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Species Description

Southern Pocketbook

Lampsilis ornata


Classification

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

Description

The Southern Pocketbook is a medium-sized freshwater mussel that typically reaches a length of about 4.0 inches (102 mm). It has an inflated or swollen shell with high umbos (rounded, raised structures on shell surface). The periostracum (outer shell surface) is greenish yellow to light tan and is decorated with narrow green rays that are widely separated. The nacre (inner surface of shell) is white to bluish-white.

Life Cycle

Some of the specific details about the complex life cycle of this mussel are not currently known, but the life history of Lampsilis ornata is presumed to be similar to related species. Male Southern Pocketbook mussels release sperm into large rivers and creeks with slow to 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. This species has been found to be bradytictic (a species that is a long-term brooder). This means that it typically spawns during the summer and females brood the developing glochidia for a long duration. Mature glochidia are finally released during late spring. The parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. In order to increase the probability that glochidia will come in contact with fish, female mussels display large mantle flaps outside of their shells that serve as a "lures." Each "lure" is cream-colored with a distinct eyespot and dark stripe that is wiggled around to attract fish. Recent studies have determined that the primary host fish for the Southern Pocketbook is the Largemouth Bass (Micropterus salmoides). The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae transform into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sand or gravel bottom of a river or creek.

Natural History

Southern Pocketbook l arvae (glochidia) are parasitic upon tissue of fish hosts while completing the metamorphosis into juvenile mussels. Adult mussels are typically sessile and are found in the sand or gravel bottoms of large creeks and rivers with slow to moderate currents. This species is sometimes found in the bottom of rivers and creeks that are less than 3 feet deep. It has also been found in the muddy bottoms of backwater areas with little or no current. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Southern Pocketbook 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 its gills and food particles are trapped and eventually digested.

Range

The Southern Pocketbook has historically been found in the Upper Coosa River system of Georgia and Tennessee , the Escambia River system of Alabama and western Florida and westward along the Gulf Coast to the Amite River of Louisiana.

Conservation Status

The status of the Southern Pocket is currently undetermined in Georgia . It is listed as Rare and Imperiled in much of its range, but the population size appears to be stable-rather than declining. Like many freshwater mussels, this species has presumably been affected by pollution, habitat degradation and excess sedimentation.

Similar Species

Within northwestern Georgia , the Southern Pocketbook is fairly distinct. The combination of yellowish surface, high umbos and separated, narrow green rays across the shell surface distinguishes this mussel from others within its range.