This habitat is no longer an MCZ Feature of Conservation Importance. Please refer to the MCZ FOCI Review 2016

File shell beds

File shell beds © Keith Hiscock

The file shell is a very distinctive bivalve.  The two halves of its shell do not close completely, and a thick fringe of bright orange or red tentacles extends between them.

File shells are usually found on sand or gravel seabeds.  They often use their sticky byssus thread ‘beards’ to form nests of debris, mud and seaweed fragments, within which the animals are completely hidden.  This is thought to be a means of defence: a file shell cannot pull in its tentacles, which are vulnerable to being nipped off by passing predators.  In tide-swept, shallow inlets and bays, where file shells occur in large numbers, the nests can join up to form a reef, which can extend to several hectares in size.

In shallow water, kelp seaweeds may settle onto the file shell beds.  Maerl and horse mussels may also form part of the reef.  Other animals that find food and shelter here include crabs, starfish, young cod and dogfish. 

File shell beds form a surface for attachment and a refuge in an otherwise featureless seascape.  Where file shell beds have been lost, the seaweeds and young fish have also disappeared, illustrating the importance of these beds as a key feature in the local environment.

Scallop dredging and trawling are main threats to file shell beds.  They have also been destroyed by pollution from the anti-fouling paints used to stop marine creatures attaching to ships’ hulls and underwater structures.

For the official habitat definition please see the documents listed below.


European distribution

File shells are found on the west and south-west coasts of the UK, and are most common off western Scotland. The European range extends south to Mediterranean and Canary Isles.  Large reefs of file shells are scarce, however, and are usually found in the mouths of sea lochs. They have only been recorded from the west coast of Scotland and from Donegal.


Conservation status/need

File shell bed fact

This is a UK BAP Priority Habitat (BAP habitats are now Habitats of Principal Importance/Priority Habitats).


Official definition

UK Biodiversity Action Plan; Priority Habitat Descriptions. BRIG (ed. Ant Maddock) 2008 (updated December 2011)


Further information

Marine Life Information Network - Limaria hians

World Register of Marine Species - Limaria hians

Marine Species Identification Portal - Limaria hians

Conchological Society of Great Britain and Ireland - Limaria hians

Marine Life Information Network - Limaria hians beds in tide-swept sublittoral muddy mixed sediment

JNCC - UK BAP Priority Species and Habitats

JNCC EUNIS habitat correlations table