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Modelling of ciliary downstream collecting in suspension‐feeding invertebrates

The motion of fluid and suspended particles in ciliary downstream collecting suspension feeding is investigated on the basis of both experimental and numerical work. Throughout the paper, the suspension‐feeding polychaete Sabella penicillus is chosen to be the model species. Particle retention rate measurements indicate that S. penicillus is able to retain effectively particles of sizes much smaller than the overall size of its filtering unit. From frame‐by‐frame analysis of microscopical video recordings of the feeding organ of S. penicillus particle trajectories and velocities are inferred. By numerically solving the quasi‐steady Stokes equations for creeping flow in a boundary integral equation formulation and by introducing simple steady and unsteady cilia models a simple computational model of the S. penicillus filtering unit is constructed. A percentage of computed fluid particle trajectories is found to follow pathlines which resemble the experimentally observed particle capture. The results indicate that particle capture in suspension‐feeding can be realized solely by particle kinematics of locally driven creeping flow field as they exist in ciliary driven flow. Copyright © 2001 John Wiley & Sons, Ltd.