Particle capture in the mussel Mytilus edulis: role of latero-frontal cirr

Microscope video graphs of particle paths near one-filament-thick mussel gill preparations, stimulated with a nerve transmitter (10^-6 M serotonin which restores normal ciliary activity), were used to disclose the capture of 6 μm algal cells. Suspended algal cells carried with the water were stopped for a while at the entrance to the interfilament gap by the action of the laterofrontal cirri (1fc), and transferred to the frontal side of the filament to be transported towards the marginal food groove. The event of transfer took place during approximately a time interval of 1/50 to 1/25 s. To gain a better understanding of the capture mechanism and retention efficiency versus particle size, the flow through and around the 1fc was theoretically estimated. Normally beating 1fc create periodic, unsteady, three-dimensional flows at the entrance to the interfilament canal. During the active beat most of the water is deflected to flow around the branching cilia of the 1fc while some of the water is strained by these. Large particles (> 4 μm) are stopped and transferred to the frontal current, whereas smaller particles either follow the flow around the 1fc and escape or they are stopped by the branching cilia.