Functional significance of the spines of the Ordovician lingulate brachiopod Acanthambonia

The hollow spines of an unusually well preserved specimen of the minute lingulate Acanthambonia are interpreted as having three functions. The short curved spines along the posterior margin are envisaged as attachment spines, supplementing a pedicle which is functional throughout ontogeny and regarded as anchoring the animal possibly to algal strands above the sea floor. Apart from rare undersized spines with tapering apices, the bulk of the spines on the shell surface are open-ended, with a length attaining half that of the shell itself. The open distal ends of these thin-walled spines would have housed mantle tissue during life, interpreted as being sensory and substituting for setae in the post larval stages. The alternation of spines along successive laminae indicates their interfingering disposition along the anterior and antero-lateral valve margins, where an additional function would have been to screen out coarse particles from the mantle cavity.