A primitive group of deep sea fishes, with two suborders, the Alepocephaloidei (slickheads and allies - Alepocephalidae, Bathylaconidae and Platytroctidae), and the Argentinoidei (marine smelts - Argentinidae, Microstomatidae and Opisthoproctidae).
Members of the group share a number of osteological and other internal characters. They have no fin spines, the dorsal fin is behind the middle of the body and the upper jaw margin is formed from both the premaxilla and the maxilla.
They also share a complex structure called the crumenal organ (or epibranchial organ), a paired structure formed from the last two gill arches and the front of the oesophagus. Food particles are trapped in the crumenal organ and held there by large gill rakers.
Authors disagree on the composition and relationships of this group, sometimes placing argentiniform families, plus the galaxiids and retropinnids in the Osmeriformes (see Eschmeyer & Fong 2012). Others (Lavoué et al. 2008; Poulsen et al. 2009) have elevated the suborder Alepocephaloidei to the order Alepocephaliformes.
Begle, D.P. 1991. Relationships of the osmeroid fishes and the use of reductive characters in phylogenetic analysis. Systematic Zoology 40(1): 33-53
Begle, D.P. 1992. Monophyly and relationships of argentinoid fishes. Copeia 1992(2): 350-366
Diogo, R. 2008. On the cephalic and pectoral girdle muscles of the deep sea fish Alepocephalus rostratus, with comments on the functional morphology and phylogenetic relationships of the Alepocephaloidei (Teleostei). Animl. Biol. 58(1): 23-29.
Eschmeyer, W.N. & Fong, J.D. 2012. Species of Fishes by family/subfamily. Catalog of Fishes. Online version updated 15 March 2012. http://research.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp
Fink, W.A. 1984. Basal Teleosts: relationships. 202-206 in Moser, H.G. et al. (eds). Ontogeny and Systematics of Fishes. American Society of Ichthyologists and Herpetologists. Special Publication 1: 1-760
Johnson, G.D. & Patterson, C. 1996. Relationships of lower euteleostean fishes. pp. 251-332. In Stiassny, M.L.J., Parenti, L.R. & Johnson, G.D. (eds). Interrelationships of Fishes. San Diego : Academic Press 496 pp.
Lavoué S, Miya M, Poulsen J, Møller P, Nishida M. 2008. Monophyly, phylogenetic position and inter-familial relationships of the Alepocephaliformes (Teleostei) based on whole mitogenome sequences. Molecular Phylogenetics and Evolution 47: 1111–1121.
Nelson, J.S. 2006. Fishes of the World. JohnWiley & Sons, Inc., New Jersey, 601 p.
Poulsen, JY, PR Møller, S Lavoué, SW Knudsen, M Nishida, M Miya. 2009. Higher and lower-level relationships of the deep-sea fish order Alepocephaliformes ( Teleostei : Otocephala ) inferred from whole mitogenome sequences. Biological Journal of the Linnean Society 98(4): 923-936 DOI: 10.1111/j.1095-8312.2009.01323.x
Wiley, E.O. & Johnson, G.D. 2010. A teleost classification based on monophyletic groups. pp. 123-182 in Nelson, J.S., Schultze, H.-P. & Wilson, M.V.H. Origin and Phylogenetic Interrelationships of Teleosts. München, Germany : Verlag Dr. Friedrich Pfeil 480 pp.
Williams, R.R.G. 1987. The phylogenetic relationships of the salmoniform fishes based on the suspensiorium and its muscles. PhD Thesis, Department of Zoology, University of Alberta, Edmonton