Most mammals and birds have fairly straightforward mouths; two jaws with single rows of teeth (or none in most birds) and a single joint that lowers or raises the lower jaw, thus opening and closing the mouth. Fishes, however, show a truly staggering diversity in the way they use their mouths, so the coming few weekly fishes will concern fishes with distinctive ones. First up, the most gaping maw of them all.

The gulper eel (also charmingly called umbrella-mouth or pelican eel) has a long, slender body and a tiny head, thus fulfilling the primary requirements for passing the eel exam. It has comically large jaws, which are about ten times the size of the rest of its head, and a large throat sack that expands when the mouth is opened. The pelican nickname thus makes sense, but there is an important difference. For whereas in pelicans (as in most other birds and mammals, including us humans) the upper jaw is fused to the skull, in most fishes this is not the case, and only the front part of the upper jaw is connected to the skull by means of a joint. So when the gulper eel opens its maw to grab a bite, the upper jaw joint allows it to make its entire mouth come forward and produce the gaping hole that little fishes, shrimps and squids across the world tell their children to be most fearful of.

The gulper eel saying 'aah'. Top: mouth open; bottom: mouth closed.
The gulper eel saying ‘aah’. Top: mouth open; bottom: mouth closed (in case that wasn’t clear).

Many a hunting fish swiftly sucks its victim into its mouth (like so), never giving it a chance. But not the gulper eel, which instead eerily stalks its prey and rather lazily scoops it up. Like the lamprey, the gulper eel would be a great horror movie monster. Who could ever call a shark “Jaws” after seeing one of these? Cue spooky music…

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