Two new species formally attributed to Protoperidinium oblongum (Aurivillius) Park et Dodge (Peridiniales, Dinophyceae): Evidence from cyst incubation experiments

Cyst–theca relationships of the common armored dinoflagellate Protoperidinium oblongum were re-investigated by incubation experiments and molecular phylogenetic analysis. Living cysts provided for incubation experiments were collected from several places in Japan, including Omura Bay, West Japan and Lake Saroma in Hokkaido, North Japan. One hundred and four cysts were incubated and 18 motile cells were germinated from these cysts. To clarify their morphological characteristics both cysts and germinated thecate cells were observed, especially the archeopyle type, the number and shape of anterior intercalary plates, and the shape and development of apical and antapical horns. In order to provide molecular phylogenetic analysis, germinated cells from incubated cysts were examined for their LSU rDNA sequences. Results reveal that three morphologically different cysts produced three morphologically different thecate cells, which were previously known as Protoperidinium oblongum var. latidorsale, Protoperidinium oblongum var. inaequale, and Protoperidinium oblongum var. symmetricum. The molecular phylogenetic analysis demonstrated that the Oceania group in the genus Protoperidinium includes these three varieties as well as Protoperidinium divergens, Protoperidinium claudicans, and Protoperidinium steigingerae. This group is separated from Protoperidinium sensu stricto, and the three plankton forms are phylogenetically separate and independent species. Based on these facts, two new species, Protoperidinium quadrioblongum Sarai, Kawami et Matsuoka, the new name for Protoperidinium oblongum var. symmetricum and Protoperidinium paraoblongum Sarai, Kawami et Matsuoka for Protoperidinium oblongum var. inaequale are described.

► Former Protoperidinium oblongum consists of three different species.
► These three species produce morphologically and phylogenetically different cysts.
► Two new species of former Protop. oblongum are described.
► The Oceania group including these species is separated from the Protoperidinium s.s.