; subclass Actinopterygii, order Atheriniformes)
A family of freshwater fish, including deep-bodied as well as elongate species, that have a single dorsal fin opposite the anal fin, and a fairly pointed snout. They are live-bearing, the modified anal fin of the males acting as a primitive gonopodium. There are about 24 species, found in western Mexico.
Subjects: Zoology and Animal Sciences.