The manta ray, or cheap manta (Manta birostris), is the largest of the rays, with the largest known specimen having been about 7.6 m (about 25 ft) across, with a weight of about 2,300 kg (about 5,000 lb). It ranges throughout all tropical waters of the world, typically around coral reefs.

Mantas have been given a variety of common names, including Atlantic manta, Pacific manta, devilfish, and just manta. Some people just call all members of the family stingrays, though stingrays comprise a separate family of rays (Dasyatidae).

Mantas are most commonly black dorsally and white ventrally, but some are blue on their backs. A manta's eyes are located at the base of the cephalic lobes on each side of the head, and unlike other rays the mouth is found at the anterior edge of its head. To respire, like other rays, the manta has five pairs of gills on the underside.

To swim better through the ocean, they have a diamond shaped body plan, using their pectoral fins as graceful "wings".

Distinctive "horns" (from which the common name Devil ray stems) are on either side of its broad head. These unique structures are actually derived from the pectoral fins. During embryonic development, part of the pectoral fin breaks away and moves forward, surrounding the mouth. This gives the manta ray the distinction of being the only jawed vertebrate to have novel limbs (the so-called six-footed tortoise, Manouria emys, does not actually have six legs–only enlarged tuberculate scales on their thighs that look superficially like an extra pair of hind limbs). These flexible horns are used to direct plankton, small fish and water into the manta's very broad and wide mouth. The manta can curl them to reduce drag while swimming.

Manta rays are believed by some to have evolved from bottom-feeding ancestry, but have adapted to become filter feeders in the open ocean. This allowed them to grow to a larger size than any other species of ray. Because of their pelagic lifestyle as plankton feeders, some of the ancestral characteristics have degenerated. For example, all that is left of their oral teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. Their dermal denticles are also greatly reduced in number and size, but are still present, and they have a much thicker body mucus coating than other rays. Their spiracles have become small and non-functional, as all water is taken in through their mouth insted.

Evolution and taxonomy

Manta rays are believed by some to have evolved from bottom-feeding ancestry, but have adapted to become filter feeders in the open ocean. This allowed them to grow to a larger size than any other species of ray. Because of their pelagic lifestyle as plankton feeders, some of the ancestral characteristics have degenerated. For example, all that is left of their oral teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. Their dermal denticles are also greatly reduced in number and size, but are still present, and they have a much thicker body mucus coating than other rays. Their spiracles have become small and non-functional, as all water is taken in through their mouth instead.

Mantas are filter feeders: they feed on plankton, fish larvae and the like, passively filtered from the water passing through their gills as they swim. The small prey organisms are caught on flat horizontal plates of russet-coloured spongy tissue, that span the spaces between the manta's gill bars.

Mantas frequent reef-side cleaning stations where small fish such as wrasses and angelfish swim inside the manta's gills and all over its skin to feed, in the process cleaning it of parasites and removing bits of dead skin.

The predators of the Manta ray include mainly large sharks, however in some circumstances orcas have also been observed preying on them.

Mantas are extremely curious around humans, and are fond of swimming with scuba divers. Although they may approach humans, if touched, their mucus membrane is removed, causing lesions and infections on their skin. They will often surface to investigate boats (without engines running). They have the largest brain-to-body ratio of the sharks and rays.

Mantas are known to breach the water into the air.