View source for Saccopharyngiforms

{{Short description|Order of fishes}}
{{Automatic Taxobox
| image             = Eurypharynx.jpg
| image_caption     = [[Pelican eel]] (''Eurypharynx pelecanoides'')
| taxon             = Saccopharyngiformes
| authority         = Poulsen, 2018
| display_parents   = 2
| subdivision_ranks = Families
| subdivision       = See text
}}

The '''Saccopharyngiformes''' are a derived lineage of unusual eels within the order [[Eel|Anguilliformes]], and includes families Cyematidae, Monognathidae, Eurypharyngidae, Saccopharyngidae, and the proposed family Neocyematidae.<ref name=":0">{{Cite journal|last1=Poulsen|first1=Jan Y.|last2=Miller|first2=Michael J.|last3=Sado|first3=Tetsuya|last4=Hanel|first4=Reinhold|last5=Tsukamoto|first5=Katsumi|last6=Miya|first6=Masaki|date=2018-07-25|title=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|journal=PLOS ONE|language=en|volume=13|issue=7|article-number=e0199982|doi=10.1371/journal.pone.0199982|issn=1932-6203|pmc=6059418|pmid=30044814|bibcode=2018PLoSO..1399982P|doi-access=free}}</ref> 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 eel]]s (also commonly known as gulper eels) and [[bobtail eel]]s. Some can live deep in the ocean, well into the [[aphotic zone]], approximately {{convert|500|to|1800|m|sp=us}} deep. Extensive research has not been conducted on them due to being indirectly observed, with some species known only from their larvae.<ref name=":0" /> All families except for the exceptionally rare individuals of proposed family Neoceymatidae (known only from the [[Atlantic Ocean]]) are found in all major oceans.{{Not verified in body|date=November 2020}}

== Description ==
They have multiple internal differences from the rest of Anguilliformes. Notably, they have no [[symplectic bone]], [[Operculum (fish)|opercular]] bones, ribs, or [[Swim bladder|swim bladders]]. Like many other eels, they lack scales and [[pelvic fin]]s. Their [[myomere]]s (muscle segments) are V-shaped instead of W-shaped as in all other fishes, and their [[Lateral line|lateral lines]] have no pores, instead being modified to groups of elevated tubules. The jaws are quite large, lined with small teeth, and several types are notable for being able to consume fish larger than themselves. Some species in families Eurypharyngidae and Saccopharyngidae are [[bioluminescent]]. 

Like other eels, saccopharyngids have leptocephalus larvae. However, these larvae also have a number of unusual characteristics, such as remarkably deep bodies in the Cyematidae, long lower jaws in the Eurypharyngidae, and unique pigmented swellings at the ends of the gut in Saccopharyngidae and Eurypharyngidae.<ref>{{Cite journal|last=Orton|first=Grace L.|date=1963|title=Notes on Larval Anatomy of Fishes of the Order Lyomeri|journal=Copeia|volume=1963|issue=1|pages=6–15|doi=10.2307/1441268|jstor=1441268}}</ref><ref>{{Cite web|url=https://yalebooks.yale.edu/book/9780935868456/volume-1and-2-orders-anguilliformes-and-saccopharyngiformes-and-leptocephali|title=Volume 1 and 2: Orders Anguilliformes and Saccopharyngiformes and Leptocephali {{!}} Yale University Press|website=yalebooks.yale.edu|language=en|access-date=2018-09-25}}</ref>

The three established families of the suborder Saccopharyngoidei (Eupharyngidae, Monognathidae, Saccopharyngidae) all exhibit [[sexual dimorphism]].<ref>{{Cite book|last1=Böhlke|first1=Eugenia B.|title=Orders Anguilliformes and Saccopharyngiformes: Part 9, Volume 1|last2=Böhlke|first2=James E.|last3=Leiby|first3=Mark M.|last4=McCosker|first4=John E.|last5=Bertelsen|first5=E.|last6=Robins|first6=Catherine H.|last7=Robins|first7=C. Richard|last8=Smith|first8=David G.|last9=Tighe|first9=Kenneth A.|date=1989|publisher=Yale University Press|jstor=j.ctvbcd0dm|isbn=978-1-933789-19-4}}</ref>

== Taxonomy ==
Until recently,{{when|date=October 2021}}<!--What year?--> the order "Saccopharyngiformes" was accepted as a separate order from Anguilliformes, based on their distinct morphological differences from the rest of the "true eels". Genetic work over the past few years{{when|date=October 2021}}<!--Specify the year numbers--> has shown that it is instead a derived lineage within the Anguilliformes.<ref>{{Cite journal|last1=Santini|first1=Francesco|last2=Kong|first2=Xianghui|last3=Sorenson|first3=Laurie|last4=Carnevale|first4=Giorgio|last5=Mehta|first5=Rita S.|last6=Alfaro|first6=Michael E.|date=2013|title=A multi-locus molecular timescale for the origin and diversification of eels (Order: Anguilliformes)|journal=Molecular Phylogenetics and Evolution|volume=69|issue=3|pages=884–894|doi=10.1016/j.ympev.2013.06.016|issn=1095-9513|pmid=23831455}}</ref>

The four (proposed five) families in two suborders are:

* Suborder Cyematoidei
**[[Cyematidae]] (bobtail snipe eels)
* Suborder [[Saccopharyngoidei]]
**[[Eurypharyngidae]] (gulpers)
**[[Monognathidae]] (one-jaws)
**[[Saccopharyngidae]] (swallowers)
**[[Neocyematidae]] (proposed)<ref name=":0" />

== References ==
{{reflist}}

== External links ==
* [https://twitter.com/Rainmaker1973/status/1330896413841125376 Rarely-seen deep sea gulper eel (''Eurypharynx pelecanoides'') in the first time ever video of its massive jaws], November 2020.

{{Actinopterygii}}
{{Taxonbar|from=Q621582}}

[[Category:Bioluminescent fish]]
[[Category:Deep sea fish]]
[[Category:Eels]]