Unarmoured and thin-walled dinoflagellates from the Gulf of Naples, with the description of Woloszynskia cincta sp. nov. (Dinophyceae, Suessiales) RAFFAELE SIANO*, WIEBE H.C.F. KOOISTRA,MARINA MONTRESOR AND ADRIANA ZINGONE Ecology and Evolution of Plankton, Stazione Zoologica Anton Dohrn Naples, Villa Comunale 1 80121 Naples, Italy R. SIANO, W.H.C.F. KOOISTRA, M. MONTRESOR AND A. ZINGONE. 2009. Unarmoured and thin-walled dinoflagellates from the Gulf of Naples, with the description of Woloszynskia cincta sp. nov. (Dinophyceae, Suessiales). Phycologia 48: 44–65. DOI: 10.2216/08-61.1. The unarmoured dinoflagellate assemblage of the Gulf of Naples has been investigated in the frame of a 1-year sampling of natural surface samples collected weekly at a coastal station c. 2 miles offshore. Twenty-six strains of unarmoured dinoflagellates were brought into culture by means of serial dilution. Observations at both light and scanning electron microscopy (SEM) together with molecular phylogenetic analyses allowed identification of eight dinoflagellate species. Gymodinium aureolum, Karlodinium veneficum, Protodinium simplex and Takayama acrotrocha were previously reported in the Mediterranean; whereas, Karlodinium ballantinum and Lepidodinium viride together with a taxon identified as Karenia cf. longicanalis are recorded in the basin for the first time. A new thin-walled dinoflagellate is described as Woloszynskia cincta sp. nov. on the basis of morphological results. Molecular analysis showed that Woloszynskia cincta is closely related to W. halophila and W. pseudopalustris and only distantly related to W. pascheri. In Protodinium simplex, a straight acrobase and an arrangement of the amphiesmal vesicles in latitudinal series were revealed by SEM observations, demonstrating the relatedness of this species with woloszynskioid dinoflagellates. Based on new morphological information on Karlodinium species, Gyrodinium corsicum is transferred to Karlodinium corsicum. New morphological features are identified for the recognition of Takayama acrotrocha, such as the arrangement of the acrobase and the presence of a pore on the ventral side of the cell. The latter species was found to be genetically distinct from other species in the genus Takayama, which is monophyletic. KEY WORDS: Dinoflagellates, distribution, Gymnodinium, Karenia, Karlodinium, Lepidodinium, LSU rDNA, Mediterranean Sea, Protodinium, Takayama, SDC, taxonomy, toxic, unarmoured, Woloszynskia INTRODUCTION Dinoflagellates are one of the major components of marine phytoplankton assemblages, at times accounting for a high percentage of the microalgal biomass. They include several potentially dangerous species for both humans and marine fauna (Moestrup et al. 2004). Nevertheless, the actual biodiversity and biogeography of these microalgae is still mostly underestimated. Especially unarmoured taxa have received little attention mainly because commonly used fixatives (formaldehyde, Lugol’s solution) impair preserva- tion of their cell morphology and ultrastructure and make their identification problematic. Daugbjerg et al. (2000) revolutionised the taxonomy of unarmoured dinoflagellates by carrying out combined morphological and molecular investigations on several species. The authors discovered that genera can be distinguished – amongst other ultrastructural features – by the size, shape and arrangement of the sulcal groove present on the cell apex (acrobase). They emended the diagnosis of the genus Gyrodinium (Kofoid & Swezy) Hansen & Moestrup and separated the polyphyletic genus Gymnodinium (Stein) Hansen & Moestrup into four monophyletic genera: Akashiwo Hansen & Moestrup, Karenia Hansen & Moestrup, Karlodinium Larsen and Gymnodinium sensu stricto (Stein) Hansen & Moestrup. Additional cell surface (e.g. sulcal indentation) and ultrastructural features (e.g. shape and position of the nucleus) were subsequently shown to be useful for defining genera and species. The genera Amphidinium Clapare `de & Lachmann (Jørgensen et al. 2004a; Murray et al. 2004) and Woloszynskia Thompson (Lindberg et al. 2005; Moestrup et al. 2008) were revisited, and the genera Takayama de Salas, Bolch, Botes & Hallegraeff (de Salas et al. 2003); Togula Flo Jørgensen, Murray & Daugbjerg (Jørgensen et al. 2004b); Baldinia Hansen & Moestrup (Hansen et al. 2006); Tovellia Moestrup, Lindberg & Daugbjerg; Jadwigia Moestrup, Lindberg & Daugbjerg (Lindberg et al. 2005) and Borghiella Moestrup, Hansen & Daugbjerg (Moestrup et al. 2008) were erected. First, pioneering studies on phytoplankton taxonomy included several species collected in the Gulf of Naples (GON) (Schu ¨tt 1895; Kofoid & Swezy 1921; Schiller 1928, 1933). However, little further progress has been made in assessing the diversity of unarmoured dinoflagellates in this region. Nevertheless, these organisms, especially smaller ones (, 15 mm), are important in the GON, particularly during the late spring–early summer period (May–July), and they seem to have increased in both abundance and biomass in recent years (Montresor et al. 1998; Ribera d’Alcala ` et al. 2004). Last but not least, several unarmoured species known to be harmful (e.g. Karlodinium, Karenia) occur in the Mediterranean Sea (Go ´mez 2003; Garce ´s et al. 2006; Zingone et al. 2006). We investigated the unarmoured dinoflagellate microflo- ra of the GON during a 1-year sampling program of the * Corresponding author (siano@szn.it). Phycologia (2009) Volume 48 (1), 44–65 Published 2 January 2009 44