Evidence from partial large-subunit (LSU) rDNA sequencing has been combined with ultrastructure, including details of the flagellar apparatus, in a number of phototrophic dinoflagellates, with the aim of trying to solve some of the most pressing taxonomic problems and to contribute to an improved understanding of the phylogeny within the group. Special attention has been paid to the unarmoured (naked) genera, many of which were described during the 1800s or early 1900s and whose taxonomy is artificial and misleading. This is particularly unsatisfactory because many of the species cause extensive plankton blooms, fish kills and other harmful events. Our studies have indicated that the path of the so-called apical groove (acrobase) is of particular importance for the taxonomy of the unarmoured genera of dinoflagellates. Features presently used to characterize many of the genera, such as the relative size of the epicone and hypocone, are misleading. Our data have resulted in the splitting of the lar...

The new classification of protists from the International Society of Protistologists (Adl et al., 2005) could not apply both the International Code of Botanical

In order to elucidate the phylogeny and evolutionary history of the Bacillariaceae we conducted a phylogenetic analysis of 42 species (sequences were determined from more than two strains of many of the Pseudo-nitzschia species) based on the first 872 base pairs of nuclear-encoded large subunit (LSU) rDNA, which include some of the most variable domains. Four araphid genera were used as the outgroup in maximum likelihood, parsimony and distance analyses. The phylogenetic inferences revealed the Bacillariaceae as monophyletic (bootstrap support ≥90%). A clade comprising Pseudo-nitzschia, Fragilariopsis and Nitzschia americana (clade A) was supported by high bootstrap values (≥94%) and agreed with the morphological features revealed by electron microscopy. Data for 29 taxa indicate a subdivision of clade A, one clade comprising Pseudo-nitzschia species, a second clade consisting of Pseudo-nitzschia species and Nitzschia americana, and a third clade comprising Fragilariopsis species. Pseudo-nitzschia as presently defined is paraphyletic and emendation of the genus is probably needed. The analyses suggested that Nitzschia is not monophyletic, as expected from the great morphological diversity within the genus. A cluster characterized by possession of detailed ornamentation on the frustule is indicated. Eighteen taxa (16 within the Bacillariaceae) were tested for production of domoic acid, a neurotoxic amino acid. Only P. australis, P. multiseries and P. seriata produced domoic acid, and these clustered together in all analyses. Since Nitzschia navis-varingica also produces domoic acid, but is distantly related to the cluster comprising the Pseudo-nitzschia domoic acid producers, it is most parsimonious to suggest that the ability of species in the Bacillariaceae to produce domoic acid has evolved at least twice.