The manta ray is classified as one of the largest fish. Manta rays, along with sharks and rays, belong to a subclass of cartilaginous fishes, which do not possess a hard bony skeleton. The reef manta ray and the giant oceanic manta ray are the largest species of rays in the family Mobulidae, as well as the largest rays in the world. Oceanic manta rays may grow to about 7 meters (23 ft.), while reef manta rays may reach 5.5 meters (18 ft.). Manta rays are usually found in tropical and subtropical seas of the world. Oceanic mantas reside in deep water, visiting periodically coastal reefs and seamounts, while reef mantas inhabit shallower coastal waters.
Not long ago, it was believed that manta rays could be classified into different species based on size variation, color and geographic location; however, scientific studies discovered that manta rays can be grouped into only one species (Manta birostris). Tim Clark from the University of Hawaii, who studies manta rays, plans to publish a comparison of genetic samples from populations of manta rays around the world to confirm this hypothesis. Other studies, including the DNA of white and black manta rays, confirmed the hypothesis of one unique species.
All manta rays have a distinctive triangular body shape in their physical structure. They have two fins on their heads known as cephalic lobes, which they utilize to bring plankton into their mouths as they swim through the water. Unlike most rays, which have their mouth on the dorsal side. Manta rays´ mouth is at the front of the head, and contains rows of teeth, probably ancestral vestiges of an evolutionary adaptation, on the lower jaw. these teeth are not used for feeding. A pair of spiracles located on top of their heads, which some animals use for respiration, are useless in mantas since they use five pairs of gills located on the ventral side.
Manta rays are generally dark on the upper side, varying from black to bluish-grey and brown. Unlike other rays, manta rays lack a spine on their tails and their only defenses against predators are their wings and size. Their wing span can reach over 7 meters (23 ft.) across, although, larger mantas have been spotted, and their average weight is 1,300 kg (2900 lbs.). The brain to body ratio of mantas, which is similar in ratio to that of marsupials and birds, is the largest compared to other cartilaginous fish, such as the shark and rays.
The movement of their fins through water resembles that of a bird, flapping its wings in the air. Mantas have a mucus coating on their body which is used as defense against infection, although not as abundant as that of other rays. They can swim at over 24 km/h (15miles/h) gracefully while trying to eat plankton. Sometimes, they swim on the surface of water, propelling themselves by flapping their pectoral fins, occasionally jumping out of the water. Manta rays have tiny nerves on their heads that allow them to detect objects and movement underwater.
Male manta rays are differentiated from female mantas by two small male sex organs situated along the inner margins of the pelvic fins. The male manta is sexually mature when its sex organs grow larger than the pelvic fin and are long enough to penetrate the female opening (cloaca). Female manta rays are believed to reach sexual maturity when their wingspan reaches 3.4 meters (11 ft.). The exact time of gestation is not known, although, it may take 13 months. Females can give birth to one or perhaps up to two pups.
The average life span of manta rays is approximately 20 years. Their natural predators include large sharks and occasionally killer whales (Orcas). Manta ray populations are not considered to be threatened, although, pollution and coastal development may present a threat. Unlike other marine animals, such as the shark which has been the subject of numerous studies, the manta ray has not been researched as much. The Pacific Manta Research Group has been collecting manta data for more than thirty years. Their studies have led to a better understanding of reef manta rays; however, little is known about oceanic manta rays.