Clay outcrops in the mid to lower eulittoral which are bored by a variety of piddocks including Pholas dactylus, Barnea candida and Petricola pholadiformis. The surface of the clay is characterised by small clumps of the mussel Mytilus edulis, the barnacle Elminius modestus and the winkle Littorina littorea. Seaweeds are generally sparse on the clay, although small patches of the red seaweeds Mastocarpus stellatus, Halurus flosculosus and Ceramium spp. can occur, usually attached to loose-lying cobble or mussel shells. Also the green seaweeds Enteromorpha spp. and Ulva lactuca may be present. The sand mason Lanice conchilega can sometimes be present in the clay, while the shore crab Carcinus maenas is present as well. More data are required to validate this description. Situation: This unit can usually be found beneath a M. edulis or barnacle and Littorina spp.-dominated biotope (A2.721; A2.431). It is found above a Laminaria digitata and piddocks-dominated biotope (unit A3.2113). Temporal variation: The C. maenas population may migrate offshore during the winter season.