Among the huge army of living organisms inhabiting our planet, there are also 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 the protist group, 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 belonging to the paraphyletic group, which includes all eukaryotes that were not part of the plants, fungi and animals familiar to us. This name was introduced by Ernst Haeckel 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 the 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 number of 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 are 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, mostly of the marine type. Existforms inhabiting brackish and fresh waters. You can also meet representatives of species that live at great depths or in loose muddy bottoms.
Foraminifera are divided into planktonic and benthic. In planktonic animals, 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 planet's total area.
Data obtained from 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 set 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 andocean 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 are observed.
In the zoobenthos, animals are distinguished by habitat, mobility, penetration into the ground or the method of attachment to it. According to the way of feeding, they are divided into predators, herbivores and organisms that feed on particles of organic nature.
The concept of planktonic protists
Planktonic-type 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.
Sink design features
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.
SecondThe (agglutinated) type of shells is formed by capturing a series of debris 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 foraminifera is the oldest form found in the early Paleozoic.
- Agglutinated - consisting of a variety of particles, up to carbonate cement.
- Secretionary calcareous - stacked with calcite.
Foraminifera shells in 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.
Cycles of life
The class of foraminifers is characterized by a haplo-diplophase life cycle. In a generalized scheme, it looks like this: representatives of haploid generations undergo nuclear division, as a result of which a single-type row of gametes with two flagella appears. These cells merge in pairs and form the integral structure of the zygote. From herin the future, an adult individual belonging to the agamont generation will develop.
The fact that the doubling of the chromosome set occurs during the fusion causes 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
Let's consider the role and significance of foraminifers in nature and human activity.
Feeding on bacterial organisms and the remains of organic nature, protozoa do a great job of cleaning up water bodies from pollution.
Protozoa, among which there are many foraminifera, have a high fertility rate under certain environmental conditions. They act as food for the fry.
Euglenas, in addition to serving as 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 widely used by man.
Systematic 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 highlights the presence of 15 subclasses and 39 squads in them.
Results
Based on the material of the article, it can be understood that foraminifera 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 planet's soils.