Jumat, 13 Mei 2011

RAHANG KERONGKONGAN SIDHAT 1 - 咽颌 - Pharyngeal jaw

RAHANG KERONGKONGAN SIDHAT 1 - 咽颌 - Pharyngeal jaw



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]

 In fiction

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.

 References

 External links

http://en.wikipedia.org/wiki/Pharyngeal_jaw




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

Rita S. Mehta1 & Peter C. Wainwright1
  1. Section of Evolution and Ecology, University of California, One Shields Avenue, Davis, California 95616, USA
Correspondence to: Rita S. Mehta1 Correspondence and requests for materials should be addressed to R.S.M. (Email: rsmehta@ucdavis.edu).


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.
http://www.nature.com/nature/journal/v449/n7158/abs/nature06062.html


Moray Eels Are Uniquely Equipped to Pack Big Prey Into Their Narrow Bodies

Two sets of jaws capture and move prey to throat for swallowing

How do long, slender snake-like creatures manage to stuff large, struggling prey into their narrow mouths and down their throats without using paws or claws? A new study reveals that the slender, snake-like moray eel--which may reach up to about nine feet in length--captures and consumes its prey (usually large fish, octopuses and squid) with a unique strategy that involves using two sets of jaws.
According to the study, the moray eel starts feeding by seizing its prey in the jaws of its oral cavity. This set of jaws is armed with sharp, piercing teeth that curve backwards, pointing towards the eel's throat. So structured, these teeth are specially designed to help prevent prey from backing out of the eel's mouth, much like spike-strips in parking lots help prevent cars from backing out of entrance ramps.
Once prey is secured in the eel's oral jaws, a second set of toothy jaws (known as the pharyngeal jaws) located behind the eel's skull lunges forward, advancing along almost the full length of its skull, to snatch and deliver the prey to the eel's esophagus for swallowing.
An article describing the moray eel feeding study, which was partially funded by the National Science Foundation (NSF), appears in the September 6 edition of Nature. The article identifies the moray eel as the only known vertebrate to use a second set of jaws to both restrain and transport prey. Rita Mehta, a researcher at the University of California at Davis and the article's lead author, describes the eel's feeding method as "an amazing innovation for the feeding behavior of fishes."
About 30,000 fish species besides the moray eel have a second set of jaws in their throat region. But as far as we know, such jaws have only limited mobility and so only grind or crush prey; they cannot provide the essential functions provided by the moray eel's jaws.
Mehta documented the moray eel's unique feeding method by using high-speed digital video equipment to record the split-second movements of feeding laboratory eels, analyzing X-ray and other images and conducting anatomical dissections.
Unlike the moray eel, most fish capture and move prey into their throats by using suction. For example, some fish rapidly expand their mouths and thereby draw in water and associated food. Others overtake prey with their open mouths or grab prey in their jaws, but then create suction to move the prey from their mouths to their esophagus. But moray eels have little ability to generate suction through their mouths, Mehta found.
More than 200 species of moray eels dwell in tropical waters worldwide. Reclusive and secretive, moray eels are most frequently observed in coral reefs, with their heads poking out of holes in rocks or coral structures. Serving as top predators in coral reefs, they may have evolved their unique feeding method to enable them to hunt large prey in confined spaces, where they cannot expand their heads to create suction.
Mehta points out that, like moray eels, snakes must also fit large food items through a relatively narrow mouth into a long, thin body. But snakes solved the problem by separating the left and right sides of their jaw while eating; they hold onto the food with one side while they work the other side of the mouth round it. Snakes thereby "jaw walk over their prey," says Mehta.
"Moray eels and snakes are not related," says Mary Chamberlin, an NSF program director. "So this study provides an excellent example of convergent evolution--where similar functions evolve independently in unrelated organisms."
Mehta said that she is now investigating how the moray eel evolved its extraordinary jaws and working to identify the maximum size of the moray eel's prey. "Eels are an amazingly diverse and bizarre group of fishes, and not very well known," said Peter C. Wainwright of the University of California, Davis, who is a co-investigator of the study.
In addition to receiving NSF support, the new eel study also received support from the American Association of University Women.
-NSF-

http://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=109985&preview=false



  
Moray eels live in confined spaces in coral reefs, where it would be impossible to use the type of suction used by most bony fish to capture and move prey into the throat. Scientists believe that the moray eel's inner set of jaws (their pharyngeal jaws), which move food from their oral jaws to their esophagus, represent an adaptation to their cramped environment. This photo was taken on a dive in Indonesia.





 
A moray eel eating a piece of squid. This photo is from a series of movies that the lead researcher took while studying the eels' feeding anatomy.









X-ray of an eel. Note how far the eel's pharyngeal jaw is from its mouth.



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