Chaos (genus) - Early History and Naming Controversy

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 "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 amoeba, unlike the modern Chaos.

In 1900, the biologist H. V. Wilson, at the University of North Carolina, discovered and isolated a giant amoeba that resembled Amoeba proteus but had cellular nuclei numbering in the hundreds. Since there existed already a genus of giant multinucleate amoebae, Pelomyxa, Wilson placed his organism in that taxon, naming it Pelomyxa carolinensis. This amoeba was easily cultivated and became a widely distributed and studied laboratory organism.

In 1926, Asa A. Schaeffer argued that Pelomyxa carolinensis was, in fact, identical to the amoeba that had been seen by Rösel in 1755, the "little Proteus" which Linnaeus had named Chaos chaos. Therefore, he urged that, in keeping with the principle of priority governing biological nomenclature, the name of the organism should be Chaos chaos. Several investigators argued vigorously against the validity of that name, but others adopted it. A third faction accepted the validity of the genus Chaos for Wilson's amoeba, but retained the second half of the binomial, referring to the organism as "Chaos carolinensis." By the early 1970s, all three names were in use concurrently, by various investigators. However, studies of the fine structure and physiology of the amoeba made it increasingly clear that there were profound differences between it and the other Pelomyxa (including the complete absence, in true Pelomyxa, of mitochondria). Since then, a nomenclatural consensus has emerged, and today the organism is generally known as Chaos carolinensis, as first proposed by Robert L. King and Theodore L. Jahn in 1948.