tonguefish
{{Short description|Family of fishes}}
{{Automatic taxobox
| image = Symphurus pusillus.jpg
| image_caption = Northern tonguefish, Symphurus pusillus
| taxon = Cynoglossidae
| authority = Jordan, 1888
| subdivision_ranks = Subfamilies and genera
| subdivision_ref = {{FishBase family | family = Cynoglossidae| month = October | year = 2012}}
| subdivision =
Subfamily Cynoglossinae
Subfamily Symphurinae
}}
File:A preserved tongue sole at the lab.jpg
Tonguefishes are flatfish in the family Cynoglossidae. They are distinguished by the presence of a long hook on the snout overhanging the mouth, and the absence of pectoral fins. Their eyes are both on the left side of their bodies, which also lack a pelvic fin.{{cite book |editor1-last = Paxton | editor1-first = J. R. | editor2-last = Eschmeyer | editor2-first = W. N. | author1-last = Chapleau | author1-first = Francois | author2-last = Amaoka | author2-first = Kunio | date = 1998 | title = Encyclopedia of Fishes | publisher = Academic Press | location = San Diego | isbn = 0-12-547665-5 | page = 225 }} This family has three genera with a total of more than 140 species. The largest reaches a length of {{convert|66|cm|abbr=on}}, though most species only reach half that size or less.{{FishBase genus | genus = Cynoglossus| month = May | year = 2014}}{{FishBase genus | genus = Paraplagusia| month = May | year = 2014}}{{FishBase genus | genus = Symphurus| month = May | year = 2014}}
They are found in tropical and subtropical oceans, mainly in shallow waters and estuaries, though some species are found in deep sea floors,{{Cite journal|title = Taxonomic status of three nominal species of Indo-Pacific symphurine tonguefishes (Symphurus: Cynoglossidae: Pleuronectiformes) |url = https://www.researchgate.net/publication/227310648 |journal = Ichthyological Research |year = 1997 |accessdate = 2015-11-01|doi = 10.1007/BF02678697|last1 = Munroe |first1 = Thomas A. |last2 = Marsh |first2 = Barnaby N. |volume = 44 |issue = 2–3 |pages = 189–200 |s2cid = 46661658 }} and even a few in rivers.
Symphurus thermophilus lives congregating around "ponds" of sulphur at hydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents.{{cite journal | last1 = Munroe | first1 = Thomas A. | last2 = Hashimoto | first2 = Jun | date = 1 August 2008 | title = A new Western Pacific Tonguefish (Pleuronectiformes: Cynoglossidae): The first Pleuronectiform discovered at active Hydrothermal Vents | url = http://www.mapress.com/zootaxa/2008/f/zt01839p059.pdf | journal = Zootaxa | volume = 1839 | pages = 43–59 | doi = 10.11646/zootaxa.1839.1.2 }} Scientists are unsure of the mechanism that allows the fish to survive and even thrive in such a hostile environment.{{cite news| url=http://news.bbc.co.uk/1/hi/sci/tech/6212716.stm | first = Jonathan | last = Amos | publisher = BBC News | title=Fish dance on sulphur cauldrons | date=14 December 2006 | accessdate=25 May 2010}}
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