Morphological and molecular characterization of Tovellia cf. aveirensis (Dinophyceae) from Jiulong River, China

The dinoflagellate genus Tovellia is exclusively freshwater and characterized by the presence of an extraplastidial eyespot (Type C sensu Moestrup & Daugbjerg), a straight apical line of narrow plates (ALP) and a bipolar cyst with axial horns. Here we establish a Tovellia strain TSJL01 through incubation of a cyst with a pronounced paracingulum and bearing long, hollow and tapering processes collected from Jiulong River (China). The morphology of motile cells and cysts was investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. Cells of strain TSJLO1 possess a long ALP on the apex, with 10 or 11 narrow elongated vesicles lined at each side. The amphiesma has many pentagonal or hexagonal latitudinal vesicles, with 7-10 series on the epicone, 4-5 on the hypocone and 2 in the cingulum. Thin sections reveal a type C eyespot, and numerous chloroplasts radiating from a central pyrenoid complex. Cysts produced in culture differ from those observed in the field in the shape of their processes. Phylogenetic analyses based on large subunit ribosomal DNA (LSU rDNA) support that TSJL01 is nested within the genus Tovellia, and is closely related to T. aveirensis. The Chinese strain differs from T aveirensis mainly in the number of elongated plates surrounding ALP and thus was tentatively identified as T. cf. aveirensis. Another closely related species, Gymnodinium dodgei, is transferred to Tovellia based on the eyespot and cyst morphology.