How do bivalve gills function in both feeding and respiration?

In bivalves, the gills—often referred to as ctenidia—serve as dual-purpose organs for both respiration and feeding.12

Respiration

The gills provide a large surface area for gas exchange, allowing the animal to extract oxygen from the water. Millions of microscopic, hair-like structures called cilia beat to create a continuous flow of water through the mantle cavity, a process known as ventilation. While the gills are the primary respiratory site, some bivalves also exchange gases across their mantle and body surfaces, particularly when exposed to air during low tide.3142

Feeding

In most modern bivalves, the gills have evolved into complex filtering devices. As cilia draw water into the mantle cavity, they simultaneously act as a sieve to trap food particles—such as bacteria, algae, and plant detritus—from the water column. These particles are bound in mucus and transported along specialized ciliary tracts on the gill filaments toward the labial palps, which further sort the material before it is ingested. In primitive species, however, the gills remain primarily respiratory, while feeding is handled by the palp proboscides.12