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Species Description

Tennessee Heelsplitter

Lasmigona holstonia


Classification

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

Description

This small to medium-sized freshwater mussel typically measures less than 3.0 inches (76 mm) in length. The Tennessee Heelsplitter is thin-shelled and somewhat elongated in shape. The periostracum (outer shell surface) is a dull, greenish brown or yellow-brown color in younger specimens and becomes dark brown with age. The outer surface of the shell is roughened with numerous darkened lines. The nacre (internal layer of the shell) is bluish white.

Life Cycle

Many of the specific details about the complex life cycle of this mussel are not currently known, but the life history of Lasmigona holstonia is presumed to be similar to related species. Male Tennessee Heelsplitter mussels release sperm into shallow creeks and headwater streams. 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. The parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. Recent studies have identified the Rock Bass (Ambloplites rupestro) and Banded Sculpin (Cottus carolinae) as suitable hosts. The glochidia parasitize a fish host for a variable length of time, likely depending upon water temperature, fish species and other factors. Larvae metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sand or mud bottom of a shallow creek or stream.

Natural History

Many of the details about the natural history of the Tennessee Heelsplitter are not currently known, but they are believed to be similar to better known, related species. Larvae (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 within the mud or sand bottom of shallow creeks and headwater streams. This species is sometimes the only mussel within its shallow water habitat. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Tennessee Heelsplitter 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.

Range

Historically, this freshwater mussel was widely distributed throughout small streams and creeks of the Alabama River and Tennessee River drainages. This range included portions of Georgia , Tennessee , Alabama , Virginia and North Carolina . However, today this range has declined and the distribution is patchier. The Tennessee Heelsplitter can be found within shallow streams that are part of the Tennessee River system, Etowah River and Conasuaga River in the northwestern portion of Georgia .

Conservation Status

This species is listed as uncommon or rare in Georgia . This species has been found to be slightly more tolerant of degradation of its habitat than many other species of freshwater mussels. However, it is still susceptible to pollution and sedimentation within its mud and sand-bottomed, shallow water environment. These factors are believed to have contributed tremendously to the declining population size and range of the Tennessee Heelsplitter today.

Similar Species

Within the Georgia portion of its range, the Tennessee Heelsplitter is quite distinct. The combination of thin shell, elongate shape and yellowish or brownish color sets it apart from other mussels within the state.