The pelican eel's jaws are extraordinarily long and loosely articulated, and the skin between them forms a distensible pouch reminiscent of a pelican's. In 2018 the exploration vessel Nautilus filmed a pelican eel near the Papahanaumokuakea Marine National Monument expanding this pouch into a near-spherical shape, then collapsing it and swimming off as a narrow ribbon.
The swelling looks like a swallowing structure, and the name gulper eel reflects an old assumption that the fish engulfs very large prey. Stomach contents tell a more modest story: crustaceans dominate, along with smaller fishes and cephalopods, which sits awkwardly with the idea of a specialist big-prey predator.
The pouch may instead serve to take in a large volume of water and prey together, or as a startle display. The luminous tip of the tail is often described as a lure, but how the eel uses it, and whether the inflation is defensive, remain matters of inference from very few encounters.