The pelican eel, Eurypharynx pelecanoides, is a deep-sea fish rarely seen by humans, though it is occasionally caught in fishing nets. It is an eel-like fish and the only known member of the genus Eurypharynx and the family Eurypharyngidae. It belongs to the order Saccopharyngiformes, which is closely related to the true eels in Anguilliformes. It is also referred to as the gulper eel, pelican gulper, and umbrella-mouth gulper. The specific epithet pelecanoides refers to the pelican, as the fish's large mouth is reminiscent of that of the bird.
The pelican 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 pouch-like 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 via the gills.
Gulper eels are black and some subspecies may have a thin lateral white stripe. They are ray-finned fish, and only resemble eels in appearance.
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 not so much what it has, but 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. Specimens that have been brought to the surface in fishing nets have been known to have their long tails tied into several knots.
The gulper eel uses a whip-like tail for movement. The end of the tail bears a complex organ with numerous tentacles, which glows pink and gives off occasional bright-red flashes. This is presumably a lure to attract prey, although its presence at the far end of the body from the mouth suggests the eel may have to adopt an unusual posture to use it effectively. Gulper eels are also unusual that the ampullae of the lateral line system projects from the body, rather than being contained in a narrow groove; this may increase its sensitivity.
The gulper eel grows to about 0.75 m (2.5 ft) in length.
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 like a large net. The eel can swim into a large groups of shrimp or other crustaceans with its mouth wide open, scooping them up as it goes. The gulper eel is also known to feed on cephalopods (squid) and other small invertebrates. When the eel gulps its prey into its massive jaws, it also takes in a large amount of water, which is then slowly expelled through its gill slits. Gulper eels themselves are preyed upon by lancet fish and other deep sea predators.
Reproduction and Life Cycle
Not much is known about the reproductive habits of the gulper eel. As they mature, the males undergo a change that causes enlargement of the olfactory organs, responsible for the sense of smell, and degeneration of the teeth and jaws. The females, on the other hand, remain relatively unchanged as they mature. The large olfactory organs in the males indicates that they may locate their mates through pheromones released by the females. Many researchers believe that the eels die shortly after reproduction.
Distribution and habitat
Importance to Humans
Because of the extreme depths at which it lives, most of what we know 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.
The gulper eel has also been described as Gastrostomus pacificus, Macropharynx longicaudatus, Gastrostomus bairdii, Eurypharynx richardi, and Leptocephalus pseudolatissimus; despite this, nobody has been able to demonstrate that more than one species of pelican eel exists.
- Froese, Rainer and Pauly, Daniel, eds. (2015). "Eurypharynx pelecanoides" in FishBase. February 2015 version.
- McCosker, John E. (1998). Paxton, J.R.; Eschmeyer, W.N., eds. Encyclopedia of Fishes. San Diego: Academic Press. p. 90. ISBN 0-12-547665-5.
- Dianne J. Bray, 2011, gulper Eel, Eurypharynx pelecanoides, in Fishes of Australia, accessed 7 October 2014, http://www.fishesofaustralia.net.au/home/species/3300
- Nielsen, Jørgen G.; E. Bertelsen; Åse Jespersen (September 1989). "The Biology of Eurypharynx pelecanoides (Pisces, Eurypharyngidae)". Acta Zoologica (Oxford: The Royal Swedish Academy of Sciences) 70 (3): 187–197. doi:10.1111/j.1463-6395.1989.tb01069.x.