Vulcanodinium rugosum gen. nov., sp. nov. (Dinophyceae): a new marine dinoflagellate from the French Mediterranean coast. A new armoured marine dinoflagellate, Vulcanodinium. rugosum Nezan et Chomerat, gen. nov., sp. nov. is described from water samples of Mediterranean lagoons. The thecal plate formula is Po, X, 4', 3a, 7 '', 6c, 6s, 5'", 2'. The apical pore plate Po is very large and a mucous matrix is extruded from its centre. The plate X is rather long and just below is the narrow and short first apical plate 1'. The intercalary anterior plates are contiguous. The first cingular c1 plate is narrow. The number, the shape of plates and the presence of lists characterize the sulcus. The thecal surface is covered by longitudinal striae with often cross reticulations and is perfored by large pores. According to the studied feature, the morphology of Vulcanodinium rugosum looks like, either a peridinioid or a gonyaulacoid species. A phylogenetic study, based on LSU rDNA sequence data, confirms that this taxon is new and that it belongs to the order Peridiniales. However, it is not possible to affiliate it neither to a particular family nor to a known genus. As a consequence, a new generic name, Vulcanodinium is proposed with V. rugosum as type species, assigned in the order Peridiniales, incertae sedis for the time being.