The Gulper Eel, other wise known as the Pelican Eel or the Umbrella Mouthed Gulper, has the scientific name Eurypharynx pelecanoides, and is in the order of Saccopharyngiformes. Though they are not true eels, nor are they of the order of true eels, they look vaguely similar: just with an extremely big mouth! They are normally black or dark green in colour, and they live in the extreme depths of the oceans, between 500m and 7500m down, which is why so little is known about it.
Deep down in the depths of the ocean, food is scarce, so most of the animals down there have evolved some highly specialised feeding mechanisms. The Gulper eel has adapted in two specific ways. The first is its giant mouth. The head of the Gulper Eel is about a quarter of its total length, which is normally between one and two meters. The jaws are hinged, so that the Gulper can ingest food bigger than its own body. It also uses its mouth like a trawler, increasing its chances of catching smaller, quicker food. The stomach of the Gulper Eel can also distend in order for it to eat and digest large meals. As the jaws of the Gulper Eel are so big, vast amounts of water are ingested. Their method of dealing with this is to use the gill slits to slowly expel the excess water.
The second evolutionary modification of the Gulper Eel is its tail, which is very long and thin, and some of the ones found in fishing nets were discovered with knots in the tails. While the long tail is primarily used for movement, there has been a more interesting discovery: the tip of the tail has a developed a photophore, an organ which produces light by a process called bioluminescence. The light produced is usually pink in colour, but the Gulper Eel can produce red flashes.
As most of its prey is small and fast, it is thought that the bioluminescence is used as a lure, getting inquisitive victims close enough for the Gulper to snatch. It usually feeds on cephalopods (squid), crustaceans and small invertebrates. As the Gulper Eel has very small teeth, it is unlikely that it regularly feasts on larger animals, though it probably does so if it is forced to. The known predators of the Gulper Eel are Lancet Fish, though other deep sea predators are thought to prey on it.
There are other interesting features that are worthy of note. Like all Saccopharyngiforms, the Gulper Eel lacks some of the bones present in other inhabitants of the oceans: these include the lack of a symplectic bone, and the bones of the ribs and the opercle. Also, they have no scales, pelvic fins, or swim bladder, and only very tiny pectoral fins. The lateral line, a sense organ used to detect vibrations in the water, projects from the body, instead of being concealed in a grove in the body. Most intriguingly, it has very small eyes, which is unusual in deep sea animals. It is possible that the Gulper’s eyes are used to detect the presence of light, rather than detailed images.
We do not know very much about the reproduction cycle of the Gulper Eel. What is known is that the male Gulper Eel undergoes changes in the maturation process which result in an enlargement of the olfactory organs, and the degeneration of the teeth and jaws, while the female of the species does not. It is likely that the enlarged olfactory organs are used to detect pheromones from the females. Some researchers are of the opinion that the Eels die soon after copulating.
Please do have a look at the video below which has footage of the Gulper Eel, starting at 0:37.