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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.

   Foraminiferans and Thyasira sp. in deep circalittoral fine mud

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure
Tidal streams Very weak (negligible)
Substratum Soft mud
Zone Circalittoral
Depth Band 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.SMu.OMu.ForThy Foraminiferans and <I>Thyasira</I> sp. in deep circalittoral fine mud

  • 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.


In deep water and soft muds of Boreal and Arctic areas, a community dominated by foraminiferans and the bivalve Thyasira sp. (e.g. T. croulinensis and T. pygmaea) may occur (Thorson 1957; Künitzer et al. 1992). Foraminiferans such as Saccammina, Psammosphaera, Haplophragmoides, Crithionina and Astorhiza are important components of this community with dead tests numbering thousands per m2 (see Stephen 1923; McIntyre 1961) and sometimes visible from benthic photography (Mackie, Oliver & Rees 1995). It is likely that a community dominated by Astorhiza in fine sands in the Irish Sea may be another distinct biotope (E.I.S. Rees pers. comm. 2002). Polychaetes, e.g. Paraonis gracilis, Myriochele heeri, Spiophanes kroyeri, Tharyx sp., Lumbrineris tetraura, are also important components of this biotope. These communities appear to have no equivalent on the continental plateau further south (Glemarec 1973) but are known from the edge of the Celtic Deep in the Irish Sea (Mackie, Oliver & Rees 1995). The benthos in these offshore areas has been shown to be principally Foraminifera and similar, rich communities may exist in Scottish sea lochs (McIntyre 1961). Communities from yet deeper (northern) waters at the extremes of the North Sea may be reminiscent, although dissimilar to SS.SMu.OMu.ForThy (see Pearson et al. 1996) reflecting a higher proportion of silt/clay. A fully Arctic version of this biotope has also been described (Thorson 1934, 1957) although it should be noted that Jones (1950) considered this Boreal foraminiferan community to be part of a 'Boreal Deep Mud Association'.


This community typically occurs in water deeper than 100 m in the northern North Sea (Künitzer et al. 1992) and have been referred to as 'Foraminifera communities' by other workers (e.g. Stephen 1923; Thorson 1957; McIntyre 1961).

Temporal variation

No temporal data available.

Characterising species

Taxon % of core records where taxon was recorded
Aricidea (Acmira) catherinae
Exogone verugera
Prionospio cirrifera
Thyasira flexuosa

Similar biotopes or habitat types

In shallower water a Brissopsis-dominated community (SS.SMu.CFiMu.BlyrAchi) may develop.

SS.SMu.CSaMu.ThyEten is similar to this biotope in terms of high numbers of Thyasira spp. but lacks the foraminiferan component and is generally found at shallower depths.

Classification history of this biotope or habitat type

Classification version Code Habitat name
2015 (15.03) SS.SMu.OMu.ForThy Foraminiferans and Thyasira sp. in deep circalittoral fine mud
2004 (04.05) SS.SMu.OMu.ForThy Foraminiferans and Thyasira sp. in deep circalittoral fine mud
1997 (97.06) SS.COS.ForThy Foraminiferans and Thyasira sp. in deep circalittoral soft mud

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