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

## TL;DR

This study combines physical traits and genetic data to better understand and classify the ponyfish Nuchequula longicornis from Chinese waters.

## Contribution

The first complete mitochondrial genome of Nuchequula longicornis is decoded and analyzed, offering new phylogenetic insights.

## Key findings

- The mitogenome of N. longicornis is 16,514 bp with typical gene order and moderate AT bias.
- Phylogenomic analysis clarifies the evolutionary position of N. longicornis within Leiognathidae.
- The study supports the potential monophyly of the genus Nuchequula.

## Abstract

To accurately identify species and trace their evolutionary history, scientists combine detailed physical examination with genetic analysis. For the poorly studied ponyfish Nuchequula longicornis, we first conducted a thorough morphological study of specimens from the Beibu Gulf. We then employed the 16S rRNA gene as a molecular tool to genetically confirm their identity by comparing them to known references. Finally, we decoded and analyzed the fish’s complete mitochondrial genome (“mitogenome”) for the very first time. This new genetic blueprint details its structure and clarifies its evolutionary relationships within the ponyfish family. Beyond providing a vital resource for future identification and conservation, our integrative approach—morphology plus molecules—offers fresh insights for refining the classification of this group.

The ponyfish genus Nuchequula 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 Nuchequula longicornis 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 N. longicornis. 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 N. longicornis within Leiognathidae, contributing to the discussion on the phylogenetic relationships and potential monophyly of Nuchequula and contributing to the understanding of intra-familial relationships. Our study provides an essential mitogenomic resource for N. longicornis and offers insights into mitochondrial evolutionary patterns within this family.