Integrative Taxonomy of Nuchequula longicornis (Teleostei: Leiognathidae) from Chinese Waters: Morphological Analysis, Mitogenomic Characterization, and Phylogenetic Implications

The ponyfish genus <i>Nuchequula</i> is presents taxonomic challenges within Leiognathidae due to morphological complexities and a lack of genomic resources. However, the absence of a complete mitochondrial genome for <i>Nuchequula longicornis</i> has hindered comprehensive phylogenetic comparisons. Here, we employed an integrative approach combining detailed morphology with molecular validation via 16S rRNA gene sequencing to confirm the identity of specimens from the Beibu Gulf. Furthermore, we present the first complete mitogenome of <i>N. longicornis</i>. This circular 16,514 bp molecule exhibits a typical gene order, a moderate AT bias (54.8%), and strong purifying selection across all protein-coding genes. Phylogenomic analysis based on the complete mitogenome reliably resolved the position of <i>N. longicornis</i> within Leiognathidae, contributing to the discussion on the phylogenetic relationships and potential monophyly of <i>Nuchequula</i> and contributing to the understanding of intra-familial relationships. Our study provides an essential mitogenomic resource for <i>N. longicornis</i> and offers insights into mitochondrial evolutionary patterns within this family.