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Species Description

Upland Combshell

Epioblasma metastriata


Classification

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

Description

The Upland Combshell is a freshwater mussel that often measures less than 2.4 inches (60 mm) in length. It is rhomboidal in shape and is sexually dimorphic. Male specimens are moderately inflated, whereas females are greatly inflated, with the width and height of the shell being nearly the same. The periostracum (outer shell surface) is yellowish brown to tan in color. The outer surface may also have green rays or spots.

Life Cycle

Many of the specific details about the complex life cycle of this endangered mussel are not currently known, but the life history of Epioblasma metastriata is presumed to be similar to related species. Male Upland Combshell mussels release sperm into moderate to swiftly-flowing 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 has been found to be bradytictic. This means that spawning usually occurs during the summer and glochidia are released the following spring. When released, the parasitic glochidia must find and attach to the gills or fins of the appropriate host fish to complete development. The required fish hosts are not currently known 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 metamorphose into juvenile mussels on the fish and then release from the host to find a suitable substrate, often the sand or gravel bottoms of moderate to swiftly-flowing rivers.

Natural History

Many of the details about the natural history of the Upland Combshell 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 to the sand or gravel bottom of a river. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Upland Combshell 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, the Upland Combshell was found in the Black Warrior River and its tributaries, the Cahiba River and its tributaries and the Coosa River and its tributaries (including the Conasauga and Chattooga Rivers ) in portions of Georgia , Alabama and Tennessee . However, recent surveys have indicated dramatic declines in the population size and range of this freshwater mussel. It may be extirpated from Tennessee and Alabama , and may currently be restricted to a portion of the Conasauaga River in Georgia .

Conservation Status

The Upland Combshell is currently listed as endangered by both state and federal agencies. The primary factors that are believed to have contributed to the diminished range and numbers of Upland Combshell mussels are sedimentation, pollution and habitat degradation. Recent surveys have not located the species from much of its range and it appears to be restricted to a portion of the Conasuaga River near the Georgia/Tennessee border.

Similar Species

The most similar species to the Upland Combshell is the Southern Combshell (Epioblasma penita). However, the Southern Combshell has a gently rounded posterior margin and the Upland Combshell (Epioblasma metastriata) has a broadly curved posterior margin.