Ctenidium (mollusc)

{{short description|Mollusk anatomic feature}}

File:Pleurobranchaea meckelii.jpg; the ctenidium is visible as a feather-like structure in this view of the right-hand side of the animal]]

A ctenidium is a respiratory organ or gill which is found in many molluscs. This structure exists in bivalves, cephalopods, polyplacophorans (chitons), and in aquatic gastropods such as freshwater snails and marine snails.{{cite book |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard S. |last3=Barnes |first3=Robert D. |name-list-style=amp |title=Invertebrate Zoology: A Functional Evolutionary Approach |date=2004 |publisher=Thomson-Brooks/Cole |isbn=978-0-03-025982-1 |page=286 |url=https://books.google.com/books?redir_esc=y&id=A3opAQAAMAAJ&focus=searchwithinvolume&q=ctenidia }} Certain molluscs, such as the bivalves,{{cite encyclopedia|last=Morton|first=Brian|title=Bivalve: Food and feeding|encyclopedia=Encyclopedia Britannica|date=18 March 2024|access-date=11 November 2024|url=https://www.britannica.com/animal/bivalve/Food-and-feeding}} possess paired ctenidia, but others, such as members of the Ampullariidae,{{cite journal|last1=Rodriguez|first1=Cristian|last2=Prieto|first2=Guido I.|last3=Vega|first3=Israel A.|last4=Castro-Vazquez|first4=Alfredo |name-list-style=amp |title=Functional and evolutionary perspectives on gill structures of an obligate air-breathing, aquatic snail|journal=PeerJ|year=2019 |volume=7 |page=e7342 |doi=10.7717/peerj.7342|doi-access=free|pmid=31396441|pmc=6679647}} bear a single ctenidium.{{cite web|url=https://ucmp.berkeley.edu/taxa/inverts/mollusca/mollusca.php|title=Lophotrochozoa: The Mollusca, Sea slugs, squid, snails, and scallops|website=UC Museum of Paleontology|publisher=University of California Museum of Paleontology|last=Bunje|first=Paul|year=2003|access-date=11 November 2024}}{{cite web|url=https://www.molluscs.at/gastropoda/index.html?/gastropoda/morphology/respiration.html|website=The Living World of Molluscs|title=Respiration and Circulation|last=Nordsieck|first=Robert|others=Support and scripting by Martina Eleveld|year=2012|access-date=11 November 2024}}

A ctenidium is shaped like a comb or a feather, with a central part from which many filaments or plate-like structures protrude, lined up in a row. Some aquatic gastropods possess a single row of filaments on their ctenidium, known as the monopectinate condition, and others have a pair of filament rows, known as the bipectinate or aspidobranch condition.{{cite web|url=https://ns-mollusca.linnaeus.naturalis.nl/linnaeus_ng/app/views/glossary/term.php?id=45507&epi=183|title=aspidobranch|website=Macrobenthos of the North Sea - Mollusca|publisher=Naturalis Biodiversity Center|access-date=11 November 2024}} The ctenidium hangs into the mantle cavity and increases the area available for gas exchange.[http://www.applesnail.net/content/anatomy/respiration.php Respiratory system] {{Webarchive|url=https://web.archive.org/web/20200809024542/https://www.applesnail.net/content/anatomy/respiration.php |date=2020-08-09 }} The apple snail. Retrieved 2012-04-20. The word is Latinized but is derived from the Greek ktenidion which means "little comb", being a diminutive of the word kteis meaning comb.

File:Gills inside giant squid mantle cavity.jpg|Pair of large, grey gills visible inside the mantle cavity of a giant squid