Practice question

Jawless fishes retain ancestral craniate morphology lacking innovations of gnathostomes. Most conspicuously they lack paired pectoral and pelvic fins that provide stabilization, braking and maneuvering in cartilaginous and bony fishes. Instead, locomotion depends on median dorsal and caudal fins plus body undulation creating anguilliform waves. Additional primitive characters include absence of true scales in hagfishes, cartilaginous cranium, single nostril and persistence of notochord. Gill basket supports branchial structures. Absence of paired fins reflects evolutionary stage predating appendage duplication and fin module development via Tbx genes, distinguishing Agnatha from Gnathostomata.