A number of specimens of snakes which are lacking most of their dorsal scales have been found. Only two species with this mutation are currently in breeding programs, as far as I am aware: the Texas ratsnake and a gopher snake.
Bechtel, H.B., and E.Bechtel. 1991. Scaleless snakes and a breeding report of scaleless Elaphe obsoleta lindheimeri. Herpetological Review 22(1): 12-14.
Bennett, A.F., and P. Licht. 1975. Evaporative water loss in scaleless snakes. Comparative Biochemical Physiology 52A: 213-215.
Gray, B. 1997. How common are scaleless snakes? (letter to editor) Reptile & Amphibian Magazine. (No. 51): 8-9.
LeClere, J.B. 1996. Natural history & captive care of the northern water snake (Nerodia sipedon sipedon). (photo) Reptile & Amphibian Magazine (Mar./Apr.): 46+
Licht, P., and A.F. Bennett. 1972. A scaleless snake: tests of the role of reptilian scales in water loss and heat transfer. Copeia 1972(4): 702-707.
Murphy, J.B., et al. 1987. Scutellation and pigmentation defects in a laboratory colony of western diamondback rattlesnakes, Crotalus atrox: mode of inheritance. Herpetologica 43: 292-300.
Stickel, W.H. 1942. A partially scaleless garter-snake. Copeia 1942: 181.
Online Article: "Nekked Snakes" by Steve Campbell