# New mitochondrial genomes of Saccostrea (Mollusca, Ostreidae) specimens from Hainan Island

## TL;DR

This study sequenced mitochondrial genomes of oysters from Hainan Island to improve their taxonomic classification.

## Contribution

The study provides new mitochondrial genome data and identifies two novel OTUs in the genus Saccostrea.

## Key findings

- The four Saccostrea specimens had conserved mitochondrial gene arrangements with a fragmented 16S rRNA gene.
- Two novel OTUs were identified, with one showing high intraspecific divergence.
- Publicly available Saccostrea genomes were reclassified into nine OTUs, highlighting mislabeling in GenBank.

## Abstract

The taxonomic classification of oysters, particularly within the genus Saccostrea, remains poorly resolved due to limitations in traditional morphological and single-gene approaches. To address this, we sequenced the mitochondrial genomes of four Saccostrea specimens (Saccostrea MBSR 211-214) from Hainan Island. The complete mitochondrial genomes (16,280–16,289 bp) revealed a conserved gene arrangement, including 12 protein-coding genes (PCGs), 23 transfer RNA (tRNA), and two ribosomal RNA (rRNA) genes on a single strand, with a fragmented 16S rRNA gene as a distinctive feature. Different OTU delimitation methods consistently identified these four lineages as two novel operational taxonomic units (OTUs). Within one of the OTUs, there are high levels of intraspecific divergence, exhibiting the potential for independent evolution. Our analysis reclassified the publicly available mitochondrial genomes of Saccostrea into nine OTUs, further revealing significant mislabeling on GenBank as indicated by previous studies. The study adds new mitogenomic resources for Saccostrea and provides data useful for future integrative taxonomic work.