Amoeba

The word amoeba is a descriptive term for various single-celled organisms which move about by means of temporary projections, called pseudopods. Sometimes the term is used to mean any such organism, here called amoeboids, but most often it applies only to those with blunt (lobose) or tapering (filose) pseudopods. These are found in sluggish waters, fresh and salt, all over the world, as well as in soils and as parasites. They readily make appearances in putrefying infusions, carried aerially, and are generally able to form protective cysts.

When capitalized and italicized, Amoeba refers to a particular genus, of which the best-known species is A. proteus. They are found in freshwater, typically on decaying vegetation from streams, but are not especially common in nature. They are often found in biology labs, however, serving as common objects of study. This stems both from the ease which they may be obtained and kept alive under the microscope, and from their simple demonstration of certain aspects of cellular structure and function, such as fission.

Amoeba may be as large as 700-800 μm in size, though some are much smaller. The cells usually form many lobose pseudopods, including a dominant one which is broader than the others, into which the cell mass flows during locomotion. They ingest smaller organisms which are surrounded by the pseudopods, which then merge together. 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.