Plants and Animals

Toxolasma parvum Lilliput

Key Characteristics

The small (to 2 inches), inflated and oblong shell of the lilliput features a straight to moderately curved ventral margin, and a beak sculpture made up of 4-6 obliquely aligned concentric ridges. Shell color ranges from yellowish-tan or green to brownish grey. The nacre is primarily white, with light irridescent blues to purples sometimes seen.

Status and Rank

US Status: No Status/Not Listed
State Status: E - Endangered (legally protected)
Global Rank: G5 - Secure
State Rank: S1 - Critically imperiled


CountyNumber of OccurrencesYear Last Observed
Allegan 1 2019
Benzie 1 1936
Berrien 2 2018
Clinton 2 2019
Hillsdale 1 2014
Ingham 1 1960
Ionia 6 2020
Kent 5 2020
Lenawee 1 1936
Macomb 1 1933
Monroe 9 2017
Oakland 2 2020
Ottawa 1 2020
Saginaw 2 2010
St. Clair 1 1965
St. Joseph 1 2019
Wayne 10 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.


The lilliput most commonly occurs in creeks with mud or clay substrates, but can also be found in rivers, lakes, and impoundments (Watters et al. 2009).

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
  • River (5th-6th order), pool
  • 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

Major alterations to aquatic habitat through dredging, siltation, construction and dam removal negatively affect this species, and mussels in general. Where these activities occur, monitoring to assess impacts, and mitigation measures such as relocation of potentially affected specimens, should be carried out. Healthy populations of host fish are necessary to the maturation and dispersal of glochidia, and should also be managed for. As the unionid mussel family has shown high rates of absorption and mortality in the presence of pollutants such as ammonia (Wang et al. 2007), chlorine (Valenti et al. 2006), and heavy metals (March et al. 2007, Valenti et al. 2005, Wang et al. 2007), high water quality standards must be met. In areas where lilliput and other native mussels occur, treatment with herbicides and pesticides containing copper should be avoided. Zebra mussels attach to native mussels and restrict movement and feeding, eventually causing mortality. The extirpation of entire unionid communities has sometimes resulted (Schloesser et al. 1996). Preventing the spread of zebra mussel adults and larvae by cleaning boat hulls, trailers, scuba and fishing gear, will aid in maintaining lilliput populations.

Active Period

Gravid from first week of July to fourth week of June

Survey Methods

Due to the small size of lilliput, extra effort should be made to ensure they are being detected. 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

  • Cosgrove, P.J., and L.C. Hastie. 2001. Conservation of threatened freshwater pearl mussel populations: river management, mussel translocation and conflict resolution. Biological Conservation 99:183-190.
  • March, Ferrella A., F. James Dwyer, Tom Augspurger, Christopher G. Ingersoll, Ning Wang, and Christopher A. Mebane. 2007. An evaluation, of freshwater mussel toxicity data in the derivation of water quality guidance and standards for copper. Environmental Toxicology and Chemistry 23(10): 2006-74.
  • Oesch, R.D. 1984. Missouri Naiades: a Guide to the Mussels of Missouri. Conservation Commision of the State of Missouri, Jefferson City. 270pp.
  • 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.
  • Sethi, Suresh A., Andrew R. Selle, Martin W. Doyle, Emily H. Stanley, and Helen E. Kitchel. 2004. Response of unionid mussels to dam removal in Koshkonong Creek, Wisconsin (USA). Hydrobiologia 525:157-165.
  • Valenti, T.W., D.S. Cherry, R.J. Currie, R.J. Neeves, J.W. Jones, R. Mair, and C.M. Kane. 2006. Chlorine toxicity to early like stages of freshwater mussels (Bivalvia: Unionidae). Environmental Toxicology and Chemistry 25(9):2512-18.
  • Valenti, T.W., D.S. Cherry, R.J. Neves, and J. Schmerfeld. 2005. Acute and chronic toxicity of mercury to early life stages of the rainbow mussel, Villosa iris (Bivalvia: Unionidae). Environmental Toxicology and Chemistry 24(5):1242-6.
  • Wang, N., C.G. Ingersoll, I.E. Greer, D.K. Hardesty, C.D. Ivey, J.L. Kunz, W.G. Brumbaugh, F.J. Dwyer, A.D. Robers, T. Augspurger, C.M. Cane, R.J. Neves, and M.C. Barnhart. 2007. Assessing contaminant sensitivity of early life stages of freshwater mussels (Unionidae): Chronic toxicity testing of juvenile mussels with copper and ammonia. Environmental Toxicology and Chemistry. 35pp.
  • Watters, G. Thomas, Michael A. Hoggarth, and David H. Stansbery. 2009. The Freshwater Mussels of Ohio. The Ohio State University Press, Columbus. 421 pp.