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Species Description

Fat Threeridge

Amblema neislerii


Classification

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

Description

Amblema neislerii is a medium-sized freshwater mussel with a dark brown to black shell that usually measures less than 4.0 inches (102 mm) in length. Its shell is heavy and often very inflated, with the width and height approximately equal in large specimens. The outer surface is marked with 7-9 conspicuous parallel ridges. Its nacre (inner shell surface) is very iridescent in appearance and ranges from bluish white to light purple in color.

Life Cycle

Many of the specific details about the life cycle of this endangered mussel are not currently known, but the life history of Amblema neislerii is presumed to be similar to related species. Male Fat Threeridges release sperm into the water column of moderately flowing waters. 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. Glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. Recent research suggests that Amblema neislerii may parasitize several species of minnows (Cyprinidae) or species of the sunfish family (Centrarchidae) 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, often the muddy or sandy bottom of rivers and streams.

Natural History

Many of the details about the natural history of the Fat Threeridge 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 and are often found buried in the muddy or sandy bottoms of moderately flowing rivers. They are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Fat Threeridge 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

The Fat Threeridge was historically found in the main channels of muddy and sandy-bottomed rivers throughout the Apalachicolan region (the Apalachicola-Chattahoochee-Flint River system) of southwestern Georgia and Florida . It was historically found within the Flint River in Baker, Decatur, Dougherty and Macon counties; however it has not been found during recent surveys and may be extirpated within Georgia .

Conservation Status

The Fat Threeridge is listed as endangered by federal and state agencies. Recent surveys indicate, however, that it could have been extirpated during the last 20 years in Georgia . Several factors are believed to have contributed to the dwindling population size of Amblema neislerii, including sedimentation, habitat degradation, pollution, disappearance of required host fish and introduction of the Asian Clam (Corbicula fluminea).

Similar Species

There are no other freshwater mussels within the historical range of the Fat Threeridge that possess its inflated, dark brown to black shell with 7-9 prominent parallel ridges.