The composition and spatial distribution of the polychaete fauna on the subtidal soft sediments of the Ría de Aldán (Galicia, north-western Spain) were studied by means of quantitative sampling and multivariate analysis. The faunal distribution was mainly conditioned by a sediment gradient defined by decreasing grain size, from the mouth towards the inner margins of the ría. The coarse and medium sand fauna was mainly dominated by pisionids, spionids and syllids. Finer sediments (fine sand to mud) showed a greater abundance of paraonids, spionids and cirratulids and deposit feeding species. The greatest number of species and diversity were found in coarse sediments.
