The Role of Latero-Frontal Cirri in Particle Capture by the Gills of Mytilus edulis

In this study we examined the mechanism of particle capture in Mytilus edulis, using radioactive-label clearance studies, progressive fixation, and scanning electron microscopy to visualize in detail the cirri and their range of motion. Confocal laser scanning microscopy was used to observe the interaction of cirri with 1 μm fluorescent latex particles on live strips of control and serotonin-treated isolated gill tissue. The gills of M. edulis possess large, complex latero-frontal cirri composed of 18-26 pairs of cilia. Particles that were intercepted by the cirri were transferred to the water current on the frontal surface of the filament where they were propelled toward the ventral particle groove. Clearance studies demonstrated that M. edulis removed Escherichia coli from 5°C seawater bathing medium at 4.9 ml g-1 dry tissue min-1. When the gills were exposed to 10-3 M serotonin, the latero-frontal cirri stopped moving and became fixed in a flexed position that partially blocked the frontal surface of the filament. Clearance studies demonstrated that removal of E. coli from the seawater bathing medium was reduced 90% to 0.5 ml g-1 dry tissue min-1 when 10-3 M serotonin was present. These data demonstrated that for small particles (< 2 μm) in the near field, movement of cirri was essential for successful capture either by direct contact or with water acting as a hydromechanical coupler.