Editing Nautilus (section)

===Buoyancy and movement===
[[File:Nautilus.ogv|thumb|Nautilus locomotion<br/>File format: Ogg<br/>File size: 1.29 MB<br/>Duration: 5 seconds|alt=Video]]
[[Image:Nautilus oceanworld thailand.png|thumb|left|upright|Nautilus with extended tentacles and hyponome visible|alt=]]

To swim, the nautilus draws water into and out of the living chamber with its [[hyponome]], which uses [[jet propulsion]]. This mode of propulsion is generally considered inefficient compared to propulsion with fins or [[undulatory locomotion]], however, the nautilus has been found to be particularly efficient compared to other jet-propelled marine animals like [[squid]] and [[jellyfish]], or even [[salmon]] at low speeds.<ref>{{Cite journal|title=Swimming mechanics and propulsive efficiency in the chambered nautilus|journal=Royal Society Open Science|volume=5|issue=2|page=170467|doi=10.1098/rsos.170467|pmc=5830708|pmid=29515819|year = 2018|last1 = Neil|first1 = T. R.|last2=Askew|first2=G. N.|bibcode=2018RSOS....570467N}}</ref> It is thought that this is related to the use of asymmetrical contractile cycles and may be an adaptation to mitigate metabolic demands and protect against [[Hypoxia (environmental)|hypoxia]] when foraging at depth.<ref>{{Cite book|last=Askew|first=Graham|date=2017|title=Dataset associated with study on swimming mechanics and propulsive efficiency in the chambered nautilus|chapter-url=http://archive.researchdata.leeds.ac.uk/305/|language=en|publisher=University of Leeds|doi=10.5518/192|type=Data Set|chapter=B120}}</ref> While water is inside the chamber, the [[siphuncle]] extracts [[salt]] from it and diffuses it into the blood.

The animal adjusts its [[buoyancy]] only in long term density changes by [[osmosis]], either removing liquid from its chambers or allowing water from the blood in the siphuncle to slowly refill the chambers. This is done in response to sudden changes in buoyancy that can occur with predatory attacks of fish, which can break off parts of the shell. This limits nautiluses in that they cannot operate under the extreme [[hydrostatic pressure]]s found at depths greater than approximately {{convert|800|m}}, and in fact implode at about that depth, causing instant death.<ref name="Dunstan et al. 2011" /> The gas also contained in the chambers is slightly below atmospheric pressure at sea level.<ref>{{cite book |last1= Saunders |first1= W. Bruce |last2= Landman |first2=Neil H. |orig-date= 1987 |year=2009 |title= Nautilus: The Biology and Paleobiology of a Living Fossil | edition = 2nd |publisher= Springer Netherlands |page= 552 |isbn=978-90-481-3298-0 }}</ref> The maximum depth at which they can regulate buoyancy by osmotic removal of chamber liquid is not known.<ref name=Ward1987 />

The nautilus has the extremely rare ability to withstand being brought to the surface from its deep natural habitat without suffering any apparent damage from the experience. Whereas fish or crustaceans brought up from such depths inevitably arrive dead, a nautilus will be unfazed despite the pressure change of as much as {{convert|80|atm|psi|lk=in}}. The exact reasons for this ability, which is thought to be coincidental rather than specifically functional, are not known, though the perforated structure of the animal's [[vena cava]] is thought to play an important role.<ref name=grif/>{{rp|p. 188}}