1) Fresh-water mussel 2) Genus of mussels 3) Genus unio 4) Mollusk genus 5) Mussel 6) Mussel genus 7) Mussel used by button makers 8) Pearly mussel 9) River mussel 
[genus] Unio is a genus of medium-sized freshwater mussels, aquatic bivalve mollusks in the family Unionidae, the river mussels. Unio is the type genus of the family Unionidae. Species in the genus Unio include: ...
• (n.) Any one of numerous species of fresh-water mussels belonging to Unio and many allied genera.
[n] - type genus of the family Unionidae
genus Unio noun type genus of the family Unionidae