A New Kind of Swallowing
For some organisms, one set of sharp teeth is not enough. Imagine having these in your throat:
Those are the second set of jaws possessed by moray eels, according to this paper in Nature.* There are even videos here and here where you can actually see the secondary jaws shooting out to pull the prey down the eel’s throat.
Fish that have two sets of jaws sound exotic enough, but this is actually a common feature amongst bony fish. These so-called pharyngeal jaws are actually modified gill arches which many fish use to process or transport food. What’s special about the pharyngeal jaws of the moray eels is that they are the only known example of pharyngeal jaws that bite the prey in order to drag it into the oesophagus. In other species of bony fish, pharyngeal jaws have been known to have grinding functions, but not biting. Moray eels need such a mechanism because they consume prey that are comparable in size to their own heads. This means a considerable amount of force is required to drag the food through their mouths into their gullets. It also means that suction, a common method of capturing and swallowing prey in fish, is probably too weak a mechanism. A second set of biting jaws also gives moray eels a ’second chance’ at grasping recalcitrant prey. If the prey is too unwieldy to be pulled into the oesophagus in one go, then it is pulled stepwise through the head via a ‘ratchet’ mechanism where the jaws in the mouth hold the prey in place after each attempt from the pharyngeal jaws at pulling the prey further in. It is no coincidence that snakes, another group of animals that consume prey comparable in size to their own heads, also have a ‘ratcheting’ mechanism for swallowing food: the left and right sides of their heads take turns to hold on to the prey as the snake advances its head over the prey.
*Rita S. Mehta & Peter C. Wainwright. Raptorial jaws in the throat help moray eels swallow large prey. Nature 449, 79-82 (6 September 2007).
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