| Summary: | This thesis investigates the diversity and distribution of polychaetes from Canadian marine waters employing both morphological (literature reports) and molecular (mtDNA) approaches. Collation of species reports from the literature indicated that nearly 15% of the 1,023 Canadian polychaete species occur in all three of Canada's oceans. In contrast, DNA barcode analysis of these widespread species indicated that most were species complexes. Barcode analysis of 333 provisional polychaete species revealed 40 times more sequence divergence between than within species, and extensive cryptic diversity in 36 morphospecies. Further examination of genetic discontinuities between Pacific and Atlantic-Arctic sister taxa indicated that periodic ice retreats during the Pleistocene enabled multiple migrations of polychaete species across the Bering Strait, ultimately increasing polychaete diversity in Canada. This thesis demonstrates the utility of DNA barcoding as a tool for species identification in polychaetes and for illuminating evolutionary and biogeographic patterns among species.
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