Fresh water mussels are innocuous creatures that live on the gravelly bottoms of streams. They are bivalves and the insides of their shells have a pearly appearance. They are filter feeders, constantly pumping water through their bodies and filtering out nutrients. In this way they are an important factor in keeping water clean.
In the nineteenth century, America's freshwater mussels were nearly driven to extinction. They were collected in vast numbers so that their shells could be made into buttons. They were ultimately saved from extinction when chemical engineers developed cheap plastics.
Today mussels are again threatened, this time by the heavy use of pesticides on cotton fields. It would be nice if they were once again saved from extinction, this time by genetic engineers.