The Sepia and the oegopsid mt genomes are considered to have evolved through the entire mt genome duplication and random loss events from theOctopus-type genome ( Akasaki et al., 2006), although complicated mt genome structures of Semirossia and Sepioteuthis make it difficult to deduce their evolutionary histories. Accordingly, it is reasonable to consider that the Octopus-type genome had been maintained before the divergence of the three lineages of Oegopsida, Myopsida and Sepiolida. The ocutopus-like mt genome was probably the origin of all the decapodiform mt genomes including Semirossia and Sepioteuthis.