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Species Description

Sculptured Pigtoe

Quincuncina infucata


Classification

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

Description

The Sculptured Pigtoe is a small freshwater mussel that often measures between 1.2 and 2.2 inches (30-55 mm) in length. It has a heavy shell that is nearly circular in shape. The periostracum (outer shell surface) is quite variable in appearance. Shells may be dull brown, greenish brown or dark black in color. Most of the surface is usually decorated with distinctive "V"-like ridges. The nacre (inner surface of the shell) is bluish white.

Life Cycle

Some of the details about the complex life cycle of this mussel are not currently known, but the life history of Quincuncina infucata is presumed to be similar to related species. Male Sculptured Pigtoe mussels release sperm into the slow current of creeks, lakes and backwater areas of rivers. 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. Parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. The required fish hosts have not been identified for this species. 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, mud, gravel or limestone rock bottom of a large creek or river.

Natural History

Sculptured Pigtoe 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 attached or buried in the mud, sand, rock or gravel bottoms of large creeks and rivers. This species appears to prefer a habitat of moderate to swiftly flowing water and is sometimes found at the bottom of deeper portions of rivers and creeks. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Sculptured 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 its gills and food particles are trapped and eventually digested.

Range

This species is native to the Apalachicola region of Georgia , Florida and Alabama . This region includes the Chipola River and Appalachicola-Chattahoochee-Flint River system. In Georgia , the Sculptured Pigtoe has been found in portions of the Flint and Chattahoochee Rivers in the western half of the state.

Conservation Status

This species is listed as Uncommon or Rare in Georgia . Excess sedimentation, introduction of the Asiatic Clam (Corbicula fluminea), pollution and habitat degradation are believed to be the primary factors for the decline of this species. Quincuncina infucata has apparently been extirpated from portions of its historical range, including portions of the Chattahoochee River in Georgia. Despite these apparent losses, the population size of the Sculptured Pigtoe is remaining fairly stable-unlike many of the other mussels that are native to the Apalachicola region.

Similar Species

This species is fairly distinct within Georgia . The small size, heavy shell and conspicuous surface sculpturing distinguish it from other freshwater mussels within its range.