Editing Cephalopod (section)

=== <span id="Renal appendage"></span> Excretory system ===
Most cephalopods possess a single pair of large [[nephridium|nephridia]]. Filtered [[nitrogenous waste]] is produced in the [[pericardium|pericardial]] cavity of the [[branchial heart]]s, each of which is connected to a nephridium by a narrow canal. The canal delivers the excreta to a bladder-like renal sac, and also resorbs excess water from the filtrate. Several outgrowths of the lateral [[vena cava]] project into the renal sac, continuously inflating and deflating as the branchial hearts beat. This action helps to pump the secreted waste into the sacs, to be released into the mantle cavity through a pore.<ref name=IZ>{{cite book |last=Barnes|first=Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |location=Philadelphia, PA |pages=450–460 |isbn=978-0-03-056747-6}}</ref>

''Nautilus'', unusually, possesses four nephridia, none of which are connected to the pericardial cavities.

The incorporation of [[ammonia]] is important for shell formation in terrestrial molluscs and other non-molluscan lineages.<ref name=Loest1979>{{cite journal|jstor=30155937 |pages=461–469 |title=Ammonia Volatilization and Absorption by Terrestrial Gastropods_ a Comparison between Shelled and Shell-Less Species |journal=Physiological Zoology|volume=52|issue=4 |year=1979 |last1=Loest |first1=R. A. |doi=10.1086/physzool.52.4.30155937|s2cid=87142440 }}</ref> Because [[protein]] (i.e., flesh) is a major constituent of the cephalopod diet, large amounts of [[ammonium ion]]s are produced as waste. The main organs involved with the release of this excess ammonium are the gills.<ref name="Boucher-Rodoni1994">{{cite journal|doi=10.1080/10236249409378907 |title=Ammonia production in cephalopods, physiological and evolutionary aspects |year=1994 |last1=Boucher-Rodoni|first1=R. |last2=Mangold |first2=K. |journal=Marine and Freshwater Behaviour and Physiology|volume=25|issue=1–3 |pages=53–60}}</ref> The rate of release is lowest in the shelled cephalopods ''[[Nautilus]]'' and ''[[Sepia (genus)|Sepia]]'' as a result of their using [[nitrogen]] to fill their shells with gas to increase buoyancy.<ref name="Boucher-Rodoni1994"/> Other cephalopods use ammonium in a similar way, storing the [[ion]]s (as [[ammonium chloride]]) to reduce their overall density and increase buoyancy.<ref name="Boucher-Rodoni1994"/>