Plants and Animals

Utterbackia imbecillis Paper pondshell

Key Characteristics

Paper pondshell is a medium-sized (to about 4.5 inches), elongate, inflated, and very thin-shelled mussel. Other key features include its general oval shape, wide and flattened beak, and two posterior ridges often descending into a low dorsal wing. The shell varies in color from yellow or tan to light green, with dim green rays sometimes visible. Nacre is iridescent silvery-white.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G5 - Secure
State Rank: S2S3 - Rank is uncertain, ranging from imperiled to vulnerable


CountyNumber of OccurrencesYear Last Observed
Allegan 8 2019
Barry 2 2018
Bay 1 2019
Berrien 3 2018
Calhoun 2 2019
Cass 1 1918
Cheboygan 1 2015
Clinton 7 2019
Eaton 1 Historical
Grand Traverse 1 1949
Gratiot 1 2020
Hillsdale 1 1949
Ingham 1 2014
Ionia 9 2019
Jackson 2
Kalamazoo 5 2019
Kent 3 2016
Macomb 1 2017
Mason 1 Historical
Monroe 6 2017
Muskegon 1 2004
Oakland 5 2011
Ottawa 1 Historical
Saginaw 4 2019
Sanilac 1 2005
St. Clair 2 2001
St. Joseph 5 2019
Van Buren 1 2023
Washtenaw 6 1946
Wayne 5 2011

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.


Paper pondshell is most often observed in lakes, ponds and impoundments with soft mud or sand substrates (Watters et al.)

Natural Community Types

  • Great lake, littoral, benthic
  • Great lake, pelagic, benthic
  • 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

Approximately 70% of North American unionids are imperiled. Threats include alteration of physical habitat, host fish population declines, invasive species introduction and compromised water quality (Bringolf et al. 2007). As with all species of this group, paper pondshell has been found to be highly vulnerable to chemical pollutants (Conners and Black 2004) and heavy metals (Pip 1995) found in many herbicides and pesticides, and in other forms of point and non-point source pollution. Sedimentation of waterways causes harm to a wide variety of freshwater organisms. Management of all native mussels must include maintaining healthy habitat structure and high water quality standards. Zebra mussels must be prevented from spreading to new waterways through the careful cleaning of fishing gear, boats and trailers, and scuba equipment in order to protect paper pondshell populations from infestation.

Active Period

Gravid from first week of July to fourth week of June

Survey Methods

Visual and tactile search using scuba or glass-bottom buckets. Tactile search (by hand) is especially important where water turbidity and pebbles/rocks make visual detection difficult. After identification, live mussels should be planted back into the substrate anterior end down. Surveys should not take place after heavy rains or during periods of high water as these conditions can make detection much more difficult. Methods of documenting survey effort include: searching a large measured area, e.g. 128m2; taking multiple quadrat samples; and recording search time (person hours). For all methods, at least some excavation of substrate (by hand, 5-10cm down) should be done to detect buried mussels. Searching a large measured area or timed searches are generally better for detecting rare species and generating a species list than quadrat sampling.  These two methods allow more types of microhabitats and a larger area to be covered. Quadrat sampling is better suited for documenting changes in density and other statistical analyses at the site level (Strayer and Smith 2003).

Glass-bottom bucket less than waist deep water

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

Time of Day: Daytime
Water Level: Low Water Levels
Water Turbidity: Low Turbidity

SCUBA greater than waist deep water

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

Time of Day: Daytime


Survey References

  • Strayer, D.L. and D.R. Smith. 2003. A Guide to Sampling Freshwater Mussel Populations. American Fisheries Society Monograph 8, Bethesda. 103pp.

Technical References

  • Bogan, A.E. 1993. Freshwater Bivalve Extinctions (Mollusca: Unionida): A Search for Causes.
  • Box, J.B. and J. Mossa. 1999. Sediment, land use, and freshwater mussels: prospects and problems. Journal of the North American Benthological Society 18:99-117.
  • Bringolf, R.B., W.G. Cope, C.B. Eads, P.R. Lazaro, M.C. Barnhart, and D. Shea. 2007. Acute and chronic toxicity of technical-grade pesticides to glochidia and juveniles of freshwater mussels (Unionidae). Environmental Toxicology and Chemistry 26(10):2086-2093.
  • Conners, D.E., and M.C. Black. 2004. Evaluation of lethality and genotoxicity in the freshwater mussel Utterbackia imbecillis (Bivalvia: Unionidae) exposed singly and in combination to chemicals used in lawn care.
  • Levengood, J.M., D.J. Soucek, J. Esarey, R.J. Hudson, W. Wimer, and R.S. Halbrook. 2004. Contaminants in Mussels from the Mississippi and Illinois Rivers Confluence Area. Final Report to the National GReat Rivers Research and Education Center. 35pp.
  • Pip, E. 1995. Cadmium, lead and copper in freshwater mussels from the Assiniboine River, Manitoba, Canada. Journal of Molluscan Studies 61:295-302.
  • Scholesser, Don W., Thomas F. Nalepa, Gerald L. Mackie. 1996. Zebra Mussel Infestation of Unionid Bivalves (Unionidae) in North America. American Zoology 36:300-10.