river mussel

noun3

1. •
   Certain bivalve mollusks of order Unionida, found in flowing fresh water.
2. •
   (US) especially of genera Unio and Anodonta, both found in rivers of the central U.S. with a shell lined with mother-of-pearl.
3. •
   (Australia) species Alathyria jacksoni within the family Hyriidae