There are 151 species of ray-finned fish in this order, grouped into seven families.

All species are marine, and most live in tropical to temperate deepwater environments around the world. They are commonly found along the continental shelf and slope, with some species living as deep as 6,000 feet (2,000 m) below the surface. Some move closer to the surface at night, while others remain in shallower waters and are nocturnal, hiding in rock crevices and caves during the day.

These fish range in color from red and yellow to brown and black, and are typically 3 to 24 inches (8–61 cm) long. They often have large eyes that help them see in low-light conditions. Many species have spiny fins and tough, rough scales. Some can even glow in the dark using special light-producing organs called photophores.

Their diet consists of smaller fish, plankton, and other tiny drifting animals.