Definition of Agnatha in US English:


  • A group of primitive jawless vertebrates which includes the lampreys, hagfishes, and many fossil fishlike forms.

    Superclass "Agnatha": the living forms are in the classes "Myxini" (hagfishes) and "Cephalaspidomorphi" (lampreys)

    Compare with cyclostome
    • ‘Here, we use the sequences of 35 nuclear protein-encoding genes to provide definitive evidence for the monophyly of the Agnatha (jawless vertebrates, a group encompassing the hagfishes and lampreys).’
    • ‘By the mid 1970s, insulin had been isolated and sequenced from all classes of vertebrates, including Agnatha.’
    • ‘The earliest fossil vertebrates belong to a group called the Agnatha or jawless vertebrates.’
    • ‘All of these jawless fish are traditionally placed in the order Agnatha, but as you can see, this group is paraphyletic, including some but not all descendants of the common ancestor.’
    • ‘In modern classification schemes, living vertebrates consist of two main groups, the jawless Agnatha (represented by hagfishes and lampreys) and the jawed Gnathostomata.’


From modern Latin Agnatha, from a- ‘without’ + Greek gnathos ‘jaw’.