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. Over 300 species have been found in file shell reefs.
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.
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.
UKBAP Priority Habitat
Limaria hians (WoRMS)
Limaria hians (Marine Species Identification Portal)
Limaria hians (Conchological Society of Great Britain and Ireland)
File shells are one of the few species of bivalve that can swim: they achieve jet propulsion by ‘clapping’ their shells to force out streams of water.