Hey, Myers, two can play at this game. An article in the Journal of Molecular Evolution presents structural and sequence analysis of hemocyanin (an oxygen carrying protein) from the cephalopod, Nautilus pomilius (shown at the left). They also compared the sequence to another cephalopod, Octopus dofleini, and found that the two species diverged approximately 415 million years ago.
Bergmann, S, B Lieb, P Ruth, and J Markl. 2006. The Hemocyanin from a Living Fossil, the Cephalopod Nautilus pompilius: Protein Structure, Gene Organization, and Evolution. J Mol Evol 62: 362-374.