Three New Mitochondrial Genomes of Neritidae (Gastropoda, Neritimorpha) From China and Insights Into Their Phylogenetic Position

Marine-to-freshwater transitions are frequent in neritid snails. However, phylogenetic relationships among genera remain incompletely resolved, largely because many lineages lack mitogenome data and public records sometimes contain misidentified sequences. Here we assembled complete mitochondrial genomes for three Neritidae species from China-the seagrass specialist Smaragdia rangiana, the brackish-water Neripteron pileolus, and the brackish-to-freshwater Vittina cumingiana-using genome skimming. The mitogenomes range from 15.68 to 15.82 kb, each containing the typical 37 genes and a major non-coding region. All three mitogenomes are AT-rich (62.8%-66.0%) with negative AT-skews and positive GC-skews. Codon usage analysis revealed that UCU (Serine) exhibits the highest relative synonymous codon usage across all three species, while nucleotide diversity among Neritidae PCGs is highest at third codon positions. Phylogenetic analyses were conducted using multiple datasets (13PCGs123, 13PCGs12, 13PCGsAA, with/without rRNA genes) under maximum likelihood and Bayesian inference, with TreeSpace analysis revealing three distinct topological clusters. All trees recovered the two-subfamily framework (Neritinae vs. Neritininae). Within Neritininae, S. rangiana clustered with other Smaragdia sequences, N. pileolus grouped with Neripteron violaceum, and V. cumingiana formed a lineage sister to Vitta and Puperita. Several public sequences showed discordant placements consistent with historical synonymy or mislabeling, underscoring the need for voucher-supported identifications. These new mitogenomes improve taxon sampling for Neritidae and provide a foundation for revisiting habitat transitions with broader genomic data.