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The Seashore

Sand Gaper (Mya arenaria)
Sand Gaper

An exposed Sand Gaper. Note the black on the shell which is staining from the sulphide layer deep in the mud, caused by a lack of oxygen. The siphon is contracted as much as possible but it is impossible to contract it completely as it is so long. The pair of siphons are joined together, compared with, say, the Tellin Shell.

These bivalves grow quite large, around 15 cm in length. The shells are thin and soft and invariably stained black by the sulphide layer (a black, deoxygenated region) in the mud.

These permanently burrowed bivalves never surface but rely upon the siphons to reach the water above. In fact, the adult muscular foot is greatly reduced and so cannot reburrow if dug up. As the Sand Gaper grows it moves deeper into the mud with the siphons increasing in length to reach the surface. These are so long that they cannot be withdrawn into the shell. They grow up to 0.5 metres long. These siphons are joined along the length unlike some bivalves where they are separate. They feed as suspension feeders, i.e. on detritus caught up in the water. The thin shell is typical of a mud burrower and could not cope with gravel or hard sand. Compare this with the cockle.

Although the name suggests a sand dweller it is more at home in mud but not too far up an estuary as it is not very tolerant of low salinities. Widespread on sheltered depositing shores and mudflats around the northern coast of Europe.

See Cockle, Tellin Shell, Wedge Shell and Razor Shell


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