The morphology of pelican eel specimens can be hard to describe because they are so fragile that they become damaged when they are recovered from the deep sea's immense pressure.

This transformation is possible due to the dual-mode biological morphing mechanism that takes place: geometric unfolding of the mouth followed by stretching.

The inflation is made possible given the highly stretchable skin of the head, an additional characteristic that enables the eel to partake in this mechanism and engage in lunge feeding to consume large amounts of prey.

Instead of having a swim bladder, the pelican eel has an aglomerular kidney that is thought to have a role in maintaining the gelatinous substance filling the "lymphatic spaces" that are found around the vertebrae.

[9] Pelican eels are also unusual because the ampullae of the lateral line system project from the body, rather than being contained in a narrow groove; this may increase its sensitivity.

The end of the tail bears a complex organ with numerous tentacles, which glows pink and gives off occasional bright-red flashes.

[14] 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.

Recent studies have shown that pelican eels are active participants in their pursuit of food, rather than passively waiting for prey to fall into their large mouths.

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.

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.

[18] Observations of gut contents and teeth morphology indicate that Eurypharynx pelecanoides larva, categorized as a type of leptocephali, feed on marine snow.

Furthermore, the lesser number, larger size, and inwardly-pointing direction of leptocephali larval teeth point indicate that pelican eel larva rely on marine snow as a source of nutrients.

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.

Because of the extreme depths at which it lives, most of what is known about the pelican eel comes from specimens that are inadvertently caught in deep sea fishing nets.

The team witnessed the aggressive nature of the eel's hunting process, as it was constantly moving around in the water column to attempt to find prey.

[16] In September 2018, the E/V Nautilus team also witnessed a juvenile gulper eel inflating its mouth in attempt to catch prey in the Papahānaumokuākea Marine National Monument (PMNM).