Definition of "agnathan"

Haikouichthys is one of three species of jawless (or agnathan) fish to be found in the Early Cambrian period.

2005, Tim Haines, Paul Chambers, The Complete Guide to Prehistoric Life, BBC Books, page 20

Thus should the cranial neural crest in cyclostomes prove to be non-skeletogenous this might be a reflection either of its own primitiveness or of the different evolutionary origins and morphological status of the visceral skeleton in agnathans and gnathostomes.

1956, D. R. Newth, “On the Neural Crest of the Lamprey Embryo”, in Journal of Embryology and Experimental Morphology, volume 4, page 358

The hagfish is an agnathan, a modern representative of the earliest evolved group of vertebrates, the ostracoderms or jawless fishes, which arose prior to the ancient placoderms (3).

1992, Peter J. Hanley et al., “Hagfish Humoral Defense Protein Exhibits Structural and Functional Homology with Mammalian Complement Components”, in Proceedings of the National Academy of Sciences, volume 89, page 7910