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.
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.
Xenomorph (Latin, Internecivus raptus, meaning "Murderous Thief") are endoparasitoid* extraterrestrial species with multiple life cycle. One of the most deadly of all known alien species, these creatures need a host organism in order to reproduce. The appearance of the xenomorph varies depending on its parent host. The human phenotype is generally around 7'8 inches, and roughly 136.0 to 181.4 kg with a long muscular tail and large oblong head. The Queen of the species is generally twice as large, weighing ten times as much, having much greater speed, strength, and intelligence. The term Xenomorph is derived from the greek words xeno ("stranger", "alien", sometimes "foreigner") and morphe ("form", "shape").http://aliens.wikia.com/wiki/Xenomorph
Raptorial jaws in the throat help moray eels swallow large prey
Correspondence to: Rita S. Mehta1 Correspondence and requests for materials should be addressed to R.S.M. (Email: firstname.lastname@example.org).
Most bony fishes rely on suction mechanisms to capture and transport prey1. Once captured, prey are carried by water movement inside the oral cavity to a second set of jaws in the throat, the pharyngeal jaws, which manipulate the prey and assist in swallowing1, 2. Moray eels display much less effective suction-feeding abilities3. Given this reduction in a feeding mechanism that is widespread and highly conserved in aquatic vertebrates, it is not known how moray eels swallow large fish and cephalopods4, 5, 6, 7. Here we show that the moray eel (Muraena retifera) overcomes reduced suction capacity by launching raptorial pharyngeal jaws out of its throat and into its oral cavity, where the jaws grasp the struggling prey animal and transport it back to the throat and into the oesophagus. This is the first described case of a vertebrate using a second set of jaws to both restrain and transport prey, and is the only alternative to the hydraulic prey transport reported in teleost fishes. The extreme mobility of the moray pharyngeal jaws is made possible by elongation of the muscles that control the jaws8, coupled with reduction of adjacent gill-arch structures9. The discovery that pharyngeal jaws can reach up from behind the skull to grasp prey in the oral jaws reveals a major innovation that may have contributed to the success of moray eels as apex predators hunting within the complex matrix of coral reefs10, 11. This alternative prey transport mode is mechanically similar to the ratcheting mechanisms used in snakes12, 13—a group of terrestrial vertebrates that share striking morphological, behavioural14 and ecological convergence with moray eels.
Moray Eels Are Uniquely Equipped to Pack Big Prey Into Their Narrow BodiesTwo sets of jaws capture and move prey to throat for swallowing
X-ray of an eel. Note how far the eel's pharyngeal jaw is from its mouth.