Brook floater

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Brook floater
Alasmidonta varicosa - Springfield Science Museum - Springfield, MA - DSC03461.JPG
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Unionoida
Family: Unionidae
Genus: Alasmidonta
Species: A. varicosa
Binomial name
Alasmidonta varicosa
(Lamarck, 1819)

Alismodonta varicosa (Lamarck, 1819)

The brook floater (also known as swollen wedgmussel),[1] Alasmidonta varicosa, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. It measures 25.1 mm to 80.2 mm in length[2] although other research also suggests it rarely exceeds three inches (75 mm).[1]


This species is found in Canada (New Brunswick and Nova Scotia)[3] and northeastern United States (Connecticut, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Pennsylvania, South Carolina, Vermont, Virginia and West Virginia);[4] It was formerly found in Rhode Island and four watersheds in Massachusetts.[1] 1897 Research by Arnold Edward Ortmann showed it to be common in the Delaware and Susquehanna Rivers.[5]

Habitat and behavior[edit]

This mussel lives in high relief streams, under boulders and in sand. Research has shown that it is highly sensitive to increased thermal temperature.[6] It associates with longnose and eastern blacknose dace, golden shiner, pumpkinseed, slimy sculpin and yellow perch.[7]

Survival threats and conservation[edit]

The brook floater is sensitive to habitat loss for development, dams and road crossings, pollution, summer droughts, trampling, sedimentation, flow alteration, and low oxygen conditions. Hybridization with elktoe (Alasmidonta marginata), a longtime ally, has also shown to be a threat.[8] Research has also shown the population is highly fragmented, low in density, prone to mortality due to old age and there are also low chances of longevity and viable reproduction.[1] Trematoda rhopalocercous cercaria is a parasite of the brook floater.[9] Current research shows population that were largely and widespread known declined by 50% t0 95% to almost extinct.[10]

While the IUCN lists it as Data Deficient, the states of New Jersey, Virginia, Massachusetts and New Hampshire[1] all list it as Endangered,[11] Threatened in Vermont, Maine and New York,[12] Rare/Endangered in Connecticut,[7] and "Species of Special Concern" by the federal government.[13]


  1. ^ a b c d e Nedeau, Ethan (2007). "Brook Floater" (PDF). Retrieved June 23, 2015. 
  2. ^ Janet L. Clayton, Craig W. Stihler and Jack L. Wallace (2001). "STATUS OF AND POTENTIAL IMPACTS TO THE FRESHWATER BIVALVES (UNIONIDAE) IN PATTERSON CREEK, WEST VIRGINIA". Northeastern Naturalist. 8 (2): 179. doi:10.1656/1092-6194(2001)008[0179:SOAPIT]2.0.CO;2. Retrieved June 23, 2015. 
  3. ^ Caroline Caissie, Dominique Audet, Freshwater Mussel Inventory in the Shediac and Scoudouc Rivers, New Brunswick Wildlife Trust Fund, 2006, p. 12. Accessed August 21, 2014
  4. ^ "Brook floater (Alasmidonta varicosa)". Retrieved June 23, 2015. 
  5. ^ Arnold Edward Ortmann (1897). Collected papers, Volume 1. self-published. Retrieved June 23, 2015. 
  6. ^ "Thermal History Impacts Thermal Tolerance of Freshwater Mussels". Retrieved June 23, 2015. 
  7. ^ a b Hammerson, Geoffrey A. (2004). Connecticut Wildlife: Biodiversity, Natural History, and Conservation. University Press of New England. p. 205. ISBN 1584653698. Retrieved June 23, 2015. 
  8. ^ Strayer, David L.; Fetterman, Andrew R. (1999). "Changes in the Distribution of Freshwater Mussels (Unionidae) in the Upper Susquehanna River Basin, 1955–1965 to 1996–1997". The American Midland Naturalist. 142 (2): 328. doi:10.1674/0003-0031(1999)142[0328:CITDOF]2.0.CO;2. Retrieved June 23, 2015. 
  9. ^ "Cercaria tiogae Fischthal, 1953, a Rhopalocercous Form from the Clam, Alasmidonta varicosa (Lamarck)". American Microscopical Society. 1954. JSTOR 3223759. 
  10. ^ "The conservation status of the brook floater mussel, Alasmidonta varicosa, in the Northeastern United States: trends in distribution, occurrence, and condition of populations". Retrieved June 23, 2015. 
  11. ^ Thomas F. Nalepa, Don W. Schloesser (2013). Quagga and Zebra Mussels: Biology, Impacts, and Control, Second Edition. CRC Press. p. 206. ISBN 1439854378. Retrieved June 23, 2015. 
  12. ^ McBroom, Matthew (2013). The Effects of Induced Hydraulic Fracturing on the Environment: Commercial Demands vs. Water, Wildlife, and Human Ecosystems. CRC Press. p. 285. ISBN 1926895835. Retrieved June 23, 2015. 
  13. ^ Bruce E. Beans, Larry Niles (2003). Endangered and Threatened Wildlife of New Jersey. Rutgers University Press. p. 257. ISBN 0813532094. Retrieved June 23, 2015.