Editing Coelacanth (section)

== Description ==
[[File:Latimeria chalumnae replica.jpg|thumbnail|Reconstruction of [[West Indian Ocean coelacanth]]]]
[[File:Latimeria menadoensis.jpg|thumb|upright|Preserved ''Latimeria menadoensis'', [[Tokyo Sea Life Park]], Japan]]
''[[Latimeria chalumnae]]'' and ''[[Latimeria menadoensis|L. menadoensis]]'' are the only two known living coelacanth species.<ref name="ref1" />{{rp|1,6}}<ref name="ref6">{{cite book |last1=Nelson |first1=Joseph S. |title=Fishes of the World |location=Hoboken, New Jersey |publisher=John Wiley |year=2006 |isbn=978-0-471-75644-6 |page=461}}</ref> Coelacanths are large, plump, lobe-finned fish that can grow to more than {{Convert|2|m|ft|abbr=on}} and weigh around {{Convert|90|kg|lb|abbr=on}}.<ref>{{cite web|title = Coelacanths, Coelacanth Pictures, Coelacanth Facts – National Geographic|url = http://animals.nationalgeographic.com/animals/fish/coelacanth/|archive-url = https://web.archive.org/web/20100114080556/http://animals.nationalgeographic.com/animals/fish/coelacanth|url-status = dead|archive-date = 14 January 2010|website = National Geographic|access-date = 2015-10-28|date = 2011-05-10}}</ref> They are estimated to live up to 100 years, based on analysis of annual growth marks on scales, and reach maturity around the age of 55;<ref>{{cite web |url=https://www.eurekalert.org/pub_releases/2021-06/cp-cml061021.php |title=Coelacanths may live nearly a century, five times longer than researchers expected |work=[[Eurekalert]] |date=17 June 2021 |access-date=17 June 2021}}</ref> the oldest known specimen was 84 years old at the time of its capture in 1960.<ref>{{cite journal |last1=Mahé |first1=Kélig |last2=Ernande |first2=Bruno |last3=Herbin |first3=Marc |title=New scale analyses reveal centenarian African coelacanths |journal=[[Current Biology]] |publisher=[[Cell Press]] |date=17 June 2021 |volume=31 |issue=16 |pages=3621–3628.e4 |doi=10.1016/j.cub.2021.05.054 |pmid=34143958 |issn=0960-9822|doi-access=free |bibcode=2021CBio...31E3621M }}</ref> 
Even though their estimated lifetime is similar to humans, gestation can last 5 years, which is 1.5 years more than the deep-sea [[frilled shark]], the previous record holder.<ref>{{cite magazine |url=https://www.economist.com/science-and-technology/2021/06/19/coelacanths-live-for-as-long-as-people |title=Coelacanths live for as long as people |magazine=[[The Economist]] |date=19 June 2021 |access-date=19 August 2021}}</ref>

They are nocturnal [[piscivorous]] drift-hunters.<ref name="ref7">{{cite journal |bibcode=1987Natur.329..331F |title=Locomotion of the coelacanth Latimeria chalumnae in its natural environment |last1=Fricke |first1=Hans |last2=Reinicke |first2=Olaf |last3=Hofer |first3=Heribert |last4=Nachtigall |first4=Werner |volume=329 |year=1987 |pages=331–3 |journal=Nature |doi=10.1038/329331a0 |issue=6137|s2cid=4353395 }}</ref>

The body is covered in [[Fish scale#Leptoid scales|ctenoid]] [[Fish scale#Elasmoid scales|elasmoid]] scales that act as armor.<ref name="Sherman 2016">{{Cite journal |last=Sherman |first=Vincent R. |title=A comparative study of piscine defense: The scales of ''Arapaima gigas'', ''Latimeria chalumnae'' and ''Atractosteus spatula'' |journal=Journal of the Mechanical Behavior of Biomedical Materials |volume=73 |pages=1–16 |year=2016 |doi=10.1016/j.jmbbm.2016.10.001 |pmid=27816416 }}</ref> Coelacanths have eight fins – two dorsal fins, two pectoral fins, two pelvic fins, one anal fin and one caudal fin. The tail is very nearly equally proportioned and is split by a terminal tuft of fin rays that make up its caudal lobe. The eyes of the coelacanth are very large, while the mouth is very small.{{citation needed|date=December 2021|reason=Contradicted by most every picture here, esp. the one adjacent to this text, dropped here 10 years ago (Jhende34) then editor disappeared, can't find any support for this statement "very small"}} The eye is acclimatized to seeing in poor light by rods that absorb mostly short wavelengths. Coelacanth vision has evolved to a mainly blue-shifted color capacity.<ref name="ref8">{{cite journal |bibcode=1999PNAS...96.6279Y |title=Adaptive Evolution of Color Vision of the Comoran Coelacanth (''Latimeria chalumnae'') |last1=Yokoyama |first1=Shozo |last2=Zhang |first2=Huan |last3=Radlwimmer |first3=F. Bernhard |last4=Blow |first4=Nathan S. |volume=96 |year=1999 |pages=6279–84 |journal=Proceedings of the National Academy of Sciences of the United States of America |doi=10.1073/pnas.96.11.6279 |pmid=10339578 |issue=11 |pmc=26872 |jstor=47861|doi-access=free }}</ref> [[maxilla|Pseudomaxillary]] folds surround the mouth and replace the maxilla, a structure absent in coelacanths. Two nostrils, along with four other external openings, appear between the premaxilla and lateral [[Anatomical terms of location#Other directional terms|rostral]] bones. The nasal sacs resemble those of many other fish and do not contain an internal nostril. The coelacanth's rostral organ, contained within the [[ethmoid]] region of the braincase, has three unguarded openings into the environment and is used as a part of the coelacanth's laterosensory system.<ref name="ref1" />{{rp|14-16, 19}} The coelacanth's auditory reception is mediated by its inner ear, which is very similar to that of tetrapods and is classified as being a [[basilar papilla]].<ref name="ref9">{{cite journal |bibcode=1987Natur.327..153F |title=Inner ear of the coelacanth fish ''Latimeria'' has tetrapod affinities |last1=Fritzsch |first1=B. |volume=327 |year=1987 |pages=153–4 |journal=Nature |doi=10.1038/327153a0 |pmid=22567677 |issue=6118|s2cid=4307982 }}</ref>

Coelacanths are a part of the [[clade]] [[Sarcopterygii]], or the lobe-finned fishes. They share membership in this clade with lungfish and tetrapods. Externally, several characteristics distinguish coelacanths from other lobe-finned fish. They possess a three-lobed [[caudal fin]], also called a trilobate fin or a diphycercal tail. A secondary tail extending past the primary tail separates the upper and lower halves of the coelacanth. Ctenoid elasmoid scales act as thick armor to protect the coelacanth's exterior. Several internal traits also aid in differentiating coelacanths from other lobe-finned fish. At the back of the skull, the coelacanth possesses a hinge, the [[intracranial]] joint, which allows it to open its mouth extremely wide. Coelacanths also retain an oil-filled [[notochord]], a hollow, pressurized tube which is replaced by a [[vertebral column]] early in embryonic development in most other vertebrates.<ref>{{Cite web|url=http://www.scienceinafrica.co.za/2002/february/coela.htm|archive-url=https://web.archive.org/web/20130921055458/http://www.scienceinafrica.co.za/2002/february/coela.htm|url-status=dead|title=What do we know about the coelacanths – Science in Africa|archive-date=21 September 2013}}</ref> The coelacanth's heart is shaped differently from that of most modern fish, with its chambers arranged in a straight tube. The coelacanth's [[braincase]] is 98.5% filled with fat; only 1.5% of the braincase contains brain tissue. The cheeks of the coelacanth are unique because the [[Operculum (fish)|opercular]] bone is very small and holds a large soft-tissue opercular flap. A spiracular chamber is present, but the [[Spiracle (vertebrates)|spiracle]] is closed and never opens during development.<ref>{{Cite book|url=https://books.google.com/books?id=4j9AKGsQ1msC&q=%22spiracular+chamber+is+closed+in+coelacanths%22&pg=PA391|title=Gaining Ground, Second Edition: The Origin and Evolution of Tetrapods|first=Jennifer A.|last=Clack|date=27 June 2012|page=391|publisher=Indiana University Press|isbn=978-0-253-00537-3}}</ref><ref name="ref1" />{{rp|15}}<ref name="ref5">{{cite web |title=The Coelacanth – a Morphological Mixed Bag |publisher=ReefQuest Centre for Shark Research |url=http://www.elasmo-research.org/education/classification/coelacanth.htm}}</ref> Also unique to extant coelacanths is the presence of a "fatty lung" or a fat-filled single-lobed [[vestigial]] [[lung]], homologous to other fishes' [[swim bladder]]s. The parallel development of a fatty organ for buoyancy control suggests a unique specialization for deep-water habitats. There are small and hard but flexible plates around the vestigial lung in adult specimens, though not around the fatty organ. The plates most likely had a regulation function for the volume of the lung.<ref name="Brito">{{cite journal |doi=10.1111/j.1475-4983.2010.01015.x |title=The histological structure of the calcified lung of the fossil coelacanth ''Axelrodichthys araripensis'' (Actinistia: Mawsoniidae) |year=2010 |last1=Brito |first1=Paulo M. |last2=Meunier |first2=François J. |last3=Clément |first3=Gael |last4=Geffard-Kuriyama links|first4=Didier |journal=Palaeontology |volume=53 |issue=6 |pages=1281–90|bibcode=2010Palgy..53.1281B |doi-access=free }}</ref> Due to the size of the fatty organ, researchers assume that it is responsible for the kidney's unusual relocation. The two kidneys, which are fused into one,<ref>{{Cite book|url=https://books.google.com/books?id=hPEJAwAAQBAJ&q=%22amounts.+The+paired+kidneys+are+fused%2C+%22&pg=PA92|title=From fish to philosopher|first=H. W.|last=Smith|date=24 October 2018|publisher=Рипол Классик|isbn=9785873926930|page=92}}</ref> are located ventrally within the abdominal cavity, posterior to the cloaca.<ref>{{Cite book|url=https://books.google.com/books?id=wHZ6WwqbrmkC&q=%22amongst+vertebrates+in+being+located+ventrally%22&pg=PA26|title=History of the Coelacanth Fishes|first=Peter|last=Forey|date=30 November 1997|publisher=Springer Science & Business Media|isbn=978-0-412-78480-4|page=26}}</ref>

[[File:Latimeria chalumnae.jpg|thumbnail|West Indian Ocean coelacanth caught on 21 January 1965, near [[Mutsamudu]] (Anjouan, Comoro Islands)]]
[[File:Pectoral fin Latimeria chalumnae.jpg|thumb|[[Pectoral fin]] of a West Indian Ocean coelacanth]]

=== Genetics ===
In 2013, a research group published the [[genome sequence]] of the coelacanth in the scientific journal ''[[Nature (journal)|Nature]]''.<ref name="genome">{{cite journal | title = The African coelacanth genome provides insights into tetrapod evolution | journal = Nature | date = 18 April 2013 | doi = 10.1038/nature12027 | last1 = Amemiya | first1 = Chris T. | last2 = Alföldi | first2 = Jessica | last3 = Lee | first3 = Alison P. | last4 = Fan | first4 = Shaohua | last5 = Philippe | first5 = Hervé | last6 = MacCallum | first6 = Iain | last7 = Braasch | first7 = Ingo | last8 = Manousaki | first8 = Tereza | last9 = Schneider | first9 = Igor | volume = 496 | issue = 7445 | pages = 311–6 | pmid = 23598338 | pmc = 3633110|bibcode = 2013Natur.496..311A | display-authors = 9 | last10 = Rohner | first10 = Nicolas | last11 = Organ | first11 = Chris | last12 = Chalopin | first12 = Domitille | last13 = Smith | first13 = Jeramiah J. | last14 = Robinson | first14 = Mark | last15 = Dorrington | first15 = Rosemary A. | last16 = Gerdol | first16 = Marco | last17 = Aken | first17 = Bronwen | last18 = Biscotti | first18 = Maria Assunta | last19 = Barucca | first19 = Marco | last20 = Baurain | first20 = Denis | last21 = Berlin | first21 = Aaron M. | last22 = Blatch | first22 = Gregory L. | last23 = Buonocore | first23 = Francesco | last24 = Burmester | first24 = Thorsten | last25 = Campbell | first25 = Michael S. | last26 = Canapa | first26 = Adriana | last27 = Cannon | first27 = John P. | last28 = Christoffels | first28 = Alan | last29 = De Moro | first29 = Gianluca | last30 = Edkins | first30 = Adrienne L. }}</ref>

Due to their lobed fins and other features, it was once hypothesized that the coelacanth might be the youngest diverging non-[[tetrapod]] [[Sarcopterygii|sarcopterygian]].<ref name=ref9 /><ref>{{cite journal |doi=10.1002/jmor.1051900418|title=Lungfish neural characters and their bearing on sarcopterygian phylogeny|journal=Journal of Morphology|volume=190|pages=277–297|year=1986|last1=Northcutt|first1=R. Glenn|hdl=2027.42/50281|s2cid=35473487|url=https://deepblue.lib.umich.edu/bitstream/2027.42/50281/1/1051900418_ftp.pdf|hdl-access=free}}</ref> But after sequencing the full genome of the coelacanth, it was discovered that the lungfish instead is more closely related to tetrapods. Coelacanths and [[rhipidistia]]ns (the [[concestor]] of lungfish and tetrapods) had already diverged from each other before the lungfish made the transition to land.<ref name="smithsonianmag.com">{{cite web|url=http://www.smithsonianmag.com/science-nature/dna-sequencing-reveals-that-coelacanths-werent-the-missing-link-between-sea-and-land-25025860/?no-ist|title=DNA Sequencing Reveals that Coelacanths Weren't the Missing Link Between Sea and Land|first=Joseph|last=Stromberg|publisher=Smithsonian Magazine}}</ref>

Another important discovery made from the genome sequencing is that the coelacanths are still evolving today. While phenotypic similarity between extant and extinct coelacanths suggests there is limited [[evolutionary pressure]] on these organisms to undergo morphological divergence, they are undergoing measurable genetic divergence. Despite prior studies showing that protein coding regions are undergoing evolution at a substitution rate much lower than other sarcopterygians (consistent with phenotypic stasis observed between extant and fossil members of the taxa), the non-coding regions subject to higher transposable element activity show marked divergence even between the two extant coelacanth species.<ref name="genome" /> This has been facilitated in part by a coelacanth-specific endogenous retrovirus of the Epsilon retrovirus family.<ref>{{Cite journal|doi=10.1371/journal.pone.0114382|doi-access=free|title=Interspecies Insertion Polymorphism Analysis Reveals Recent Activity of Transposable Elements in Extant Coelacanths|year=2014|last1=Naville|first1=Magali|last2=Chalopin|first2=Domitille|last3=Volff|first3=Jean-Nicolas|journal=PLOS ONE|volume=9|issue=12|pages=e114382|pmid=25470617|pmc=4255032|bibcode=2014PLoSO...9k4382N}}</ref>[[File:Fishapods.svg|thumb|upright=1.4|In the [[Devonian|Late Devonian]] [[vertebrate]] speciation, descendants of [[Pelagic zone|pelagic]] [[Sarcopterygii|lobe-finned fish]]—like ''[[Eusthenopteron]]''—exhibited a sequence of adaptations: ''[[Panderichthys]]'', suited to muddy shallows; ''[[Tiktaalik]]'' with limb-like fins that could take it up onto land; and [[Tetrapod|Early tetrapods]] in weed-filled swamps, such as ''[[Acanthostega]]'' which had feet with eight digits and ''[[Ichthyostega]]'' with limbs. Descendants also included pelagic lobe-finned fish such as the coelacanth species.]]