The common name of any of several viviparous fishes of the genus Poecilia. They range from the Atlantic and Gulf coasts of North America from
southeastern North Carolina to Argentina in South America. Mollies were originally put in the genus Mollienesia, named after the French politician Comte François Nicolas Mollien (1758–1850) but were later added to Poecilia, which includes other common aquarium fish such as guppies and swordtails. Their current taxonomic classification is:
Superorder: Acanthopterygii (spiny-rayed fishes)
Order: Atheriniformes
Family: Poeciliidae (livebearing toothcarps)
Genus: Poecilia
Some of the better known species include:
The Amazon molly, P. formosa, is extremely interesting to geneticists. It is a gynogenetic fish that reproduces through the development of ameiotic diploid eggs triggered by insemination by males of related species without following karyogamie.
In other words, this species consists only of females, which copulate with males of other molly species but which do not receive any genetic material from those males. The sperm is used only to stimulate the development of the eggs. This process, termed pseudogamy is basically stimulated parthenogenesis. As you may have guessed, the name "Amazon" has nothing to do with where these fish are found (southwestern Texas into northeastern Mexico), but rather with the fact that all members are female.