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This biotope is found on heavily silted, moderately wave-exposed circalittoral bedrock and boulders (often limestone) that are subject to moderately strong tidal streams. A very high silt loading in the water column means that this 'circalittoral' biotope occurs at unusually shallow depths (1 - 10 m BCD). It is characterised by a mixed faunal turf and `massive' examples of the sponges Suberites ficus, Suberites carnosus and Hymeniacidon perlevis. Other sponges recorded in this biotope are Cliona celata, Halichondria panicea, Amphilectus fucorum, Raspailia ramosa, Polymastia mamillaris, Dysidea fragilis, Sycon ciliatum, Stelligera montagui and Haliclona oculata. Also characteristic of this biotope is a dense bryozoan turf with one or more crisiid species, Flustra foliacea and Crisularia plumosa. The polychaete Polydora spp. and the rock-boring bivalve Hiatella arctica are able to bore into the relatively soft limestone. There is an ascidian component to the biotope, with Morchellium argus and Clavelina lepadiformis among the most abundant. There may be scattered clumps of the hydroids Abietinaria abietina and Hydrallmania falcata. Other species present include the anemones Metridium senile, Cylista elegans and Urticina felina, the starfish Asterias rubens, the crab Necora puber, the nudibranch Antiopella cristata and the soft coral Alcyonium digitatum. This biotope has currently only been recorded off the east coast of Anglesey, Wales.