Editing Nautilus (section)

===Tentacles===
The arm crown of modern nautilids (genera ''[[Nautilus (genus)|Nautilus]]'' and ''[[Allonautilus]]'') is very distinct in comparison to coleoids. Unlike the ten-armed [[Squid|Decabrachia]] or the eight-armed [[Octopodiformes]], nautilus may possess any number of tentacles (cirri) from 50 to  over 90 tentacles depending on the sex and individual.<ref>{{cite journal |last1=Kröger |first1=Björn |last2=Vinther |first2=Jakob |last3=Fuchs |first3=Dirk |title=Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules: Extant cephalopods are younger than previously realised and were under major selection to become agile, shell-less predators |journal=BioEssays |date=August 2011 |volume=33 |issue=8 |pages=602–613 |doi=10.1002/bies.201100001|pmid=21681989 |s2cid=2767810 }}</ref><ref name=":1">{{cite book |last1=Sasaki |first1=T |last2=Shigeno |first2=S|last3=Tanabe |first3=K |date=2010 |title=Cephalopods - Present and Past |publisher=Tokai University Press |chapter=Anatomy of living Nautilus: reevaluation of primitiveness and comparison with Coeloidea |name-list-style=amp}}</ref> These tentacles are classified into three distinct categories: ocular, digital, and labial (buccal).<ref name=":2">{{cite book |last1=Owen |first1=Richard |title=Memoir on the pearly nautilus (Nautilus pompilius, Linn). With illustrations of its external form and internal structure |date=1832 |publisher=Richard Taylor |location=London |url=https://www.biodiversitylibrary.org/bibliography/10441}}</ref> There are two sets of ocular tentacles: one set in front of the eye (pre-ocular) and one set behind the eye (post-ocular). The digital and labial tentacles are arrayed circularly around the mouth, with the digital tentacles forming the outermost ring and the labial tentacles in between the digital tentacles and the mouth. There are 19 pairs of digital tentacles that, together with the ocular tentacles, make up the 42 appendages that are visible when observing the animal (not counting the modified tentacles that form the hood). The labial tentacles are generally not visible, being smaller than the digital tentacles, and more variable both in number and in shape.<ref name=":1" /><ref name=":2" /><ref>{{Cite journal |last=Griffin |first=Lawrence E. |date=1899 |title=XXVI.— Notes on the tentacles of Nautilus pompilius |journal=Annals and Magazine of Natural History |language=en |volume=3 |issue=14 |pages=170–176 |doi=10.1080/00222939908678098 |issn=0374-5481|url=https://www.biodiversitylibrary.org/part/58804 }}</ref> Males modify three of their labial tentacles into the [[Spadix (zoology)|spadix]], which delivers [[spermatophore]]s into the female during copulation.<ref name=":1" />

The tentacle is composed of two distinct structures: the first structure, a fleshy sheath that contains the second structure: an extendable [[cirrus (biology)|cirrus]] (plural: cirri).<ref name=":2" /><ref name=":3">{{Citation |last=Kier |first=William M. |title=The Functional Morphology of the Tentacle Musculature of Nautilus pompilius |date=2010 |url=https://doi.org/10.1007/978-90-481-3299-7_18 |work=Nautilus: The Biology and Paleobiology of a Living Fossil, Reprint with additions |pages=257–269 |editor-last=Saunders |editor-first=W. Bruce |access-date=2023-11-28 |series=Topics in Geobiology |volume=6 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-90-481-3299-7_18 |isbn=978-90-481-3299-7 |editor2-last=Landman |editor2-first=Neil H.|url-access=subscription }}</ref> The sheaths of the digital tentacles are fused at their base into a single mass referred to as the cephalic sheath. The digital cirri can be fully withdrawn into the sheath and are highly flexible, capable of extending just over double their fully retracted length and show a high degree of allowable bendability and torsion.<ref name=":3" /> Despite not having suckers, the digital tentacles show strong adhesive capabilities. Adhesion is achieved through the secretion of a neutral (rather than acidic) [[Glycosaminoglycan|mucopolysaccharide]] from secretory cells in the ridges of the digital cirri.<ref>{{Citation |last=Fukuda |first=Yoshio |title=Histology of the Long Digital Tentacles |date=2010 |url=https://doi.org/10.1007/978-90-481-3299-7_17 |work=Nautilus: The Biology and Paleobiology of a Living Fossil, Reprint with additions |pages=249–256 |editor-last=Saunders |editor-first=W. Bruce |access-date=2023-11-28 |series=Topics in Geobiology |volume=6 |place=Dordrecht |publisher=Springer Netherlands |language=en |doi=10.1007/978-90-481-3299-7_17 |isbn=978-90-481-3299-7 |editor2-last=Landman |editor2-first=Neil H.|url-access=subscription }}</ref><ref>{{Cite journal |last1=Muntz |first1=W. R. A. |last2=Wentworth |first2=S. L. |date=1995 |title=Structure of the Adhesive Surface of the Digital Tentacles of Nautilus Pompilius |journal=Journal of the Marine Biological Association of the United Kingdom |language=en |volume=75 |issue=3 |pages=747–750 |doi=10.1017/S0025315400039163 |bibcode=1995JMBUK..75..747M |s2cid=83497566 |issn=1469-7769}}</ref><ref name=":4">{{Cite journal |last1=von Byern |first1=Janek |last2=Wani |first2=Ryoji |last3=Schwaha |first3=Thomas |last4=Grunwald |first4=Ingo |last5=Cyran |first5=Norbert |date=2012-02-01 |title=Old and sticky—adhesive mechanisms in the living fossil Nautilus pompilius (Mollusca, Cephalopoda) |journal=Zoology |volume=115 |issue=1 |pages=1–11 |doi=10.1016/j.zool.2011.08.002 |issn=0944-2006 |pmc=3311398 |pmid=22221553|bibcode=2012Zool..115....1V }}</ref> Release is triggered through contraction of the tentacle musculature rather than the secretion of a chemical solvent, similar to the adhesion/release system in ''[[Euprymna]]'', though it is unclear whether these adhesives are [[Homology (biology)|homologous]].<ref name=":4" /><ref>{{Cite journal |last1=von Byern |first1=Janek |last2=Cyran |first2=Norbert |last3=Klepal |first3=Waltraud |last4=Nödl |first4=Marie Therese |last5=Klinger |first5=Lisa |date=February 2017 |title=Characterization of the adhesive dermal secretion of Euprymna scolopes Berry, 1913 (Cephalopoda) |url=https://linkinghub.elsevier.com/retrieve/pii/S0944200616300836 |journal=Zoology |language=en |volume=120 |pages=73–82 |doi=10.1016/j.zool.2016.08.002|pmid=27646066 |bibcode=2017Zool..120...73V |url-access=subscription }}</ref> The ocular tentacles show no adhesive capability but operate as sensory organs. Both the ocular tentacles and the eight lateral digital tentacles show chemoreceptive abilities; the preocular tentacles detect distant odor and the lateral digital tentacles detect nearby odor.<ref>{{Cite journal |last1=Basil |first1=Jennifer |last2=Bahctinova |first2=Irina |last3=Kuroiwa |first3=Kristine |last4=Lee |first4=Nandi |last5=Mims |first5=Desiree |last6=Preis |first6=Michael |last7=Soucier |first7=Christian |date=2005 |title=The function of the rhinophore and the tentacles of Nautilus pompilius L. (Cephalopoda, Nautiloidea) in orientation to odor |journal=Marine and Freshwater Behaviour and Physiology |language=en |volume=38 |issue=3 |pages=209–221 |doi=10.1080/10236240500310096 |bibcode=2005MFBP...38..209B |s2cid=33835096 |issn=1023-6244}}</ref><ref>{{Cite journal |last1=Ruth |first1=Peter |last2=Schmidtberg |first2=Henrike |last3=Westermann |first3=Bettina |last4=Schipp |first4=Rudolf |date=March 2002 |title=The sensory epithelium of the tentacles and the rhinophore of Nautilus pompilius L. (cephalopoda, nautiloidea) |journal=Journal of Morphology |volume=251 |issue=3 |pages=239–255 |doi=10.1002/jmor.1086 |issn=0362-2525 |pmid=11835362|s2cid=38377665 }}</ref>