How do ctenidia help mollusks breathe and feed?

Ctenidia are specialized respiratory structures in mollusks that typically resemble a comb or feather and develop from the inner side of the mantle. They facilitate both breathing and feeding through the following mechanisms:1

• Respiration: Ctenidia serve as gills, providing a large surface area for gas exchange. In many mollusks, they contain small blood vessels that allow for the extraction of oxygen from the surrounding water.2
• Feeding and Ventilation: In many species, such as bivalves, the ctenidia have evolved into complex filtering devices. Microscopic, hair-like structures called cilia cover the ctenidia and beat in a coordinated fashion to create a water current. This current, known as ventilation, serves two purposes: it brings oxygenated water to the respiratory surfaces and simultaneously draws in food particles, such as algae and bacteria.32
• Transport: Once food particles are captured by the filtration barrier of the ctenidia, they are trapped in mucus and transported along the gill filaments to food grooves, eventually reaching the mouth.3