Chaos (amoeba)

''Chaos'' is a genus of single-celled amoeboid organisms in the family Amoebidae. The largest and best-known species, the so-called "giant amoeba" ''Chaos carolinensis'', can reach lengths of 5 mm, although most specimens fall between 1 and 3 mm.

Members of the genus closely resemble those of genus ''Amoeba'' and share the same general morphology, producing numerous cylindrical pseudopods, each of which is rounded at the tip. However, while ''Amoeba'' have a single nucleus, ''Chaos'' can have as many as a thousand. Because of this attribute, ''C. carolinensis'' was once placed in the genus ''Pelomyxa'' alongside the giant multinucleate amoeba ''Pelomyxa palustris.'' Recently, molecular phylogenetic studies of this species have confirmed the view of some earlier researchers that it is more closely related to ''Amoeba'' than to ''Pelomyxa''. The species is now placed in the independent genus ''Chaos'', a sister group to ''Amoeba''.

Dietary habits

''Chaos'' species are versatile heterotrophs, able to feed on bacteria, algae, other protists, and even small multicellular invertebrates. Like all Amoebozoa, they take in food by phagocytosis, encircling food particles with its pseudopodia, then enclosing them within a food ball, or vacuole, where they are broken down by enzymes. The cell does not have a mouth or cytostome, nor is there any fixed site on the cell membrane at which phagocytosis normally occurs.

Movement

The cell's membrane, or plasmalemma, is extremely flexible, allowing the organism to change shape from one moment to the next. The cytoplasm within the membrane is conventionally described as having two parts: the internal fluid, or endoplasm, which contains loose granules and food vacuoles, as well as organelles such as nuclei and mitochondria; and a more viscous ectoplasm around the perimeter of the cell, which is relatively clear and contains no conspicuous granules. Like other lobose amoebae, ''Chaos'' move by extending pseudopodia. As a new pseudopod is extended, a variable zone of ectoplasm forms at the leading edge and a fountaining stream of endoplasm circulates within. The effort of describing these motions, and explaining how they result in the cell's forward movement, has generated a large body of scientific literature.

Early history and naming controversy

The genus ''Chaos'' has had a long and often confusing history. In 1755, Rösel von Rosenhof saw and depicted an amoeboid he named "''der kleine Proteus''" ("the little Proteus"). Three years later, Linnaeus gave Rösel's creature the name ''Volvox chaos''. However, because the name ''Volvox'' had already been applied to a genus of flagellate algae, he later changed it to ''Chaos chaos''. In subsequent decades, as new names and species proliferated, accounts of ''Chaos'', under a variety of synonyms, became so thoroughly entangled with descriptions of similar organisms, that it is virtually impossible to differentiate one historic amoeboid from another. In 1879, Joseph Leidy suggested collapsing all the "common" large, freshwater amoebae into one species, which he proposed to call ''Amoeba proteus''. A dozen species, including several that had been identified as belonging to ''Chaos'', were to be regarded as synonyms of ''Amoeba proteus''. However, in the description he gives of this organism, it is clearly defined as a uninucleate