Moray Eels Grab Prey With "Alien" Jaws

Sara B. McPherson
for National Geographic News
September 5, 2007
Much like the fearsome star of the Alien movies, moray eels have a second set of toothed jaws that drag prey into their throats, a new study has found.

In a series of experiments, scientists at the University of California, Davis, recently discovered that moray eels possess an extremely mobile set of jaws in their throat that they can project forward into their mouth to aid in feeding.

However, unlike the fictitious alien's second mandible, which it menacingly extended toward its prey, the eel's jaws are much more practical, said lead author and evolutionary biologist Rita Mehta. (Get fish pictures, sounds, news, and more.)

"The [jaws] are functionally specialized to grasp large prey and assist in swallowing," Mehta said.

Suction Feeding

Most fish catch their prey using a suction method. When food is within reach, a fish will rapidly open its mouth.

This motion expands the mouth cavity, creating negative pressure and drawing water—and the prey—down their throats. (Related news: "Ancient Amphibians Bit Instead of Sucking, Skull Study Says" [April 16, 2007].)

But, suction feeding has several restrictions. For one, the method limits the size of prey that a fish can draw into its mouth. The technique also requires room around the fish's head to accommodate the space generated when it expands its mouth cavity.

These limitations can pose problems for species such as the predatory moray eel, which resides in the tight spaces and crevices of the oceans' coral reefs.

So instead of suction, the eels rely on strong jaws filled with sharp teeth to bite their prey.

Biting allows morays to feed on larger animals without having to expand their mouth cavity when stuck in the confining quarters of the reefs.

Though scientists understood how moray eels caught their food, exactly how they swallowed it remained a mystery until this recent study.

The findings will be published tomorrow in the journal Nature.

Fancy Forceps

Using high-speed video, Mehta and study co-author Peter Wainwright observed moray eels eating squid and noticed that the eels used a very unique set of secondary, or pharyngeal, jaws to devour their prey.

While most fish use these secondary jaws to manipulate prey and help in swallowing, Mehta and Wainwright noticed an important distinction in the moray's jaws. (Related news: "Jaws, Teeth of Earliest Bony Fish Discovered" [August 1, 2007].)

"The pharyngeal jaws in their throat exhibit a very different architecture from the jaws of other bony fishes," Mehta said. "[They] look like a fancy pair of forceps with large, sharp recurved teeth."

And unlike most pharyngeal jaws, which have a limited range of motion, the moray's inner mandibles have elongated muscles that allow for extreme mobility.

This unique feature allows the eels to protrude their secondary jaws forward from their throats and into their mouths, where they grasp prey and guide it toward the esophagus.

This dual-jaw system allows morays to maintain a grip on their food at all times, Mehta said.

Mark Westneat is the curator of zoology at the Field Museum of Natural History in Chicago.

"That's what's fascinating about this discovery," he said. "Lots of fish have pharyngeal jaws, but they tend to be hard grinding plates or jaws with little teeth that don't move much.

"What's unusual about the morays' jaws is their ability to drag prey from the mouth back into the throat."

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