The present paper report two species of epibenthic dinoflagellates viz., Gambierdiscus caribaeus and G. carpenteri from Nha Trang Bay, South Central Vietnam for the first time as a result of experiments with artificial substrates. Detailed descriptions of these two species with illustrations by light and scanning electron micrographs were provided. Both G. caribaeus and G. carpenteri recorded during the study had morphological features similar to the original descriptions of these species. The apical plate 2' of them is large, rectangular and symmetrical. Plate 3'' and 3''' of G. caribaeus are slightly symmetrical, compared with asymmetrical 3'' and 3''' plates in G. carpenteri. Plates 2'''' of G. caribaeus seem to be shorter in comparison with that of G. carpenteri. The plate formula: Po, 4', 6'', ?c, ?s, 5''' and 2''''.

Artificial substrate, epibenthic dinoflagellate, Gambierdiscus, Vietnam