Sarcodinos: Definition, History and Origins of This Group of Unicellular and Microscopic Protist Organisms

It is an ancient phylum of unicellular protists that encompasses about 200 species.

Sarcodine is any superclass (sometimes class or subfilter) protozoan.

These organisms have a continuous cytoplasm and use temporary cytoplasmic extensions called pseudopods in locomotion (called amoeboid movement) and feeding.

Sarcodines include the genus Ameba and pathogenic species, for example, Entamoeba histolytica which causes dysentery . The cells of these protozoa can be spherical or irregular in shape; the film (or envelope) is usually thin and flexible.

Sometimes there is an outer shell or skeleton. The cytoplasm, composed of ectoplasm and endoplasm, can contain more than one nucleus.

Food, which sticks to the surface of the body or becomes trapped by pseudopods, is digested in food vacuoles.

Sarcodines reproduce sexually by syngamy (fusion of two gametes) and asexually by division or budding.

In multinucleated forms, cytoplasmic division occurs with distribution of the nuclei. Some sarcodines have flagella during certain stages of their development; in other groups flagellated and non-flagellated generations alternate.

Sarcodines can be solitary or colonial. Although some are parasites of plants and animals, most sarcodines live in the wild, feeding on bacteria, algae, other protozoa, or organic debris.

The genera are distinguished by the structure of their pseudopods. Sarcodina, the largest phylum (11,500 living species and 33,000 fossil species) of protozoa).

Includes amoebae and related organisms; which are all solitary cells that move and capture food by means of pseudopods, which flow temporary extensions of the cell.

Most sarcodines are free-living; others are parasites. One of these parasites is the organism that causes amoebic dysentery. With the exception of chloroplasts, sarcodins are identical to amoeboid members of the phylum Chrysophyta.

Sarcodins can reproduce asexually by cell division, often without disruption of the nuclear envelope that is typical in mitosis, or sexually by meiosis and the production of haploid gametes, followed by gamete fusion and zygote formation.

Sarcodines include the naked forms (amoebae) and forms with perforated shells, or evidence, through which pseudopodia can spread. The best known shell forms are foraminifera, with calcium carbonate shells.

Sarcodina (phylum Protozoa, subphylum Sarcomastigophora) A superclass of protozoa that form pseudopods for food and locomotion.

Most species live in marine aquatic environments, but some are found in freshwater (and are important members of the soil fauna) and some are parasitic in the intestinal tracts of vertebrates and invertebrates.

The superclass includes Radiolaria, known from the Cambrian, and Heliozoa, which are exclusively freshwater and have a fossil record dating back only to the Pleistocene.

Early history and origins of Sarcodina

The oldest record of an amoeboid organism was produced in 1755 by August Johann Rösel von Rosenhof, who called his discovery “Der Kleine Proteus” (“the little Proteus”).

Rösel’s illustrations show an unidentifiable freshwater amoeba, similar in appearance to the common species now known as Amoeba proteus.

The term “Proteus animalcule” remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid.

In 1822, the French naturalist Bory de Saint-Vincent erected the genus Amoeba (from the Greek ἀμοιβή amoibe, meaning “change”).

Bory’s contemporary, CG Ehrenberg, adopted the genus in his own classification of microscopic creatures, but changed the spelling to Amoeba.

In 1841, Felix Dujardin coined the term “sarcode” (from the Greek σάρξ sarx, “meat” and εἶδος eidos, “form”) for the “thick, glutinous and homogeneous substance” that fills the bodies of protozoal cells.

Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells.

Thirty years later, Austrian zoologist Ludwig Karl Schmarda used ‘sarcode’ as the conceptual basis for his division Sarcodea, a phyl-level group made up of ‘unstable, changeable’ organisms with bodies largely composed of ‘sarcode’.

Later workers, including the influential taxonomist Otto Bütschli, amended this group to create the class Sarcodina, a taxon that remained in wide use for most of the 20th century.

Within the traditional Sarcodina, amoebas were generally divided into morphological categories, based on the shape and structure of their pseudopods.

Amoebas with pseudopods supported by regular microtubule arrangements (such as freshwater Heliozoa and Radiolaria marina) were classified as Actinopods; while those with unsupported pseudopods were classified as Rhizopods.

Rhizopods were subdivided into lobose, phylum, and reticulose amoebas, according to the morphology of their pseudopods.

Sarcodina dismantling

In the last decade of the 20th century, a series of molecular phylogenetic analyzes confirmed that Sarcodine was not a monophyletic group.

In view of these findings, the old scheme was abandoned and the Sarcodina amoebas dispersed among many other high-level taxonomic groups.

Today, most traditional sarcodines are placed in two supergroups of eukaryotes: Amoebozoa and Rhizaria.

The rest has been distributed among the excavations, opisthokonts and stramenopiles. Some, like the Centrohelida, have yet to be placed in any supergroups.

Subfilo Sarcomastigofora

The subphylum Sarcomastigofora belongs to the kingdom Protista and includes many unicellular or colonial, autotrophic or heterotrophic organisms. It is divided into three superclasses, the Mastigophora, the Sarcodina and the Opalinata.

Mastigofora Superclass : This group of protozoa is also flagellated. They move with the help of flagella. They feed on bacteria, algae, and other protozoa.

Sarcodina superclass : This group includes amoebae, heliozoa, radiozoa, and foraminifera. The amoeba has pseudopods that are used for locomotion and food.

In the amoeba, flagella are lobular protrusions that extend from the cell membrane. In heliozoa, radiozoa, and foraminifera, pseudopods are like needles that protrude from cells.

Opalinata Superclass : Opalinata are a small group of protists that belong to the Opalinidae family.

The microscopic organisms in this group are opalescent (having or emitting an iridescence like that of an opal) in appearance when in full sunlight.

Most opaline live as endocomberals (a commensal life within the body of their host) in the large intestine and cloaca of frogs and toads. They are sometimes found in fish, reptiles, mollusks, and insects.