What role do labial palps play in bivalve feeding?

In bivalves, the labial palps serve as critical organs for processing and selecting food particles before ingestion. Their specific role depends on the bivalve's feeding strategy:1

• Deposit Feeders: In primitive bivalves like Nucula, the palps feature long, extensible proboscides that collect organic material directly from the sediment surface.1
• Suspension Feeders: In most modern bivalves, the gills (ctenidia) filter food particles from the water and transport them in mucus toward the labial palps.21

Once the material reaches the palps, they perform a sorting function. The inner and outer pairs of palps evaluate the particles:1
* Ingestion: Suitable food particles are transferred to the mouth via ciliary currents on the inner pair of palps.1
* Rejection: Unsuitable material is directed by the outer palps into the mantle cavity as a mucus-bound mass known as pseudofeces, which is subsequently ejected from the animal.1

In some specialized predatory bivalves, such as certain deepwater Anomalodesmata, the palps also assist in pushing captured prey into the mouth.21