General information
FishBase

Catalog of Fishes

Fishes of the World, fourth Edition (Hardcover)
by Joseph S. Nelson

Freshwater Fish Distribution (Hardcover)
by Tim M. Berra

Divergence time estimation among cyclostomes
Kuraku, S, S Kuratani. 2006.
Time scale for cyclostome evolution inferred with a phylogenetic diagnosis of hagfish and lamprey cDNA sequences. Zoological Science 23:1053-1064.

Phylogenetics of agnathans
Takezaki N, Figueroa F, Zaleska-Rutczynska Z, et al.
Molecular phylogeny of early vertebrates: Monophyly of the Agnathans as revealed by sequences of 35 genes
MOLECULAR BIOLOGY AND EVOLUTION 20 (2): 287-292 FEB 2003