Pharyngeal jaws are a "second set" of

jaw The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth ...

s contained within an animal's throat, or

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

, distinct from the primary or oral jaws. They are believed to have originated as modified

gill arches Branchial arches or gill arches are a series of paired bony/cartilaginous "loops" behind the throat ( pharyngeal cavity) of fish, which support the fish gills. As chordates, all vertebrate embryos develop pharyngeal arches, though the eventual ...

, in much the same way as oral jaws. Originally hypothesized to have evolved only once, current morphological and genetic analyses suggest at least two separate points of origin. Based on connections between musculoskeletal morphology and dentition, diet has been proposed as a main driver of the evolution of the pharyngeal jaw. A study conducted on cichlids showed that the pharyngeal jaws can undergo morphological changes in less than two years in response to their diet. Fish that ate hard-shelled prey had a robust jaw with molar-like teeth fit for crushing their durable prey. Fish that ate softer prey, on the other hand, exhibited a more slender jaw with thin, curved teeth used for tearing apart fleshy prey. These rapid changes are an example of

phenotypic plasticity Phenotypic plasticity refers to some of the changes in an organism's behavior, morphology and physiology in response to a unique environment. Fundamental to the way in which organisms cope with environmental variation, phenotypic plasticity encompa ...

, wherein environmental factors affect genetic expression responsible for pharyngeal jaw development. Studies of the genetic pathways suggest that receptors in the jaw bone respond to the mechanical strain of biting hard-shelled prey, which prompts the formation of a more robust set of pharyngeal jaws.

Cichlids

A notable example are fish from the family

Cichlid Cichlids () are a large, diverse, and widespread family of percomorph fish in the family Cichlidae, order Cichliformes. At least 1,760 species have been scientifically described, making it one of the largest vertebrate families, with on ...

ae. Cichlid pharyngeal jaws have become very specialized in prey processing and may have helped cichlid fishes become one of the most diverse families of vertebrates. However, later studies based on

Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropics, tropical lake, and the world's second-largest fresh water lake by surface are ...

cichlids suggest that this trait may also become a handicap when competing with other

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

species.

Moray eels

Most

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

species with pharyngeal teeth do not have extendable pharyngeal jaws. A particularly notable exception is the highly mobile pharyngeal jaw of the

moray eel Moray eels, or Muraenidae (), are a family (biology), family of eels whose members are found worldwide. There are approximately 200 species in 15 genera which are almost exclusively Marine (ocean), marine, but several species are regu ...

s. These are possibly a response to their inability to swallow as other fishes do by creating a

negative pressure Negative may refer to: Science and mathematics * Negative number * Minus sign (−), the mathematical symbol * Negative mass * Negative energy * Negative charge, one of the two types of electric charge * Negative (electrical polarity), ...

in the mouth, perhaps induced by their restricted

environmental niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for e ...

(burrows) or in the air in the

intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

. 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.

Popular culture

The fictional

Xenomorph The xenomorph (also known as a Xenomorph XX121, ''Internecivus raptus'', ''Plagiarus praepotens'', or simply the alien or the creature)Alien: The Weyland-Yutani Report is a fictional parasitoid, endoparasitoid Extraterrestrials in fiction, extra ...

from the ''Alien'' film series has a mobile inner jaw, but that art predates the discovery of the exceptional mobility of the moray's pharyngeal jaw and its unique role in feeding. While pharyngeal jaws in other fish were already known, artist

H. R. Giger Hans Ruedi Giger ( ; ; 5 February 1940 – 12 May 2014) was a Swiss artist best known for his airbrushed images that blended human physiques with machines, an art style known as " biomechanical". He was part of the special effects team that won ...

claimed he "hadn't studied any animal" when designing the double jaw of the xenomorph. In the game ''

Hungry Shark Evolution Hunger is a sensation that motivates the consumption of food. The sensation of hunger typically manifests after only a few hours without eating and is generally considered to be unpleasant. Satiety occurs between 5 and 20 minutes after eating. T ...

'', the character "Big Daddy (Dunkleosteus)" is shown depicting a pharyngeal jaw. The final boss of ''

Monster Hunter Rise is a 2021 action role-playing game developed and published by Capcom for the Nintendo Switch. It was released worldwide in March 2021, with a Windows port released in January 2022 and ports for PlayStation 4, PlayStation 5, Xbox One, and Xbox Se ...

'' Thunder Serpent Narwa, as well as her male counterpart Wind Serpent Ibushi and variant form Narwa the Allmother, all possess pharyngeal jaws within their throats.

References

External links

* * (article explaining moray eel pharyngeal jaws) * {{cbignore Fish anatomy Pharynx