The Collaborative International Dictionary of English v.0.48:

Agnatha \Agnatha\ n.
   a class of eel-shaped chordates with a cartilaginous skeleton
   lacking jaws, scales, and pelvic fins. Among these are the
   lampreys and hagfishes. There are some extinct forms.

   Syn: class Agnatha.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Agnatha
    n 1: superclass of eel-shaped chordates lacking jaws and pelvic
         fins: lampreys; hagfishes; some extinct forms [syn:
         Agnatha, superclass Agnatha]