Editing Nautiloid (section)

==Modern nautiloids==
{{Main article|Nautilus}}
[[Image:Nautilus belauensis profile.jpg|thumb|250px|''[[Nautilus belauensis]]'']]
Much of what is known about the extinct nautiloids is based on what we know about modern [[nautilus]]es, such as the [[chambered nautilus]], which is found in the southwest [[Pacific Ocean]] from [[Samoa]] to the [[Philippines]], and in the [[Indian Ocean]] off the coast of [[Australia]]. It is not usually found in waters less than {{convert|100|m|ft|0|abbr=off|sp=us}} deep and may be found as far down as {{convert|500|to|700|m|ft|-1|abbr=off|sp=us}}.

Nautili are free swimming animals that possess a head with two simple [[Evolution of the eyes|lens-free eyes]] and arms (or tentacles). They have a smooth shell over a large body chamber, which is divided into subchambers filled with an inert gas (similar to the composition of atmospheric air, but with more [[nitrogen]] and less [[oxygen]]) making the animal neutrally buoyant in the water. As many as 90 [[tentacles]] are arranged in two circles around the mouth. The animal is predatory, and has jaws which are horny and beak-like, allowing it to feed on [[crustacean]]s.

Empty nautilus shells may drift a considerable distance and have been reported from [[Japan]], [[India]] and [[Africa]]. Undoubtedly the same applies to the shells of [[fossil]] nautiloids, the gas inside the shell keeping it buoyant for some time after the animal's death, allowing the empty shell to be carried some distance from where the animal lived before finally sinking to the seafloor.

Nautili propel themselves by jet propulsion, expelling water from an elongated funnel called the [[hyponome]], which can be pointed in different directions to control their movement. Unlike the [[Belemnitida|belemnites]] and other cephalopods, modern nautili do not have an ink sac, and there is no evidence to suggest that the extinct forms possessed one either. Furthermore, unlike the extinct [[ammonoids]], the modern nautilus lacks an [[aptychus]], a biomineralized plate which is proposed to act as an operculum which closes the shell to protect the body. However, aptychus-like plates are known from some extinct nautiloids, and they may be homologous to the fleshy hood of a modern nautilus.<ref>{{cite journal | vauthors = Stridsberg S |date=1984 |title=Aptychopsid plates - jaw elements or protective operculum |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1502-3931.1984.tb00670.x |journal=Lethaia |language=en |volume=17 |issue=1 |pages=93–98 |doi=10.1111/j.1502-3931.1984.tb00670.x |bibcode=1984Letha..17...93S |issn=0024-1164|url-access=subscription }}</ref>