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Species Description

Ovate Clubshell

Pleurobema perovatum


Classification

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

Description

This small freshwater mussel usually measures less than 2.0 inches (50 mm) in length. It has a yellow to dark brown outer shell (periostracum) and is occasionally marked with broad green rays. The Oval Clubshell also has a rounded and often concave posterior ridge. The nacre (inner shell surface) is white in appearance.

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 Pleurobema perovatum is presumed to be similar to related species. Male Ovate Clubshells release sperm into clean rivers with moderate currents. 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. The required fish hosts are not currently known for this species. The glochidia parasitize the fish host(s) 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 sandy or gravel bottoms of rivers with moderate currents.

Natural History

Many of the details about the natural history of the Ovate Clubshell 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 often found attached to the sandy or gravel bottom of moderately flowing rivers. Adult mussels are filter feeders and usually feed upon plankton and detritus from their aquatic environment. Ovate Clubshell 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 small freshwater mussel was found in numerous small and large rivers within Georgia , Alabama , Mississippi , South Carolina and Tennessee . However, recent scientific surveys have raised speculation that the Ovate Clubshell may be extirpated from Georgia and Tennessee . Within Georgia , it has historically been found within the Conasauga, Coosa and Etowah Rivers .

Conservation Status

The Ovate Clubshell is currently listed as as endangered by both federal and state agencies. Like many freshwater mussels, the Ovate Clubshell is rather sensitive to changes within its habitat and requires a high quality, clean river with sandy or gravel bottom to survive. Due primarily to habitat degradation, sedimentation and pollution, its population size is decreasing and it may be extirpated from Georgia .

Similar Species

The most similar freshwater mussel to the Ovate Clubshell is the endangered Southern Clubshell (Pleurobema decisum). However, the Ovate Clubshell is distinguished by its thinner shell and rounded posterior ridge.