There are 12 species of fish in this order, all belonging to a single family. Most live in deep ocean waters where sunlight does not reach. They are found in tropical and subtropical regions of the Atlantic, Indian, and western Pacific Oceans. These fish are bottom-dwellers, typically living at depths of up to 2,600 feet (800 m).

Most species are small, but one species, Polymixia berndti, found in the Indian and Pacific Oceans, can grow to over 16 inches (40 cm) in length.

They have long, thin, whisker-like feelers called barbels that hang from their chins. These help them sense food, such as crustaceans and plankton, in the dark ocean. They usually have large eyes, silvery or reddish bodies, and a somewhat elongated shape.

One species, Polymixia lowei can be found from Maine to Brazil.