Corresponding Author's Institution: Instituto Español de Oceanografía

Abstract: A new benthic toxic dinoflagellate is described from the Canary Islands, Spain. Gambierdiscus excentricus sp. nov. was isolated from seaweeds growing in tidal ponds and was observed in winter and summer. Its ' morphology was studied by means of Light Microscopy (LM) and Scanning Electron Microscopy (SEM); G. excentricus is a lenticular species having a Po plate ventrally displaced in relation to other species of the genus Gambierdiscus. Phylogenetic trees from large subunit (LSU) of ribosomal RNA gene LSUrDNA sequences displayed a topology confirming that G. excentricus clustered in its ' own group, separated from the rest of Gambierdiscus species and with G. australes as its closest relative. Pigment composition studied from G. excentricus cultures, included peridinin, as the major carotenoid, chlorophyll a and the accessories accessory chlorophylls c1 and c2. The Neuroblastoma cell-based assays for ciguatoxins (CTX) and maitotoxin (MTX) allowed identifyingconfirmed G. excentricus as a CTX- and MTX-like compounds producer. The finding of a toxic species of Gambierdiscus in the Canary Islands may explain the recent reported cases of ciguatera in the area