The deepest mitochondrial genome sequenced from Mariana Trench Hirondellea gigas (Amphipoda)

Hirondellea gigas is an amphipod that is a dominant animal resident living in the Challenger Deep (~11,000m depth) of the Mariana Trench, which is the world deepest point in the ocean. Here we report a nearly complete mitochondrial genome of H. gigas, the world deepest mitogenome. The genome consists of two contigs with lengths of 8,603 bp and 6,984 bp, respectively, and it includes 13 complete protein-coding genes, 2 rRNA genes, and 21 tRNA genes. The ends of both contigs are highly repetitive and AT rich. The gene order of H. gigas is similar to another amphipod (Onisimus nanseni) in the same superfamily, Lysianassoidea. Phylogenetic analysis showed that Lysianassoidea is grouped with Gammaroidea and Calliopioidea in the same clade. Our result also suggested that the H. gigas collected from Izu-Bonin Trench and Japan Trench are indeed the same species as those from the Mariana Trench. These results will contribute to a better understanding of the phylogeny of amphipod and other hadal species.