The megamouth shark is a species of deepwater shark. It is rarely seen by humans and is the smallest of the three extant filter-feeding sharks alongside the whale shark and basking shark. Since its discovery in 1976, few megamouth sharks have been seen, with fewer than 100 specimens being observed or caught. Like the other two planktivorous sharks, it swims with its enormous mouth wide open, filtering water for plankton and jellyfish. It is distinctive for its large head with rubbery lips.

The first megamouth shark was captured on November 15, 1976, about 25 miles off the coast of Kāneʻohe, Hawaiʻi, when it became entangled in the sea anchor of United States Navy ship AFB-14. The species was identified as being of a new genus within the planktivorous shark species. Examination of the 4.5-m (14.7-ft), 750-kg (1,650-lb) specimen by Leighton Taylor showed it to be an entirely unknown type of shark, making it (along with the coelacanth) one of the more sensational discoveries in 20th-century ichthyology. The pectoral fin of the megamouth shark was studied, along with the skeletal and muscular system of the megamouth shark to show its phylogenetic relationship to the other two sharks.

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