Agnatha

n. class of vertebrates that have no jaws or paired limbs (including lampreys, hagfishes, etc.)

Agnatha (Greek, "no jaws") is a paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. Agnatha have existed since the Cambrian, and continue to live in modern times. There are two extant groups of jawless fish (sometimes called cyclostomes), the lampreys and the hagfish, with about 100 species between them. In addition to the absence of jaws, Agnatha are characterised by absence of paired fins; the presence of a notochord both in larvae and adults; and seven or more paired gill pouches. The bronchial arches supporting the gill pouches lie close to the body surface. There is a light sensitive pineal eye (homologous to the pineal gland in mammals). There is no identifiable stomach. Fertilization is external. The Agnatha are ectothermic, with a cartilaginous skeleton, and the heart contains 2 chambers.
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Noun
1. superclass of eel-shaped chordates lacking jaws and pelvic fins: lampreys; hagfishes; some extinct forms
(synonym) superclass Agnatha
(hypernym) class
(member-holonym) Vertebrata, subphylum Vertebrata, Craniata, subphylum Craniata
(member-meronym) jawless vertebrate, jawless fish, agnathan

(means jawless): The Class Agnatha represents the most primitive 'jawless' vertebrates. MHC genes have been cloned from all vertebrate classes except Agnatha.