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Ptychobranchus foremanianus (I. Lea, 1842)
Rayed Kidneyshell
Federal Protection: Listed Endangered
State Protection: Endangered
Global Rank: G1
State Rank: S1
Element Locations Tracked in Biotics: Yes
SWAP 2015 Species of Greatest Conservation Need (SGCN): Yes
SWAP 2025 Species of Greatest Conservation Need (SGCN): Yes
2025 SGCN Priority Tier: Highest Conservation Concern
Element Occurrences (EOs) in Georgia: 11
Habitat Summary for element in Georgia: Medium to large rivers in moderate to swift current; sand and gravel substrate
Shell profile typically sub-triangular or elliptical and inflated with a maximum length of approximately 100 mm (4 inches). Anterior margin broadly rounded and posterior margin bluntly pointed to rounded. Ventral margin is straight to broadly rounded. Umbos positioned anteriorly elevated slightly above hingeline. Posterior ridge is angular with a smooth posterior slope. Pseudocardinal teeth are relatively heavy and triangular. Periostracum is yellow to brown, sometimes with several dark rays present. Dark, prominent growth rings often present on surface of the shell. Pseudocardinal teeth triangular and divergent. Lateral teeth short and straight. Umbo cavity shallow. Nacre color typically white.
The Rayed Kidneyshell can strongly resemble the Southern Pigtoe (Pleurobema georgianum), but the Rayed Kidneyshell typically is more elongated.
Typically occupies riffles in medium to large rivers with moderate flow and gravel and sand substrates.
The diets of unionids are poorly understood but are believed to consist of algae and/or bacteria. Some studies suggest that diets may change throughout the life of a unionid with juveniles collecting organic materials from the substrate though pedal feeding and then developing the ability to filter feed during adulthood (Vaughn and Hakenkamp 2001).
Females of the Triangular Kidneyshell (Ptychobranchus greenii) were found releasing glochidia in April. Glochidia successfully transformed on the Warrior Darter (Ethostoma bellator), Tuskaloosa Darter (E. douglasi), Blackbanded Darter (Percina nigrofasciata), and Mobile Logperch (P. kathae). Ortmann found gravid individuals of the Rayed Kidneyshell brooding glochidia from late summer through the following summer. The known primary glochidial hosts for the Kayed Kidneyshell is the Greenbreast Darter (E. jordani), while the Banded Sculpin (Cottus carolinae) served as a secondary host (Haag and Warren 1997).
Surveyors should consider sampling during periods when female individuals are spawning or brooding as this species may have higher detection rates during this period. However, since basic life history information for many of Georgia’s unionids is lacking, sampling during periods when closely related species are spawning or brooding may increase probability of detection.
This species is endemic to the eastern Mobile River basin of Alabama, Georgia, and Tennessee. Historically, this species was known from the Black Warrior, Alabama, Cahaba, Coosa, and Tallapoosa rivers and their tributaries. In Georgia, this species appears to be restricted to the Conasauga River and its tributaries and to the mainstem Coosawattee River downstream of Carters Reservoir.
Excess sedimentation due to inadequate riparian buffer zones, development, and agriculture covers suitable habitat and could potentially bury mussels. Poor agricultural practices may also cause eutrophication and degrade water quality. Industrial effluent as well as sewage treatment plant discharges may also be degrading water quality.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Agriculture & aquaculture | Residential & commercial development | None |
| Specific Threat | None | None | None |
The Rayed Kidneyshell is not known from any state or federal lands in Georgia. Unlike terrestrial species, the occurrence of an aquatic species on state or federal lands may not eliminate habitat degradation due to the influences of upstream and downstream disturbances.
Minimizing sedimentation in the Conasauga River and its tributaries is a key component to conserving the Rayed Kidneyshell. Restoration of riparian buffers will stabilize banks providing clean gravel and sand substrates for the species. If habitat degradation can be minimized, reintroduction/augmentation of the Rayed Kidneyshell populations should be explored in order to re-establish viable populations of the species. However, prior to initiating any reintroduction/augmentation projects for the Rayed Kidneyshell, the effective population size of this species should be examined to ensure that these actions would not negatively affect the genetic integrity of the population.
Haag, W.R., and M.L. Warren, Jr. 1997. Host fish and reproductive biology of six freshwater mussel species from the Mobil Basin, U.S.A. Journal of the North American Benthological Society 16: 576-585.
Vaughn C.C. and C.C. Hakenkamp. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46: 1431-1446.
Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater mussels of Alabama and the Mobile Basin in Georgia, Mississippi, and Tennessee. The University of Alabama Press, Tuscaloosa.
Jason Wisniewski
2018-03-20
