Biological taxonomy is a hypothesis regarding the evolutionary relationships of populations. Thus there is never a correct scientific name for any organism, although at any point in time there may a preferred name, and a series of names that have lost favor with the advance of science. Older, less-likely names become synonyms. A proliferation of synonyms is a healthy indicator of an active research interest in a group of organisms.

Synonyms may also be viewed negatively, however, as an impediment to governmental regulation. For this reason, natural resource agencies generally favor standardized taxonomies, such as that offered for mollusks by Turgeon and colleagues (1998). Although well meaning, efforts at taxonomic standardization are science-killers, and cannot be condoned.

Note in the following table that some taxa listed as synonyms in North America remain valid on other continents. Although Ancylus remains the preferred genus for the European Ancylus fluviatilis, for example, here in America all the species previously referred to Ancylus have been transferred to Ferrissia.