Villosa fabalis
Rayed bean

Key Characteristics

The rayed bean is a small (to 1.5 inches), elliptical mussel with a solid shell. The hinge teeth are heavy. The shell is light to dark green or olive with heavy wavy rays and the nacre is white to whitish-blue, and often iridescent posteriorly.

Status and Rank

  • State Status: E
  • US Status: LE
  • State Rank: S1S2
  • Global Rank: G2

Occurrences

County NameNumber of OccurrencesYear Last Observed
Hillsdale11997
Lenawee11941
Macomb21935
Monroe61984
Oakland42009
St. Clair122012
Wayne52006
Distribution map for Villosa fabalis

Updated 7/21/2017. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.

Habitat

The rayed bean occurs in small, shallow rivers, in and near riffles and often near aquatic vegetation. It also occurs along shallow, wave-swept shores of lakes. This species is often buried deep in sand and/or gravel.

Specific Habitat Needs

Sand or gravel substrates, macrophytes needed in Headwater Stream (1st-2nd order), Riffle, Mainstem Stream (3rd-4th order), Riffle, Inland Lake, Littoral, Benthic, Inland Lake, Pelagic, Benthic

Natural Community Types

Methodology

For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Management

The rayed bean is historically rare in Michigan (Goodrich 1932). Like other mussels, threats to the rayed bean include: natural flow alterations, siltation, channel disturbance, point and non-point source pollution, and exotic species. Maintenance or establishment of vegetated riparian buffers can help protect mussel habitats from many of their threats. Control of zebra mussels is critical to preserving native mussels. And as with all mussels, protection of their hosts habitat is also crucial.

Survey Methods

These species bury themselves into substrates and so sampling may need to include excavation.

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Nov 22, 2017]

More Information

See MNFI Species Abstract

References

Survey References

Technical References

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