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Medium-coarse sands with gravel, shells, pebbles and cobbles on moderately exposed coasts may support populations of the slipper limpet Crepidula fornicata with ascidians and anemones. C. fornicata is common in this biotope though not as abundant as in the muddier estuarine biotope SS.SMx.SMxVS.CreMed to which this is related. Anemones such as Urticina felina and Alcyonium digitatum and ascidians such as Styela clava are typically found in this biotope. Bryozoans such as Flustra foliacea are also found along with polychaetes such as Lanice conchilega. Little information is available with regard to the infauna of this biotope but given the nature of the sediment the infaunal communities are liable to resemble those in biotopes from the SS.SCS habitat complex. As with SS.SMx.CMx.FluHyd this biotope could be considered a superficial or epibiotic overlay but more data is required to support this.

Shallow mixed (heterogeneous) sediments in fully marine or near fully marine conditions, supporting various animal-dominated communities, with relatively low proportions of seaweeds. This habitat may include well mixed muddy gravelly sands or very poorly sorted mosaics of shell, cobbles and pebbles embedded in mud, sand or gravel. Due to the quite variable nature of the sediment type, a widely variable array of communities may be found, including those characterised by bivalves (SS.SMx.IMx.VcorAsquAps, SS.SMx.IMx.CreAsAn, and SS.SMx.IMx.Ost), polychaetes (SS.SMx.IMx.SpavSpAn) and file shells (SS.SMx.IMx.Lim). This has resulted in many species being described as characteristic of this biotope complex all contributing only a small percentage to the overall similarity (see below). This biotope complex may also include a newly proposed Chaetopterus biotope (Rees pers com.) recently found in the eastern English Channel. This biotope is characterised by an undescribed Chaetopterus sp. and small Lanice conchilega. Further sampling is need in order to assess and fully characterise this potential biotope. As a result, the Chaetopterus biotope has not been included in this revision. Infaunal data for this biotope complex are limited to that described in the biotope SS.SMx.IMx.VcorAsquAps and so are not representative of the infaunal component of the whole biotope complex.