Editing Cephalopod (section)

==Distribution==
{{multiple image
 | align    = right
 | footer   = '''Left:''' A pair of cuttlefish (''[[Sepia officinalis]]'') in shallow water<br />'''Right:''' An octopus (''[[Benthoctopus]]'' sp.) on the [[Davidson Seamount]] at 2,422 m depth
 | image1   = Sepia officinalis Linnaeus, 1758 .jpg
 | width1   = 220
 | image2   = Benthoctopus sp.jpg
 | width2   = 190
}}
There are over 800 [[extant species|extant]] species of cephalopod,<ref>{{cite web |url=http://cephbase.eol.org/ |title=Welcome to CephBase |work=CephBase|access-date=29 January 2016 |archive-date=12 January 2016|archive-url=https://web.archive.org/web/20160112225313/http://cephbase.eol.org/ |url-status=dead }}</ref> although new species continue to be described. An estimated 11,000 extinct [[taxon|taxa]] have been described, although the soft-bodied nature of cephalopods means they are not easily fossilised.<ref name=mollusca12>{{The Mollusca|volume=12}}</ref>

Cephalopods are found in all the oceans of Earth. None of them can tolerate [[fresh water]], but the brief squid, ''[[Lolliguncula brevis]]'', found in [[Chesapeake Bay]], is a notable partial exception in that it tolerates [[brackish water]].<ref>{{cite journal|last1=Bartol |first1=I. K. |last2=Mann |first2=R. |last3=Vecchione |first3=M. |year=2002 |title=Distribution of the euryhaline squid ''Lolliguncula brevis'' in Chesapeake Bay: effects of selected abiotic factors |journal=Marine Ecology Progress Series|volume=226|pages=235–247 |doi=10.3354/meps226235 |bibcode=2002MEPS..226..235B |doi-access=free }}</ref> Cephalopods are thought to be unable to live in fresh water due to multiple biochemical constraints, and in their >400&nbsp;million year existence have never ventured into fully freshwater habitats.<ref>{{cite web |url=http://www.abc.net.au/science/articles/2013/01/16/3670198.htm |title=Are there any freshwater cephalopods? |website=ABC Science|date=16 January 2013}}</ref>

Cephalopods occupy most of the depth of the ocean, from the [[abyssal plain]]s to the sea surface, and have also been found in the [[hadal zone]].<ref>{{cite web | url=https://www.labroots.com/trending/plants-and-animals/17819/cephalopods-observed-record-shattering-oceanic-depths | title=Cephalopods Observed at Record-Shattering Oceanic Depths}}</ref> Their diversity is greatest near the equator (~40 species retrieved in nets at 11°N by a diversity study) and decreases towards the poles (~5 species captured at 60°N).<ref name=Cephalopods/>