Brigantedinium majusculumis the cyst of Protoperidinium sinuosum(Protoperidiniaceae, Dinophyceae)

Abstract:Two morphologically distinct species, Brigantedinium majusculumand Trinovantedinium applanatum, have been suggested as a cyst stage of Protoperidinium pentagonum; however, the cyst–theca relationships are still virtually undefined. In this study, we re-examined the motile stage of B. majusculumvia thecal plate analysis together with a molecular phylogenetic analysis based on partial large-subunit ribosomal DNA gene sequences. The morphological features of motile cells germinated from B. majusculumwere identical to those of Pr. sinuosum, and the molecular phylogenetic analysis showed that the germinated cells and B. majusculumare closely related to Pr. pentagonumand Pr. latissimumas a sister group. Additionally, high sequence divergences were observed between the germinated cells and B. majusculumas well as Pr. pentagonumand Pr. latissimum(18.0–19.5% according to P-values and 20.7–22.9% according to Kimura two-parameter values). On the basis of these results, our study indicates that B. majusculumshould be accepted as the cyst of Pr. sinuosum.