Amoeba

Alternate meaning: Amoeba distributed operating system

Amoebae are various single-celled protozoa which move about by means of temporary projections, called pseudopods. They are found in sluggish waters all over the world, fresh and salt, as well as in soils and as parasites. The best-known genus is Amoeba, always capitalized and italicized. Although not very common in nature, it is often used in laboratories for their simple demonstration of certain aspects of cellular structure and function, such as fission.

Sometimes all protozoa with pseudopods are called amoebae, but the term is often reserved for those where the pseudopods are lobose (broad and blunt) or filose (narrow and tapering), and without microtubule support. This use is followed here, and the others are called amoeboids.

Table of contents

1 Form and behavior 2 Groups of amoebae 3 External link

Form and behavior

Amoebae range from tiny protozoa only 10-20 μm across to the giant amoeba, Pelomyxa, which may reach several millimetres in length. The slime molds are mutlinucleate or multicellular amoebae that form giant masses of macroscopic size, called plasmodia.

In most amoebae the cell is divided into an clear outer layer, called ectoplasm, and a granular inner layer, called endoplasm. In the active form, there are usually one or more pseudopods along the anterior margin of the cell. The posterior ectoplasm may form a bulb, called the uroid. In Amoeba and many other genera, there is one primary pseudopod, and the cell moves by flowing into it. Some others crawl using relatively permanent pseudopods as limbs, or roll, the ectoplasm sliding around the cell like a tank tread.

As amoebae move, they surround potential food particles, trapping them in vacuoles so their contents may be digested. When food is scarce, they may retract their pseudopods and enter resting states. Many amoebae form cysts to survive hostile conditions, and these are often carried aerially. For instance, amoebae readily appear in putrefying infusions.

Groups of amoebae

Amoebae are found among several different groups of eukaryotes. Further, some cells in multicellular organisms are structured and function like amoebae. These include our white blood cells, which consume pathogens.

Most of the lobose amoebae probably form a monophyletic group, called the Amoebozoa. This includes naked amoebae like Amoeba and Acanthamoeba, shelled amoebae like Arcella and Difflugia, and most slime molds. They may also include the pelobionts, such as the giant amoeba, and entamoebae, such as the pathogens that cause amoebic dysentery.

Most filose amoebae appear to form a separate group, called the Cercozoa, together with various flagellates that tend have amoeboid forms. This includes shelled amoebae, like Euglypha, and the chlorarachniophytes, which have chloroplasts.

Smaller groups of amoebae include the Heterolobosea, most of which can change between flagellate and amoeboid stages, the vampyrellids and nucleariids. In addition, amoebae have appeared in many other lines of protozoa and algae.

External link

• The Amoebae website brings together information from published sources.