The aim of the BIOMOR survey was to obtain specimens of invertebrates for taxonomic and biogeographical purposes. The secondary objective was to determine the numerical abundance of the benthic invertebrate population, as well as their diversity and the extent of benthic communities. The work was carried out during the summers of 1989 and 1991, and covered the St Georges Channel, Cardigan Bay the Celtic Deep and several areas off Anglesey and the Lleyn Peninsula. A 0.1 m2 van Veen grab was used to collect samples of sediment. Three grabs were taken from each point, one was used for sediment analysis, the other two were pooled and sieved for macrofauna. Some sample points in St Georges Channel, Cardigan Bay and off the Lleyn Peninsula had to be rejected as grab sampling proved to be ineffective at these stations. Records currently considered sensitive have been removed from this dataset.