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Species Description

Atlantic Pigtoe Mussel

Fusconaia masoni


Classification

Phylum: Mollusca
Subphylum:
Class: Bivalvia
Order: Unionoida
Family: Unionidae

Description

This freshwater mussel has a medium, semi-triangular (rhomboidal) shaped shell that usually measures less than 2.4 inches (60 mm). It possesses a distinctive, angular posterior ridge. The periostracum (outer surface of the shell) is yellowish brown to greenish brown in color. The nacre (inner surface of the shell) can be iridescent blue, white, salmon or white in appearance.

Life Cycle

Many of the specific details about the life cycle of this endangered mussel are not currently known, but the life history of Fusconaia masoni is presumed to be similar to related species. Male Atlantic Pigtoe Mussels release sperm into the water column of relatively fast flowing waters. Sperm enters females through siphon-like regions and fertilization of eggs occurs. These fertilized eggs develop into special larva called glochidia. Glochidia continue to develop and are released into the water column when fully matured. Glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. Recent research suggests that Fusconaia masoni parasitizes the Bluegill Sunfish (Lepomis macrochirus) and Shield Darter (Percina peltata) for varying lengths of time, likely depending upon water temperature, fish species and other factors. The larvae metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate.

Natural History

Many of the details about the natural history of Atlantic Pigtoes are not currently known, but they are presumed to be similar to better known, related species. Larvae (glochidia) are parasitic upon fish hosts while completing the metamorphosis to juvenile mussels. Adult mussels are typically sessile. They prefer to attach to stable gravel or sandy-gravel substrates within their clean, swift water environments. They are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Atlantic Pigtoe mussels bring water from their habitat into their shells through specialized regions that are similar to the true siphons of clams. The water is then filtered over the gills and food particles are trapped and eventually digested. Water is then pushed back out another siphon-like region.

Range

Fusconaia masoni has a fairly moderate geographic range along the southern Atlantic Slope, but it is rapidly disappearing throughout the rapidly flowing streams and rivers of its range. It is found from the Ogeechee River of Georgia north to the James River of Virginia. Within Georgia it is only found in Jefferson and Jenkins counties.

Conservation Status

Due primarily to pollution, habitat degradation, impoundments and sedimentation, Fusconaia masoni is listed as endangered within Georgia . Like many of the endangered and threatened freshwater mussels, this species does not seem to be able to tolerate changes in its aquatic habitat.

Similar Species

There is not another freshwater mussel within the Ogeechee River of Georgia that has the same combination of rhomboidal shape, yellow to brown outer shell and distinctive, angular posterior ridge.