Scientific Name: Villosa iris

Classification:  State Threatened

Photo Credit: NCWRC




NOTE: Hover over the bold words for definitions or see the Glossary.

The shell of the rainbow is roughly elliptical in shape. There is slight sexual dimorphism in shell shape with males becoming more pointed posteriorly; while, females have a broader and rounder posterior end to accommodate the marsupium. The periostracum is golden brown with both broad and narrow green rays over the entire surface of the shell. Nacre color is variable including white with a salmon wash in the beak cavity to pink, salmon, or purple. The nacre of the posterior end is often iridescent. There are two triangular pseudocardinal teeth and two blade-like lateral teeth in the left valve. The right valve has only one pseudocardinal tooth and one lateral tooth. (Parmalee and Bogan 1998)


Shell Anatomy

This species is widely distributed throughout the St. Lawrence, upper Mississippi, Ohio, Tennessee, and Cumberland River Basins. In North Carolina, the species is now restricted to the Hiwassee and Little Tennessee river basins. It has been extirpated from the Watauga and French Broad River Basins of North Carolina. Distribution by County: Tennessee River Basin: Cherokee Co. (Hiwassee River); Clay Co. (Hiwassee River); Macon Co. (Little Tennessee River); Swain Co. (Little Tennessee River). NOTE: All headwater areas that flow into these occupied habitats should receive special management.


In North Carolina, the rainbow is often found in backwater areas with silt and sand substrates; however, it is also found in faster flowing areas under boulders.
This is a bradytictic species. Gravid females have been observed from July to May (Ortmann 1919). Numerous fish hosts have been identified for this species, including: largemouth bass, smallmouth bass, spotted bass, Suwannee bass, rockbass, and the western mosquitofish (Watters 1994, as reported in Parmalee and Bogan 1998). 


General Life History For Mussels