Relationship of Hediste (Annelida, Polychaeta) and the description of the complete mitochondrial genome of Hediste sinesimplex Costa et al., 2025, including a status reassessment of some Nereididae species

In this study, we update the phylomitogenomic relationships of Hediste (Annelida, Polychaeta, Nereididae), with the inclusion of Hediste sinesimplex as a recently described species from the Mediterranean and Northeast Atlantic. Phylogenetic inference using maximum likelihood, based on 13 Protein-Coding Genes (PCGs) from nereidid species, confirms the position of the recently described H. sinesimplex within the genus Hediste showing a closed relationship with the sympatric Hediste diversicolor . We also describe the complete mitochondrial genome of H. sinesimplex which is composed by of 15,876 bp genome size, with a GC content of 34.4%, and encodes 13 Protein-Coding Genes (PCGs), 22 transfer RNA (tRNA) genes, and two ribosomal RNA (rRNA) genes. Most PCGs start with the ATG codon and terminate mainly with TAA or TAG. However, three genes present incomplete stop codons: ND5 and ND1 end with T-, whereas cox1 ends with TA-. These results provide new genomic resources for nereidid systematics and contribute to a better understanding of phylomitogenomic relationships. Finally, our findings to provide a status reassessment of some species of Nereididae based on mitochondrial genes.