Plants and Animals

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

US Status: LE - Listed Endangered
State Status: E - Endangered (legally protected)
Global Rank: G2 - Imperiled
State Rank: S1S2 - Rank is uncertain, ranging from critically imperiled to imperiled

Occurrences

CountyNumber of OccurrencesYear Last Observed
Hillsdale11997
Lenawee11941
Macomb21935
Monroe61984
Oakland42016
St. Clair122012
Wayne52006

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), RiffleInland Lake, Littoral, BenthicInland Lake, Pelagic, BenthicMainstem Stream (3rd-4th order), Riffle.

Natural Community Types

  • Headwater stream (1st-2nd order), riffle
  • Inland lake, littoral, benthic
  • Inland lake, pelagic, benthic
  • Mainstem stream (3rd-4th order), riffle

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 Recommendations

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.

Active Period

Survey Methods

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

Aqua-scope searches

Survey Period: From first week of April to first week of October

Snorkeling searches

Survey Period: From first week of April to first week of October

SCUBA searches

Survey Period: From first week of April to first week of October

References

Survey References

  • Cummings, K.S. and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5, Champaign. 194pp.
  • Strayer, D.L. and D.R. Smith. 2003. A Guide to Sampling Freshwater Mussel Populations. American Fisheries Society Monograph 8, Bethesda. 103pp.

Technical References

  • Burch, J.B. 1994. Mollusk: Species Accounts. Pages 395-410 in D.C. Evers, ed. Endangered and Threatened Wildlife of Michigan. University of Michigan Press, Ann Arbor.
  • Carman, S.M. 2001. Special Animal Abstract for Villosa fabalis (Rayed bean). Michigan Natural Features Inventory, Lansing, MI. 2pp.
  • Cummings, K.S. and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5, Champaign. 194pp.
  • Dillon, R.T. Jr. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press, Cambridge, UK. 509pp.
  • Evers, D.C. 1994. Endangered and Threatened Wildlife of Michigan. The University of Michigan Press, Ann Arbor. 412pp.
  • Goodrich, C. 1932. The Mollusca of Michigan. The University of Michigan Press, Ann Arbor. 121pp.
  • LaRocque, A.C. 1966-1970. Pleistocene mollusca of Ohio. Ohio Division of Geology Survey Bulletin, 62(1-4).
  • Ortmann, A.E. 1919. Monograph of the naiades of Pennsylvania. Part III. Systematic account of the genera of the naiades. Annals of the Carnegie Museum 8:222-365.