Molecular phylogeny of the parasitic dinoflagellate Syltodinium listii (Gymnodiniales, Dinophyceae) and generic transfer of Syltodinium undulans comb. nov. (= Gyrodinium undulans).

The parasitic dinoflagellate Syltodinium listii was investigated from the open waters of the English Channel, southern North Sea and the NW Mediterranean Sea. Syltodinium listii has been unreported since its original description in the North Sea. Cells of S. listii were able to infect copepod eggs of different species, and even nauplii, and after each infection formed up to 32 cells embedded in a mucous envelope. Infection of the same host by more than one dinoflagellate was frequent; although overall, the progeny were reduced in number. Molecular phylogeny based on the small subunit ribosomal RNA (SSU rRNA) gene revealed that S. listii clusters with a group of environmental sequences from the cold North Atlantic region as a sister group of Gymnodinium aureolum. The large subunit ribosomal RNA (LSU rRNA) gene sequences of S. listii from the English Channel and cf. Gyrodinium undulans from the Mediterranean Sea were identical. Thus, we propose Syltodinium undulans comb. nov. for Gyrodinium undulans. The first internal transcribed spacer (ITS) and complete SSU rRNA gene sequences of Dissodinium pseudolunula are provided. The parasitic species of Chytriodinium, Dissodinium and Syltodinium cluster together within the family Chytriodiniaceae, including the free-living species Gymnodinium aureolum, G. corollarium and G. plasticum.