A member of the genus Physeter, the sperm whale is a toothed whale having the largest brain of any animal. Its name comes from the term spermaceti, which is the milky-white waxy substance found in the mammal's head. The sperm whale is the only living member of genus Physeter. It is one of three extant species in the sperm whale family with the other two species being the pygmy sperm whale and dwarf sperm whale. The sperm whale is also known by the name of common cachalot.