Editing Nautilus (section)

===Circulatory system===
Like all cephalopods, the blood of the nautilus contains [[hemocyanin]], which is blue in its oxygenated state. There are two pairs of [[gill]]s which are the only remnants of the ancestral [[Metamerism (biology)|metamerism]] to be visible in extant cephalopods.<ref name=Wingstrand1985>{{cite journal
|url=http://www.zmuc.dk/inverweb/Galathea/Galathea_p5.html
|format=Link to free full text + plates
|last=Wingstrand
|first=KG
|year=1985
|title=On the anatomy and relationships of Recent Monoplacophora
|journal=Galathea Rep.
|volume=16
|pages=7–94
|access-date=2009-04-21
|archive-url=https://web.archive.org/web/20160303182836/http://www.zmuc.dk/inverweb/Galathea/Galathea_p5.html
|archive-date=2016-03-03
|url-status=dead
}}</ref>{{rp|56}} Oxygenated blood arrives at the heart through four ventricles and flows out to the animal's organs through distinct aortas but returns through veins which are too small and varied to be specifically described. The one exception to this is the vena cava, a single large vein running along the underside of the crop into which nearly all other vessels containing deoxygenated blood empty. All blood passes through one of the four sets of filtering organs (composed of one pericardial appendage and two renal appendages) upon leaving the vena cava and before arriving at the gills for re-oxygenation. Blood waste is emptied through a series of corresponding pores into the [[pallial cavity]].