The Pelican Eel: Can Their Mouth Hold More Than Their Belly Can?
The creatures of the deep ocean have always been known to be peculiar. This is due to millions of years of adaptations in order to survive the extreme environmental pressures of the deep ocean. The Pelican Eel, Eurypharynx pelecanoides (E. pelecanoides) is a deep sea creature than has evolved adaptations in order to survive in its habitat. The Pelican Eel is found in tropic and temperate waters, at depth ranges between 500-7000m, but usually are found around 1200-1400m. They are also known as gulper eel, pelican gulper, and umbrella-mouth gulper.
The video below shows that this unbelievable animal actually does exist, if you thought the picture above was straight out of a horror movie.
“It is not the most intellectual of the species that survives; it is not the strongest that survives; but the species that survives is the one that is able best to adapt and adjust to the changing environment in which it finds itself” – Leon C. Megginson
The most distinctive thing about this animal is of course the mouth. This adaptation looks disproportional to the rest of its body. With E. pelecanoides mainly feeding on crustaceans, fish and squid, this species swallows its prey whole. They do this by expanding not only the lower jaw, known also as a mandible, but also the upper jaw. This is known as lunge feeding.With having such a disproportional mouth, this could prove to be a problem however this species’ stomach can expand in order to withhold what their mouth takes in. With the ability to have a proportionally larger mouth, this is a huge advantage when the animals can’t see its prey. This allows the animal to predate many prey species instead of one particular species so that they are more likely to survive.
The mouth is not the only adaptation that this creature has gained in order to survive, however this adaptation can be seen in many deep sea creatures and that is bioluminescence, this is when a chemical reaction occurs within the animal. This bioluminescence is located in the tail. It is thought that they manipulate their body by moving the tail towards the head, then use their tail and the bioluminescence in order to attract prey. They do this by flashing a red light from the end their tail.
Unlike many deep sea creatures E. pelecanoides has adapted small eyes. This is uncommon as many deep sea creatures adapt larger eyes in order to see in the dark of the deep ocean. This uncommon adaptation is thought to allow E. pelecanoides to see fragments of light rather than an entire image but may have also evolved in order to compensate for its large mouth.
Little is known about the reproduction of the species, due to the habitat and the complications of monitoring this animal. What is known however is that when male juveniles mature they go through particular changes and are thought to die after spawning. The changes that are known are that males develop larger olfactory organs, in order recognise and locate pheromones secreted by females. Another change is the weakening of the teeth and jaws, one thought is that if they die after spawning they don’t require strong teeth and jaws for prey and another theory is that they utilise the nutrients within the teeth and jaws to help with spawning. Females do not go through drastic changes like that of the males and females are thought to die after reproducing once like the males.
The Missing Bits
The most common thought is that adaptations are gaining new features in order to survive. However, that is not always the case. In the case of E. pelecanoides the loss of certain features has enabled this creature to survive in the deep ocean. Three examples of these losses are the swim bladder, pelvic fin and scales. The swim bladder is present in most fish, except for bottom dwelling fish species and it is used for buoyancy. However, with depth, gas becomes denser and it takes more energy for a specimen to fill a swim bladder under intense pressure. E. pelecanoides has evolved a more efficient way of controlling buoyancy in the deep ocean as the pelican eel has adapted fluid filled cavities throughout their body instead of a swim bladder in order to create buoyancy. Scales are known to be used for reflectors in order to deter predators and a form of protection. There has not yet been a conclusion drawn as to why E. pelecanoides lacks scales. Through evolution, many animals lose inefficient features and this maybe the case here. Through evolution Anguilliformes, this is the order all eels are classed within, have adapted not to require a pelvic fin.