Pharyngeal Jaw

In a world full of flying fish, pink dolphins and vampire squid, it’s often easy to see where many Science Fiction writers get their inspiration. Yet sometimes the natural world throws up an adaptation so bizarre that you’ll be forgiven for thinking that it’s the product of an imaginative Hollywood CGI studio rather than a fascinating feature of nature.

One such example is the Pharyngeal Jaw – essentially a second set of jaws that are contained within a fish's throat, or pharynx.

Over 30,000 species of fish sport this adaptation, using them to help break down their food, crush the exoskeletons of prey, or even grinding them together to make sounds such as clicks or grunts. Surprisingly, many popular aquarium species have these structures, such as goldfish, loaches and cichlids, but perhaps the most extreme example of the pharyngeal jaw in nature is that of the moray eel of the family Muraenidae.

Unlike those of other fishes, the pharyngeal jaw of the moray is highly mobile. When the moray bites its prey, it first bites normally with its oral jaws, capturing the prey. Immediately afterwards, the pharyngeal jaws are brought forwards 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.

This is probably an evolutionary adaptation arising from their inability to swallow normally by creating a negative pressure in the mouth as other fishes do, but anyone who’s seen the classic 80s movie Aliens will recognise what a terrifying predatory tool this is, and attest to the fact that the truth is often stranger than fiction.