Jumat, 29 Juli 2011

RAHANG KERONGKONGAN SIDHAT 5 - 咽颌 - Pharyngeal jaw

RAHANG KERONGKONGAN SIDHAT 5 - 咽颌 - Pharyngeal jaw

 The pharyngeal jaws of the moray eel - 鯙科的咽颌结构

Pharyngeal jaws (咽颌) 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.

 In fiction

Probably the most famous example of pharyngeal jaws is the fictional extraterrestrial creature from the Alien film series 《 异形 》 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. http://aliens.wikia.com/wiki/Xenomorph


 External links



ever see a moray eel (gymnothorax tile) eat?

Moray Eel Eating 1

Moray Eel Eating 2

Radiographs in left lateral view depicting the extreme positions of the pharyngeal jaws in Muraena retifera Goode & Bean, 1882 
during prey transport.

a, Posterior placement of the pharyngeal jaws in relation to the skull. The arrow points to the pharyngeal jaws. b, Pharyngeal jaws in their protracted position. The arrow points to the upper pharyngobranchial. Scale bar for a and b, 1 cm. 

It appears that moray eels have two sets of fanged jaws, one to grab with and one launched from their throats to grasp their squirming victims.



These X-rays of a moray eel’s head reveal a second set of jaws — at rest in the eel’s throat, top, and launched forward, bottom, to seize its food. (Rita Mehta and Candi Stafford/UC Davis)  






The oral gape cycle in relation to the pharyngeal jaw cycle 
in Muraena retifera Goode & Bean, 1882.

After peak oral gape (blue trace), oral jaws make contact with the prey (pink rectangle) by biting. Pharyngeal jaws (red trace) are fully protracted and the recurved teeth on the upper pharyngeal teeth are in contact with the prey. Pharyngeal jaws grip prey and begin retracting prey towards the oesophagus. Prey is pulled into the oesophagus as the moray extends its neurocranium forward and advances its body over the prey while increasing its oral gape, similar to a snake.


 Detailed anatomy of the pharyngeal jaw apparatus 
in Muraena retifera Goode & Bean, 1882.

a, Left lateral view of a cleared and alizarin red-stained pharyngeal jaw apparatus, illustrating the sharp, recurved teeth on the pharyngobranchials used to grasp prey. Scale bar, 1 cm. b, Left anterior upper pharyngobranchial revealing highly recurved teeth. Scale bar, 500 micron.

A scanning electron microscope's view of the moray eel's inner toothy jaw. The teeth help grasp prey and drag it toward the moray's gut.


How does a 12-foot-long eel move food down its throat? 
Sliding rear jaws. After the front jaws bite, 
the rear ones slide up and grab the prey. 
As those retract, the front jaws release. 
The eel then juts its head forward, 
which aids in the swallowing process.

Pulsing mouth, vacant stare, snakelike body: The moray eel truly suggests alien origins. But there’s more. Back behind this giant reef fish’s already toothy maw looms a second set of jaws, which launch from the throat, grab prey from the front teeth, then retreat into the dark tunnel of the eel’s esophagus. It’s the stuff of science fiction. But to scientists studying this unique morphology, it’s a brilliant feeding mechanism for such an elongated creature.

Unlike most bony fishes, morays don’t seem to generate enough suction to help in swallowing, says Rita Mehta of the University of California at Davis. Instead, the novel dual-jaw arrangement, which she and colleagues recently examined with high-speed video, allows the animals to both restrain and transport big prey—the most efficient nourishment for big animals—down the long throat. This is the first report of such a mechanism in a vertebrate. Though on a different branch of the evolutionary tree, snakes have a related system, a set of ratcheting jaws that grip and maneuver food into the gullet. Says Mehta, “It’s a wonderful example of convergence”—when distant organisms facing the same problem develop similar solutions.  —Jennifer S. Holland
Art: Raúl Martín

Functional morphological model of pharyngeal jaw movement 
in Muraena retifera Goode & Bean, 1882.

The left dentary has been removed in ac, and the left maxilla has been removed in b and c. a, Pharyngeal jaw apparatus at rest. b, Pharyngeal jaw protracted: the levator internus (LI) and levator externus (LE) protract the upper jaw into the oral cavity, whereas the rectus communis (RC) protracts the lower jaw. During protraction, the upper pharyngobranchial is dorsally rotated by contraction of the LI and the obliqus dorsalis (OD). c, After prey contact, the adductor (AD) contracts to bring the upper and lower jaws together to deliver a second bite. The dorsal retractor (DR) and pharyngocleitheralis (PHC) retract the pharyngeal jaws back to their resting position behind the skull. Scale bar, 1 cm.


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