October 26th, 2007
Mussels containing inclusions or ‘pearls’ were found in Loch Long in Scotland. Mytilus edulis, known as the common mussel, is a bivalve; 80-100mm in length and dark blue to purple and sometimes brown in colour. It attaches firmly to rocks and stones etc. by byssus threads. The pearls found in these mussels are formed around parasitic worm larvae that infect the mussels. The parasite is usually the flatworm Gymnophallus bursicola, which enters as larvae and lodges itself in the mantle of the mussel. In order to protect itself, the mussel forms layers of a shell-like nacreous (iridescent) material over the worm to form a pearl. Mytilus edulis, alongside other bivalves, can also be infected by the pea crab (Pinnotheres pisum) which commonly inhabits the mantle cavity of the mussel.
Added by Rachelle Long