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

  • State Status: SC
  • State Rank: SNR
  • Global Rank: G2G3


County NameNumber of OccurrencesYear Last Observed
Distribution map for Valvata perdepressa

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.


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 needed in Mainstem Stream (3rd-4th order), Riffle, Mainstem Stream (3rd-4th order), Pool, Mainstem Stream (3rd-4th order), Run, River (5th-6th order), Riffle, River (5th-6th order), Pool, River (5th-6th order), Run, Inland Lake, Littoral, Benthic, Inland Lake, Pelagic, Benthic, Great Lake, Littoral, Benthic, Great Lake, Pelagic, Benthic

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.


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).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at [Accessed Sep 22, 2018]


Survey References

Technical References

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