Freshwater mussels serve at the base of the food web and provide a variety of ecosystem services. They filter our water for us, help stabilize the bottom of our rivers and serve as water quality indictors. Unfortunately, due to many anthropogenic affects, freshwater mussels are one of the most imperiled groups of animals in the world. The Georgia pigtoe, Pleurobema hanleyianum, is a freshwater mussel in the family Unionidae and endemic to the Coosa River drainage of the Mobile River Basin in Alabama, Georgia, and Tennessee. The Georgia pigtoe was listed in 2010 as endangered due to population decline, and has disappeared from 90 percent or more of its historical range, primarily due to the impoundment of riverine habitats
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Although the diets of freshwater mussels are poorly understood, it is believed to consist of algae, and or, bacteria. Some studies suggest that the diets of freshwater mussels may change throughout their life, with juveniles collecting organic materials from the substrate though pedal feeding and then developing the ability to filter feed during adulthood. Pedal feeding is a form of deposit feeding where the animal uses their muscular foot to bury into the sediment, collecting organic matter. Filter feeding is a process by which mussels feed off suspended organic material by pumping in water through their incurrent aperture and out through their excurrent apertures, capturing the particles and using them as food.
Many freshwater mussels spend the majority of their life sedentary and filter feeding on the bottom of rivers and streams. Sometimes they will bury into the sediment, only revealing a small portion of their aperture, which is used for gas exchange and filter feeding.
The shell of the Georgia pigtoe is oval to elliptical and somewhat inflated. The shell of adults reach about 50 to 65 millimeters (mm) (2 to 2.5 inches (in)) in length. The posterior ridge of the shell is low and evenly rounded, when evident. The anterior end is rounded, while the posterior margin is bluntly pointed below. Dorsal and ventral margins are curved, and the beaks rise slightly above the hinge line.
The periostracum (membrane on the surface of the shell) is yellowish-tan to reddish-brown and may have concentric green rings. The beak cavity is shallow, and the shell interior is white to dull bluish-white.
Freshwater mussels live an interesting multi-stage life cycle which depends upon a fish host to complete. Males release sperm into the water column, to be hopefully siphoned in by the incurrent aperture of the females, where the eggs held within her gills are then fertilized. Once the fertilized eggs start to develop, the female becomes inflated, or gravid. The fertilized eggs develop into glochidia, which is the mussels larval stage. This stage requires a fish host for transformation into the juvenile stage, which sometimes requires a little coaxing by females. Glochidia are housed in packets called conglutinates and often mimic a food source of the fishes within that ecosystem to lure the fish to bite. Once the fish bites, the glochidia clamp down onto the fish, becoming encysted, and feed from the fish for several weeks until dropping off as juveniles. The host fish for glochida of the Georgia pigtoe is currently unknown.
Little is known about the habitat requirements or life history of the Georgia pigtoe; however, it is most often found in shallow runs and riffles with strong to moderate current and coarse sand-gravel-cobble bottoms.
A natural body of running water.
The Georgia pigtoe most similarly resembles the southern pigtoe, Pleurobema georgianum, but is more enlongate.
The Georgia pigtoe is endemic to the Coosa River drainage of the Mobile River basin in Alabama, Georgia, and Tennessee. It has disappeared from 90 percent or more of its historical range, primarily due to the impoundment of riverine habitats. It is currently known from a few isolated shoals in the Upper Conasauga River in Murray and Whitfield counties, Georgia; in Polk County, Tennessee; and in the Big Canoe and Little Canoe creeks in St. Clair and Etowah counties, Alabama. Single records have been documented from the Weiss Bypass of the Coosa River (2002) and from Hatchet Creek (2001), though more surveys are required before it can be confidently declared that Georgia pigtoe populations exist at these locations.
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