The deep‑sea quill worm Hyalinoecia robusta (Annelida: Onuphidae) is an ecologically important benthic species, yet its mitochondrial genomic resources remain extremely limited. In this study, we assembled and characterized the complete mitochondrial genome of H. robusta using Illumina short‑reads, and performed a preliminary phylogenetic analysis based on concatenated mitochondrial protein‑coding genes (PCGs). The circular mitogenome is 15,029 bp in length and contains the standard set of 37 metazoan mitochondrial genes, including 13 PCGs, 22 transfer RNA genes, and 2 ribosomal RNA genes. The overall nucleotide composition shows a strong A+T bias (66.45%), with negative AT and GC skews. Maximum‑likelihood phylogenetic analyses using both nucleotide and amino‑acid sequences of the 13 PCGs consistently recovered H. robusta as the sister group to two Diopatra species (Onuphidae), while three Marphysa species (Eunicidae) formed a separate lineage. The newly characterized mitogenome provides a valuable genetic resource for molecular identification, comparative mitogenomic studies, and biodiversity assessment of marine annelids, and offers preliminary mitogenomic support for the close affinity between Hyalinoecia and Diopatra within Onuphidae.
Huang et al. (Wed,) studied this question.