Endangered Resources Program Species Information
Rainbow Shell (Villosa iris)

Overview

Species Overview

Rainbow shell (Villosa iris), a mussel listed as Endangered in Wisconsin, is found in shallow, flowing, clean small streams with stable gravel substrate in the eastern part of the state. It has a very restricted geographical range in Wisconsin. The known host fish include smallmouth and largemouth basses and rockbass.

Status and NHI Documented Occurrences in Wisconsin

The table below provides information about the protected status (State and Federal Status) and the rank (S and G Ranks) for Rainbow Shell (Villosa iris). See the Working List Key for more information about the abbreviations used. Counties shaded blue have documented occurrences for this species in the Wisconsin Natural Heritage Inventory database. For invertebrates, dots depict locations from the "Invertebrate Atlas," a database with occurrences of rare and common aquatic and select terrestrial invertebrate species found in Wisconsin and adjacent areas. While the invertebrate atlas is a quality assured database, not all records have been verified. The map is provided as a general reference of where this species has been found to date and is not meant as a range map.

Summary Information State Status: END Federal Status in Wisconsin: none State Rank: S1 Global Rank: G5Q Tracked by NHI: Y Species of Greatest Conservation Need: Y

Detailed Information

Identification: The shell is elongate and elliptical, relatively thin. The male shell is compressed and the female shell inflated. Females are more expanded in the post-dorsal region and are more broadly rounded, while the male is rather sharply pointed. The beak is small and sculptured with distinctive, double-looped bars. The outer surface is colored yellowish-green to brown with dark green rays. The nacre is silvery white and highly iridescent posteriorly. Shell is small, usually less than 3 inches (7.6 cm).

Habitat: Inhabits small streams, living within and below riffles on a sand, gravel or mud bottom in water less than a meter deep.

State Distribution: Occurs in the Mukwonago River. This species may yet be found in rivers of southeastern Wisconsin for which we currently have only historical records. See the species map.

Phenology: Breeding has been observed from May through September. Glochidia have been found on rock bass (Ambloplites rupestris), and smallmouth bass (Micropteris dolomieu) from May through August. Largemouth bass (M. salmoides) are also used as hosts.

Management Guidance: Because this species inhabits small streams, this mussel is most vulnerable to pollution from runoff and siltation. Habitat protection and water quality improvements would benefit this species. Increased development along waterways in southeastern Wisconsin is of great concern for the continued existence of this species.

Information compiled from publication PUB-ER-085-99 (now out-of-print).

Photos

Click on a photo to view a larger version. Please considering donating your photos to the Endangered Resources Program for educational uses. See also information regarding use of photos

Photo by Lisie Kitchell, WDNR.

Related Links

Links to Additional Rainbow Shell Information

• Illinois Natural History Survey [Exit DNR]
• Michigan Natural Features Inventory [Exit DNR]

Other Links Related to Mussels and Clams

• Illinois Natural History Survey [Exit DNR]
• The Field Museum [Exit DNR]
• Conchologists of America [Exit DNR]
• EPA Biological Indicators of Watershed Health [Exit DNR]
• Milwaukee Public Museum [Exit DNR]