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Which species of piddock would depend on the size of the holes:were they about 2cm wide or about 4cm?
the candida sp is not at all common and usually is a soft rock borer - I guess I would like to see one out of it's burrow to be convinced. Hence my comment about removing a dead looking one.
I Forgot to ask what kind of 'rock' .Looks like clay.MarLIN site says wood,peat & soft rocks (as doesCollins' sea shore '96 ); but I've found many in clay on Swansea bay beach. I don't believe uncommon, but Marlin's maps show a more restricted distribn than the common piddock. The marlin site pic shows a B.c. in the hole with the long end pointing to the opening (which the other related species must do also); & comparing the 'long ends' of these species I find only white piddock shows the 'raised lines with little peaks' found in Manhoot's picture (bottom row, central hole) + common piddocks much wider than these 2cm holes.
Lat/Lng: 50.7325, -2.9147
OS grid ref: SY355929