Cyst‐theca relationships and phylogenetic positions of P eridiniales ( D inophyceae) with two anterior intercalary plates, with description of A rchaeperidinium bailongense sp. nov. and P rotoperidinium fuzhouense sp. nov

Summary P rotoperidinium species with two anterior intercalary plates were originally classified by J örgensen in the subgenus A rchaeperidinium and assigned to the sections E xcentrica , A vellana and A rchaeperidinium by T aylor, on the basis of the relative size of anterior intercalary plates and the extent of cingulum displacement. Phylogenetic relationships among these three sections have not been fully explored. Recently, A rchaeperidinium was reinstated as a genus, but several species fitting the emended description have not been transferred formally as molecular data were not available. In the present study we examined the cyst‐theca relationship of seven species with two anterior intercalary plates: four species assigned to P rotoperidinium and three to A rchaeperidinium , from the C hina S ea. Partial large subunit ribosomal DNA sequences were obtained from these seven species by single‐cell polymerase chain reaction, and for the cyst of P rotoperidinium stellatum from F rance. Two new species, A rchaeperidinium bailongense and P rotoperidinium fuzhouense , were described based on both theca and cyst morphology, and the cyst‐theca relationships of A . constrictum and P . abei var. rotunda were established for the first time. Maximum‐likelihood and Bayesian inference analyses revealed that P . fuzhouense was nested within the P rotoperidinium sensu stricto clade despite having only six postcingular plates, and sections E xcentrica , A vellana and the genus A rchaeperidinium were all monophyletic. Our results suggest that the presence/absence of a sulcal fin and antapical horns and the displacement of the cingulum are the most stable characteristics of the motile stages within the respective clades.