Pisidium equilaterale
Round peaclam

Key Characteristics

The round peaclam grows to about .2 inches long, with the thick, inflated and semi-glossy shell being of a round to somewhat oval shape, and varying in color from yellow or green to brown. The shell is distinctly striated and the centrally located beak is raised, large and broad.

Status and Rank

  • State Status: SC
  • State Rank: SNR
  • Global Rank: G4G5


No known occurrences in Michigan

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 round peaclam can be found in creeks, rivers and lakes with substrates of fine sand (Herrington 1962).

Specific Habitat Needs

Sandy substrate needed in Headwater Stream (1st-2nd order), Riffle, Headwater Stream (1st-2nd order), Pool, Headwater Stream (1st-2nd order), Run, Mainstem Stream (3rd-4th order), Riffle, Mainstem Stream (3rd-4th order), Pool, Mainstem Stream (3rd-4th 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.


Projects such as dam removals, river impoundments, dredging and construction result in siltification and general habitat disruption, negatively affecting a wide variety of aquatic species, and should include monitoring and mitigation plans in order to limit impacts. As filter feeders, pea clams are vulnerable to heavy metals and chemical pollutants from sources such as agricultural/urban runoff, herbicide/pesticide applications and industrial waste. Improved water quality is correlated with rising populations and greater diversity of pea clams (Diggins and Snyder 2003). The round peaclam and others in this group compete with zebra mussels for food,  sometimes resulting in dramatic population declines (Lozano et al. 2000, Nalepa et al. 1998). Zebra mussel larvae and adults can be kept from invading new areas by careful cleaning of boats, trailers, and fishing/scuba gear before moving between bodies of water.

Survey Methods

Peaclams are best surveyed for by collecting with a grab sampler, such as an Ekman or Peterson grab, or dip net. Collected samples are washed through sieves with a fine mesh (.40 mm openings) in order to retain the smallest individuals. Light-duty forceps can be used to hand-pick peaclams from debris (Mackie 2007).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Aug 17, 2018]


Survey References

Technical References

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