Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webs of skin supported by radially extended bony spines, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii (lobe-finned fish).
Actinopterygii (; ), also known as ray-finned fish or actinopterygians, comprises a large percentage of all living vertebrate species. They are distinguished by their slender, web-supported fins in contrast to the more substantial, fleshy fins found in Sarcopterygii.