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: No Status/Not Listed
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
Allegan 1 Historical
Alpena 2 1932
Arenac 1 Historical
Barry 4 2018
Berrien 2 1934
Branch 1 2000
Calhoun 12 2018
Cass 2 2009
Clinton 7 2019
Eaton 8 2018
Genesee 3 2019
Gladwin 1 1926
Gratiot 5 2015
Hillsdale 20 2018
Huron 2 1942
Ingham 10 2015
Ionia 9 2018
Iosco 1 Historical
Isabella 4 2018
Jackson 20 2018
Kalamazoo 6 2018
Kent 9 2017
Lapeer 2 1926
Lenawee 15 2004
Livingston 5 2018
Macomb 17 2018
Mecosta 2 2002
Menominee 1 1927
Midland 4 2015
Missaukee 1 2002
Monroe 15 2017
Montcalm 8 2015
Muskegon 1 1936
Oakland 13 2016
Ogemaw 1 1926
Ottawa 1 1929
Roscommon 4 2002
Saginaw 4 2011
Sanilac 5 2009
Shiawassee 5 2001
St. Clair 21 2016
St. Joseph 10 2016
Tuscola 6 2004
Van Buren 4 2009
Washtenaw 11 2018
Wayne 6 2007

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, benthic; Inland lake, littoral, benthic; Inland lake, pelagic, benthic; 

Sand and gravel substrates; moderate currents needed in: Headwater stream (1st-2nd order), riffle; Headwater stream (1st-2nd order), pool; Headwater stream (1st-2nd order), run; Mainstem stream (3rd-4th order), pool; Mainstem stream (3rd-4th order), run; Mainstem 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.

Survey Methods

Glass-bottom bucket less than waist deep water

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

SCUBA searches

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

Snorkeling searches

Survey Period: From first week of June 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.