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Strophitus radiatus (Conrad, 1834)
Rayed Creekshell
Federal Protection: No US federal protection
State Protection: Threatened
Global Rank: G2G3
State Rank: S2
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: High Conservation Concern
Element Occurrences (EOs) in Georgia: 34
Habitat Summary for element in Georgia: Small creeks to large rivers,mud, sand, or gravel substrates
Shell is thin, moderately inflated, elongate, and rarely exceeds 75 mm (3 inches) in length. Umbos slightly elevated above the hingeline and positioned anteriorly. Anterior margin of shell is rounded while posterior margin is bluntly pointed to rounded. Ventral margin broadly rounded. Posterior ridge rounded near umbo, but flattens ventrally. Adults typically with dark green or amber periostracum often with dark green rays. One rudimentary, pseudocardinal tooth and with lateral teeth absent. Beak cavity shallow and wide. Nacre white.
The Rayed Creekshell can be distinguished from the Southern Rainbow (Villosa vibex) by the latter having well developed teeth. The umbos in the Rayed Creekshell typically are narrower and elevate above the hingeline more than that of the southern rainbow. Recent publications suggest that individuals identified as the Southern Creekmussel (Strophitus subvexus) from the Apalachicola River Basin were incorrectly identified and were actually the Rayed Creekshell.
Typically occupies mud, sand, or gravel substrates in small creeks to large rivers.
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).
The brooding period and host fish are unknown for this species. Gravid Rayed Creekshells have been collected out of the Mobile River basin from August through December. Furthermore, In the ACF basin, gravid females were collected in late September and early December.
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. Since this species may be a headwater specialist, surveys for the rayed creekshell should be done in headwater reaches of streams in the lower Chattahoochee and Flint River basins.
Endemic to the Apalachicola River Basin from Alabama, Florida, and Georgia. The Rayed Creekshell was known from the Chattahoochee and Flint Rivers and their tributaries. Current distribution in Georgia appears to be restricted to the lower Flint River tributaries as well as the mainstem river up to the Fall Line.
Habitat fragmentation may isolate populations and prevent fish movement, limiting the distribution of host fishes carrying glochidia. Additionally, construction of impoundments could further fragment populations and inundate suitable habitat. Excessive water withdrawals in the Lower Flint River Basin coupled with severe drought could cause this species to become extirpated from Georgia. Excess sedimentation due to inadequate riparian buffer zones and incompatible agricultural practices may also cover suitable habitat and could potentially bury individuals. Rapid development of the northern extent of the Flint River Basin could severely impact the remaining populations of this species.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Natural system modifications | Pollution | Natural system modifications |
| Specific Threat | Dams & water management/use | None | Dams & water management/use |
The Rayed Creekshell is known from Montezuma Bluff Wildlife Management Area. 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.
Developing propagation and culture techniques was identified as a top research priority needed for the conservation of this species in the 2015 Georgia State Wildlife Action Plan. Understanding the basic life history of this species will provide the foundation upon which all other research and conservation actions should be built. Investigating the instream flow needs of this species was also identified as a high priority research need for this species.
Brim Box, J. and J.D. Williams. 2000. Unionid mollusks of the Apalachicola Basin in Alabama, Florida, and Georgia. Alabama Museum of Natural History Bulletin 21. 143 pp.
Vaughn C.C. and C.C. Hakenkamp. 2001. The functional role of burrowing bivalves in freshwater ecosystems. Freshwater Biology 46: 1431-1446.
Shea, C.P., J.T. Peterson, M.J. Conroy, and J.M. Wisniewski. 2013. Evaluating the influence of land use, drought, and reach isolation on the occurrence of freshwater mussel species in the lower Flint River Basin, Georgia (U.S.A.). Freshwater Biology 58:382-395.
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.
Williams, J.D., R.S. Butler, G.L. Warren, and N.A. Johnson. 2014. Freshwater Mussels of Florida. University of Alabama Press, Tuscaloosa, Alabama.
Wisniewski, J.M., N.M. Rankin, D.A. Weiler, B.A. Strickland, and H.C. Chandler. 2013. Occupancy and detection of benthic macroinvertebrates: a case study of unionids in the lower Flint River, Georgia, USA. Freshwater Science 32:1122-1135.
Wisniewski, J.M., N.M. Rankin, D.A. Weiler, B.A. Strickland, and H.C. Chandler. 2014. Use of occupancy modeling to assess the status and habitat relationships of freshwater mussels in the lower Flint River, Georgia, USA. Walkerana 17:24-40.
Jason Wisniewski
2018-03-20
