A jawless vertebrate, representing the most primitive group of living vertebrates that lacks paired jaws and typically has a circular, sucker-like mouth. Modern examples include lampreys and hagfish.
From Greek 'a-' meaning 'without' and 'gnathos' meaning 'jaw,' literally 'jawless.' The term was established in the 19th century when paleontologists and zoologists recognized that the earliest vertebrates lacked the hinged jaws that characterize most modern fish.
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