Dense beds of the oyster Ostrea edulis can occur on muddy fine sand or sandy mud mixed sediments. There may be considerable quantities of dead oyster shell making up a substantial portion of the substratum. The clumps of dead shells and oysters can support large numbers of Ascidiella aspersa and Ascidiella scabra. Sponges such as Halichondria bowerbanki may also be present. Several conspicuously large polychaetes, such as Chaetopterus variopedatus and terebellids, as well as additional suspension-feeding polychaetes such as Myxicola infundibulum and Sabella pavonina may be important in distinguishing this biotope, whilst the Opisthobranch Philine aperta may also be frequent in some areas. A turf of seaweeds such as Plocamium cartilagineum, Nitophyllum punctatum and Spyridia filamentosa may also be present. This biotope description may need expansion to account for oyster beds in England.