Pharyngeal jaws are a "second set" of jaws contained within an animal's throat, or pharynx, distinct from the primary (oral) jaws. They are believed to have originated as modified gill arches, in much the same way as oral jaws.
Although approximately 30,000 species of fishes are known to have pharyngeal jaws, in many species having their own teeth, the most notable example of animals possessing them is the moray eels of the family Muraenidae. Unlike those in other fishes known to have them, those of the moray are highly mobile. This is possibly a response to their inability to swallow as do other fishes by creating a negative pressure in the mouth, perhaps induced by their restricted environmental niche (burrows). Instead, when the moray bites prey, it first bites normally with its oral jaws, capturing the prey. Immediately thereafter, the pharyngeal jaws are brought forward and bite down on the prey to grip it; they then retract, pulling the prey down the moray eel's gullet, allowing it to be swallowed.[1]
Probably the most famous example of pharyngeal jaws is the fictional extraterrestrial creature from the Alien film series called the "Xenomorph". In the films, Xenomorphs are depicted with a secondary, inner set of jaws mounted onto a proboscis inside of the throat, in place of a tongue. This proboscis is shown to rapidly shoot forward with force to attack prey.