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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: pygmy peaclam

Synonyms and Other Names: Moitessier’s pea/pill clam, pisidiid clam, P. (Neopisidium) moitessierianum

Identification: This triangle- to trapezoid-shaped pea clam displays a relatively rounded, thick, and coarsely striated shell with a height to length ratio of 0.88–0.90. The somewhat flattened beaks barely protrude above the dorsal margin, which exhibits a fold or ridge that is parallel to the growth rings. The 3rd cardinal tooth inside the right valve is curved and thick at both ends, with a bifurcated posterior part. The 2nd cardinal in the left valve is triangular and the 4th cardinal is a thin plate-like structure that is somewhat curved. In live individuals, there is only one siphon (Grigorovich et al. 2000).

Size: around 1.8 to 2.8 mm long (Grigorovich et al. 2000, Holopainen 1979).

Native Range: Pisidium moitessierianum is native to eastern and western European countries as well as Asia in southwestern Siberia and northeastern Kazakhstan (Grigorovich et al. 2000).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Moitessier’s pea clam occurs in mud, silty sand, sand, silty gravel, and amongst macrophytes. It occurs from 0.5–20 m depth in the littoral zone of lakes and in wide slow rivers. It usually favors oligotrophic water with oxygen content over 50% saturation but it can tolerate some anoxic conditions over winter. Pisidium moitessierianum is relatively thermophilic, preferring lower river reaches, and has recently been able to colonize Lake Annecy, France, possibly due to increasingly warm lake water. It can, however, tolerate an annual water temperature range of 1–20ºC. Maximum population densities in the Great Lakes reach 145–178 individuals per m² (Bishop and Hewitt 1976, Grigorovich et al. 2000, Grigorovich et al. 2003a, Holopainen and Hanski 1986, Mouthon 1999,Mouthon and Magny 2004, Smit et al. 1994, Zittler and Kuiper 2002).

Pisidium moitessierianum is ovoviviparous, hermaphroditic, can undergo self-fertilization, and generally carries 1–10 embryos. In Lake Paajarvi, Finland, it becomes sexually mature around 1 year, lays eggs in August to September, broods its offspring, releases them in July around 2 years of age, and then dies (Grigorovich et al. 2000, Holopainen 1979).            

Species in the genus Pisidium are interstitial feeders, creating burrows into which they draw water by using their cilia and foot. They feed on suspended material in the water column and also directly ingest deposits from the substrate in which they live (Lopez and Holopainen 1987).

Means of Introduction: Pisidium moitessierianum was very likely introduced in ships to the Great Lakes sometime in the 1890s, most likely in solid ballast, which was in use at the time (Grigorovich et al. 2000; Grigorovich et al. 2003a; Grigorovich et al. 2003b).

Status: Established where recorded.

Impact of Introduction: The impacts of this species are currently unknown, as no studies have been done to determine how it has affected ecosystems in the invaded range. The absence of data does not equate to lack of effects. It does, however, mean that research is required to evaluate effects before conclusions can be made.

Remarks: Pisidium moitessierianum is considered rare in some parts of its native range (Beran and Horsak 1998, Dyduch and Falniowski 1979, Horsak 2001).

Pisidium moitessierianum is really P. (Neopisidium) moitessierianum, part of the polyphyletic subgenus Neopisidium (Kurniushin and Glaubrecht 2002).

References: (click for full references)

Beran, L., and M. Horsak. 1998. Aquatic molluscs (Gastropoda, Bivalvia) of the Dolonomoravsky uval lowland, Czech Republic. Acta Societatis Zoologicae Bohemicae 62(1):7-23.

Bishop, M.J., and S.J. Hewitt. 1976. Assemblages of Pisidium spp. (Bivalvia: Sphaeriidae) from localities in eastern England. Freshwater Biology 6(2):177-182.

Dyduch, A., and A. Falniowski. 1979. Mollusks of Gardno Lake, Poland and the necessity of their protection. Ochrona Pryzyrody 42:150-182.

Grigorovich, I.A., A.V. Korniushin, and H.J. MacIsaac. 2000. Moitessier’s pea clam Pisidium moitessierianum (Bivalvia, Sphaeriidae): a cryptogenic mollusk in the Great Lakes. Hydrobiologia 435:153-165.

Grigorovich, I.A., A.V. Korniushin, D.K. Gray, I.C. Duggan, R.I. Colautti, and H.J. MacIsaac. 2003a. Lake Superior: an invasion coldspot? Hydrobiologia 499(1-3):191-210.

Grigorovich, I.A., R.I. Colautti, E.L. Mills, K. Holeck, A.G. Ballert, and H.J. MacIsaac. 2003b. Ballast-mediated animal introductions in the Laurentian Great Lakes: retrospective and prospective analysis. Canadian Journal of Fisheries and Aquatic Sciences 60:740-756.

Holopainen, I.J. 1979. Population dynamics and production of Pisidium spp. (Bivalvia, Sphaeriidae) in the oligotrophic and meso humic Lake Paajarvi, southern Finland. Archiv fur Hydrobiologie Supplement 54(4):466-508.

Holopainen, I.J., and I. Hanski. 1986. Life history variation in Pisidium (Bivalvia: Pisidiidae). Holarctic Ecology 9:85-98.

Horsak, M. 2001. Contribution to our knowledge of macroinvertebrate fauna of the Dyje River downstream of the Nove Mlyny Reservoirs (Czech Republic). Scripta Biology (Brno) 27:41-62.

Korniushin, A.V., and M. Glaubrecht. 2002. Phylogenetic analysis based on the morphology of viviparous freshwater clams of the family Sphaeriidae (Mollusca, Bivalvia, Veneroida). Zoologica Scripta 31(5):415-459.

Korniushin, A.V., I.A.Grigorovich, and G.L. Mackie. 2001. Taxonomic revision of Pisidium punctatum Sterki, 1895 (Bivalvia: Sphaeriidae). Malacologia 43(1-2):337-347.

Lopez G.R., and I.J. Holopainen. 1987. Interstitial suspension-feeding by Pisidium spp. (Pisidiidae: Bivalvia): A new guild in the lentic benthos? American Malacological Bulletin 5:21–30.

Mouthon, J. 1999. Longitudinal organisation of the mollusc species in a theoretical French river. Hydrobiologia 390:117-128.

Mouthon, J.  2011.  Response of bivalve populations to drying disturbance and life history traits of two Pisicium species (Bivalvia: Sphaeriidae) in a reservoir of the French Upper Rhone river.  EDP Sciences http://hal.archives-ouvertes.fr/docs/00/62/11/85/PDF/LY2011-PUB00032037.pdf

Mouthon, J., and M. Magny. 2004. Malacological history of Lake Annecy (France): a comparison of Late Holocene (since 4700 BC) and present mollusk assemblages. Archiv für Hydrobiologie 160(4):555-573.

Smit, H., J.A. Van Der Velden, and A. Klinik. 1994. Macrozoobenthic assemblages in littoral sediments in the enclosed Rhine-Meuse Delta. Netherlands Journal of Aquatic Ecology 28(2):199-212.

Trebitz, A.S., C.W. West, J.C. Hoffman, J.R. Kelly, G.S. Peterson, and I.A. Grigorovich. 2010. Status of non-indigenous benthic invertebrates in the Duluth-Superior Harbor and the role of sampling methods in their detection. Journal of Great Lakes Research 36:747-756.

US Army Corp of Engineers (USACE).  2012.  Molluscicides.  Accessed 10/28/13.  http://glmris.anl.gov/documents/docs/anscontrol/Molluscicides.pdf

Zettler, M.L., and J.G.J. Kuiper. 2002. On the distribution and ecology of Pisidium moitessierianum (Paladilhe 1866) with special focus on northeastern Germany (Mollusca: Bivalvia: Sphaeridae). Mitteilungen der Deutschen Malakozoologischen Gesellschaft 67:9-26.

Other Resources:
Great Lakes Water Life

Author: Kipp, R.M., J. Larson, and A. Fusaro

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.