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.

Lasmigona subviridis
Lasmigona subviridis
(green floater)
Native Transplant

Copyright Info
Lasmigona subviridis Conrad, 1835

Common name: green floater

Taxonomy: available through www.itis.govITIS logo


This freshwater bivalve exhibits a somewhat compressed to slightly inflated thin shell that is subrhomboid to subovate in shape. The periostracum is yellow, tan, dark green, or brown with dark green rays, and the nacre is white or light blue and sometimes pink near the beaks. The height to width ratio is greater than 0.48 and the beaks are low compared to the line of the hinge. There are two true lamellate pseudocardinal teeth and one relatively small interdental tooth in the left valve, as well as one long and thin lateral tooth in the right valve (Burch 1975, Peckarsky et al. 1993, Bogan 2002). Lasmigona subviridis can grow to 60–65 mm in length (Peckarsky et al. 1993, Bogan 2002).

Size: up to 65 mm

Native Range: Lasmigona subviridis was historically found throughout the Atlantic slope drainages in the Hudson, Susquehanna, Potomac, upper Savannah, Kanawha-New, and Cape Fear rivers. However, its range has retracted and it now occurs as disjunct populations in headwaters of coastal and inland rivers and streams of these drainages (Burch 1975, Mills et al. 1993, King et al. 1999, Clayton et al. 2001).

Native range data for this species provided in part by NatureServe NS logo
Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Lasmigona subviridis are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
NY195919802Oneida; Seneca

Table last updated 4/19/2024

† Populations may not be currently present.

Ecology: Lasmigona subviridis usually occurs in streams, small rivers, and canals of low to medium gradient with slow pools and eddies, fine gravel and sand bottom, and mid-range calcium concentrations. It cannot tolerate either flooding or droughts. In general, freshwater mussels (unionids) are filter feeders and remove particulate organic matter from the water column (Bogan 2002, Harman 1970, Howard and Cuffey 2006, Strayer 1993).

Unionids typically require fish hosts for glochidial (larval) dispersal and transformation to the juvenile stage. The host species for L. subviridis is unknown, although evidence indicates that it may: a) rely on different fish species depending on different localities; or b) may not require a host fish, which is rare in North American unionids. Lasmigona subviridis is usually a simultaneous hermaphrodite and is bradytictic, or a long term brooder (Bogan 2002, King et al. 1999, Van der Schalie 1966).

Means of Introduction: Lasmigona subviridis very likely dispersed into the Lake Ontario drainage from its native range or migrated via the Erie Canal but it could have been intentionally introduced.

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: Found in small to medium-sized streams with sand and gravel bottoms and low current.  Spawns in August and releases glochidia the following June. Lasmigona subviridis is considered a species of concern, rare, imperiled, or critically imperiled in different parts of the United States. Populations in the Susquehanna and Potomac Rivers are genetically distinct from populations found further south due to reproductive isolation, and thus the two groups should be managed as two separate conservation units (Bogan 2002, Clayton et al. 2001, King et al. 1999, New York State Department of Environmental Conservation 2005).

References: (click for full references)

Bogan, A.E. 2002. Workbook and Key to the Freshwater Bivalves of North Carolina. North Carolina Freshwater Mussel Conservation Partnership, Raleigh, North Carolina. 101 pp., 10 color plates.

Burch, J.B. 1975. Freshwater Unionacean Clams (Mollusca: Pelecypoda) of North America. Malacological Publications, Hamburg, Michigan. 204 pp.

Clark, A.H., and C.O. Berg. 1959. Freshwater mussels of central New York. Cornell University Agricultural Experiment Station Memoir 367:1-79.

Clayton, J.L., C.W. Stihler, and J.L. Wallace. 2001. Status of and potential impacts to the freshwater bivalves (Unionidae) in Patterson Creek, West Virginia. Northeastern Naturalist 8(2):179-188.

Harman, W.N. 1970. New distribution records and ecological notes on central New York Unionacea. American Midland Naturalist 84(1):46-58.

Howard, J.K., and K.M. Cuffey. 2006. The functional role of native freshwater mussels in the fluvial benthic environment. Freshwater Biology 51:460-474.

Johnson, R.I. 1980. Zoogeography of North American Unionaceae (Mollusca: Bivalvia) north of the maximum Pleistocene glaciation. Bulletin of the Museum of Comparative Zoology (Harvard University) 149:77-189.

King, T.L., M.S. Eackles, B. Gjetvaj, and W.R. Hoeh. 1999. Intraspecific phylogeography of Lasmigona subviridis (Bivalvia: Unionidae): conservation implications of range discontinuity. Molecular Ecology 8(suppl. 1):65-78.

Mills, E.L., J.H. Leach, J.T. Carlton, and C.L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.

New York State Department of Environmental Conservation. 2005. New York State Comprehensive Wildlife Conservation Strategy. Appendix A8: Comprehensive Wildlife Conservation Strategy Species Group Reports for Mollusks. 53 pp.

Peckarsky, B.L., P.R. Fraissinet, M.A. Penton, and D.J. Conklin Jr. 1993. Freshwater Macroinvertebrates of Northeastern North America. Cornell University Press, Ithaca, New York State. 442 pp.

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

van der Schalie, H. 1966. Hermaphroditism among North American freshwater mussels. Malacologia 5(1):77-78.

Strayer, D.L. 1993. Macrohabitats of freshwater mussels (Bivalvia: Unionacea) in streams of the northern Atlantic Slope. Journal of the North American Benthological Society 12(3):236-246.

Other Resources:
Great Lakes Water Life

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

Revision Date: 11/6/2019

Citation Information:
Kipp, R.M., A.J. Benson, J. Larson, and A. Fusaro, 2024, Lasmigona subviridis Conrad, 1835: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=146, Revision Date: 11/6/2019, Access Date: 4/20/2024

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.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [4/20/2024].

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