Sphaerium fabale
River fingernail clam

Key Characteristics

The river fingernail clam has a dull yellow to brown, laterally compressed and rounded shell reaching a length of about .5 inches. The shell is finely striated near the low and somewhat pointed beak, becoming coarsely and unevenly striated toward the ventral margin.

Status and Rank

  • State Status: SC
  • State Rank: SNR
  • Global Rank: G5


County NameNumber of OccurrencesYear Last Observed
Distribution map for Sphaerium fabale

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 prefers coarse sand or gravel in both creeks and rivers (Herrington 1962). It has also been found in the Great Lakes (Mackie 2007).

Specific Habitat Needs

needed in Mainstem Stream (3rd-4th order), Riffle, Mainstem Stream (3rd-4th order), Pool, Mainstem Stream (3rd-4th order), Run, Great Lake, Littoral, 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.


Invading zebra mussels can outcompete pea clams for food, and have been linked to drastic declines of this group in the Great Lakes (Lozano et al. 2000, Nalepa et al. 1998). Controlling the spread of zebra mussels by cleaning boat hulls, trailers, and scuba/fishing gear before moving between waterbodies will benefit the river fingernail clam. The pea clam family is especially sensitive to chemical pollutants (Zischke and Arthur 1987), heavy metals and low dissolved oxygen conditions (Kullman et al. 2007). Taking steps to improve water quality should be part of any effort to manage for benthic macroinvertebrates. Monitoring and mitigation for resident aquatic organisms should be put in place before major alterations to habitat  such as river impoundment, dredging, or construction are undertaken.

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 Sep 22, 2018]


Survey References

Technical References

Facebook link