Sarcodinos Characteristics and Classification

Simon Doyle

The sarcodinos, also known as rhizopods or class rhizopoda, they are one of the four classes into which the protozoan phylum was traditionally divided, belonging to the animal kingdom.

It is necessary to highlight that, at present, it is recognized that sarcodins do not belong to the animal kingdom but to the protist, since protozoa do not have enough complexity to be considered animals.

Being protozoa, it is a group of unicellular and microscopic protist organisms that usually live in colonies (conglomerates formed from a common ancestor).

They have the ability to become entrenched in order to protect themselves from the environment. This means that they can isolate external agents that are not favorable to them, wrapping them with their body.

These have limb-like structures (called pseudopods), which allow them to move around and get their food..

In this order of ideas, they do not produce their own food, but take advantage of other elements that they find in the environment. This is why they are called heterotrophs.

Formerly, it was considered that all amoebas were part of the sarcodinos, as they are organisms characterized by the presence of pseudopods. However, today it has been established that amoebas do not constitute a taxonomic group but can be found in any kingdom, in addition to the protista: animal, plant, fungi.

The protist kingdom and the sarcodinos

The protist kingdom brings together eukaryotic organisms that are composed of a single cell (unicellular) that is responsible for carrying out all the functions of organisms.

Within this kingdom, there are two large groups: unicellular algae and protozoa. The latter in turn is divided into flagellates, sporozoans, ciliates and sarcodines..


Sarcodines, called rhizopods or rhizopodas, are a group of protozoa that differ from the others by the use of foot-like structures for their locomotion. These structures are known as pseudopods (which means "false feet")..

Most of these are found on the seabed, where they are part of the microplankton while other species are parasitic and live inside other animals..

Characteristics of sarcodinos

-They are eukaryotic, that is, they have a nucleus that contains the genetic material and this is not scattered in the cytoplasm.

-They are unicellular.

-They do not have a proper mouth or digestive system. They feed through phagocytosis and endocytosis.

-They produce pseudopods that they use to move around and, in some cases, feed themselves. Pseudopodia can be produced from any part of the body of the sarcodinum and can return to the body in the same way in which they were removed..

There are three types of pseudopodia: 1) Reticulopodia, they are long and thin and form a network of pseudopodia. 2) Filopodia, fine and sharp. Similar to reticulopodia but do not form networks. 3) Lobopodia, are thicker than the previous ones, have blunt tips and resemble the fingers of a hand. These are made up of amoebae.

-Some have shells or skeletons called teak. Others are just naked.

-The size of the sarcodinos varies from one organism to another. There are tiny rhizopods (such as microscopic amoebas) and larger ones (such as foraminifera, which can measure several millimeters).

-Some of the aquatic sarcodins (especially the foraminifera) tend to form symbiotic relationships with green algae and with dinoflagellate algae..

-Most sarcodins live as independent organisms. However, a small group of these constitute parasitic organisms. In fact, some of the pathogens that affect humans are sarcodines, such as entamoeba histoloytica, which causes dysentery..

-Upon death, the skeletons of the foraminifera, and to a lesser extent the other sarcodines with teak, become part of the marine sediments. These have contributed to paleontological studies, since the remains of the sarcodines date from various geological eras.

-They can be found both in aquatic and terrestrial spaces.

-They reproduce through binary fission, which consists of the division of the cell nucleus to give rise to two organisms. When the cytoplasm is to be separated, both cells produce pseudopods that help them separate from each other. If it is an organism with teak, it may be that the teak separates in two equally or that one cell touches a shell while the other does not..


In the sarcodinos there are two great groups; those with a naked body and those with a body endowed with complementary structures.

Naked-bodied sarcodinos are primarily amoebae. Your body is covered only by the plasma membrane, which is responsible for keeping the contents of the cell inside.

Sarcodins with complementary structures, in addition to having the plasma membrane, have a theca that can be materialized in two ways: in the form of a shell or in the form of a false skeleton.

Teak is created from elements or particles that are found in the environment and that are compacted to form more complex structures.

There are three types of sarcodines with complementary structures: foraminifera, radiolaria and heliozoa.

  1. Foraminifera are found in the sea and have a shell (exoskeleton) made up of salts and other minerals. When they die, their exoskeleton becomes part of the sediments of the seabed.
  2. Radiolaria have a kind of internal skeleton made of silica that takes radial shapes that are pleasing to the eye (hence the name)..
  3. Heliozoans have a mineral skeleton also organized in radial shapes, which make them look like a tiny sun (helium = sun).


Sarcodines can be herbivores or carnivores and feed through phagocytosis and endocytosis, which consist of the absorption and assimilation of organic particles..

In some cases, these organisms use their pseudopods to trap nutrient particles. The process consists of forming a cage with the pseudopods and attracting the particle into the sarcodinum, where they will be digested..


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