Plants and Animals

Pisidium cruciatum Ornamanted peaclam

Key Characteristics

The ornamanted peaclam is less than .1 inch long, round to triangular in shape and of a pale yellowish color. The shell is high as it is long,  thick, coarsely striated and dull, with a prominent, ridged beak and long, steeply curving hinge.

Status and Rank

US Status:
State Status: SC - Special Concern (rare or uncertain; not legally protected)
Global Rank: G4? - Apparently secure (inexact)
State Rank: SNR - Not ranked

Occurrences

CountyNumber of OccurrencesYear Last Observed
Ottawa31959
Washtenaw11941

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.

Habitat

The ornamanted peaclam occurs in lakes, rivers and streams with soft, muddy substrates, often among aquatic plants (Herrington 1962).

Specific Habitat Needs

needed in: Great Lake, Littoral, BenthicGreat Lake, Pelagic, BenthicInland Lake, Littoral, BenthicInland Lake, Pelagic, BenthicMainstem Stream (3rd-4th order), PoolMainstem Stream (3rd-4th order), RunMainstem Stream (3rd-4th order), RiffleRiver (5th-6th order), PoolRiver (5th-6th order), RunRiver (5th-6th order), Riffle.

Natural Community Types

  • Great lake, littoral, benthic
  • Great lake, pelagic, benthic
  • Headwater stream (1st-2nd order), riffle
  • Headwater stream (1st-2nd order), pool
  • Headwater stream (1st-2nd order), run
  • 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

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. Siltification and general habitat disruption resulting from dam removal projects, impoundments, dredging and construction can negatively affect a wide variety of aquatic species and should plan ahead for monitoring and mitigation in order to limit impacts. The ornamanted pea clam and others in this group compete with zebra mussels for food, sometimes resulting in dramatic population declines where zebra mussels are abundant (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.

Active Period

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).

d-frame net, dip net

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

Time of Day: Daytime

References

Survey References

  • Mackie, G.L. 2007. Biology of Freshwater Corbiculid and Sphaeriid Clams of North America. Ohio Biological Survey Bulletin New Series. Volume XV, Number 3. ix + 436 pp.

Technical References

  • Cummings, K.S. and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey Manual 5, Champaign. 194pp.
  • Herrington, H.B. 1962. A revision of the Sphaeriidae (Mollusca: Pelecypoda) of the North American Great Lakes. American Midland Naturalist 67(1):194-198.
  • Kullman, M.A., C.L. Podemski, and K.A. Kidd. 2007. A sediment bioassay to assess the effects of aquaculture waste on growth, reproduction, and survival of Sphaerium simile (Say) (Bivalvia: Sphaeriidae). Auquaculture 266:144-152.
  • Lozano, S.J., J.V. Scharold, and T.F. Nalepa. 2001. Recent declines in benthic macroinvertebrate densities in Lake Ontario. Canadian Journal of Fisheries and Aquatic Sciences 58(3):518-29.
  • Mackie, G.L. 2007. Biology of Freshwater Corbiculid and Sphaeriid Clams of North America. Ohio Biological Survey Bulletin New Series. Volume XV, Number 3. ix + 436 pp.
  • Nalepa, T.F., D.J. Hartson, D.L. Fanslow, G.A. Lang, S.J. Lozano. 1998. Declines in benthic macroinvertebrate populations in southern Lake Michigan, 1980-1993. Canadian Journal of Fisheries and Aquatic Sciences 55:2402-13.
  • Zischke, J.A., and J.W. Arthur. 1987. Effects of elevated ammonia levels on the fingernail clam, Musculium transversum, in outdoor experimental streams. Archives of Environmental Contamination and Toxicology 16:225-31.