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Alternate meanings: Amoeboid, Amoebozoa, Amoeba distributed operating system

Amoeba is a genus of protozoa that moves by means of temporary projections called pseudopods, and is well-known as a representative unicellular organism. The word amoeba is variously used to refer to it and its close relatives, now grouped as the Amoebozoa, or to all protozoa that move using pseudopods, otherwise termed amoeboids. They are found in sluggish waters all over the world, both fresh and salt, as well as in soils and as parasites.

Amoeba itself is found in freshwater, typically on decaying vegetation from streams, but is not especially common in nature. However, because of the ease which they may be obtained and kept in the lab, they are common objects of study, both as representative protozoa and to demonstrate cell structure and function. The cells have several lobose pseudopods, with one large tubular pseudopod at the anterior and several secondary ones branching to the sides. The most famous species, A. proteus, is 700-800 μm in length, but many others are much smaller. Each has a single nucleus, and a simple contractile vacuole which maintains its osmotic pressure, as its most recognizable features.

Early naturalists referred to Amoeba as the Proteus animalcule, after a Greek god who could change his shape. The name "amibe" was given to it by Bery St. Vincent, from the Greek amoibe, meaning change.

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