Dwarf Wedgemussel (I. Lea, 1830)

Scientific Name: Alasmidonta heterodon

Classification:  Federal and State Endangered

Photo Credit: NCWRC
   

Interior

 

Exterior 

NOTE: Hover over the bold words for definitions or see the Glossary.

In 1830, Isaac Lea (see Conrad illustration) described the dwarf wedgemussel. The name is appropriate as shells rarely exceed 45 mm in length. Clean young shells are usually greenish-brown with green rays. As the animal ages, the shell color becomes obscured by diatoms or mineral deposits and appears black or brown. The shell is thin but does thicken somewhat with age, especially toward the anterior end. The anterior end is rounded while the posterior end is angular forming a point near the posterio-ventral margin. The ventral margin is only slightly curved. The nacre is bluish-white, appearing whiter in the thickened anterior end. The most distinctive shell character of the dwarf wedgemussel is the arrangement of the lateral teeth. There are two lateral teeth in the right valve and one in the left valve. The typical arrangement for most freshwater mussel species consists of two lateral teeth in the left valve and one in the right valve. The incurrent and excurrent apertures and their associated papillae are usually white. The foot and other organs are also white.

 

Conrad Mussell Illustration

 

 

Shell Anatomy

 
The dwarf wedgemussel was once found in rivers and streams from New Brunswick, Canada to North Carolina. Some of the known populations are found in the Nottoway River of Virginia, Neversink River in New York, and the Ashuelot River of New Hamshire. The largest known population is found in the Connecticut River in Vermont and New Hampshire. North Carolina supports the greatest number of known sites: Neuse River Basin: Orange Co. (Eno River Subbasin), Wake Co. (Swift Cr. and Little River subbasins), Johnston Co. (Swift Cr., Middle Cr., Little River, and Moccasin Cr. subbasins), Wilson Co. (Moccasin Cr. and Turkey Cr. subbasins), Nash Co. (Turkey Cr. and Moccasin Cr. subbasins); Tar River Basin: Person Co. (Tar River Subbasin - support waters for downriver population in Granville Co.), Granville Co. (Cub Cr., Shelton Cr., and Tar River subbasins), Vance Co. (Ruin Cr. Subbasin), Franklin Co. (Cedar Cr., Crooked Cr., Shocco Cr., and Fox Cr. subbasins), Warren Co. (Shocco Cr., Long Br., and Maple Br. subbasins), Halifax Co. (Rocky Swamp subbasin), Nash Co. (Stony Cr. Subbasin). Unfortunately, most of these populations are very small and isolated. Based upon recent surveys, the Eno River, Middle Creek, Cedar Creek, Rocky Swamp, Fox Creek, and Stony Creek populations may be extirpated. NOTE: All headwater areas that flow into these occupied habitats should receive special management.

 


Individual dwarf wedgemussels are found in large rivers and small streams, often burrowed into clay banks among the root systems of trees. They may also be found associated with mixed substrates of cobble, gravel, and sand. Occasionally they may be found in very soft silt substrates. Stream banks are stable with extensive root system holding soils in place. The associated landscape is largely wooded, especially near streams. Trees near the stream are relatively mature and tend to form a closed canopy over smaller streams, creeks, and headwater river habitats. Water quality is good to excellent.
Maximum age for the dwarf wedgemussel is around twelve years. The species is a bradytictic breeder. Females become gravid in the early fall and glochidia are released by mid-spring. Fish hosts include the tessellated and johnny darters in North Carolina (Michaelson 1993).

 

General Life History For Mussels