Radiolaria, the representatives of which we will consider in our article, are the simplest animals. Despite the primitive structure, they are the record holders in the number of chromosomes among all living organisms.
Radiolaria: representatives and habitat
These organisms are part of plankton. Radiolar body consists of one cell. Most often they can be found in the warm waters of the ocean. Plankton is not capable of independent movement. It consists of small organisms that drift in the water column.
In nature, about 8 thousand species are known. Many representatives of the type of radiolaria are found exclusively in a fossil state. Their second name is radial. It is explained by the structure of the skeleton. Its rays, which strengthen pseudopodia from the inside, determine the bizarre shape of the radiolar body. These are animals with radial symmetry.
There are various types of pseudopodia, or pseudopods of radiolarians. Some of them are derivatives of the internal capsule. They are in the form of rays and are called axopodia. This type of pretopodia determines the motor activity of these unicellular organisms.
If the surface cytoplasm takes part in the formation of the organelles of movement, pseudopodia become threadlike. They are called phylopodia. They perform the function of capturing food particles.
Skeleton structure
Living radiolarians have an intracellular skeleton. Its formation takes place in several stages. First, the central cytoplasm forms a skeletal capsule, then radial needles depart from it.
Representatives of the Radiolaria class are grouped into several subclasses. This classification is based on several features. This is the structure and chemical composition of the skeleton, as well as the structure of axopodia - organelles of radiolar movement. In representatives of the Akantaria subclass, the skeleton includes up to 20 needles. All of them are formed by strontium sulfate. The protozoan skeleton of the Polycystinea subclass consists entirely of silicon sulfate. The deepest radiolarians are Feodaria. The basis of their skeleton is a combination of organic matter and silica.
Life processes
Since radiolarians are representatives of the simplest, all the physiological features of this sub kingdom are also characteristic of them. Digestion occurs in special vacuoles. Radiolar reproduction is carried out in two ways. This may be cell division in half or spore formation. Radiolaria breathe through the cell membrane.
In some species, the cytoplasm contains unicellular algae, which absorb carbon dioxide for photosynthesis. In this case, they emit additional oxygen. Radiolaria use it for respiration and oxidation of organic substances. At the same time, cytoplasm algae needs radiolarians as a home. Such a mutually beneficial existence is called symbiosis. It is observed only in radiolarians, which live in the zone of water illuminated by the sun.
Representatives of radiolarians and solarians: the main differences
The simplest organisms are very diverse. Sometimes radiolarians are compared with their "relatives" - solar cells. The latter also belong to the class Sarkodovye, have a spherical shape of the cell. But sunwalkers prefer to live in fresh water. Their cytoplasm is devoid of a central capsule.
Unlike representatives of radiolarians, they do not have an internal skeleton. It is located outside the rounded cell. But in terms of chemical composition, the skeletons of radiolarians and solarians are similar. These are mainly silicon compounds.
Their axopodia, similar to rays, depart from the cell. Stinging organelles are located in these structures, with the help of which the sunstrokes capture prey. They prey on bacteria, unicellular algae, invertebrate larvae, ciliates and euglena.
Unique features
Despite the fact that radiolarians are representatives of the most primitive animals, many of their features remain a mystery to scientists. Just imagine, their genetic apparatus consists of 1600 chromosomes! For comparison, a person has only 46.
When you look at the photo radiolarium, it may seem that their cell is inside the skeleton. In fact, this is not so at all. Living radiolarians have an internal skeleton. And it becomes visible after the death of cell structures.
Value in nature
Skeletons of radiolarians are the basis of many rocks. These are quite ancient organisms. Their first fossil remains were found in Precambrian strata. Therefore, in geology, radiolarians are often used when necessary to determine the age of rocks.
When they die, the skeletons of these protozoa initially settle to the bottom in the form of radiolaria sludge. Over time, it turns into sedimentary rocks. These include radiolarites, flasks, silica, quartz. Sludge can also turn into special minerals. This is jasper and opal. They are widely used in the jewelry industry in the form of precious stones.
So, radiolarians are representatives of the subdomain Unicellular animals, the Sarcode group. They have an internal skeleton, which may consist of silicon dioxide, strontium salts or organic matter. Radiolaria are part of plankton, found in warm tropical seas. These are very ancient organisms, among which there are many fossil species. Therefore, in geology they are used to determine the age of rocks. The skeletons of radiolarians are part of many sedimentary rocks and minerals: silica, flasks, radiolarites, quartz, and opal.