Nacreous Pearly or iridescent nacre as the interior of some Unios. The common name used for freshwater mussels of the Superfamily Unionacea. A freshwater bivalve or Unionid. Often called a mussel. Ciliated structures that surround the mouth.
Food is sorted here and moved toward the mouth.
Suitable particles that have been received from the gills are taken into the mouth and digested. Non-suitable food is rejected, falls on the mantle tissue, and is transported from the inhalent siphon. Often branched like a feather or a tree. Use is restricted to unionids and byssate bivalves in freshwater. Periostracum The outside layer or covering of the shell.