What is the meaning of River_mussel?

Certain Any bivalve mollusks of family Unionidae, found in flowing fresh water:

  1. especially of genera Unio and Anodonta, both found in rivers of the central U.S. with a shell lined with mother-of-pearl.
  2. especially of species Alathyria jacksoni.

especially of genera Unio and Anodonta, both found in rivers of the central U.S. with a shell lined with mother-of-pearl.

especially of species Alathyria jacksoni.

Source: wiktionary.org