agnathan /ˈæɡ.nə.θən/adjective 1noun 1forms 1 adjective1 •Belonging or pertaining to the superclass Agnatha, the jawless vertebrates.Haikouichthys is one of three species of jawless (or agnathan) fish to be found in the Early Cambrian period. — 2005 noun1 •A member of the superclass Agnatha of jawless vertebrates.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 formsagnathans
