Morphology, toxin composition and molecular analysis of Dinophysis ovum Schütt, a dinoflagellate of the “Dinophysis acuminata complex”

This work provides a morphological, toxinological and molecular description of Dinophysis ovum Schütt, a species included in the Dinophysis acuminata complex, and often misidentified as D. acuminata Claparède and Lachmann. A dinoflagellate bloom occurred in the Galician Rías Baixas (NW Spain) in June 2006, where D. ovum was the overwhelmingly dominant (97%) Dinophysis species, accompanied by small numbers of D. acuminata, and other Dinophysis spp., Protoperidinium spp. and Ceratium spp. D. ovum was discriminated from D. acuminata at the light microscope on the basis of their different cell contours; it had only okadaic acid (OA) (7.1 pg cell−1) as a detectable lipophilic toxin component. Molecular analyses of the ITS1-5,8S-ITS2 rDNA region showed that D. ovum was grouped in a common clade of small-sized species of Dinophysis, close to D. sacculus. Analyses of mitochondrial genes (Cytochrome c oxydase 1) of D. ovum and D. acuminata showed this region exhibited a much higher variability −25 bp difference between the 2 species under study and was therefore more appropriate than rDNA genes for phylogenetic analyses of Dinophysis spp. This is the first report of lipophilic shellfish toxins in D. ovum, and of analyses of mitochondrial genes to discriminate between different species of Dinophysis.