The mt genome of S. patagonica shows a gene arrangement different from that of any other cephalopod. The ATP6 and ATP8 genes are separated like those in the Nautilus mt genome. It is expected that mt genomes of Decapodiformes are probably derived from an octopus-type mt genome ( Akasaki et al., 2006, Yokobori et al., 2004 and Yokobori et al., 2007). Considering the mt block structures, the Semirossia mt genome appears to retain the structural features ([ND3–tRNASer–ND2–COX1–COX2] and [Cytb–ND6–tRNAPro–ND1]) of the octopus-type mt genome. However, any possible genome evolution (gene rearrangement process) of Semirossia from the octopus mt genome or from another squid’s mt genome could not be inferred. There are still some missing parts in the mt genome evolution of coleoids. Additional new mt gene arrangements which fill the missing parts of squid mt genome evolution may be discovered in the future.