Further examination of the cyst-theca relationship of Protoperidinium thulesense (Peridiniales, Dinophyceae) and the phylogenetic significance of round brown cysts

Abstract

K. Matsuoka, H. Kawami, R. Fujii and M. Iwataki. 2006. Further examination of the cyst-theca relationship of Protoperidinium thulesense (Peridiniales, Dinophyceae) and the phylogenetic significance of round brown cysts. Phycologia 45: 632–641. DOI: 10.2216/05-42.1The heterotrophic armored dinoflagellate Protoperidinium thulesense has an unusual combination of morphological characters, i.e. the thecal plate arrangement of the motile cell resembles a typical Protoperidinium, whereas the shape and archeopyle of the cyst are like the diplopsalids. We have re-examined the cyst-motile relationship of P. thulesense by cyst incubation and thecal plate analysis together with a molecular phylogenetic study based on small subunit (SSU) rDNA sequences. Five isolates of P. thulesense, including motile cells and cysts, and three Protoperidinium and three diplopsalid species were examined by using the single cell PCR method. The thecal plate arrangement of the motile cells isolated from field samples and those germinated from cysts were identical. The plate formula was: Po, X, 3′, 3a, 7″, 3c+t, 4s, 5′″, 2″″. The cysts of P. thulesense were round and brown with a theropylic archeopyle, and rather similar to the diplopsalid species, Diplopsalis lenticula, D. lebourae, Gotoius abei and others. SSU rDNA sequence analysis reveals P. thulesense is closely related to the subgenus Protoperidinium, especially species of the section Conica, and distant from the diplopsalid species. The phylogenetic and taxonomic significances of Protoperidinium and diplopsalid round brown cysts with a theropylic archeopyle are discussed.