A manta ray's 'wings' are actually giant pectoral fins. The biggest manta rays can have a wingspan of over seven metres - wider than a bus is long. Despite their size, they are completely harmless to people. They eat only tiny animals called zooplankton, which they filter through special gill plates as they cruise through the water.
Manta rays are known for leaping out of the ocean and landing with a huge splash. Scientists are not completely sure why they do this - it might be to shake off parasites, to communicate with other rays, or just for fun. From a boat, watching a manta breach is one of the most spectacular sights in the Pacific.
Around the Marshall Islands, manta rays gather near the outer edges of atolls where currents bring rich food up from the deep ocean. They are often seen 'cleaning stations' on coral reefs - spots where small fish called wrasse nibble away tiny creatures living on the ray's skin. The ray hovers patiently while the wrasse do their work.
Manta rays are intelligent and curious. Divers in the Marshall Islands sometimes have mantas swim slowly up to them to investigate, hovering just above before gliding away. It is a moment that people remember for the rest of their lives.