Mid and lower eulittoral exposed to moderately exposed bedrock, often with nearby sediment, may be densely covered by large individuals of the mussel Mytilus edulis. Three biotopes have been described: In the mid eulittoral, the mussels may form a band or large patches with scattered bladder wrack Fucus vesiculosus (A1.221). In the lower eulittoral a range of red seaweeds including Mastocarpus stellatus and Palmaria palmata occur amongst the mussels (in higher abundance than the mid eulittoral) (A1.222). Clay outcrops in the mid to lower eulittoral may be bored by a variety of piddocks including Pholas dactylus, Barnea candida and Petricola pholadiformis, while the surface is characterised by small clumps of the mussel M. edulis, the barnacle Elminius modestus and the winkle Littorina littorea (A1.223). Ephemeral green seaweeds such as Enteromorpha intestinalis and Ulva lactuca commonly occur on the shells of the mussels. Barnacles are common on both the mussel valves and on patches of bare rock, where the limpet Patella vulgata is found as well, often at high abundance. The whelk Nucella lapillus and a range of littorinids also occur within the mussel bed. A dense M. edulis community may be found on more sheltered coasts on mixed substrata (A2.721). Situation: Above this habitat type is a M. edulis and S. balanoides dominated zone or a F. vesiculosus dominated biotope (A1.213). In the lower eulittoral zone below is a zone dominated by the wrack Fucus serratus, M. edulis and a variety of red seaweeds (A1.21) while kelp dominate the sublittoral fringe.