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Marine Habitat Classification

Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   Modiolus modiolus beds on open coast circalittoral mixed sediment

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Sheltered
Tidal streams Moderately strong (1-3 kn)
Substratum Muddy gravel and sand, with shells and stones
Zone Circalittoral
Depth Band 50-100 m
Other Features

Biotope origin

Derived using data from Various
Faunal group Epifauna/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.SBR.SMus.ModMx <I>Modiolus modiolus</I> beds on open coast circalittoral mixed sediment

  • 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.


Muddy gravels and coarse sands in deeper water of continental seas may contain venerid bivalves with beds of Modiolus modiolus. The clumping of the byssus threads of the M. modiolus creates a stable habitat that attracts a very rich infaunal community with a high density of polychaete species including Glycera lapidum, Paradoneis lyra, Aonides paucibranchiata, Laonice bahusiensis, Protomystides bidentata, Lumbrineris spp., Mediomastus fragilis and syllids such as Exogone spp. and Sphaerosyllis spp. Bivalves such as Spisula elliptica, Timoclea ovata and other venerid species are also common. Brittlestars such as Amphipholis squamata may also occur with this community. This biotope is very similar to SS.SMx.OMx.PoVen and the 'boreal off-shore gravel association' and the 'deep Venus community' described by previous workers (Ford 1923; Jones 1951). Similar Modiolus beds (though with a less diverse infauna) on open coast stable boulders, cobbles and sediment are described under SS.SBR.SMus.ModT.


No situation data available.

Temporal variation

No temporal data available.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale Typical abundance - (count per m2) % of core records where taxon was recorded
Modiolus modiolus 4 Super abundant 385 81-100%
Aonides paucibranchiata 3 Common 164 81-100%
Exogone verugera 3 Common 151 81-100%
Glycera lapidum 3 Common 94 81-100%
Amphipholis squamata 2 Abundant 71 81-100%
Echinocyamus pusillus 2 Abundant 140 61-80%
Parexogone hebes 2 Frequent 75 81-100%
Harmothoe impar 2 Common 54 81-100%
Laonice bahusiensis 2 Common 69 81-100%
Leptochiton asellus 2 Abundant 122 81-100%
Hilbigneris gracilis 2 Common 75 81-100%
Mediomastus fragilis 2 Common 288 81-100%
Nemertea 2 Common 58 81-100%
Paradoneis lyra 2 Common 90 81-100%
Polycirrus 2 Common 50 81-100%
Protomystides bidentata 2 Common 53 81-100%
Sphaerosyllis 2 Frequent 41 81-100%
Spisula elliptica 2 Common 51 81-100%
Asclerocheilus intermedius 1 Frequent 32 81-100%
Leiochone johnstoni 1 Abundant 52 61-80%
Eusyllis blomstrandi 1 Frequent 39 81-100%
Grania 1 44 81-100%
Hydroides norvegica 1 Frequent 35 81-100%
Lysilla 1 Abundant 26 81-100%
Nereiphylla lutea 1 Abundant 56 81-100%
Dipolydora flava 1 Frequent 35 81-100%
Sphaerosyllis bulbosa 1 Frequent 203 61-80%
Syllis 1 Frequent 22 81-100%
Timoclea ovata 1 Common 29 81-100%

Similar biotopes or habitat types

SS.SMx.OMx.PoVen is similar to SS.SBR.SMus.ModMx but lacks the epifaunal Modiolus bed.

SS.SBR.SMus.ModT tends to occur at the entrance to channels where tidal streams are strong.

Classification history of this biotope or habitat type

Classification version Code Habitat name
2015 (15.03) SS.SBR.SMus.ModMx Modiolus modiolus beds on open coast circalittoral mixed sediment
2004 (04.05) SS.SBR.SMus.ModMx Modiolus modiolus beds on open coast circalittoral mixed sediment
1997 (97.06) SS.CMX.ModMx Modiolus modiolus beds on circalittoral mixed sediment

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