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Species Description

Purple Bankclimber

Elliptoideus sloatianus


Classification

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

Description

This large freshwater mussel can reach a length of greater than 8.0 inches (200 mm), but usually measures between 4.0 and 5.5 inches (100-140 mm). The Purple Bankclimber has a characteristic lumpy grey to black heavy outer shell (periostracum). Its nacre (inner shell surface) is white in the center and becomes a dark purple color near the inner shell edges.

Life Cycle

Many of the specific details about the complex life cycle of this threatened mussel are not currently known, but the life history of Elliptoideus sloatianus is presumed to be similar to related species. Male Purple Bankclimbers release sperm into the deep water of large rivers with moderate currents. Sperm enters females through siphon-like regions and fertilization of eggs occurs within female shells. These fertilized eggs develop into special larva called glochidia. Glochidia continue to develop and are released into the water column when fully matured. The parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. The required fish hosts are not currently known for this species, but recent research suggests that the Mosquitofish (Gambusia holbrooki) and Blackbanded Darter (Etheostoma edwini) may be the required fish hosts. The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sandy or gravel bottoms of rivers with moderate currents.

Natural History

Many of the specific details about the natural history of the Purple Bankclimber are not currently known, but they are believed to be similar to better known, related species. Larvae (glochidia) are parasitic upon the tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult mussels are typically sessile and are often found attached or buried deeply within the sand or gravel bottom of large, moderately flowing rivers. Adult mussels are often found in water that is greater than 9.8 feet (3 m) in depth. Adults are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Purple Bankclimber 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.

Range

Historically, the Purple Bankclimber was found at a number of sites within the Appalachicola-Chattahoochee-Flint (ACF) and Ochlockonee River systems of Georgia , Florida and Alabama . However, today it has likely been extirpated from Alabama and is greatly reduced in numbers from all other portions of its range. In Georgia , it has been found within the Flint , Chattahoochee and Ochlockonee rivers.

Conservation Status

The Purple Bankclimber is currently listed as threatened by both state and federal agencies. This large freshwater mussel was once abundant and recent archeological evidence suggests that the Purple Bankclimber was a staple of Native Americans of the Chattahoochee Valley . However, like many of the freshwater mussels of the region, it is highly susceptible to changes within its habitat and by the 1850's its population size had been greatly reduced. It is still not abundant today and the population size is drastically reduced from its pre-1850's levels. Recent surveys suggest that it has likely been extirpated from within Alabama . The primary factors that are believed to have contributed to the dwindling numbers of Purple Bankclimbers are habitat degradation, pollution, sedimentation and collection by individuals.

Similar Species

There are no similar species of freshwater mussels within the range of the Purple Bankclimber. No other freshwater mussel can be confused with the large, heavily sculptured shell and purple nacre (inner surface of shell) of the Purple Bankclimber