In this study, we provide the first report of the complete mitochondrial genome of Emydocephalus ijimae. The mitogenome length is 18,259 bp and includes 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and three non-coding regions. The sequence presented could be very useful for further phylogenetic and evolutionary study.

The complete mitochondrial genome of the highly venomous blue-lined octopus, Hapalochlaena fasciata (Hoyle, 1886), was analyzed by the primer walking method. Its mitogenome was 15,479 bp in total length, comprising 13 protein-coding genes, 2 ribosomal RNA genes, and 23 transfer RNA genes. In the phylogenetic tree, the gene content and order were congruent with those of typical octopodiform species. The mitogenomic sequence presented could be very useful as the first record of the complete mitogenome for the genus Hapalochlaena.

The full-length mitochondrial genome of Pseudohelice subquadrata (Dana, 1851) was analyzed by the primer walking method. Its mitogenome is 16,884 bp in length, comprising 13 protein-coding genes, 2 ribosomal RNA genes, and 22 transfer RNA genes. The phylogenetic tree confirmed that P. subquadrata belonged to the subsection Thoractotremata within the Crustacea. This is the first record of the complete mitogenome for the genus Pseudohelice.

We here report the complete mitochondrial genome of the Hydrophis melanocephalus slender-necked sea snake from Okinawa, Japan. Its length is 17,182 bp, consisting of 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and three non-coding regions, providing the basis for further phylogenetic and evolutionary studies of sea snakes.