three branches: algae, mushroom-like organisms and protozoa. All of them have a polyphyletic nature and cannot assume the role of a taxon.
Protists are not isolated in accordance with 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. A number of representatives may be multicellular.
General phenotypic data
The simplest foraminifers have an external skeleton in the form of a shell. Most of them are limestone and chitinoid structures. Only sometimes come across creatures with a shell of foreign particles glued together through the activity of a cell.
The cavity located inside the shell, through numerous pores communicates with the environment present around the body. There is also a mouth - an opening leading into the cavity of the shell. Through the pores there is a germination of the thinnest, outer and branching pseudopods, which form a connection with each other using reticulopodia. They are necessary for moving the cell on the surface or in the water column, as well as for the extraction of food. Such pseudopods form a special net, the diameter of which extends far beyond the shell itself. Particles that will serve as food for foraminifera begin to adhere to such a network.
Lifestyle
Foraminifera belong to protists, mainly of the marine type. There are forms that inhabit brackish and fresh waters. You can also meet representatives of species that live at great depths or in a loose muddy bottom.
Foraminifer are divided into planktonic and benthic. In the planktonic
type of animals, the shell is considered the most widespread "organ" of their biogenic activity, which takes the form of sediments at the bottom of the oceans. However, after a mark of 4 thousand meters they are not observed, which is caused by the rapid process of their dissolution in the water column. Sludge from these organisms covers about a quarter of the total planet.
Data obtained through the study of fossil foraminifera, allows you to determine the age of sediments formed in the distant past. Modern species have very small sizes, from 0.1 to 1 mm, and extinct representatives could reach up to 20 cm. Most of the shells are represented by sand fractions, up to 61 microns. The maximum concentration of foraminifera in seawater. There are a lot of them in the water area near the equator and waters of high latitudes. They are also found in the Mariana Trench. It is important to know that the diversity of species and the complexity of their shell structure is characteristic 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
Bentos is the totality of animal species that inhabit the strata of ordinary soils and those at the bottom of water bodies. 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 zoobenthos, animals are distinguished by habitat, mobility, penetration into the ground or the method of attachment to it. In accordance with the method of nutrition, they are divided into predators, herbivores and organisms that feed on particles of organic nature.
The concept of planktonic protists
Species of foraminifera of the plankton type are tiny organisms that drift in the water column and do not know how to confront the current (swim wherever they want). Such species include some species of bacteria, diatoms, protozoa, mollusks, crustaceans, fish larvae, eggs, etc. Plankton serves as food for a large number of animals inhabiting the waters of rivers, seas, lakes and oceans.
The word "plankton" was coined by the German oceanologist W. Hansen in the last years of the 1880s.
Features of the device sinks
Foraminifera are animals whose shells are classified according to the way they are formed. Two forms are distinguished - secretory and agglutinated.
The first type is characterized in that the formation of the shell occurs through the combination of mineral and organic substances that the animal secrets.
The second (agglutinated) type of shells is formed by capturing a number of fragments from the skeletons of other organisms and particles of sand. 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, these types of protists are distinguished:
- Organic foraminifera is the oldest form found at the beginning of the Paleozoic.
- Agglutinated - consisting of a variety of particles, up to carbonate cement.
- Secretory calcareous - folded with calcite.
The foraminiferal shells in the structure differ in the number of chambers. The "house" of an organism may consist of one chamber or a plurality. Multi-chamber sinks are divided by a linear or spiral method of the device. The rounding of the roundings in them can occur in a clew-shaped and planospiral, as well as trochoidal way. There were foraminifera with orythoid type of shell. In almost all organisms, the first chamber has the smallest size, while the last one has the largest. Secretion-type shells often have "stiffening ribs" increasing the mechanical strength index.
Life cycles
The class of foraminifers is characterized by a haplo-diphasic life cycle. In a generalized scheme, it looks like this: representatives of haploid generations undergo nuclear fission, as a result of which a similar series of gametes with two flagella appears. These cells fuse 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 during fusion the doubling of the chromosome set occurs causes the formation of a diploid generation. Inside the agamont, a nuclear fission process takes place, which is already due to meiosis. The space around the haploid nucleus, which has become so due to reduction fission, is isolated by the cytoplasm and forms a shell. This leads to the formation of agamonts, which in their purpose are similar to spores.
Protozoa in nature
Consider the role and importance of foraminifera in nature and human life.
Feeding on bacterial organisms and residues of an organic nature, protozoa do a tremendous job of cleaning water bodies from pollution.
Protozoa, among which there are many foraminifera, have a high fertility rate under certain environmental conditions. They serve as food for fry.
Euglena, in addition to serving as a food for other inhabitants of water bodies and engaged in their purification, carry out photosynthesis processes, reducing the concentration of CO2 and increasing the content of O2 in the waters.
The degree of contamination can be determined by analyzing the amount of euglen 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 euglen. Amoebas are most often concentrated where the content of organic substances is low.
The “houses” of protozoa participated in the formation of limestone and chalk minerals. Therefore, they play an important role in industry, since they formed substances widely used by man.
Taxonomy data
In our time, about ten thousand species of foraminifera are known, and the number of known minerals exceeds the mark of forty thousand. The most famous examples are the amoeba foraminifera, miliolides, globigerins, etc. In the hierarchical table of taxonomic elements of wildlife, they were awarded the title of a class, which is also called the type of simple eukaryotic organisms. Previously, this domain consisted of five suborders and was included in the only order Foraminiferida Eichwald. A little later, the researchers decided to raise the status of foraminifera to a whole class. Classification distinguishes in them the presence of 15 subclasses and 39 orders.
Summary
Based on the material of the article, it can be understood that foraminifera are representatives of protists, single-celled organisms that are part of the eukaryotic supremacy. They have shells that are formed from two basic materials, namely, from sand grains and from minerals, as well as from the substances that they secrete. Foraminifera occupy an important place in the food chain. They had a huge impact on the formation of the modern picture of the planet’s soil.