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I am amazed that this has attracted no comment - Mark's ID is correct (I think!) .
It is so obviously the Corallina officinalis we are used to seeing in the strandline.
Maybe Steve, you could be persuaded to alter the title and mark it Marine - it is, or was, a marine alga.
THREE MARINE PROJECTS
There are some Spirorbis worm tubes also encrusting it...
Yes, there's a good chance they are Spirorbis corallinae - I am trying to chase them down here but I need to be certain.before posting
Lat/Lng: 57.274, -5.864
OS grid ref: NG671269