Editing Squid (section)

===Cardiovascular and excretory systems===
The squid mantle cavity is a seawater-filled sac containing three hearts and other organs supporting circulation, respiration, and [[excretion]].<ref name="hanlon">{{cite book |author1=Roger Hanlon |author2=Mike Vecchione |author3=Louise Allcock |title=Octopus, Squid, and Cuttlefish: A Visual, Scientific Guide to the Oceans' Most Advanced Invertebrates |date=1 October 2018 |publisher=University of Chicago Press |isbn=978-0-226-45956-1 |url=https://books.google.com/books?id=YtmUswEACAAJ&pg=PA33 |access-date=12 December 2018}}</ref> Squid have a main [[systemic circulation|systemic]] heart that pumps blood around the body as part of the general [[circulatory system]], and two [[branchial heart]]s. The systemic heart consists of three chambers, a lower [[Ventricle (heart)|ventricle]] and two upper [[Atrium (heart)|atria]], all of which can contract to propel the blood. The branchial hearts pump blood specifically to the gills for oxygenation, before returning it to the systemic heart.<ref name=hanlon/> The blood contains the [[copper]]-rich protein [[hemocyanin]], which is used for [[oxygen transport]] at low ocean temperatures and low oxygen concentrations, and makes the oxygenated blood a deep, blue color.<ref name=hanlon/> As systemic blood returns via two [[venae cavae]] to the branchial hearts, excretion of [[urine]], [[carbon dioxide]], and waste [[solute]]s occurs through outpockets (called [[nephridiopore|nephridial appendages]]) in the venae cavae walls that enable gas exchange and excretion via the mantle cavity seawater.<ref name=hanlon/>