Poecilia sphenops was created in 1846.
The scientific name for the black molly (fish) is Poecilia latipinna.
Poecilia wingei was created in 2005.
Poecilia vetiprovidentiae was created in 1950.
Poecilia velifera was created in 1914.
The commoner "Poecilia sphenops" gets to around 2 inches but the larger members of the species, the P. latipinna and P. velifera grow to around just under 5 inches.
The fish you are referring to is likely the Black Molly (Poecilia sphenops). They are known for their distinct black coloration with white or yellow dots on their tail.
The Balloon molly is a Black Molly (Poecilia sphenops) that has been bred with a deformed spine. (It was an inevitable accident of (bad) inbreeding) This deformity shortens the fishes lifespan. If this deformity had occured in any fish I had bred I would have euthanased the fish rather than perpetuate a deformity. I personally believe that the breeders who deliberately breed and allow this deformed fish to be sold are doing the wrong thing by the species.
Poecilia reticulata
There are hundreds of "sports" that unscrupulous people have given names to like "Dalmation" "Lyretail" etc. There are actually only three types of molly. Mollies were once classified as "Mollienesia" but the taxonomists have now placed the Molly into the same classification/genera as the Guppy and they are now classified as "Poecilia". The three species are P. velifera, P. latipinna and P. sphenops.
Dalmatian mollies, a popular aquarium fish variant, do not exist in the wild as a distinct breed; they are selectively bred for their unique coloration and patterns. The wild ancestors of mollies, including the black molly (Poecilia sphenops), can be found in freshwater and brackish environments in parts of Central and South America. In their natural habitats, these fish inhabit rivers, lakes, and coastal areas. Therefore, while mollies do live in the wild, Dalmatian mollies specifically do not.
Poecilia reticulata is the current taxonomic name. They used to be Lebistes reticulata.
Yes, guppies are freshwater fish. Their scientific name is Poecilia reticulata.