Villosa iris, the rainbow mussel or rainbow-shell, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. In 2018, Watters proposed to move the species into a new genus, Cambarunio.[1]
All Unionidae are known to use the gills, fins, or skin of a host fish for nutrients during the larval glochidia stage. Female villosa iris attract host fish by imitating a crayfish. Elongate papillae on the mantle margin resemble antennae, legs, and eyes. They also mimic crayfish behavior, moving the papillae independently like legs, and use "tail tucking" motions.[2] Juvenile mussels bury in the sediment just below its surface, and feed on bacteria and bacterial-sized particles including algae.
This species is widely distributed throughout the St. Lawrence, upper Mississippi, Ohio, Tennessee, and Cumberland River Basins.[3]
Villosa iris is the focus of conservation concern in areas like Ontario, Illinois, West Virginia, Pennsylvania and Wisconsin. In Canada, V. iris is listed as a species of Special Concern by COSEWIC and under the Species at Risk Act,[4] having been downgraded to this status in 2019 after its initial listing as Endangered in 2013.[5] In Wisconsin, it is listed as state endangered.[6]