Comparison of taxa of the mussel Mytilus (Bivalvia) by analysis of the nuclear small-subunit rRNA gene sequence

Small-subunit rRNA gene sequences (18S rDNA) were determined for Mytilus californianus and Atlantic and Pacific representatives of the blue mussel complex, Mytilus edulis, Mytilus trossulus, and Mytilus galloprovincialis (Mytilinae). A sequence from the modiolid mussel Geukensia demissa was used as the outgroup. Differences among the mytilid sequences were small, 2-10 nucleotide positions in 1825-1827 base pairs, whereas the sequence from G. demissa was 1810 base pairs long and differed from M. edulis edulis in 81 positions. The "edulis-trossulus-galloprovincialis" taxa in this study have diverged from one another, and this complex appears to comprise at least six genetically distinct entities, some of which have previously held specific status. Recognition of this array may lead to the identification of morphological or biological characters that reflect the observed genetic differences.