This order includes three families of largely freshwater species (Nelson 2006). The group occurs worldwide. All species are characterised by an elongate body with a ventral gill opening. Johnson & Patterson (1993) suggested a relationship with atherinoform, mugiloform and gasterosteiform fishes.
Johnson, G.D. & Patterson, C. 1993. Percomorph phylogeny: a survey of acanthomorphs and a new proposal. Bulletin of Marine Science 52(1): 554–626
Nelson, J.S. 2006. Fishes of the World. Hoboken, New Jersey : John Wiley & Sons, Inc. 601 pp.