Gene rearrangements in the mitochondrial genome of Eucleoteuthis luminosa (Ommastrephidae, Cephalopoda) and phylogenetic implications for Coleoidea

The complete mitochondrial genome provides crucial information for comprehending gene rearrangement, molecular evolution, and phylogenetic analysis. Here, we have determined the complete mitogenome sequence of Eucleoteuthis luminosa for the first time. The total length is 20,300 bp, including 18 protein-coding genes, COI-COIII, ATP6, and ATP8 are duplicated, 22 transfer RNA genes, and 2 ribosomal RNA (rRNA) genes (12S and 16S rRNA). Specifically, the overall A + T content is 69.23% and the C + G content is 30.77%. It shows a significant AT bias. The whole mitogenome indicates a negative GC skew (-0.275) and a positive AT skew (0.049). Furthermore, the gene order has been rearranged comparing with that of the ancestor of Oegopsida. The tandem duplication random loss model and the slipped strand mispairing mechanism were determined as most likely to explain the observed gene rearrangements. Phylogenetic analysis shows that Vampyroteuthidae and Octopodidae are sister groups that belong to Octopodiformes, while Sepiolidae had been classified in the order Sepiida. Interestingly, the families Sepiolidae and Idiosepiidae are grouped into one branch. These results will help to better understand the gene rearrangements and evolution of E. luminosa and lay a foundation for further phylogenetic studies of Cephalopoda.