View source for Biology:Hexanchus

{{Short description|Genus of sharks}}
{{Automatic taxobox
| fossil_range = {{Fossil range|196|0}} Sinemurian to present<ref>{{cite journal |last=Sepkoski |first=Jack |title=A compendium of fossil marine animal genera (Chondrichthyes entry) |journal=Bulletins of American Paleontology |volume=364 |page=560 |year=2002 |url=http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=575&rank=class |access-date=2008-01-09  |url-status=dead |archive-url=https://web.archive.org/web/20110930154826/http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=575&rank=class |archive-date=2011-09-30}}</ref>
| image = Hexanchus griseus (Bluntnose sixgill shark).gif
| image_caption = [[Biology:Bluntnose sixgill shark|Bluntnose sixgill shark]]<br />(''Hexanchus griseus'')
| taxon = Hexanchus
| authority = [[Biography:Constantine Samuel Rafinesque|Rafinesque]], 1810
| type_species = ''Hexanchus griseus''<ref>{{cite web | url=https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/hexanchus-griseus/ | title=Hexanchus griseus | date=9 May 2017 }}</ref>
| subdivision_ranks = Species
| subdivision = See text
}}

The '''sixgill sharks''' are a genus, '''''Hexanchus''''', of deepwater [[Biology:Shark|shark]]s in the family [[Biology:Cow shark|Hexanchidae]]. These sharks are characterized by a broad, pointed head, six pairs of [[Biology:Gill|gill]] slits, comb-like, yellow lower teeth, and a long tail. The largest species can grow up to 8&nbsp;m long and weigh over 600&nbsp;kg (1320&nbsp;lb).<ref name="Animal">{{cite book |last=Kindersley |first=Dorling |year=2001 |title=Animal |location=New York City |publisher=DK Publishing |isbn=978-0-7894-7764-4}}{{page needed|date=April 2019}}</ref> They are continental shelf-dwelling and [[Earth:Abyssal plain|abyssal plain]] scavengers with a keen sense of smell and are among the first to arrive at carrion, together with [[Biology:Hagfish|hagfish]] and rattails. They show a characteristic rolling motion of the head when feeding.

They have been found at depths of up to {{convert|2500|m|ft|abbr=on}}.{{citation needed|date=February 2012}} Though only two extant species (the [[Biology:Bluntnose sixgill shark|bluntnose sixgill shark]] and the [[Biology:Bigeyed sixgill shark|bigeyed sixgill shark]]) were originally known, a third, the [[Biology:Atlantic sixgill shark|Atlantic sixgill shark]], was found to exist.<ref name="sciencedaily.com">{{cite web |url=https://www.sciencedaily.com/releases/2018/02/180220122928.htm |title=New shark species confirmed: Genetic testing finds a different sixgill shark |website=ScienceDaily |access-date=7 February 2019}}</ref><ref name="phys.org">{{cite web |url=https://phys.org/news/2018-02-species-shark-genetic.html |title=New species of shark discovered through genetic testing |website=phys.org |access-date=7 February 2019}}</ref>

==Swimming behavior==
The bluntnose sixgill shark, ''Hexanchus griseus'', is relatively common to scientists. However, very little information exists about its distribution patterns, migrations and behavior. Data on occurrence and behavior of sixgill sharks inhabiting waters north of Spain (Galicia and Cantabrian Sea, NE Atlantic) were obtained from yearly oceanographic trawl surveys. 
Data obtained from one electronic pop-up tag (Mini PAT), provided information about depth and temperature preferences over 75&nbsp;days. Mean depth obtained during that period was 913&nbsp;m (depth range 727–1247&nbsp;m), and the mean temperature was 10.3&nbsp;°C, (range 8.0–10.8&nbsp;°C). Movements up and down in the water column within a single day ranged from 50 to 385&nbsp;m. No cyclic diel vertical migration was however observed, the shark moved smoothly without a defined pattern.<ref>{{cite journal |last1=Rodríguez-Cabello |first1=Cristina |last2=González-Pola |first2=César |last3=Rodríguez |first3=Augusto |last4=Sánchez |first4=Francisco |title=Insights about depth distribution, occurrence and swimming behavior of ''Hexanchus griseus'' in the Cantabrian Sea (NE Atlantic) |journal=Regional Studies in Marine Science |date=September 2018 |volume=23 |pages=60–72 |doi=10.1016/j.rsma.2017.10.015 |s2cid=134282217 }}</ref>

The six-gill sharks have the ability to alter their feeding behaviors due to the situation that they are in. A feeding behavior analysis displayed that the six-gill sharks are able to utilize a bite of food compared to other aquatic vertebrates.{{clarify|date=March 2020}}<ref>{{cite journal |title=[no title cited] |journal=PLOS ONE|year=2016 |doi=10.1371/journal.pone.0156730 |pmid=27243237 |s2cid=2448005 |doi-access=free |last1=McNeil |first1=B. |last2=Lowry |first2=D. |last3=Larson |first3=S. |last4=Griffing |first4=D. |volume=11 |issue=5 |pages=e0156730 |pmc=4887027 }}{{full citation needed|date=March 2020}}</ref>

==Extant species==
* ''[[Biology:Bluntnose sixgill shark|Hexanchus griseus]] '' <small>{Bonnaterre, 1788)</small> (bluntnose sixgill shark)
* ''[[Biology:Bigeyed sixgill shark|Hexanchus nakamurai]]'' <small>Teng, 1962</small> (bigeyed sixgill shark)
*''[[Biology:Atlantic sixgill shark|Hexanchus vitulus]]'' <small>Springer & Waller, 1969</small> (Atlantic sixgill shark)<ref name="sciencedaily.com"/><ref name="phys.org"/>

==Extinct species==
[[File:Hexanchidae - Hexanchus andersoni.JPG|thumb|240px|Fossil teeth of ''Hexanchus andersoni'' from Jurassic]]
* ''Hexanchus agassizi''  <small>Cappetta, 1976</small>
* ''Hexanchus andersoni'' <small>Jordan, 1907</small>
* ''Hexanchus casieri'' <small>Kozlov, 1999</small>
* ''[[Biology:Hexanchus collinsonae|Hexanchus collinsonae]]'' <small>Ward, 1979</small>
* ''Hexanchus gracilis'' <small>Davis, 1887</small>
* ''Hexanchus hookeri'' <small>Ward, 1979</small>
* ''Hexanchus microdon'' <small>Agassiz, 1843</small>
* ''Hexanchus tusbairicus'' <small>Kozlov in Zhelezko & Kozlov, 1999</small>

==See also==
*Shark teeth
*List of prehistoric cartilaginous fish genera

==References==
{{Reflist|25em}}

==External links==
* {{ITIS |id=159815 |taxon=Hexanchus |access-date=6 June 2006}}
*{{cite journal |last1=Ebert |first1=David A. |title=Biological Aspects of the Sixgill Shark, ''Hexanchus griseus'' |journal=Copeia |date=10 February 1986 |volume=1986 |issue=1 |pages=131–135 |doi=10.2307/1444898 |jstor=1444898}}
*{{cite journal |last1=Ebert |first1=D.A. |title=Diet of the sixgill shark ''Hexanchus griseus'' off southern Africa |journal=South African Journal of Marine Science |date=June 1994 |volume=14 |issue=1 |pages=213–218 |doi=10.2989/025776194784287030|doi-access=free }}
*{{cite journal |last1=Andrews |first1=Kelly S. |last2=Williams |first2=Greg D. |last3=Farrer |first3=Debbie |last4=Tolimieri |first4=Nick |last5=Harvey |first5=Chris J. |last6=Bargmann |first6=Greg |last7=Levin |first7=Phillip S. |title=Diel activity patterns of sixgill sharks, ''Hexanchus griseus'': the ups and downs of an apex predator |journal=Animal Behaviour |date=August 2009 |volume=78 |issue=2 |pages=525–536 |doi=10.1016/j.anbehav.2009.05.027|s2cid=53161681 }}
*{{cite journal |last1=Cione |first1=Alberto L. |last2=Reguero |first2=Marcelo |title=New records of the sharks ''Isurus'' and ''Hexanchus'' from the Eocene of Seymour Island, Antarctica |journal=Proceedings of the Geologists' Association |date=January 1994 |volume=105 |issue=1 |pages=1–14 |doi=10.1016/S0016-7878(08)80134-4}}

{{Taxonbar|from=Q311682}}

[[Category:Hexanchus| ]]
[[Category:Shark genera]]

{{Sourceattribution|Hexanchus}}