Plants and Animals

Villosa iris Rainbow

Key Characteristics

The rainbow is a small (to 3 inches), elongate mussel with a relatively thin shell. The beak sculpture has 4 to 6 distinct double-looped bars. The cardinal teeth are small, triangular, and somewhat divergent; there are 2 in the left valve and 2 in the right valve. The shell is yellow or greenish-yellow with dark green rays. The nacre is silvery white and highly iridescent on the posterior half.

Status and Rank

US Status:
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G5Q - Secure. Questionable taxonomy that may reduce conservation priority
State Rank: S3 - Vulnerable

Occurrences

CountyNumber of OccurrencesYear Last Observed
Allegan1
Alpena21932
Arenac1
Barry32010
Berrien21934
Branch12000
Calhoun72015
Cass22009
Clinton72010
Eaton82015
Genesee22001
Gladwin11926
Gratiot52015
Hillsdale192005
Huron21942
Ingham102015
Ionia82016
Iosco1
Isabella42015
Jackson192017
Kalamazoo41960
Kent92017
Lapeer21926
Lenawee152004
Livingston52007
Macomb172011
Mecosta22002
Menominee11927
Midland42015
Missaukee12002
Monroe152017
Montcalm82015
Muskegon1
Oakland132016
Ogemaw11926
Ottawa11929
Roscommon42002
Saginaw42011
Sanilac52009
Shiawassee52001
St. Clair212016
St. Joseph102016
Tuscola62004
Van Buren42009
Washtenaw112010
Wayne62007

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 rainbow occurs in coarse sand or gravel in small to medium streams.

Specific Habitat Needs

Sand and gravel substrates needed in: Great Lake, Littoral, BenthicInland Lake, Littoral, BenthicInland Lake, Pelagic, Benthic

Sand and gravel substrates; moderate currents needed in: Headwater Stream (1st-2nd order), RiffleHeadwater Stream (1st-2nd order), PoolHeadwater Stream (1st-2nd order), RunMainstem Stream (3rd-4th order), PoolMainstem Stream (3rd-4th order), RunMainstem Stream (3rd-4th order), Riffle

Natural Community Types

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

Like other mussels, threats to the rainbow 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

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.
  • 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.
  • Smith, P.W. 1971. Illinois streams: A classification based on their fishes and an analysis of factors responsible for the disappearance of native species. Illinois Natural History Survey Biological Notes 76: 1-14.
  • Watters, G.T. 1993. A guide to the freshwater mussels of Ohio. Revised Edition. The Ohio Department of Natural Resources, Columbus. 106 pages.