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Elliptio fraterna (I. Lea, 1852)
Brother Spike
Federal Protection: No US federal protection
State Protection: No Georgia state protection
Global Rank: G1G2
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: 5
Habitat Summary for element in Georgia: Large rivers with sand substrate; little info available
Moderately lanceolate shape to 80 mm. Anterior margin rounded, posterior margin pointed with point below the midline of the shell. Posterior ridge sharp forming a low wing with weak corrugations. Periostracum brown to black with irregular rays possible on shell disk. Teeth are triangular and moderately thick. Nacre white to purple (Williams et al., 2008; Williams et al., 2014).
E. fraterna can be a challenging species to differentiate from similar species. The most easily identifiable feature for separating this species from other species in the Apalachicola basin are the fine corrugations on the posterior slope. The most similar species to E. fraterna in the Apalachicola is Elliptio crassidens which also has corrugations on the posterior slope. E. fraterna is more dorsoventrally compressed and is much thinner shelled than E. crassidens which is immediately evident when handling the two species due to the difference in weight. E. fraterna can also closely resemble Elliptio pullata in the Apalachicola or Elliptio complanata in the Savannah River though both of these species have a less sharp posterior ridge and lack corrugations on the posterior slope.
Preferred habitat for E. fraterna is not very well understood due to only a small number of individuals having been collected. E. fraterna appears to prefer large rivers, and known specimens were found in sand or sandy mud substrates in very low flow areas along river margins in the Apalachicola and Savannah 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 through pedal feeding and then developing the ability to filter feed during adulthood (Vaughn and Hakenkamp, 2001).
Like all unionids, E. fraterna has an obligate parasitic life cycle. Larval mussels, known as glochidia, develop in water tube present in the gills of the female mussel and are released when disturbed by an appropriate host fish. E. fraterna is believed to be a short-term brooder, like other members of its genus, and is presumed to be gravid in spring and early summer. Glochidia attach to the gills, fins, and skin of the host fish and encyst as an ectoparasite. Typical glochidia infestation appears to be minimally invasive to the host fish and is not fatal. Glochidia remain attached to the host for several weeks to several months before dropping off as juvenile mussels. These juveniles hopefully land in a new, suitable location and burrow into the sand where they feed on detritus using their foot and eventually grow into filter-feeding, adult mussels. Specific host species for E. fraterna are unknown, and the variety of host fish utilized by different species within this genus make host fish speculation based on congeners tenuous.
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. Investigators should conduct tactile searches of unconsolidated, but stabilized, habitats (i.e. sand around an embedded log) along the margins of rivers in depositional areas with low to moderate flow. The low number of individuals of this species that have been collected make specific survey recommendations difficult.
E. fraterna is restricted to the Apalachicola River basin in Georgia and Florida as well as the Savannah River in Georgia and South Carolina.
Like most native freshwater mussels in Georgia, E. fraterna is threatened by habitat destruction in the form of flow alteration, excessive water withdrawal, watershed land use changes, impoundments, and pollution. While the host fish species for E. fraterna are not known, freshwater mussels are dependent on them to complete their life cycle and threats to host fish or barriers to host fish movement are also serious threats.
| Threat 1 | Threat 2 | Threat 3 | |
|---|---|---|---|
| General Threat | Pollution | Natural system modifications | Natural system modifications |
| Specific Threat | None | Dams & water management/use | Dams & water management/use |
Conservation of E. fraterna will primarily rely on habitat protection in the Apalachicola and Savannah rivers in the form of drainage area, riparian, and water resource management. Due to a lack of basic knowledge about this species, specific management recommendations are difficult. Further research into the specific distribution, life history, host fish, and habitat requirements of this species are still needed to guide management efforts.
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.
Williams, J.D., R.S. Butler, G.L. Warren, and N.A. Johnson. 2014. Freshwater Mussels of Florida. University of Alabama Press, Tuscaloosa, Alabama.
Matthew Rowe
1/9/2020