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Dwarf Wedge Mussel in North CarolinaDwarf Wedge Mussel in North Carolina

Alasmidonta heterodon

STATUS: Endangered - Listed March 14, 1990

DESCRIPTION: The dwarf-wedge mussel is relatively small, rarely exceeding 1.5 inches in length.  The shell's outer surface (periostracum) is usually brown or yellowish brown in color, with faint green rays that are most noticeable in young specimens.  Unlike some mussel species, the male and female shells differ slightly, with the female being wider to allow greater space for egg development.  A distinguishing characterictic of this mussel is it's dentition pattern; the right valve possesses two lateral teeth, while the left valve has only one.  This trait is opposite of all other North American species having lateral teeth (Clark 1981).

This mussel is considered to be a long-term brooder, with gravid females reportedly observed in fall months. Like other freshwater mussels, this species' eggs are fertilized in the female as sperm are taken in through their siphons as they respire.  The eggs develop with the female's gills into a larvae (glochidia).  The females later release the glochidia which then attach to the gills or fins of specific host fish species.  Based on anecdotal evidence, such as dates when gravid females are present or absent, it appears that release of glochidia occurs primarily in April in North Carolina (Michaelson and Neves 1995).  Recent research has confirmed at least three potential fish host species for the dwarf-wedge mussel to be the tessellated darter, Johnny darter, and mottled sculpin ( Michaelson 1995).

RANGE AND POPULATION LEVEL: The dwarf-wedge mussel occurs in at least 25 stream reaches along the Atlantic Coast from New Brunswick, Canada, to North Carolina.  Documented populations in North Carolina are located in the following drainages and streams: Neuse River Drainage - Little River (Wake and Johnston County); Swift Creek (Wake and Johnston County); Middle and Buffalo Creek (Johnston County); Turkey Creek (Nash and Wilson County); Stony Creek (Nash); and Moccasin Creek (Nash, Wilson, and Johnston Counties);  Tar River Drainage - Tar River and Shelton Creek (Granville County); Ruin, Little Ruin, and Tabbs Creek (Vance County); Cedar, Crooked, Fox, Shocco, and Little Shocco Creeks (Franklin County); and Shocco Creek (Warren County)

HABITAT: The dwarf wedge mussel inhabits creek and river areas with a slow to moderate current and a sand, gravel, or muddy bottom.

REASONS FOR CURRENT STATUS:  Toxic effects from industrial, domestic and agricultural pollution are the primary threats to this mussel's survival.  Increased acidity, caused by the mobilization of toxic metals by acid rain, is thought to be one of the chief causes of the species' extirpation from the Fort River in Massachusetts. One of the largest remaining populations has declined dramatically in the Ashuelot River, downstream of a golf course. This population probably has been affected by fungicides, herbicides, insecticides, and fertilizers which have been applied to the golf course. Agricultural runoff from adjacent corn fields and pastures also is contributing to this population's decline (Masters 1986). Freshwater mussels, including the dwarf wedge, are sensitive to potassium, zinc, copper, cadmium, and other elements associated with industrial pollution (Havlik and Marking 1987). 

Species Distribution from known occurrences. Species may occur in similar habitats in other counties.

Green counties indicate observed within 20 years. Yellow counties indicate an obscure data reference to the species in the county. Red counties indicate observed more than 20 years. Yellow counties indicate an obscure data reference to the species in the county.ago.

Species distribution of Dwarf Wedge Mussel in NC

Species Location Map based on information provided by the North Carolina Natural Heritage Program.

For additional information regarding this Web page, contact John Fridell, in Asheville, NC, at john_fridell@fws.gov

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