Sorting happens on the radioles themselves. Ciliary tracts carry captured particles toward the mouth along a graded groove, and size determines the destination. The smallest fraction is ingested, a middle fraction is diverted to ventral sacs near the mouth, and the coarsest is discarded into the water.
The stored middle fraction is the building material. It is mixed with mucus secreted by glands and applied to the rim of the tube, so the animal manufactures its own housing from suspended sediment it never eats. The finished tube is leathery and flexible rather than calcareous, which distinguishes sabellids from the coral-boring serpulids.
The species matters beyond its plumbing. Introduced to Australian ports, probably through ballast water and hull fouling, it forms dense aggregations that alter soft-sediment habitat and compete with native filter feeders, and it is a declared pest in some jurisdictions. The magnitude of its ecological effect relative to other harbour disturbances is still argued over.