agnathan

n.eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms

同义词：jawless vertebratejawless fish

1. The study of agnathans provides insight into the early evolution of vertebrates.
   对无颌类的研究为脊椎动物的早期进化提供了见解。
2. Agnathans lack true jaws, which distinguishes them from more advanced vertebrates.
   无颌类缺乏真正的颌骨，这使它们与更进化的脊椎动物区别开来。