Brachiopod internal mould

3D Model

This internal mould of a Palaeozoic brachiopod displays the diagnostic bilateral symmetry perpendicular to the hingeline, which distinguishes the group from pelecypods (bivalve molluscs), which have bilateral symmetry parallel to the hingeline. Brachiopods (also known as ‘lamp shells’) have one valve (shell) larger than the other. The larger pedicle valve (‘foot’ valve) was either attached to or buried in the seafloor substrate, while the brachial valve was uppermost in life position. Internal moulds are formed from sediment that has filled the internal cavity whereas external moulds are are an imprint of the outside of the shell.