Truncilla donaciformis

Key Characteristics

The small (to 3 inches), thick-shelled fawnsfoot is characterized by a low and anteriorly off-centered beak, a rounded anterior end and pointed posterior. The shell color is yellow, grayish-tan or green, and marked with widely varying patterns such as solid, broken or smudged green to brown rays, zigzags, or a combination of these.

Status and Rank

  • State Status: T
  • State Rank: S1
  • Global Rank: G5


County NameNumber of OccurrencesYear Last Observed
Distribution map for Truncilla donaciformis

Updated 5/15/2018. 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.


Preferring firm gravel or sand substrates, the fawnsfoot occurs primarily in small to large rivers and lakes (Watters et al. 2009).

Natural Community Types


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.


Maintaining healthy populations of host fish species, and open water conditions to facilitate their movement, will benefit glochidia. As all unionid species are vulnerable to pollutants and heavy metals, reducing point and non-point source water pollution such as pesticide/herbicide applications, agricultural and urban runoff, industrial waste, and mine drainage is a priority (Bringolf et al. 2007, Grabarkiewicz and Davis 2008). Efforts to control the spread of zebra mussels, such as cleaning boat hulls, trailers, and scuba and fishing gear before traveling between bodies of water, are necessary to the welfare of the fawnsfoot. Habitat alteration through river impoundment, bridge construction, dam removal and dredging can isolate host fish populations or increase siltation, causing the extirpation of native mussel communities (Oesch 1995, Box and Mossa 1999). Monitoring and mitigation measures should be planned for prior to such activities taking place.

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).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Aug 17, 2018]


Technical References

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