Gymnotiformes - True Knifefish

Suborder Gymnotoidei - Naked-back Knifefishes

Hagfish

Gymnotidae
Naked-back Knifefishesh

Suborder Sternopygoideii - Bluntnose, Ghost, Glass, & Sand Knifefishes,

Hagfish

Apteronotidae
Ghost Knifefishes
Lamprey

Rhamphichthyidae
Sand Knifefishes
Lamprey

Sternopygidae
Glass Knifefishes
Osteoglossidae

Hypopomidae
Bluntnose Knifefishes

References:
Betancur-R, R., E. Wiley, N. Bailly, M. Miya, G. Lecointre, and G. Ortí. 2014. Phylogenetic Classification of Bony Fishes --Version 3 (http://www.deepfin.org/Classification_v3.htm)
Eschmeyer, W. N. (ed). Catalog of Fishes Classification (http://www.calacademy.org/scientists/catalog-of-fishes-classification/). Electronic version accessed 11 Nov 2014
Froese, R. and D. Pauly. Editors. 2014. FishBase. World Wide Web electronic publication. www.fishbase.org, version (08/2014).