What shark species is the only living member of the family Megachasmidae?

The megamouth shark is the only living member of the family Megachasmidae.

Its scientific name is Megachasma pelagios, and it is generally treated as the sole living species in its family. The megamouth is one of only three living filter-feeding sharks, alongside the whale shark and basking shark. It swims with its enormous mouth open, filtering plankton and small drifting animals such as krill, jellyfish, shrimp larvae, and fish larvae through specialized gill structures.

The species remained unknown to science until November 15, 1976, when a roughly 4.5-metre specimen became entangled in the sea anchor of a U.S. Navy research vessel near Hawaii. Scientists recognized it as not merely a new species, but a new genus and family. Its rarity and deep-water habits explain why it was so late to be discovered.

The main possible source of confusion is taxonomy: fossil teeth have been attributed to extinct megamouth species, so Megachasmidae is not necessarily a family with only one species across all geological time. The quiz asks about living members, for which the megamouth is the canonical answer.