A thick shell, light brown to grey in colour with a violet border and often with concentric bands on the shell . The inner shell is shiny with a purplish-blue tinge around the edge. It can grow up to 12 cm in length. I often find large hard clam shells on the shore on Southampton Water one of these is the largest one I have come across.
They are found in UK waters (buried in muddy/sandy sediment at low tide in esturies and bays) recorded from Burnham-on Crouch, the south coast of England, Pembrokeshire and Loch Sunart, Scotland. (not recorded in Ireland.)
They were introduced from North America where it is known as a quahog clam into British waters several times since the middle of the nineteenth century. The first live specimen was found in 1864 in the Humber. It successfully introduced from the USA into Southampton Water in 1925.
On line I found this information :- A clam dredged from Icelandic waters had said to lived for 400 years. Is this the longest-lived animal known to science.