Very exposed to moderately exposed upper and mid eulittoral bedrock and boulders characterised by a dense community of barnacles, including Chthamalus montagui, Chthamalus stellatus and Semibalanus balanoides, and the limpet Patella vulgata. Damp cracks and crevices in the rock provide a refuge for small individuals of the mussel Mytilus edulis and the winkles Melarhaphe neritoides and Littorina saxatilis. These crevices can also be occupied by encrusting coralline algae and the anemone Actinia equina. Black patches of the lichen Verrucaria maura may be found in this zone. There is much regional variation in the distribution and zonation of Chthamalus spp. On the west coast Chthamalus spp. dominate the upper eulittoral, often forming a distinct white band above a darker band of S. balanoides in the mid eulittoral zone. C. montagui is better adapted to resist desiccation and, therefore, extends further up the shore. On some shores, particularly in the south-west, Chthamalus spp. is the dominant barnacle throughout the eulittoral zone (A1.1121). On other shores, particularly in the south, Lichina pygmaea can form a distinct zone (A1.1122). Situation: This unit is found below the black lichen Verrucaria maura (B3.1131 or B3.1132) on very exposed shores and above the mussel Mytilus edulis and barnacle biotope (A1.111). On slightly less exposed shores the wrack Fucus vesiculosus is able to survive and a mixed barnacle and F. vesiculosus biotope may occur (A1.1132) beneath A1.112. On such moderately exposed shores A1.112 may still occur on steep and vertical faces, while fucoids dominate the flatter areas (A1.1132 or A1.1132), though these communities should not be confused with A1.1132. This unit can also occur above A1.113. On very sheltered sea lochs in Argyll, West Scotland Chthamalus spp. are unusually abundant in the upper eulittoral zone.