The Rayed Bean…a Species at Risk

This species has been identified as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). It is listed under the federal Species at Risk Act (SARA) and is afforded protectionunder the SARA as of June 2004. Additional protection is afforded through the federal Fisheries Act. Under the SARA, a recovery strategy must be developed for this species.

General Description

Villosa fabalis (I.Lea, 1838)

Photo by E. Pip (University of Winnipeg)

The Rayed Bean (Villosa fabalis) has the following characteristics:

• Shell is very small, thick and subelliptical in shape;
• Midanterior shell wall thickness of 2.5 mm;
• Females tend to be more inflated and more broadly rounded posteriorly than males;
• Outside of shell is normally light or dark green with crowded, wavy, darker green rays;
• Inside of shell is silvery white and iridescent;
• Narrow beak (raised part at the top of the shell), slightly elevated above the hinge line and not excavated;
• Fine beak sculpture with five crowded double- looped ridges; and
• Hinge teeth are very heavy with serrated triangular teeth and shorter, elongated teeth.

Distribution

The Rayed Bean was historically known from 11 states and the Province of Ontario. In Canada, this species was known from western Lake Erie, the Detroit River, and the Sydenham and Thames rivers in the Lake St. Clair drainage. However, it is now restricted to the middle reach of the Sydenham River.

Habitat and Life History

The Rayed Bean is usually found in or near riffle areas of headwater and small tributaries of river systems. It is typically found deeply buried in the sand and gravel substrate among the roots of aquatic vegetation, generally in low flow areas.

The Rayed Bean is a moderately long-lived, sexually-dimorphic species with a lifespan of at least 10 years. It is believed that spawning occurs in late summer and the glochidia (larvae) are released the following spring.

Host

The host fishes for this species in Canada are the Greenside Darter (Etheostoma blennioides), Mottled Sculpin (Cottus bairdi), Rainbow Darter (Etheostoma caeruleum) and Largemouth Bass (Micropterus salmoides).

Diet

Like all species of freshwater mussels, the Rayed Bean uses bacteria and algae as its primary food source.

Threats

The Rayed Bean is sensitive to pollution from municipal, industrial and agricultural sources. Siltation, habitat perturbation and impoundment of rivers have also likely destroyed much of the habitat for this species over the last century. More recently, the Zebra Mussel (Dreissena polymorpha) has devastated some Rayed Bean populations in the Great Lakes. Access to suitable host species may also threaten this species.

Similar Species

Rainbow (Villosa iris); Kidneyshell (Ptychobranchus fasciolaris) (young specimens); Spike (Elliptio dilatata) (juveniles)

Text Sources: West et al. 2000.

For more information, visit the SARA Registry Website at www.SARAregistry.gc.ca.