Integrative Taxonomic Revision of Goatfishes (Mullidae) in the Northern South China Sea Based on Morphology and Multilocus Molecular Data

The goatfishes (Mullidae) are widely distributed in tropical and subtropical seas, yet taxonomic resolution in the northern South China Sea remains limited. We conducted an integrative taxonomic revision combining morphological characteristics with multilocus molecular markers (mitochondrial COI, 16S rRNA, and nuclear IRBP) for 283 mullid specimens collected from the northern South China Sea, providing updated species-level diagnoses and a dichotomous identification key for the regional fauna. Morphological examination identified 18 species belonging to three genera, and principal component analysis (PCA) revealed intergeneric differences in quantitative traits, with depth-related and head-region variables contributing strongly to genus-level separation despite partial overlap in morphospace. Molecular phylogenetic analyses showed that some single-locus trees provided limited resolution at certain nodes, whereas the concatenated COI + 16S rRNA dataset recovered monophyly for all examined species with higher support. Species delimitation results indicated that Automatic Barcode Gap Discovery (ABGD) and Bayesian Poisson Tree Processes (bPTP) were concordant, recovering 22 molecular operational taxonomic units (MOTUs) across the full COI dataset, including four MOTUs represented only by GenBank reference sequences; among our sampled specimens, the 18 morphologically identified species each corresponded to a single MOTU. Based on integrated morphological and multilocus evidence, we revised the diagnoses and diagnostic characters for three genera and 18 goatfish species from the northern South China Sea and compiled a dichotomous identification key, thereby clarifying species boundaries within Mullidae, improving identification accuracy, and supporting future surveys, biodiversity inventories, and monitoring in this region.