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Pelican eel

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The pelican eel, known scientifically as Eurypharynx pelecanoides, is a unique deep-sea fish. It is the only member of its genus and family, Eurypharyngidae. While it was once placed in its own order, scientists now classify it as a true eel within the order Anguilliformes. This species is often called a gulper eel or an umbrella-mouth gulper. Its scientific name, pelecanoides, refers to the pelican because of its massive mouth. This eel is a fascinating example of how life adapts to the extreme conditions of the deep ocean.

Eurypharynx head
Eurypharynx head

The most striking feature of the pelican eel is its enormous mouth. The jaw is so large that it can account for about one-quarter of the eel's total length. To feed, the eel uses a dual-mode biological morphing mechanism. First, the head and jaw undergo geometric unfolding, spreading horizontally. Second, the highly stretchable skin of the head allows the mouth to inflate. This process enables lunge feeding, where the eel scoops up large amounts of prey. Once the meal is swallowed, the eel expels the ingested water through its gills.

Eurypharynx leptocephalus
Eurypharynx leptocephalus

Pelican eels possess several specialized physical traits that differ from typical fish. Most fish have W-shaped muscle segments, but the pelican eel has V-shaped segments. Instead of a swim bladder, it has an aglomerular kidney. This kidney helps maintain gelatinous substance in lymphatic spaces around the vertebrae. These spaces are thought to function like a swim bladder to assist with buoyancy. Additionally, the ampullae of the lateral line system project from the body. This projection may increase the eel's sensitivity to movements in the water.

Survival in the dark bathypelagic zone requires incredible camouflage. The pelican eel uses ultra-black camouflage to hide from predators and prey. This special pigmentation is so dark that it reflects less than 0.5% of light. Its eyes are very small, likely evolved to detect faint traces of light rather than clear images. For movement and communication, the eel uses a long, whip-like tail. The tip of this tail features photophores, which are light-emitting organs. These organs glow pink and produce red flashes to act as a lure for prey.

Eurypharynx head
Eurypharynx head

The life cycle of the pelican eel begins in the leptocephalus stage. These larvae are extremely thin, transparent, and lack red blood cells. During this stage, they feed on marine snow, which includes organisms like thraustochytrids and hydrozoan tissue. As they mature into adults, their teeth change from fewer, larger, inward-pointing teeth to more numerous, smaller teeth. Sexual dimorphism, or physical differences between sexes, becomes apparent during maturity. Males develop a large, bulb-shaped nasal rosette to help them locate mates via pheromones. In males, the testes can occupy much of the stomach cavity.

Eurypharynx leptocephalus
Eurypharynx leptocephalus

History shows that much of our knowledge comes from accidental encounters. Because they live at extreme depths, many specimens are caught in deep-sea fishing nets. Since 1970, hundreds of specimens have been recovered, mostly in the Atlantic Ocean. Direct observations are rare, but significant progress occurred in 2018. Researchers near the Azores made the first direct observation of a gulper eel. They witnessed its aggressive hunting behavior in the water column. Another team from the E/V Nautilus observed a juvenile inflating its mouth in the Papahānaumokuākea Marine National Monument.

Eurypharynx head
Eurypharynx head

Pelican eels have a wide global distribution across temperate and tropical oceans. They have been found near the Hawaiian islands, the coast of Portugal, and Greenland. In the North Atlantic, they inhabit depths ranging from 500 to 2,000 meters. One specimen was even recorded in the Davis Strait at a depth of 1,000 meters. Their diet primarily consists of small crustaceans, though they also eat squid and other invertebrates. While their jaws are massive, they have tiny teeth, suggesting they use their mouths to capture a wide variety of prey when food is scarce. This flexibility is vital in a low-biomass environment.

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File:Eurypharynx head.png
Eurypharynx head.png
File:Eurypharynx leptocephalus.png
Eurypharynx leptocephalus.png
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