Physella parkeri
Broadshoulder physa

Key Characteristics

The subglobose shell of the broadshoulder physa is moderately glossy, cream to dark brown in color, and measuring up to 1 inch in length. The 5-6 finely striated whorls meet at shallow sutures and terminate at a pointed spire, the large body whorl being strongly shouldered. The aperature is teardrop-shaped with a sharp outer lip. The snail body is bluish-gray with small flecks of white.

Status and Rank

  • State Status: T
  • State Rank: SNR
  • Global Rank: G2Q


County NameNumber of OccurrencesYear Last Observed
Grand Traverse1
Distribution map for Physella parkeri

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.


The broadshoulder physa occurs in medium to large lakes of clean and cold water and substrates of sand or marl, where it is often found clinging to stones (Burch and Jung 1992).

Specific Habitat Needs

Oligotrophic needed in Inland Lake, Littoral, Benthic, Inland 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.


74% of North American freshwater snail species are either extinct, endangered, threatened or vulnerable (Johnson et al 2008). Major threats include habitat loss, sedimentation, and population fragmentation from dredging, channelization, impoundments and other construction projects in or around waterways. Lakes and rivers with increased pH levels from acid rain are incapable of supporting healthy snail populations (Okland 1992, Shaw and Mackie 2011). Additionally, contaminated water from agricultural and urban runoff, industrial waste, pesticide application and other forms of point and non-point source pollution can be fatal to adult snails and prevent reproduction (Besser et al. 2007, Johnson 2009). Efforts to protect this imperiled group should therefore center around the preservation and restoration of aquatic habitats as well as pollution reduction.

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 Aug 17, 2018]


Survey References

Technical References

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