Mainly mid shore mud or sandy mud subject to variable salinity on sheltered estuarine shores. Typically, the sediment is wet in appearance and has an anoxic layer below 1 cm depth. The surface of the mud has the distinctive 'crow's foot' pattern formed by the peppery furrow shell Scrobicularia plana. The infauna is additionally characterised by a range of polychaete and bivalve species, including the ragworm Hediste diversicolor, Pygospio elegans, Streblospio shrubsolii, Tharyx killariensis and the baltic tellin Macoma balthica. Oligochaetes, most notably Tubificoides benedii, and the spire shell Hydrobia ulvae may be abundant. Other species that sometimes occur in this biotope are the cockle Cerastoderma edule, the sand gaper Mya arenaria and the polychaetes Eteone longa and Nephtys hombergii. Situation: This unit may occur on the same shores as units A2.311, A2.312, NhomAph, A2.3221 and A2.3222. Higher up on the shore, and/or further towards the head of the estuary, A2.3223 may occur, changing to A2.323 at the upper extreme of the estuary. Temporal variation: Enteromorpha spp. and Ulva lactuca may form mats on the surface of the mud during the summer months, particularly in areas of nutrient enrichment.