Bayesian inference majority-rule tree of bivalve mt genome relationships based on an analysis using the M3 codon substitution model and a nucleotide alignment of 12 mitochondrial protein-coding genes ( atp8 excluded). Numbers above an internal branch, from top to bottom, indicate nodal support values from BI, ML and MP nucleotide-based analyses, respectively. Numbers below an internal branch, from top to bottom, indicate nodal support values from BI, ML and MP amino acid-based analyses, respectively. Only nodal support values > 50% are presented. An asterisk above an internal branch indicates that all three nucleotide-based nodal support values are 100; an asterisk below an internal branch indicates that all three amino acid-based nodal support values are 100. Branch lengths reflect substitutions per site and the taxonomic and gender-specific transmission affiliations of the individual sequences are indicated at the right. All phylogenetic analyses strongly indicate that the unionoids represent the basal lineage for the bivalve taxa represented in this analysis.