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.
Agnathans are living fossils that show us what our 500-million-year-old ancestors looked like - they're basically swimming vacuum cleaners with no jaws! Lampreys can attach to other fish and literally drill through their skin with rows of rasping teeth, proving you don't need jaws to be a successful predator.
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