Plants and Animals

Pyganodon subgibbosa Round lake floater

Key Characteristics

The lake floater is ovate in shape and inflated mussel with a thin shell. Adults are typically less than 3.5 inches in length. They have double-looped beak sculpture and they lack teeth. The shell is light or dark olive-green and the nacre is typically white or bluish white.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G1Q - Critically imperiled. Questionable taxonomy that may reduce conservation priority
State Rank: S1 - Critically imperiled


CountyNumber of OccurrencesYear Last Observed
Muskegon 3 1930
Ottawa 1 1930

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.


The Lake floater occurs in natural river impoundments more than 3 feet deep with mud or mud-sand substrates.

Natural Community Types

  • Inland lake, littoral, midwater

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

Changes to its habitat, such as river impoundment, siltation and other disturbances, including dredging, negatively affect this species. Pollution from point (industrial and residential discharge) and non-point (siltation, herbicide and surface run-off) sources is also a threat to mussels and should be limited and monitored to insure compliance with the Clean Water Act. Control of zebra mussels is critical to preserving native mussels. And as with all mussels, protection of their hosts habitat is also crucial. It is essential to protect not only the habitat of the Lake floater, but also the white sucker, northern hog sucker, shorthead redhorse, rockbass and warmouth, as they serve as hosts for the glochidia. Very little is known about this species, its habitat, or host species.

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


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.
  • Evers, D.C. 1994. Endangered and Threatened Wildlife of Michigan. The University of Michigan Press, Ann Arbor. 412pp.