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Species Description

Alabama Spike

Elliptio arca


Classification

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

Description

The Alabama Spike is a small freshwater mussel that typically measures less than 3.0 inches (76 mm) in length. It has a fairly thin, elliptical shell that is compressed in young specimens and moderately inflated or swollen in older specimens. The periostracum (outer shell surface) is olive-yellow and becomes dark brown in older specimens. The distinct, concentric growth lines give the shell surface a roughened texture. The nacre (inner surface of the shell) is bluish-white or salmon in color.

Life Cycle

Some of the specific details about the complex life cycle of this mussel are not currently known, but the life history of Elliptio arca is presumed to be similar to related species. Male Alabama Spike mussels release sperm into shallow riffles or slow-moving 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. This species is a short-term brooder and recent laboratory studies determined that glochidia were released during June and July. Parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. The Redspot Darter (Etheostoma artesiae) and the Blackbanded Darter (Percina nigrofasciata) have recently been identified as suitable host fish. 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 gravel, mud or sand bottom of a river.

Natural History

Alabama Spike 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 to the sand, mud or gravel bottom of shallow riffles or slow-moving rivers. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Alabama Spike 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 Alabama Spike is found in the Conasauga River of northwestern Georgia and southern Tennessee , the Mobile Bay Basin of Alabama, the Pearl River in Mississippi and Amite River in Louisiana .

Conservation Status

The status of this species is currently undetermined within Georgia . However, it is rare and imperiled in other states and be have been extirpated from portions of its range. The Alabama Spike has presumably been adversely affected by gravel mining, habitat degradation, pollution and excess sedimentation.

Similar Species

Within its narrow range in Georgia , the Alabama Spike is rather distinct. Its thin, elliptical shell, roughened surface and olive yellow or dark brown surface distinguish it from other freshwater mussels of the Conasuaga River .