Species of the dinoflagellate genus Gambierdiscus are the cause of Ciguatera Fish Poisoning, common in tropical areas. Nevertheless, until recently this syndrome was not reported in the NE Atlantic Ocean. A new photosynthetic dinoflagellate species, Gambierdiscus silvae sp. nov. is described based on samples taken from tide pools on rocky shores of the Canary Islands (NE Atlantic Ocean). Its morphology was studied by light and scanning electron microscopy. The new species is anterioposteriorly compressed, lenticular in shape with an epitheca slightly higher than the hypotheca. It is round in apical view and has a thick smooth theca with many scattered pores. Plate formula is Po, 4', 0a, 6″, 6c, 6s?, 5'″, 0p, 2″″. Plate 2' is hatchet-shaped and Plate 2″″ is very wide and the largest of the hypotheca. Phylogenies inferred from the large subunit nuclear rRNA showed that three G. silvae strains clustered in a well supported sister clade to G. polynesiensis, distinct from the other species. G. australes was observed for the first time in the Atlantic, together with G. excentricus already reported from these islands. This work increases the number of Gambierdiscus species described and shows their unexpected diversity in the Canary Islands.