Editing Sea cucumber (section)

===Respiratory system===
Sea cucumbers use [[cloacal respiration]] via a pair of "respiratory trees" that branch in the [[cloaca]] just inside the [[anus]], so that they "breathe" by drawing water in through the anus, extracting [[dissolved oxygen]] from water, and then expelling it.<ref>{{cite web | url = http://www.fegi.ru/prim/sea/golot.htm | title = Holothurians or sea cucumbers | access-date = 2007-10-03 | archive-date = 2007-09-30 | archive-url = https://web.archive.org/web/20070930154932/http://www.fegi.ru/prim/sea/golot.htm | url-status = dead }}</ref><ref>{{cite web | url = http://www.comoxvalleynaturalist.bc.ca/knowing_nature/2006/sea_cucumbers.html | title = Knowing Nature... Cool as a Sea Cucumber | access-date = 2007-10-03 | last = Ingram | first = Jocie | date = 2006-06-16 | url-status = dead | archive-url = https://web.archive.org/web/20071021183031/http://www.comoxvalleynaturalist.bc.ca/knowing_nature/2006/sea_cucumbers.html | archive-date = 2007-10-21 }}</ref> The "trees" consist of a series of narrow tubules branching from a common duct, and lie on either side of the [[digestive tract]]. [[Gas exchange]] occurs across the thin walls of the tubules, to and from the fluid of the main body cavity.

Together with the intestine, the "respiratory trees" also act as [[excretory]] organs, with nitrogenous waste diffusing across the tubule walls in the form of [[ammonia]] and [[phagocytosis|phagocytic]] [[coelomocyte]]s depositing particulate waste.<ref name=IZ/>