Particle transport in the zebra mussel, Dreissena polymorpha (Pallas)

The capture, transport, and sorting of particles by the gills and labial pa lps of the freshwater mussel Dreissena polymorpha were examined by endoscop y and video image analysis. More specifically, the morphology of the feedin g organs in living zebra mussels was described; the mode and speeds of part icle transport on the feeding organs was measured; and the sites of particl e selection in the pallial cavity were identified. Particle velocities (out er demibranch lamellae, 90 mum s(-1); inner demibranch lamellae, 129 mum s( -1); marginal food groove of inner demibranchs, 156 mum s(-1); dorsal cilia ted tracts, 152 mum s(-1)), as well as the movement of particles on the cte nidia and labial palps of D. polymorpha, are consistent with mucociliary, r ather than hydrodynamic, transport. Particles can be sorted on the ctenidia of zebra mussels, resulting in a two-layer transport at the marginal food groove of the inner demibranch. That is: preferred particles are transporte d inside the marginal groove proper, whereas particles destined for rejecti on are carried superficially in a string of mucus. Sorting also occurs at t he ventral margin of the outer demibranch; desirable particles are retained on the outer demibranch, whereas unacceptable particles are transferred to the inner demibranch and ultimately excluded from ingestion. We suggest th at the structure of homorhabdic ctenidia does not preclude particle sorting , and that some ecosystem modifications attributed to zebra mussels may ult imately be due to ctenidial sorting mechanisms.