New dinoflagellate species P rotoperidinium haizhouense sp. nov. ( P eridiniales, D inophyceae), its cyst‐theca relationship and phylogenetic position within the M onovela group

Summary The number of cingular plates has been used to differentiate P rotoperidinium from P eridinium and related genera. P rotoperidinium is characterized by the presence of three cingular plates plus a transitional plate (3 C +t). However, many P rotoperidinium species have been described that exhibit different cingular plate tabulations. How these species should be classified within the genus remains unclear. To address this question, the phylogenetic relationship of four P rotoperidinium species, with three or four cingular plates and lacking a transitional plate, were examined in relationship to other P rotoperidinium species. These four species were germinated from cysts deposited in surface sediments collected from the E ast C hina S ea, the Bohai Sea and the Y ellow S ea. Three of the isolated species, P . tricingulatum , P . americanum and P . parthenopes , were described previously. The fourth is here described as P . haizhouense sp. nov. with the plate formula P o, X , 4′, 3a, 7′′, 3 C , 6 S , 5′′′, 2′′′′. Differences in the cyst stages of these four species, which can be taxonomically informative, were compared. Partial large subunit ribosomal DNA sequences were obtained by single‐cell polymerase chain reaction. Maximum‐likelihood and Bayesian inference showed that these four species, P . fukuyoi and I slandinium minutum form a monophyletic clade with maximal support. The genus as a whole, however, appeared polyphyletic. Our results suggest that the presence/absence of a transitional plate is significant in the phylogeny of P rotoperidinium .