Lamar County, Alabama

The penitent mussel is a bivalve mollusk about 2.1 inches long. It has a yellowish, rhomboid shell with irregular growth lines and a radically sculpted posterior. Females have large, grooved swellings projecting behind the shell. In the parasitic larval stage of the mollusk lifecycle, it is dependant on fish within its habitat for nutrients and mobility. However, only a few host fish are known. Mature mussels bury themselves in the riffles and shoals and feed by siphoning phytoplankton and other plant matter from the water. Reverse siphoning is used to expell undigestible particles from the shell. Silt in the water can kill mussels by clogging these feeding siphons. This species is found in shallow reaches of larger streams less than 2.3 feet deep, and rivers where there is a moderately strong current.

Historically the penitent mussel was known from the Tombigbee, Alabama, Buttahatchie, Cahaba, and Coosa rivers in Alabama, Georgia, and Mississippi. It now survives only in the Gainesville Bendway of the Tombigbee River (Sumter County, AL), and in other cut-off sections of the Buttahatchie River and the East Fork Tombigbee River. The penitent mussel has declined because of a loss of habitat due to river modifications. Dam construction, dredging, and construction have increased siltation and reduced water flow, disturbing host fish and this species. Mussel beds also suffer from pesticide and fertilizer run-offs that affect water quality. The range of the penitent mussel is currently threatened by two proposed channel improvement projects that would dredge and straighten 59 miles of the Buttahatchie River and 53 miles of the East Fork.

Matthews, J.R. (ed.), The Official World Wildlife Fund Guide to Endangered Species, Beacham Publishing Inc, Washington, DC. Vol II, pp. 966-967.