Formosania tangi, a new species of suck-loach (Cypriniformes, Gastromyzontidae) from the Jiulongjiang River, southeastern China, with taxonomic notes on F. fascicauda

For decades, populations of the suck-loach genus <i>Formosania</i> from the Jiulongjiang River in Fujian Province, China, have been identified as <i>F. fascicauda</i>, a species originally described from in a separate coastal drainage basin in Fuqing County. Employing an integrative taxonomic approach combining morphological and molecular phylogenetic analyses, we demonstrate that the Jiulongjiang River population represents a distinct species, formally described here as <i>Formosania tangi</i> <b>sp. nov</b>. It is diagnosed by a combination of characters: 13 rostral barbels arranged in two rows, a distinct straight, dark, longitudinal stripe along the lateral line, and an emarginate caudal fin. Phylogenetic analyses consistently recover it as a unique evolutionary lineage showing significant genetic divergence from true <i>F. fascicauda</i>, with a Kimura 2-parameter distance of 4.16%. The description of <i>F. tangi</i> clarifies the taxonomic status of the Jiulongjiang River population and enhances our understanding of species diversity and biogeography of <i>Formosania</i> in the coastal drainages of southeastern China.