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).
The group Actinopterygii (; ), comprising ray-finned fish or actinopterygians, comprises over 50% of all living vertebrate species. They are distinguished by their delicate, web-like fins in contrast to the more substantial, fleshy fins found in the sister class Sarcopterygii.