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Species Description

Alabama Moccasinshell

Medionidus acutissimus


Classification

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

Description

This small and delicate freshwater mussel measures only 1.2 inches (30 mm) in length. It has an acute posterior ridge that is important for identification. It has a yellow to brownish yellow periostracum (protective outer covering of the shell) with green rays across the shell surface. The internal layer (nacre) of the shell is salmon colored.

Life Cycle

Many of the specific details about the life cycle of this threatened mussel are not currently known, but the life history of Medionidus acutissimus is presumed to be similar to related species. Male Alabama Moccasinshells release sperm into the water column of moderately flowing rivers. Sperm enters females through siphon-like regions and fertilization of eggs occurs. 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 Medionidus acutissimus parasitizes several species of Darter fish for varying lengths of time, likely depending upon water temperature, fish species and other factors. The larvas metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate.

Natural History

Many of the details about the natural history of Alabama Moccasinshells are not currently known, but they are presumed to be similar to better known, related species. The Moccasinshell attaches to sandy-gravel and gravel substrates of moderately flowing rivers within its limited range. It gathers nutrients and food, such as detritus, plankton and other microorganisms, by filter feeding. Alabama Moccasinshells 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

Medionidus acutissimus is found within a narrow range of clear, moderately flowing rivers and creeks in Georgia , Alabama , Mississippi and Tennessee . In Georgia it has been found in the Conasuaga, Coosa , Etowah and Chattooga Rivers .

Conservation Status

The Alabama Moccasinshell is currently listed as threatened by state and federal agencies. Like many freshwater mussels, it is severely threatened by habitat modification and degradation. Construction of impoundments, pollution, loss of required fish host(s) and introduction of invasive species (such as the Asiatic Clam and Zebra Mussel) are all believed to have contributed to the dwindling numbers of Moccasinshells.

Similar Species

The Coosa Moccasinshell (Medionidus parvulus) is the most similar freshwater mussel to the Alabama Moccasinshell. However, the Coosa Moccasinshell lacks the distinctive acute posterior ridge, salmon-colored interior and is generally larger than the small (1.2 inch) Alabama Moccasinshell.