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Initially, at first glance it looks like Callochiton septemvalvis - http://www.ispot.org.uk/node/332429.
But the distinct angles on the topmost 'plates' are distracting. So could it be Tonicella rubra? It is very like your previous post http://www.ispot.org.uk/node/91181 which, of course, carries ChrisMcA's comment.
I'd go for the latter, put up the ID, make certain you group it in Marine Habitat.
Also in the picture is a delightful clam, probably Heteranomia squamula http://www.ispot.org.uk/node/338486 - another Marine post?.
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Lat/Lng: 54.3044, -0.4054
OS grid ref: TA038910