Plants and Animals

Pleurobema sintoxia Round pigtoe

Key Characteristics

The round pigtoe is a relatively large (to 4 inches) mussel with a moderately thick, round shell and a rounded anterior end and a rounded or bluntly pointed posterior end. The beak is low and only slightly elevated above the hinge line. This species has a shallow beak cavity and beak sculpture consisting of 2 to 3 elevated ridges. The lateral teeth are straight and cardinal teeth are well developed with 2 in the left valve and 1 in the right valve. The shell is smooth and brown with faint green rays visible near the beak. The nacre is variable in color, from white to pink to rose colored.

Status and Rank

US Status:
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G4G5 - Rank is uncertain, ranging from apparently secure to secure
State Rank: S3 - Vulnerable

Occurrences

CountyNumber of OccurrencesYear Last Observed
Allegan12000
Barry12010
Berrien82004
Branch12000
Calhoun52012
Cass22009
Clare11934
Clinton42010
Dickinson32009
Eaton32002
Genesee12001
Gratiot32010
Hillsdale132005
Huron1
Ingham52001
Ionia122016
Jackson82010
Kalamazoo32000
Kent132017
Lapeer11926
Lenawee102016
Livingston12001
Macomb102007
Manistee11918
Mecosta21934
Menominee42009
Midland12011
Missaukee12002
Monroe112000
Newaygo31934
Oakland112016
Osceola22002
Ottawa21960
Saginaw32011
Sanilac22010
Shiawassee42001
St. Clair82016
St. Joseph92016
Tuscola52004
Van Buren32009
Washtenaw62010
Wayne72012

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 round pigtoe occurs in mud, sand, or gravel substrates of medium to large rivers.

Specific Habitat Needs

Sandy or gravel substrates needed in: Mainstem Stream (3rd-4th order), RunMainstem Stream (3rd-4th order), RiffleRiver (5th-6th order), RunRiver (5th-6th order), Riffle.

Natural Community Types

  • Mainstem stream (3rd-4th order), run
  • Mainstem stream (3rd-4th order), riffle
  • River (5th-6th order), run
  • River (5th-6th 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 round pigtoe 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

  • Clarke, A.H. 1981. The Freshwater Molluscs of Canada. National Museum of Natural Science, National Museums of Canada, Ottawa. 446pp.
  • Cummings, K.S. and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5, Champaign. 194pp.
  • Smith, P.W. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey, Carbondale. Bulletin No. 28. 298 pp.