Sarcodes – general characteristics of the class, structure, life cycle

Written by Hasem

Sarcodes are a group of unicellular organisms that were previously considered a class or subtype. These include protozoa that do not have a constant body shape; they are covered with a membrane consisting of proteins and lipids. Microorganisms do not have a shell, but they can form a shell or internal skeleton.

General structure

The sarcode class is a large group of microorganisms, which unites more than 11 thousand species, differing in a wide variety of forms. It includes protozoa that lead a different way of life.

Most of them are marine life, but there are also freshwater microorganisms. Some protozoa can exist in the ground, moss of peat bogs and forests. Less common are parasitic representatives, the number of which is slightly more than one percent of other microorganisms.

The sarcode type constantly changes its appearance, as the formation of pseudopodia (pseudopods) occurs. Several years ago, biologists attributed the variability of protozoa to the absence of a coating around the cell, which was difficult to see even with an optical instrument.

If you use an electron microscope, you can see the thinnest membrane that has a fibrillar structure. Plasmalemma of sarcode representatives forms two layers:

  • outer dense ectoplasm;
  • internal liquid endoplasm.

During the life cycle, both layers easily interact with each other, in addition, the cell membrane is capable of being destroyed and restored. Apparently, such variability of plasmalemma layers and the absence of a dense covering explains the uncertainty in the configuration of the body of sarcodes.

Some microorganisms have an internal or external skeleton in the form of shells. Protozoa move with the help of pseudopodia, or pseudopods. They are processes of various configurations and are also designed to capture food.

The nutrition of microorganisms includes algae and common protozoa, which are digested by vacuoles formed in the cytoplasm. These are bubbles of liquid with digestive enzymes that the plasma membrane secretes around food particles.

Freshwater microorganisms have excretory organs – contractile vacuoles. Sarcodes are divided into 5 orders:

  • Amoeba.
  • Conch amoeba.
  • Foraminifera.
  • Beams.
  • Sunflowers.

The first 3 orders belong to rhizomes, and ray and sunflower are considered not as orders, but as subclasses.

Squad of rhizomes

The simplest microorganism belonging to rhizomes is naked amoeba. But the most common are the common protozoa, or proteus.

Common amoeba

The common amoeba lives in fresh waters, small ponds and muddy ditches, in addition, microorganisms multiply easily in laboratory conditions. This is the largest representative among the existing protozoa. When it moves, it can grow up to 0.5 mm and can be seen with the naked eye.

If you look at the amoeba through a microscope, you can see several long pseudopods, resembling lobes. The body shape of sarcodes is constantly changing, part of the pseudopodia is pulled inward, and some, on the contrary, are lengthened. The pseudopods are attached to the soil at several points, which helps the amoeba to move.

If the protozoan collides with food organics, then it grasps the entire particle and places it inside the plasma membrane along with the liquid. So bubbles with food are formed in the body, which are called digestive vacuoles, and the process of digesting organic matter takes place in them.

In addition, a transparent bubble periodically appears in the cytoplasm of an ordinary protozoan. This is a contractile vacuole that performs important vital tasks for the microorganism. It collects water from the cytoplasm, increases in size, and then contracts and throws it out through the hole.

This whole procedure takes place within 5-8 minutes. In the body of the amoeba, the amount of organic and inorganic substances is higher than in the surrounding liquid, so water enters the protoplasm of the microorganism. Thanks to the contractile vacuole, its excess is thrown out. If this did not happen, then the amoeba would simply dissolve in water.

Some species of protozoa can lead a parasitic lifestyle, settling in the intestines of vertebrates and invertebrates. In humans, five types of microorganisms live in the intestinal cavity. Four of them are considered harmless, but the fifth, which is called dysentery amoeba, can cause a serious illness – amebiasis.

Beam subclass

The most numerous marine subclass in terms of the number of species in the biological taxonomy of the sarcode is the rayworms, or radiolarians. It has more than 7-8 thousand species. Beams are planktonic organisms that mainly live in the sea waters of tropical and subtropical zones.

The body sizes of radiolarians range from 50 microns to 1 mm or more. There are some associations of sarcodes with a much larger body. A significant part of radiolarians have the shape of a sphere with a characteristic capsule in the center. It is an organic membrane located around the cytoplasm with a nucleus.

The walls of the capsule have many openings through which the intracapsular plasmalemma communicates with the extracapsular one. The membrane located in the center of the body is considered a skeletal formation that protects the plasmalemma with the nucleus. A fairly wide zone in radiolarians is formed by ectoplasm, which has numerous inclusions.

Most of them are mucus, which forms a thick layer. In addition to mucus, there are drops of fat in the cytoplasm of ray beams. All these formations facilitate sarcodes and help them move freely in the sea space. In some radiolarians, unicellular algae from the order of armored flagellates are found inside the cytoplasm.

This proves the process of symbiosis of the simplest organisms with the plant world. Algae in the body of protozoa receive nutrients and carbon dioxide, which is formed as a result of respiration. The ray-bearer subclass is divided into four orders:

  • Spumellaria.
  • Nazellarii.
  • Acantaria.
  • Feodaria.

All of them differ in typical forms of skeletal formations. The reproduction processes of ray beetles have not been sufficiently studied, although scientists have been studying these protozoa for a long time. The problem is that radiolarians do not live long in laboratory conditions, so complete results cannot be obtained.

Skeletal formation does not allow them to be divided into two parts, as is the case with amoebae. Most likely, the formation of embryos with one nucleus in them occurs as during asexual reproduction of foraminifera. This process in radiolarians requires further research.

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