Like the predator in the "Alien" movie series, moray eels thrust a second set of jaws from deep within their throat to seize their prey, astonished scientists reported Wednesday.
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The animal kingdom is full of innovative mechanisms for ensuring that a meal does not escape and moves swiftly along the digestive track.
Snakes unhinge their jaws, and most fish -- along with some eels -- use suction to draw in their victims. Some species, such as the parrotfish, have a second set of teeth-like bones between their gills.
But scientists at the University of California at Davis were amazed to discover that at least one species of moray, an eel that lurks in reef crannies and reaches up to three metres (10 feet) in length, has a mobile inner jaw lined with razor-edged, hook-like teeth.
Situated in the pharynx, this "raptorial pharyngeal jaw" can thrust forward at lightning speed into the mouth, virtually eliminating any chance a prey might have had of squirming free from the first set of jaws.
The discovery was made based on a hunch, according to the study, published in the British journal Nature.
Noting in previous research that some eel species do not use suction during feeding, marine biologists Rita Metha and Peter Wainwright wondered whether the same was true of the moray eel.
To find out, they recorded high-speed videos of Muraena retifera, one of 200 or so moray species found in reefs around the world, feeding in a laboratory aquarium.
That's when then discovered the inner jaw, which is clearly visible in the film.
To get an inside view of the mechanism, the researchers did a X-ray fluoroscopic analysis -- the kind used to film the digestive process in the humans.
The resulting images gave the first detailed view of the eel's hidden dental apparatus in action.
Almost as remarkable as the lunging jaw is that fact that it went unnoticed for so long. This could be explained, the authors conjecture, by the fact that moray eels, while common, are rarely eaten by humans.
They are also do not turn up often in fish nets as they stay close the reef crevices where they live and feed.
In a comment, also published in Nature, Mark Westneat, a biologist at the Field Museum of Natural History in Chicago, speculates that the eel's raptorial jaw "may be a primary reason for their success and diversity."
Westneat also cautions that it may be premature to generalise across all species of moray eel, though he thinks it is likely that Muraena retifera probably has like-jawed cousins.
, being an eel does it also have slime like a predator?
