Mitochondrial genomes of Terebelliformia: gene rearrangements, phylogenetic relationships, and evolutionary insights

An in-depth analysis was conducted on the mitochondrial genomes of three newly introduced Terebelliformia species (Amaeana sp., Terebellides sp.A and Terebellides sp.B), focusing on their genomic features, gene rearrangement patterns, and phylogenetic relationships. The mitogenome sequences of the three species are approximately 16,000 bp in length. Each genome encodes 38 genes, all located on the H-strand. The base composition of the mitogenome exhibits a rich A + T content ranging from 64.83% to 66.24%. The selection pressure analysis revealed that the Ka/Ks ratio of the 13 protein-coding genes (PCGs) is all less than 1, indicating that the species in Terebelliformia are under purifying selection. In gene rearrangement analysis, seven different rearrangement patterns were observed in Terebelliformia, with changes in gene order mainly involving rearrangements of tRNA genes. Phylogenetic results show that Sabellida and Terebellida were not recovered as monophyletic in this study, whereas Spionida was recovered as a monophyletic clade. Within Sedentaria, Terebelliformia formed a relatively cohesive assemblage including Ampharetidae, Alvinellidae, Melinnidae, Trichobranchidae, and Terebellidae. In addition, Echiura and Clitellata were recovered as lineages nested within Sedentaria rather than as basal or outgroup taxa. The results provide important molecular evidence for further understanding Terebelliformia and its evolutionary history.