A group of living things
Ray-finned fish
Actinopterygii
Half of all kinds of backboned animals, from seahorses to tuna.
Its members' last common ancestor lived about 380 million years ago.
You and ray-finned fish last shared an ancestor about 430 million years ago (on 24 November, if life's history were one year).
About half of all kinds of animals with backbones are ray-finned fish. Tuna and seahorses look very different, yet both belong here, along with clownfish, sunfish and flying fish. Their sister group is the lobe-finned fish.
A typical one has a streamlined body with two eyes, paired fins and a tail fin. Each of these fins is usually a thin sheet of skin held open by parallel bony rays. Most of the muscle that moves them sits inside the body. Most also have a hard gill cover, thin overlapping scales and a faint sense line along each side.
They live in almost every watery place, from deep ocean trenches and coral reefs to rivers, lakes and peat swamps. Most familiar kinds are about 10 to 50 centimetres long. The full range runs from about as small as a grain of rice to longer than a car.
Float aid linked to lungs
Most have a gas-filled swim bladder that helps them float. It grows in the same way as the lungs of land animals with backbones.
A life in under two months
The coral-reef pygmy goby finishes its whole life in under 60 days.
Part-time land walkers
A few kinds can crawl on land for a short time, such as mudskippers, or breathe air. They gained these tricks on their own, separately from the lobe-finned line that led to land animals with backbones.