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Marine Habitat Classification

Description of biotope or habitat type

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   Mediomastus fragilis, Lumbrineris spp. and venerid bivalves in circalittoral coarse sand or gravel

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Gravel with coarse to medium sand
Zone Circalittoral
Depth Band 10-20 m, 20-30 m, 30-50 m, 50-100 m
Other Features

Biotope origin

Derived using data from Various
Faunal group Infauna

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat SS.SCS.CCS.MedLumVen <I>Mediomastus fragilis</I>, <I>Lumbrineris</I> spp. and venerid bivalves in circalittoral coarse sand or gravel

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.


Circalittoral gravels, coarse to medium sands, and shell gravels, sometimes with a small amount of silt and generally in relatively deep water (generally over 15-20 m), may be characterised by polychaetes such as Mediomastus fragilis, Lumbrineris spp., Glycera lapidum with the pea urchin Echinocyamus pusillus. Other taxa may include Nemertea spp., Protodorvillea kefersteini, Owenia fusiformis, Spiophanes bombyx and Amphipholis squamata along with amphipods such as Ampelisca spinipes. This biotope may also be characterised by the presence of conspicuous venerid bivalves, particularly Timoclea ovata. Other robust bivalve species such as Moerella spp., Glycymeris glycymeris and Astarte sulcata may also be found in this biotope. Spatangus purpureus may be present especially where the interstices of the gravel are filled by finer particles, in which case, Gari tellinella may also be prevalent (Glemarec 1973). Venerid bivalves are often under-sampled in benthic grab surveys and as such may not be conspicuous in many infaunal datasets. Such communities in gravelly sediments may be relatively species-rich and they may also contain epifauna such as Hydroides norvegicus and Spirobranchus lamarcki. In sand wave areas this biotope may also contain elements of the SS.SSa.IMuSa.FfabMag biotope, particularly Magelona species. This biotope has previously been described as the 'Deep Venus Community' and the 'Boreal Off-Shore Gravel Association' (Ford 1923; Jones 1950) and may also be part of the Venus community described by Thorson (1957) and in the infralittoral stage described by Glemarec (1973). SS.SCS.CCS.MedLumVen may be quite variable over time and in fact may be closer to a biotope complex in which a number of biotopes or sub-biotopes may yet be defined. For example, Ford (1923) describes a 'Series A' and a 'Series B' characterised by Echinocardium cordatum-Chamelea gallina and Spatangus purpurea-Clausinella fasciata. Furthermore, mosaics of cobble and lag gravel often contain ridges of coarse gravelly sand and these localised patches are also characterised by robust veneriid and similar bivalves including Arcopagia crassa, Laevicardium crassum and others including Glycymeris glycymeris (E.I.S. Rees pers. comm., 2002). In the presence of pebbles, cobbles or shell, in coarse sandy gravel sediment, the biotope may support encrusting fauna such as hydroids, Sertularia cupressina and Hydrallmania falcata, bryozoa including Disporella hispida, Schizomavella spp., and Escharella immersa and encrusting polychaetes, Spirobranchus triqueter and instances of Sabellaria spinulosa. In the presence of these encrusting forms, and with the transition of sediment types to more tidally swept circalittoral mixed sediment, the biotope may form a transition to SS.SMx.CMx.FluHyd. Other variants in gravel, sands and stones in circalittoral waters, from records in the east English Channel, show this biotope may support high densities of polychaetes and copepods, Nematoda and Nemertea. The biotope may be represented in moderately exposed, shallower areas, with muddy mixed gravel or sand with shell sediments and maerl (Hapalidiaceae), supporting the characteristic fauna of Mediomastus and Hilbigneris gracilis, but absence of venerid bivalves. Furthermore, in impoverished variants of the biotopes, there may be a reduced component of Mediomastus and Hilbigneris gracilis.


This biotope and variants of it make up a significant proportion of the offshore Irish Sea benthos (Mackie, Oliver & Rees 1995).

Temporal variation

MedLumVen may be quite variable over time.

Characterising species

Taxon Relative importance of taxon for defining this community (%) % of core records where taxon was recorded Relative frequency %
Nemertea 7 1-20% 1.3
Hilbigneris gracilis 5 1-20% 3.1
Echinocyamus pusillus 5 1-20% 3
Aonides paucibranchiata 4 1-20% 1.2
Amphipholis squamata 3 1-20% 1.7
Glycera lapidum 3 1-20% 1.3
Spirobranchus triqueter 3 1-20% 1.5
Notomastus 2 1-20% 0.7
Galathea intermedia 2 1-20% 1.2
Hydrallmania falcata 2 1-20% 0.5
Eteone longa 2 1-20% 0.5
Scalibregma inflatum 2 1-20% 0.6
Pisidia longicornis 2 1-20% 3.8
Poecilochaetus serpens 2 1-20% 0.6
Mediomastus fragilis 2 1-20% 2.1
Disporella hispida 2 1-20% 0.4
Harmothoe 2 1-20% 0.8
Syllis gracilis 1 1-20% 0.4
Lumbrineris latreilli 1 1-20% 0.4
Leptochiton asellus 1 1-20% 0.4
Prionospio 1 1-20% 0.4
Psammechinus miliaris 1 1-20% 0.4
Eunice vittata 1 1-20% 0.4
Pholoe inornata 1 1-20% 0.5
Odontosyllis gibba 1 1-20% 0.4
Othomaera othonis 1 1-20% 0.5
Pionosyllis 1 1-20% 0.3
Phoronis 1 1-20% 0.8
Caulleriella alata 1 1-20% 0.7
Notomastus latericeus 1 1-20% 0.6
Laonice bahusiensis 1 1-20% 0.7
Abietinaria abietina 1 1-20% 0.3
Glycymeris glycymeris 1 1-20% 0.9
Pista cristata 1 1-20% 0.7
Polycirrus 1 1-20% 0.5
Lepidonotus squamatus 1 1-20% 0.6
Golfingia 1 1-20% 0.4
Schizomavella 1 1-20% 0.3
Exogone 1 1-20% 0.3
Leptocheirus hirsutimanus 1 1-20% 0.4
Ampelisca brevicornis 1 1-20% 0.3
Escharella immersa 1 1-20% 0.3
Spirobranchus lamarcki 1 1-20% 1.3
Lumbrineriopsis paradoxa 1 1-20% 0.3
Protodorvillea kefersteini 1 1-20% 1.2
Cirriformia tentaculata 1 1-20% 0.3
Abra alba 1 1-20% 0.5
Syllis prolifera 1 1-20% 0.3
Myrianida 1 1-20% 0.3
Eumida sanguinea 1 1-20% 0.3
Porifera 1 1-20% 0.3
Psamathe fusca 1 1-20% 0.3
Eulalia mustela 1 1-20% 0.4
Monocorophium sextonae 1 1-20% 0.7

Similar biotopes or habitat types

SS.SCS.ICS.MoeVen is the shallow water variant of the current biotope.

SS.SCS.CCS.Pkef is more impoverished and less diverse than SS.SCS.CCS.MedLumVen. It is possible that SS.SCS.CCS.Pkef is a disturbed or transitional variant of SS.SCS.CCS.MedLumVen resulting from dredging activities or storm events.

Classification history of this biotope or habitat type

Classification version Code Habitat name
2015 (15.03) SS.SCS.CCS.MedLumVen Mediomastus fragilis, Lumbrineris spp. and venerid bivalves in circalittoral coarse sand or gravel
2004 (04.05) SS.SCS.CCS.MedLumVen Mediomastus fragilis, Lumbrineris spp. and venerid bivalves in circalittoral coarse sand or gravel
1997 (97.06) Part of SS.CGS.Ven Venerid bivalves in circalittoral coarse sand or gravel

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