Description of multiple cryptic species of Obovaria Rafinesque, 1819 (Bivalvia: Unionida) from the Mississippi Embayment and Gulf coastal rivers of North America

The freshwater mussel genus Obovaria (Bivalvia: Unionidae) has long been recognized as taxonomically challenging due to plastic shell morphology, historical misidentifications, and incomplete geographic sampling across the southeastern United States. Using an integrated approach combining shell morphology, comparative conchology, geographic distribution, and molecular phylogenetic evidence, we revise the taxonomy of Obovaria in the Gulf Coastal Plain and adjacent drainages. We describe five new species: Obovaria sipseyensis sp. nov. from the Tombigbee River basin of Alabama and Mississippi; Obovaria neeskaensis sp. nov. from the White River basin of Arkansas and Missouri; Obovaria pinetorum sp. nov. from the west Gulf Coast drainages of Louisiana and Texas; Obovaria tallahattae sp. nov. from lower Mississippi River tributaries of Mississippi; and Obovaria lumbo sp. nov. from Lake Pontchartrain, Pascagoula River, and Pearl River basins of Louisiana and Mississippi. We further recognize Pseudoon olivarium comb. nov. based on its phylogenetic distinctiveness from Obovaria. Our results reveal previously unrecognized endemism and cryptic diversity within Obovaria, with significant implications for conservation and management. Several species treated herein are rare and geographically restricted, underscoring how basin-specific conservation strategies and accurate taxonomic recognition can guide freshwater mussel recovery efforts.