Assessing divergence time of Spirulida and Sepiida (Cephalopoda) based on hemocyanin sequences

► Calculated hemocyanin-based molecular clock is stable. ► Estimated divergence time (150 ± 30 mya) of Spirulida and Sepiida is reliable. ► A duplication of the FU (functional unit)-d was found for Spirula. ► This duplication appears to be a synapomorphic character of the Decabrachia.