Abstract
1. The retention efficiency, E%, of the Mytilus edulis gill for 5.0-µm diatoms (Thalassiosira pseudonana) was estimated by separating the bivalve's exhalant current through a rubber sleeve attached to the valves around the exhalant siphon. 2. The particle concentration in the 4.4- to 6.4-µm size range of inhaled and exhaled water was estimated with a model ZB coulter-counter. The mussel's pumping rate, Rp, was recorded automatically. 3. E% and Rp were observed for 11 mussels at diatom concentrations ranging from 3 x 103 to 1.1 x 105 cells/ml. Rp was maximal at 104 cells/ml and at 9.0 x 104 cells/ml decreased to about 55% of its maximum value. E% remained constantly high (about 97%) over the range of concentrations even when pseudofeces (filtered material rejected before ingestion) were produced. This result supports the argument that, in general, a continuous filtering meshwork is formed over the ostia by synchrony in alternate (or alternate pairs of) latero-frontal cirri on the same gill filament. 4. Occasionally, a low E% value (about 86%) was observed for an individual mussel and this was attributed to synchrony in ≥ 3 adjacent cirri. 5. Synchrony in one or more pairs of adjacent cirri is advanced as an explanation for published data on the retention of different sized particles.
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