Evolution of hemocyanin subunits in mygalomorph spiders: Distribution of hemocyanin subunits and higher classification of the mygalomorphae

Mygalomorph spider's hemocyanins examined contain monomer subunits which ar e the component parts of hemocyanin hexamers and dimer subunits which bond two hexamers together. We determined the N-terminal amino acid sequences of twenty-two monomer subunits and ten constituent monomers of the dimer subu nits prepared from hemolymph of seven mygalomorph spiders. We classified th ese subunits into eight groups based on the sequence comparison. From the d istribution of monomer subunits in mygalomorph spiders, it is evident that duplications and losses of monomer subunits occurred frequently. This is th e reason why we cannot detect an orthologous monomer subunit derived from a common ancestral sequence in the seven spiders. These monomer subunits wer e found in either Atypoidea or Avicularioidea. On the other hand, the dimer subunits having similar N-terminal sequences were found widely in both myg alomorph spider groups, showing that the dimer subunits are more conservati ve than monomer subunits for their function different from monomer subunits .