Flexible filaments of a fan worm make filtration functionally flexible

Fan worms (Annelida: Sabellidae) are suspension-feeding polychaetes that rely on their specialized gill crowns to filter suspended particles or microscopic cells from the surrounding water to support their growth and reproduction. However, the mechanisms underlying their remarkable efficiency and flexibility in filtration remain elusive. In this combined experimental and theoretical investigation, we reveal that fan worms passively adapt to complex fluid environments by employing an adaptive bending response of their gill filaments. This mechanism modulates microscale vortices around the filaments, enhancing particle capture efficiency. Furthermore, the high compliance of the gill filaments not only allows for dynamic shape adjustment in response to flow conditions but also enables size-selective filtration of particles, achieving a balance between structural stability and filtration performance. This structural-flexibility-driven filtration strategy offers new insights into the filtering mechanism of marine filter feeders and provides inspiration for the design of bioinspired underwater microparticle collection devices. • Structural flexibility enables fan worms to achieve functional filter feeding • Microstructures modulate flow fields and generate localized vortices • The vortices enhance particle capture efficiency • Selective filter-feeding strategy inspires the design of biomimetic filtration devices Chen et al. report the efficient filtration mechanism of fan worms (Annelida: Sabellidae), whose flexible gill filaments can passively bend in flowing water to modulate microscale vortices to enhance particle capture. This size-selective filtration strategy, driven by structural flexibility, inspires the design of bioinspired underwater microparticle collectors.