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Marine Habitat Classification

Description of biotope or habitat type

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   Ocnus planci aggregations on sheltered sublittoral muddy sediment

Physical habitat description

Salinity Full (30-35 ppt), Variable (18-35 ppt)
Wave exposure Moderately exposed, Sheltered, Very sheltered, Extremely sheltered
Tidal streams Weak (>1 kn), Very weak (negligible)
Substratum Stones or shells on muddy sediment
Zone Circalittoral, Infralittoral
Depth Band 0-5 m, 5-10 m, 10-20 m, 20-30 m
Other Features

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.SMu.IFiMu.Ocn <I>Ocnus planci</I> aggregations on sheltered sublittoral muddy 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.


Dense aggregations of Ocnus planci [?brunneus] on various substrata, typically muddy but occasionally with stones or shells, in sheltered conditions such as sealochs. Philine aperta also characterises this biotope but is present in lower abundances than in PhiVir. Other associated species vary but are typical of very sheltered muddy habitats and include the ophiuroids Ophiura spp. and Ophiothrix fragilis. Melanella alba, which parasitises holothurians, has been found in large numbers at one site.


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 % of core records where taxon was recorded
Alcyonium digitatum 1 Rare 21-40 %
Myxicola infundibulum 1 Rare 21-40 %
Liocarcinus depurator 4 Occasional 21-40 %
Buccinum undatum 2 21-40 %
Philine aperta 20 Frequent 41-60 %
Aequipecten opercularis 1 Rare 21-40 %
Mya truncata 3 Occasional 21-40 %
Asterias rubens 7 Occasional 41-60 %
Ophiothrix fragilis 4 Frequent 21-40 %
Ophiocomina nigra 3 Occasional 21-40 %
Ophiura albida 1 Rare 21-40 %
Ophiura ophiura 7 Frequent 21-40 %
Ocnus lacteus 27 Frequent 21-40 %
Ocnus planci 19 Abundant 41-60 %

Similar biotopes or habitat types

Not applicable or unknown.

Classification history of this biotope or habitat type

Classification version Code
96.7 SCR.Ocn

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