Dense loose-lying beds of the 'Trailliella' phase of Bonnemaisonia hamifera may occur in extremely sheltered shallow muddy environments. Beds of this alga are often 10 cm thick but may reach 100 cm at some sites. Other loose-lying algae may also occur such as Audouinella floridula, Phyllophora crispa and species of Derbesia. Often the mud is gravelly or with some cobbles and may be black and anoxic close to the sediment surface. This biotope is widely distributed in lagoons, sealochs and voes but should only be described as A5.526 when a continuous mat is found. It is likely that the infaunal component of this biotope may be considerably modified by the overwhelming quantity of loose-lying algae.