Plants and Animals

Valvata perdepressa Purplecap valvata

Key Characteristics

The purplecap valvata is an aquatic snail with a small (to .2 inches diameter), thin, disk-shaped shell featuring a wide, circular aperature and up to 4 finely striated whorls. The spire is either level with the whorls or slightly sunken. Snails in this family feature a single feathery gill on the left side of the body and a tentacle on the right.

Status and Rank

US Status: No Status/Not Listed
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G2G3 - Rank is uncertain, ranging from imperiled to vulnerable
State Rank: SNR - Not ranked


CountyNumber of OccurrencesYear Last Observed
Berrien 2 1939
Huron 5 1942
Kent 1 1914

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.


This species is found in cold, clean rivers and lakes, including the Great Lakes to a depth of about 55 feet (Mackie 1980, Minton 2004).

Specific Habitat Needs

Clear water needed in: 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.

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

Freshwater snail shell production requires calcium-rich habitats. Acidification of waterbodies can result in thin shells, increasing vulnerability to predation (Brown 1991), and waters with a pH below 5 have been found incapable of supporting snail life at all (Okland 1992).  Acid rain reduction will therefore benefit this group. River impoundments, dredging and channelization impact snails through habitat alteration, fragmentation of existing populations, and increased sedimentation which can physically bury individuals and eliminate food sources (Johnson 2009). Heavy metal and chemical pollution from agricultural and urban runoff, industrial waste, and pesticide treatment is lethal to many snail species, even at low levels of exposure (Kosanke et al 2004, Besser et al. 2007, Johnson 2009). Improving and protecting the quality of aquatic environments may be the most important step in freshwater snail management.

Active Period

Active from first week of June to first week of October

Survey Methods

There are several effective methods for conducting aquatic snail surveys. Areas of coarse cobble substrate are best surveyed with a glass-bottomed bucket or scuba search, and hand collecting. Stones and sunken pieces of wood can be picked up, searched, and replaced. Dip net suveys are employed at soft substrate locations. Aquatic vegetation held over a bucket and vigorously shaken to remove individual snails is another technique (Groves 2007).

D-frame net, dip net

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

Time of Day: Daytime

Glass-bottom bucket less than waist deep water

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

Time of Day: Daytime

SCUBA greater than waist deep water

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

Time of Day: Daytime

Shaking vegetation survey

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

Time of Day: Daytime


Survey References

  • Groves, K. 2007. Aquatic Spring Snail Survey and Habitat Analysis. USDA Forest Service.

Technical References

  • Besser, J.M., D.L. Hardesty, I.E. Greer, C.A. Mebane, D.R. Mount, and C.G. Ingersoll. 2007. Sensitivity of freshwater snails to contaminants: chronic toxicity tests with endangered species and surrogates. U.S. Geological Survey.
  • Brown, K.M. 1991. Mollusca: Gastropoda. Pp 285-314. In: Thorp, J.H. and A.P. Covich (eds.). 1991. Ecology and Classification of North Amercian Freshwater Invertebrates. Academic Press, Inc., San Diego, CA.
  • Burch, J.B. 1982. North American Freshwater Snails. Walkerana 1(4).
  • Burch, J.B. 1988. North American Freshwater Snails. Walkerana 2(6)
  • Johnson, P.D. 2009. Sustaining America's Aquatic Biodiversity: Freshwater Snail Biodiversity and Conservation. Virginia Cooperative Extension Publication 420-530.
  • Kosanke, G.J., W.W. Schwippert, and T.W. Beneke. 1988. The impairment of mobility and development in freshwater snails (Physa fontinalis and Lymnaea stagnalis) caused by herbicides. Comparative Biochemistry and Physiology Part C: Comparative Pharmacology 90(2):373-79.
  • Mackie, G.L., D.S. White, and T.W. Zbeda. 1980. A Guide to Freshwater Mollusks of the Laurentian Great Lakes with Special Emphasis on the Genus Pisidium. EPA Report 600/3-80-068. Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Duluth. 144 pp.
  • Minton, R. 2004. Valvatidae. Pp 30-31. In: Perez, K.E., S.A. Clark and C. Lydeard (eds.). 2004. FMCS Showing Your Shells: A Primer to Freshwater Gastropod Identification. University of Alabama, Tuscaloosa, AL.
  • Okland, J. 1992. Effects of acidic water on freshwater snails: results from a study of 1000 lakes throughout Norway. Environmental Pollution 78(1-3):127-30.