The gulper eel (Eurypharynx pelecanoides) is an eel-like deep sea creature found at benthic levels in tropical areas worldwide. It is rarely seen by humans unless it is picked up by deep fishing nets.
The gulper eel’s most notable feature is its large mouth, which is much larger than its body. The mouth is loosely hinged and can be opened wide enough to swallow a fish much larger than the eel itself. The lower jaw resembles that of a pelican, hence its name. The lower jaw is hinged at the base of the head, with no body mass behind it, making the head look disproportionately large. When it feeds on prey, water that is ingested is expelled from the gills. The gulper eel is very different in appearance to most other true eel species. What makes the gulper eel so different from other fish is what it doesn’t have. They lack pelvic fins, swim bladders, and scales. Their muscle segments have a V-shape, while other fish have W-shaped muscle segments. Unlike many other deep sea creatures, it has very small eyes. It is believed that the eyes evolved to detect faint traces of light rather than form images. The gulper eel also has a very long, whip-like tail with a bioluminescent lure at the tip. Specimens that have been brought to the surface in fishing nets have been known to have their long tails tied into several knots.
The stomach can stretch and expand to accommodate large meals, although analysis of stomach contents suggests they primarily eat small crustaceans. Despite the great size of the jaws, which occupy about a quarter of the animal’s total length, it has only tiny teeth, which would not be consistent with a regular diet of large fish. The large mouth may be an adaptation to allow the eel to eat a wider variety of prey when food is scarce. It can also be used as a large net. The eel can swim into large groups of shrimp, squids or other crustaceans with its mouth wide open.
Because of the extreme depths at which it lives, most of what is known about the gulper eel comes from specimens that are inadvertently caught in deep sea fishing nets. Although once regarded as a purely deep-sea species, since 1970, hundreds of specimens have been caught by fishermen, mostly in the Atlantic Ocean.