Agnatha (Greek, "no jaws") is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present (cyclostomes) and extinct (conodonts and ostracoderms) species. The group excludes all vertebrates with jaws, known as gnathostomes.The agnathans as a whole are paraphyletic, because most extinct agnathans belong to the stem group of gnathostomes.