Ctenidium (mollusc)

A ctenidium is a respiratory organ or gill which is found in many molluscs.

[1] Certain molluscs, such as the bivalves,[2] possess paired ctenidia, but others, such as members of the Ampullariidae,[3] bear a single ctenidium.

[4][5] 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,[3] and others have a pair of filament rows, known as the bipectinate or aspidobranch condition.

[6] The ctenidium hangs into the mantle cavity and increases the area available for gas exchange.