This and the companion volume describe and illustrate more than 2000 species, from selected protozoans to fishes, found in the coastal waters of the British Isles and north-western Europe. They cover all benthic habitats, from the intertidal zone to approximately 30 metres depth, and also include representatives of estuarine and supralittoral faunas. Each major animal group is briefly introduced, with notes on the morphology, biology, and ecology of representative species, together with suitable techniques for their collection and study. Short bibliographies list the most important specialist literature for each group. Identification is facilitated by dichotomous keys, first to families, and then to genera or species. Short diagnostic accounts are given for each family and higher taxon; descriptions of all species treated are followed by notes on their ecological and geographical distribution. All species are illustrated by line drawings, with related species grouped together to facilitate comparisons.The two volumes comprise the most comprehensive single account of the marine fauna of British and adjacent waters ever produced. It is intended as a bench work for both professional and amateur marine biologist, as well as for undergraduate and postgraduate students. It is essentially a practical work; taxonomic and synonmic detail is deliberately kept to a minimum, with emphasis given to identification procedures.