Megamouth Shark (video)
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 by the U.S. Navy. To date, only 55 sightings of this shark have been confirmed. 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 plankton. They 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 help megamouth sharks to swim at a slow pace without sinking. 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.