What class contains the ray-finned fishes, the largest group of living vertebrates?

What class contains the ray-finned fishes, the largest group of living vertebrates? The answer is Actinopterygii, the class of ray-finned bony fishes.

Actinopterygians are named for their fins, which are supported by slender bony rays called lepidotrichia. These rays are unlike the fleshy, muscular fin lobes of Sarcopterygii, the lobe-finned group. Most familiar fishes—including tuna, salmon, cod, goldfish, seahorses, eels, and many reef fishes—are actinopterygians.

The class dominates modern fish diversity. It contains nearly 99% of living fish species, and its members occupy marine, brackish, and freshwater habitats ranging from the deep ocean to mountain streams. Most living species belong to Teleostei, a highly diverse subgroup that includes the overwhelming majority of familiar modern fishes.

The wording “largest group of living vertebrates” refers to species diversity, not body size. Actinopterygians include tiny fishes such as Paedocypris as well as giants such as ocean sunfish and oarfish. The class also includes older lineages such as sturgeons, paddlefish, gars, bowfin, bichirs, and reedfish.