Pelican eel

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Pelican eel
Eurypharynx pelecanoides.jpg
The mouth of the pelican eel can open wide enough to swallow prey much larger than the eel itself.
Status TNC G5.svg
Secure  (NatureServe) [2]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Anguilliformes
Family: Eurypharyngidae
Gill, 1883
Genus: Eurypharynx
Vaillant, 1882
Species:
E. pelecanoides
Binomial name
Eurypharynx pelecanoides
Vaillant, 1882
Synonyms

Gastrostomus pacificus
Macropharynx longicaudatus
Gastrostomus bairdii
Eurypharynx richardi
Leptocephalus pseudolatissimus

Eurypharynx pelecanoides SI.jpg
Eurypharynx pelecanoides X-ray (cropped).jpg
Conventional and X-ray images of preserved Eurypharynx pelecanoides

The pelican eel (Eurypharynx pelecanoides) is a deep-sea eel. It is the only known member of the genus Eurypharynx and the family Eurypharyngidae. It belongs to the "saccopharyngiforms", members of which were historically placed in their own order, but are now considered true eels in the order Anguilliformes. [3] The pelican eel has been described by many synonyms, yet nobody has been able to demonstrate that more than one species of pelican eel exists. [4] It is also referred to as the gulper eel (which can also refer to members of the related genus Saccopharynx ), pelican gulper, and umbrella-mouth gulper. [5] The specific epithet pelecanoides refers to the pelican, as the fish's large mouth is reminiscent of that of the pelican.

Description

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. [6] However, certain observations about the physical characteristics have been noted from studied specimen.

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 lower jaw is hinged at the base of the head, with no body mass behind it, making the head look disproportionately large. Its jaw is so large that it is estimated to be about a quarter of the total length of the eel itself. [7]

While typically in a folded state, the pelican eel's mouth has the capacity to change to an inflated shape when hunting, giving the mouth its notably massive appearance. This transformation is possible due to the dual-mode biological morphing mechanism that takes place: geometric unfolding of the mouth followed by stretching. [8] When the pelican eel is in pursuit of prey and opens its mouth, the head and jaw structure unfold and spread horizontally, This un-spreading event is followed by the inflation of the mouth. 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. When it feeds on prey, water that is ingested is expelled via the gills. [9]

Pelican eels are smaller-sized eels. They grow to about 0.75 m (2.5 ft) in length, though lengths of 1 m (3 ft 3 in) are plausible. [10] Like most eels, E. pelecanoides lacks pelvic fins and scales. Otherwise, the pelican eel is very different in appearance from typical eels. 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. It has been hypothesized that these gelatinous substance filled "lymphatic spaces" could function in a similar way to a swim bladder. [11] Furthermore, the muscle segment shape of the pelican eel is different. Its muscle segments have a "V-shape", while other fish have "W-shaped" muscle segments. [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. [12]

Unlike many other deep sea creatures, the pelican eel has very small eyes. For reference, the horizontal eye size diameter of a male pelican eel specimen was measured to be 2.6 mm (0.10 in). [13] It is believed that the eyes evolved to detect faint traces of light rather than form images.

The pelican eel also has a very long, whip-like tail that it uses for movement and for communication via bioluminescence. Specimens that have been brought to the surface in fishing nets have been known to have their long tails tied into several knots. The end of the tail bears a complex organ with numerous tentacles, which glows pink and gives off occasional bright-red flashes. The colors on its tail are displayed through its light-emitting photophores. [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.

Pelican eels are black or olive and some subspecies may have a thin lateral white stripe. The coloration of E. pelecanoides is especially dark because this species exhibits ultra-black camouflage. This special pigmentation, which reflects less than 0.5% of light, allows these eels to be cloaked in darkness in their low light environments. [15] Ultra-black camouflage allows these bathypelagic eels to evade predators and hide from prey.

Pelican eels display sexual dimorphism with the largest morphological difference in the structure of the nasal rosette. [13] In female pelican eels, the nasal rosette is hardly noticeable whereas male pelican eels exhibit a larger nasal rosette. The male's nasal rosette is bulb-shaped and contains larger anterior and posterior nostrils. Sexual dimorphism is thought to aid with locating a potential mate in the bathypelagic zone. [13]

Feeding habits and diet

Pelican eels have developed adaptations and feeding patterns to help them survive in their low biomass environment. 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. [16] They are hypothesized to exhibit lunge-feeding through the expansion of their mandible and upper jaw. [17] Furthermore, their 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. [12] The large mouth may be an adaptation to allow the eel to eat a wider variety of prey when food is scarce. The eel can swim into large groups of shrimp or other crustaceans with its mouth closed, opening wide as it closely approaches prey, scooping them up to be swallowed. [6] The pelican 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. [6] Pelican eels themselves are preyed upon by lancetfish and other deep sea predators. The pelican eel is not known to undergo vertical diurnal migration like other eels. [18]

Observations of gut contents and teeth morphology indicate that Eurypharynx pelecanoides larva, categorized as a type of leptocephali, feed on marine snow. [19] Organisms, such as thraustochytrids and hydrozoan tissue, were consumed by these larva in a grouped manner such as they would be found in 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. [19] As leptocephali develop into their mature form these distinct teeth were replaced by more, smaller teeth. This particular observation may explain a shift in the size of leptocephali heads, such as E. pelecanoides, in comparison to their food source as they mature. [19]

Reproduction and life cycle

Not much is known about the reproductive habits of the pelican eel. Similar to other eels, when pelican eels are first born, they start in the leptocephalus stage, meaning that they are extremely thin and transparent. [20] Until they reach their juvenile stage, they interestingly have very small body organs and do not contain any red blood cells. 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 males also have defined reproductive organs. In a studied male, the testes occupied a majority of the space in the stomach cavity where the stomach had seemed to have shrunk. [13] The females, on the other hand, remain relatively unchanged as they mature. The large olfactory organs in the sexually-mature males indicates that they may locate their mates through pheromones released by the females. Many researchers believe that the eels die shortly after reproduction. [21] Reproducing later in life is thought to be a strategy that increases the likelihood of offspring survival for E. pelecanoides. [13]

Distribution and habitat

The pelican eel has been found in the temperate and tropical areas of all oceans. [4] In the North Atlantic, it seems to have a range in depth from 500 to 3,000 m (1,600 to 9,800 ft). [4] One Canadian-arctic specimen was found in Davis Strait at a depth of 1,136–1,154 m (3,727–3,786 ft), and also across the coasts of Greenland. [6] More recently, pelican eels have been spotted off the coast of Portugal, as well as near Hawaiian islands.

Interactions with humans

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. [21] Although once regarded as a purely deep-sea species, since 1970, hundreds of specimens have been caught by fishermen, mostly in the Atlantic Ocean. [4] In October 2018, the first direct observation of a gulper eel was made by a group of researchers near the Azores. 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). [22] Until these recent explorations, not much has been analyzed by researchers of the behavior of gulper eels.

Phylogenetic relationship to other species

In 2003, researchers from the University of Tokyo sequenced mitochondrial DNA (mtDNA) from specimens of Eurypharynx pelicanoides and Saccopharynx lavenbergi . After comparing the sequences from the specimens with other known sequences, specifically the non-coding regions, they found that E. pelicanoides and S. lavenbergi were closely related and genetically distinct from anguilliformes due to the high frequency of similarity on these regions. [23]

See also

Related Research Articles

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Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep-sea fishes include the flashlight fish, cookiecutter shark, bristlemouths, anglerfish, viperfish, and some species of eelpout.

<span class="mw-page-title-main">Leptocephalus</span> Juvenile eel

A leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 families, and 156 genera. This group is thought to have arisen in the Cretaceous period over 140 million years ago.

<span class="mw-page-title-main">Frilled shark</span> Species of shark

The frilled shark, also known as the lizard shark, is one of the two extant species of shark in the family Chlamydoselachidae. The frilled shark is considered a living fossil, because of its primitive, anguilliform (eel-like) physical traits, such as a dark-brown color, amphistyly, and a 2.0 m (6.6 ft)–long body, which has dorsal, pelvic, and anal fins located towards the tail. The common name, frilled shark, derives from the fringed appearance of the six pairs of gill slits at the shark's throat.

<span class="mw-page-title-main">Saccopharyngiforms</span> Order of fishes

The Saccopharyngiformes are a derived lineage of unusual eels within the order Anguilliformes, and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae. Most of the fish in this group are deep-dwelling and rarely seen, typically known from only a handful of specimens. Species include recognizable fish such as pelican eels and bobtail eels. Some can live deep in the ocean, well into the aphotic zone, approximately 500 to 1,800 meters deep. Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae. All families except for the exceptionally rare individuals of proposed family Neoceymatidae are found in all major oceans.

<span class="mw-page-title-main">Moray eel</span> Family of fishes

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<span class="mw-page-title-main">Black swallower</span> Species of fish

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<span class="mw-page-title-main">Pelagic fish</span> Fish in the pelagic zone of ocean waters

Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs.

<span class="mw-page-title-main">Viperfish</span> Genus of fishes

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Gulper eel may refer to:

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<span class="mw-page-title-main">Kidako moray</span> Species of fish

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<span class="mw-page-title-main">Anglerfish</span> Bony fish of the teleost order Lophiiformes

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<span class="mw-page-title-main">Pharynx</span> Part of the throat that is behind the mouth and nasal cavity

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<i>Saccopharynx ampullaceus</i> Species of fish

Saccopharynx ampullaceus, referred to as the gulper eel, gulper, taillight gulper or pelican-fish, is an ocean-dwelling eel found in the North Atlantic Ocean. They are found up to a depth of 3,000 m (9,800 ft). These fish are rarely observed, so little information is currently known about their habits or full distribution.

Saccopharynx lavenbergi is a species of gulper eel, also known as the whiptail gulper. This fish is known for its large mouth and long whiplike tail. This species is not commonly found in the wild, with fewer than twenty sightings over 30 years of ROV operation by MBARI. Even though it has rarely been sighted, this gulper eel was chosen to be the logo for MBARI.

References

  1. ↑ "IUCN Red List of Threatened Species: Eurypharynx pelecanoides". 9 May 2014.
  2. ↑ "Eurypharynx pelecanoides". NatureServe Explorer. Retrieved 19 April 2024.{{cite web}}: CS1 maint: url-status (link)
  3. ↑ Poulsen, Jan Y.; Miller, Michael J.; Sado, Tetsuya; Hanel, Reinhold; Tsukamoto, Katsumi; Miya, Masaki; Fugmann, Sebastian D. (25 July 2018). "Resolving deep-sea pelagic saccopharyngiform eel mysteries: Identification of Neocyema and Monognathidae leptocephali and establishment of a new fish family "Neocyematidae" based on larvae, adults and mitogenomic gene orders". PLOS ONE. 13 (7): e0199982. Bibcode:2018PLoSO..1399982P. doi: 10.1371/journal.pone.0199982 . PMC   6059418 . PMID   30044814.
  4. 1 2 3 4 Nielsen, Jørgen G.; E. Bertelsen; Åse Jespersen (September 1989). "The Biology of Eurypharynx pelecanoides (Pisces, Eurypharyngidae)". Acta Zoologica. 70 (3): 187–197. doi:10.1111/j.1463-6395.1989.tb01069.x.
  5. ↑ Froese, Rainer; Pauly, Daniel (eds.) (2015). "Eurypharynx pelecanoides" in FishBase . February 2015 version.
  6. 1 2 3 4 Coad, Brian W. (2018). "Family 15. Eurypharyngidae: Gulpers, Grandgousiers (1)". Marine Fishes of Arctic Canada. By Møller, Peter Rask; Renaud, Claude B.; Alfonso, Noel; et al. Coad, Brian W.; Reist, James D. (eds.). University of Toronto Press. pp. 217–218. ISBN   978-1-4426-4710-7. JSTOR   10.3138/j.ctt1x76h0b.
  7. ↑ Paxton, John R.; Eschmeyer, William N. (1998). Encyclopedia of Fishes. San Diego, CA: Academic Press. p. 90. ISBN   0-12-547665-5.
  8. ↑ Kim, Woongbae (27 November 2019). "Bioinspired dual-morphing stretchable origami". Science Robotics. 4 (36). doi: 10.1126/scirobotics.aay3493 . PMID   33137780. S2CID   208607295.
  9. 1 2 Gulper Eel – Pelican Eel, Frightening Deep Sea Jaws | Animal Pictures and Facts. FactZoo.com. Retrieved 2016-11-14.
  10. ↑ Bray, Dianne J. (2011), "Gulper Eel, Eurypharynx pelecanoides".. Fishes of Australia, accessed 7 October 2014
  11. ↑ Ozaka, Chieko; Yamamoto, Naoyuki; Nielsen, Jørgen G.; Somiya, Hiroaki (1 November 2011). "The aglomerular kidney of the deep-sea gulper eel Saccopharynx ampullaceus (Saccopharyngiformes: Saccopharyngidae)". Ichthyological Research. 58 (4): 297–301. doi:10.1007/s10228-011-0227-1. ISSN   1616-3915. S2CID   24744228.
  12. 1 2 McCosker, John E. (1998). Paxton, J.R.; Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. p. 90. ISBN   978-0-12-547665-2.
  13. 1 2 3 4 5 Gartner, John V. (1983). "Sexual Dimorphism in the Bathypelagic Gulper Eel Eurypharynx pelecanoides (Lyomeri: Eurypharyngidae), with Comments on Reproductive Strategy". Copeia. 1983 (2): 560–563. doi:10.2307/1444413. ISSN   0045-8511. JSTOR   1444413.
  14. ↑ "Gulper Eel". Our Breathing Planet. 6 December 2016. Retrieved 10 March 2020.
  15. ↑ Davis, Alexander L.; Thomas, Kate N.; Goetz, Freya E.; Robison, Bruce H.; Johnsen, Sönke; Osborn, Karen J. (7 September 2020). "Ultra-black Camouflage in Deep-Sea Fishes". Current Biology. 30 (17): 3470–3476.e3. doi: 10.1016/j.cub.2020.06.044 . ISSN   0960-9822. PMID   32679102.
  16. 1 2 Schembri, Frankie (4 October 2018). "First direct observation of hunting pelican eel reveals a bizarre fish with an inflatable head". Science | AAAS. Retrieved 10 February 2020.
  17. ↑ Motani, Ryosuke; Chen, Xiao-hong; Jiang, Da-yong; Cheng, Long; Tintori, Andrea; Rieppel, Olivier (10 March 2015). "Lunge feeding in early marine reptiles and fast evolution of marine tetrapod feeding guilds". Scientific Reports. 5 (1): 8900. Bibcode:2015NatSR...5E8900M. doi: 10.1038/srep08900 . ISSN   2045-2322. PMC   4354009 . PMID   25754468.
  18. ↑ DeVaney, Shannon C. (1 October 2016). "Species Distribution Modeling of Deep Pelagic Eels". Integrative and Comparative Biology. 56 (4): 524–530. doi: 10.1093/icb/icw032 . ISSN   1540-7063. PMID   27252208.
  19. 1 2 3 Miller, Michael J.; Marohn, Lasse; Wysujack, Klaus; Freese, Marko; Pohlmann, Jan-Dag; Westerberg, Håkan; Tsukamoto, Katsumi; Hanel, Reinhold (1 March 2019). "Morphology and gut contents of anguillid and marine eel larvae in the Sargasso Sea". Zoologischer Anzeiger. 279: 138–151. doi:10.1016/j.jcz.2019.01.008. ISSN   0044-5231. S2CID   91322691.
  20. ↑ "Reproduction". bioweb.uwlax.edu. Retrieved 10 March 2020.
  21. 1 2 Gulper Eel – Deep Sea Creatures on Sea and Sky. Seasky.org. Retrieved 2016-11-14.
  22. ↑ "Watch a Gulper Eel Inflate and Deflate Itself, Shocking Scientists". Animals. 21 September 2018. Archived from the original on 22 September 2018. Retrieved 10 March 2020.
  23. ↑ Inoue, J. G. (27 June 2003). "Evolution of the Deep-Sea Gulper Eel Mitochondrial Genomes: Large-Scale Gene Rearrangements Originated Within the Eels". Molecular Biology and Evolution. 20 (11): 1917–1924. doi: 10.1093/molbev/msg206 . ISSN   0737-4038. PMID   12949142.

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