The southern acorn riffle shell or southern acornshell, scientific name Epioblasma othcaloogensis, is a species of freshwater mussel in the family Unionidae. It is only known from the Coosa and Cahaba Rivers of the southeastern United States. This species has been heavily impacted by dam construction, dredging, and water pollution. The last living individual was seen in 1974, and subsequent surveys have failed to locate any living populations. Some scientists believe it is now extinct. It appears to be closely related to the critically endangered Epioblasma penita.