Ultrastructure and molecular phylogenetic position of a new marine sand-dwelling dinoflagellate from British Columbia, Canada: <i>Pseudadenoides polypyrenoides</i> sp. nov. (Dinophyceae)

<p>Two monospecific genera of marine benthic dinoflagellates, <i>Adenoides</i> and <i>Pseudadenoides</i>, have unusual thecal tabulation patterns (lack of cingular plates in the former; and no precingular plates and a complete posterior intercalary plate series in the latter) and are thus difficult to place within a phylogenetic framework. Although both genera share morphological similarities, they have not formed sister taxa in previous molecular phylogenetic analyses. We discovered and characterized a new species of <i>Pseudadenoides, P. polypyrenoides</i> sp. nov., at both the ultrastructural and molecular phylogenetic levels. Molecular phylogenetic analyses of SSU and LSU rDNA sequences demonstrated a close relationship between <i>P. polypyrenoides</i> sp. nov. and <i>Pseudadenoides kofoidii</i>, and <i>Adenoides</i> and <i>Pseudadenoides</i> formed sister taxa in phylogenetic trees inferred from LSU rDNA sequences. Comparisons of morphological traits, such as the apical pore complex (APC), demonstrated similarities between <i>Adenoides, Pseudadenoides</i> and several planktonic genera (e.g. <i>Heterocapsa, Azadinium</i> and <i>Amphidoma</i>). Molecular phylogenetic analyses of SSU and LSU rDNA sequences also demonstrated an undescribed species within <i>Adenoides.</i></p>