clappy-doo
(ˌklæpɪˈduː) or clabby-doo
n (Animals) Scot a large black mussel
[C19: probably from Scottish Gaelic clab enormous mouth + dubh black]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014