Fine to very fine muddy sand on the mid shore at the lower extreme of estuaries, and in moderately exposed and sheltered bays and marine inlets, sometimes subject to variable salinity. The infauna is characterised by the polychaetes Eteone longa, Hediste diversicolor (ragworm) and Pygospio elegans, oligochaetes (mostly Tubificoides benedii and T. pseudogaster), the crustaceans Corophium volutator and Crangon crangon, the spire shell Hydrobia ulvae and the baltic tellin Macoma balthica. The cockle Cerastoderma edule may be abundant, and the sand gaper Mya arenaria may be superabundant, though these species are not always present, or may be missed in core samples due to their large size. The polychaetes Arenicola marina, Polydora cornuta and Capitella capitata, the shrimp Crangon crangon, and the Mussel Mytilus edulis are sometimes present. Situation: This unit can occur on the mid shore of sheltered, lower estuaries, with the A2.31 communities in muddier sediments on the lower shore. Under moderately exposed conditions in lower estuaries and towards open coasts, it may occur alongside other muddy sand units such as A2.242 or A2.244. Temporal variation: Enteromorpha spp. or Ulva lactuca may form mats on the surface of the sediment during the summer months, particularly in areas of freshwater influence and/or where there is nutrient enrichment.