Cyst-theca relationship and phylogenetic positions of Protoperidinium (Peridiniales, Dinophyceae) species of the sections Conica and Tabulata, with description of Protoperidinium shanghaiense sp nov.

The genus Protoperidinium has been divided into several sections based on the shape of the first apical plate, the number/shape of anterior intercalary plates and the presence/absence of antapical horns/spines; however, phylogenetic relationships among these sections have not been fully explored. We examined the cyst-theca relationships of seven Protoperidinium species isolated from sediments along the Chinese coast. Ten partial nuclear-encoded large subunit ribosomal DNA (LSU rDNA) sequences were obtained by single-cell polymerase chain reaction (PCR) for seven species belonging to the Conica and Tabulata sections of the genus. New cyst-theca relationships were established for Protoperidinium biconicum and Protoperidinium humile, and the former was restricted to warmer waters. Brigantedinium majusculum was identified as the cyst of Protoperidinium pentagonum; whereas, Trinovantedinium applanatum corresponded to Protoperidinium shanghaiense sp. nov. Phylogenetic analyses based on LSU rDNA sequences were carried out using maximum likelihood and Bayesian inference and revealed that the theca-based section Conica was polyphyletic, and Tabulata was monophyletic. Surprisingly, some cyst-based genera (e.g. Brigantedinium, Selenopemphix) proved to be polyphyletic.