Megamouth sharks - Megachasma pelagios - are one of rarest types of shark in the world despite being large, growing to at least 5.5m in length.
The first specimen was discovered in 1976. To date, only 50 examples of this shark have been found.
Megamouth sharks spend daylight hours near the edge of the continental shelf, swimming slowly at depths of 150 m or deeper. At night time it rises close to the surface to feed on small shrimp that form part of the plankton.
They are one of only three species of sharks that feed on plankton (planktivorous). They probably swim along with their mouth open, filtering plankton from the water as it passes through their gills. The other two filter-feeding shark species are whale sharks and basking sharks. Like these other filter-feeding sharks, megamouth sharks only have small teeth. Megamouth sharks are also able to thrust out their jaws (called protrusible jaws).
Megamouth sharks have soft bodies with large oily livers, flabby muscles and skeletons that are poorly calcified. These features probably help megamouth sharks to swim very slowly without sinking.
Little is known about how these sharks reproduce but they probably give birth to live young which have fed on unfertilised eggs in their mothers’ uterus. This is known as oophagy.
DNA studies suggest that megamouth sharks are the most primitive of sharks of the Order Lamniformes, the group which includes white pointer, mako, basking and grey nurse sharks.
The 50 specimens of megamouth and where they were discovered are displayed on the above map. About 14 specimens are now retained at research institutes. The seventh specimen is of particular interest to scientists. This female specimen was the subject of a dissection and symposium held in Japan in 1994. After all this attention, the specimen is still in excellent condition and is now on display at Marine World umino-nakamichi.