Editing Nautilus (section)

==Physiology==

===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}}

===Senses===
[[File:Nautilus pompilius (head).jpg|thumb|Head of ''N. pompilius'' showing the rudimentary eye, which functions similarly to a [[pinhole camera]]]]

Unlike many other cephalopods, nautiluses do not have what many consider to be good vision; their [[eye]] structure is highly developed but lacks a solid [[lens (anatomy)|lens]]. Whereas a sealed lens allows for the formation of highly focused and clear, detailed surrounding imagery, nautiluses have a simple [[Pinhole camera|pinhole]] eye open to the environment which only allows for the creation of correspondingly simple imagery.

Instead of vision, the animal is thought to use [[olfaction]] (smell) as the primary sense for [[foraging]] and for locating and identifying potential mates.<ref>{{Cite journal| last1 = Grasso | first1 = F.| last2 = Basil | first2 = J.| title = The evolution of flexible behavioral repertoires in cephalopod molluscs| journal = Brain, Behavior and Evolution| volume = 74| issue = 3| pages = 231–245| year = 2009| pmid = 20029186| doi = 10.1159/000258669| s2cid = 13310728}}</ref>

The "ear" of the nautilus consists of structures called ''[[otocyst]]s'' located immediately behind the pedal [[ganglia]] near the nerve ring. They are oval structures densely packed with elliptical [[calcium carbonate]] crystals.

===Brain and intelligence===
{{Main|Cephalopod intelligence}}
Nautiluses are much closer to the first cephalopods that appeared about 500 million years ago than the early modern cephalopods that appeared maybe 100 million years later ([[ammonoids]] and [[coleoids]]). They have a seemingly simple [[brain]], not the large complex brains of [[octopus]], [[cuttlefish]] and [[squid]], and had long been assumed to lack intelligence. But the cephalopod nervous system is quite different from that of other animals, and recent experiments have shown not only memory, but a changing response to the same event over time.<ref name="callaway">{{cite magazine|url=https://www.newscientist.com/article/dn14033-simpleminded-nautilus-reveals-flash-of-memory.html|title=Simple-Minded Nautilus Shows Flash of Memory|author=Ewen Callaway|date=2 June 2008|magazine=New Scientist|access-date=7 March 2012}}</ref><ref name="phillips">{{cite journal|url=http://jeb.biologists.org/content/211/12/iii.full.pdf#page=1&view=FitH |archive-url=https://web.archive.org/web/20121029181222/http://jeb.biologists.org/content/211/12/iii.full.pdf |archive-date=2012-10-29 |url-status=live|title=Living Fossil Memories|author=Kathryn Phillips|date=15 June 2008|page=iii|volume=211|doi=10.1242/jeb.020370 |journal= Journal of Experimental Biology|issue=12|s2cid=84279320|doi-access=free|bibcode=2008JExpB.211Y...3P }}</ref><ref name="crook"/>

In a study in 2008, a group of nautiluses (''N. pompilius'') were given food as a bright blue light flashed until they began to associate the light with food, extending their tentacles every time the blue light was flashed. The blue light was again flashed without the food 3 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours later. The nautiluses continued to respond excitedly to the blue light for up to 30 minutes after the experiment. An hour later they showed no reaction to the blue light. However, between 6 and 12 hours after the training, they again responded to the blue light, but more tentatively. The researchers concluded that nautiluses had memory capabilities similar to the "[[short-term memory|short-term]]" and "[[long-term memory|long-term memories]]" of the more advanced cephalopods, despite having different brain structures.<ref name="callaway" /><ref name="phillips" /><ref name="crook"/> However, the long-term memory capability of nautiluses was much shorter than that of other cephalopods. The nautiluses completely forgot the earlier training 24 hours later, in contrast to octopuses, for example, which can remember conditioning for weeks afterwards. However, this may be simply the result of the [[classical conditioning|conditioning]] procedure being suboptimal for sustaining long-term memories in nautiluses. Nevertheless, the study showed that scientists had previously underestimated the memory capabilities of nautiluses.<ref name="crook">{{cite journal|author1=Robyn Crook  |author2=Jennifer Basil |name-list-style=amp |year=2008|title=A biphasic memory curve in the chambered nautilus, ''Nautilus pompilius'' L. (Cephalopoda: Nautiloidea) |journal=The Journal of Experimental Biology|volume=211|pages=1992–1998|doi=10.1242/jeb.018531 |url=http://jeb.biologists.org/content/211/12/1992.full.pdf#page=1&view=FitH |archive-url=https://web.archive.org/web/20110817221242/http://jeb.biologists.org/content/211/12/1992.full.pdf |archive-date=2011-08-17 |url-status=live|issue=12 |pmid=18515730|s2cid=6305526 |doi-access=free|bibcode=2008JExpB.211.1992C }}</ref>

===Reproduction and lifespan===
Nautiluses reproduce by laying [[egg (biology)|egg]]s. Gravid females attach the fertilized eggs, either singly or in small batches, to rocks in warmer waters (21–25 Celsius), whereupon the eggs take eight to twelve months to develop until the {{convert|30|mm|adj=on}} juveniles hatch.<ref>{{cite book |last1=Hanlon |first1=Roger T. |last2=Messenger |first2=John B. |title=Cephalopod Behaviour |date=1998 |publisher=Cambridge University Press |location=Cambridge, UK |isbn=9780521645836 |page=178}}</ref> Females spawn once per year and regenerate their [[gonad]]s, making nautiluses the only cephalopods to present [[iteroparity]] or [[polycyclic spawning]].<ref>{{Cite journal | last1 = Rocha | first1 = F. | last2 = Guerra | first2 = Á. | last3 = González | first3 = Á. F. | doi = 10.1017/S1464793101005681 | title = A review of reproductive strategies in cephalopods | journal = Biological Reviews of the Cambridge Philosophical Society | volume = 76 | issue = 3 | pages = 291–304 | year = 2001 | pmid =  11569786| s2cid = 5777682 }}</ref>

Nautiluses are [[sexual dimorphism|sexually dimorphic]], in that males have four tentacles modified into an organ, called the "[[spadix (zoology)|spadix]]", which transfers sperm into the female's mantle during mating. At sexual maturity, the male shell becomes slightly larger than the female's.<ref name="Bruce Saunders1978">{{Cite journal | last1 = Bruce Saunders | first1 = W. | last2 = Spinosa | first2 = C. | title = Sexual Dimorphism in Nautilus from Palau | journal = Paleobiology | volume = 4 | issue = 3 | pages = 349–358 | year = 1978 |jstor=2400210| doi = 10.1017/S0094837300006047 | bibcode = 1978Pbio....4..349S | s2cid = 85899974 }}</ref> Males have been found to greatly outnumber females in practically all published studies, accounting for 60 to 94% of all recorded individuals at different sites.<ref name="Dunstan et al. 2011" />

The lifespan of nautiluses may exceed 20 years, which is exceptionally lengthy for a cephalopod, many of whom live less than three even in captivity and under ideal living conditions.<ref>{{cite journal |author=Saunders WB |title=Nautilus Growth and Longevity: Evidence from Marked and Recaptured Animals |journal=Science |volume=224 |issue=4652 |pages=990–992 |date=June 1984 |pmid=17731999 |doi=10.1126/science.224.4652.990 |bibcode = 1984Sci...224..990S |s2cid=40891271 }}</ref> However, nautiluses typically do not reach sexual maturity until they are about 15 years old, limiting their reproductive lifespan to often less than five years.<ref name="Dunstan et al. 2011">{{cite journal |last1=Dunstan |first1=A.J. |last2=Ward |first2=P.D. |last3=Marshall |first3=N.J. |date=February 2011 |editor1-last=Solan |editor1-first=Martin |title=''Nautilus pompilius'' life history and demographics at the Osprey Reef Seamount, Coral Sea, Australia |journal=PLOS ONE |volume=6 |issue=2 |pages=e16312 |pmid=21347356 |pmc=3037366 |bibcode = 2011PLoSO...616312D |doi=10.1371/journal.pone.0016312 |doi-access=free }}</ref>

''Nautilus'' male has a reproductive organ named [[Van der Hoeven's organ]]. ''Nautilus'' female has two reproductive organs whose functions are unknown, the [[Organ of Valenciennes]] and [[Owen's laminated organ]].<ref name="Willey1902">{{cite book |author=Arthur Willey |url=https://books.google.com/books?id=Jwo4AQAAMAAJ&pg=PA778 |title=Zoological Results Based on Material from New Britain, New Guinea, Loyalty Islands and Elsewhere: The anatomy and development of Peripatus novae-britanniae |publisher=University Press |year=1902 |pages=778–9}}</ref>

{{multiple image
| align = center
| footer = '''Left:''' Frequency distribution of ''N. pompilius'' shell diameter at [[Osprey Reef]], part of the [[Coral Sea Islands]], based on  2067 captured individuals. Shells ranged in size from 76 to 145&nbsp;mm, with a mean of 128.6±28.01&nbsp;mm.<ref name="Dunstan et al. 2011" /><br/>
'''Right:''' Shell diameter of mature male and female ''N.&nbsp;pompilius'' caught at Osprey Reef. Males (''n'' = 870) had a mean shell diameter of 131.9±2.6&nbsp;mm, compared to 118.9±7.5&nbsp;mm in females (''n'' = 86). The Osprey Reef ''N.&nbsp;pompilius'' population is the second smallest known in terms of mean shell diameter, after the dwarf form from the [[Sulu Sea]] (130.7&nbsp;mm and 115.6&nbsp;mm, respectively).<ref name="Dunstan et al. 2011" />
| image1 = Size frequency distribution for Nautilus pompilius at Osprey Reef.png
| image2 = Sexual dimorphism in mature male and female Nautilus pompilius.png
| direction = 
| total_width = 660
| alt1 = 
| caption1 = 
| caption2 = 
}}