animals having a bony or cartilaginous skeleton with a segmented spinal column and a large brain enclosed in a skull or cranium

the flat broad limb of aquatic animals specialized for swimming

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

fish-like vertebrate with bony plates on head and upper body; dominant in seas and rivers during the Devonian; considered the earliest vertebrate with jaws

any of various mostly cold-blooded aquatic vertebrates usually having scales and breathing through gills

the flat broad limb of aquatic animals specialized for swimming