Dwarf Wedgemussel, Alasmidonta heterodon

The Dwarf wedge mussel, Alasmidonta Heterodon, is an endangered species of freshwater mussel, an aquatic bivalve mollusk belonging to the family Unionidae, the river mussels.

This species is rare, found solely in North America’s Atlantic coast streams and rivers of a variety of sizes and moderate current.

Its current range extends from Maryland to North Carolina. It is federally listed as endangered, and state listed as endangered, in Connecticut, Maryland, Massachusetts, New Hampshire, North Carolina, New Jersey, Pennsylvania, Vermont, Virginia, and New York.

Previously, it resided in New Brunswick, but it’s locally extinct in Canada since the year 1968.

This mussel may be found in small creeks to deep rivers in stable habitats with substrates ranging from mixed sand, pebble and gravel to clay and silty sand. In the southern part of its range, it’s often found buried under logs or root mats in shallow water, where in the northern portion of its range, it might be found in firm substrates of mixed sand, cobble or gravel, or embedded in clay banks in water depths of a few inches to more than twenty feet.

This mussel is one of 24 freshwater mussels from North America that has two lateral teeth on the right valve and only one on the left valve. As it is small, the shell rarely exceeds 45 millimeters in length and 25 millimeters in height. The shell is trapezoidal shaped and is colored brown or a yellowish olive color, with reddish brown or greenish rays in the young or pale specimens. The nacre is a bluish or silvery white, and is iridescent on the posterior.

They reproduce typically of freshwater mussels, requiring a host fish on which its larvae parasitize and metamorphose into juvenile mussels. It is not a long lived species as compared to other freshwater mussels; the life expectancy is estimated at 10 to 12 years.

Image Caption: Endangered dwarf wedgemussel (Alasmidonta heterodon). Credit: USFWS Endangered Species/Wikipedia (CC BY 2.0)