Abstract Classification of athecate dinoflagellates has historically relied on phenotypic characteristics, yet molecular phylogenetics has revealed the group to be polyphyletic, highlighting the lack of information on species richness and genetic sequences. The apical groove has been found to be an adequate character to draw group boundaries. Here, we describe Dodgeum nauticum gen. et sp. nov., a novel heterotrophic athecate dinoflagellate isolated from Acapulco Bay, Mexican Pacific. Morphological analysis revealed a small (9–11 µm long and 7–9 µm wide), chloroplast-lacking species with an excavated cingulum that descends three girdle widths and a distinctive apical groove that spirals counterclockwise along the dorsal cell surface. Morphological observation revealed our specimens do not display any similarities to known groups of dinoflagellates. Molecular phylogenetic analyses of combined SSU and LSU rDNA sequences position Dodgeum as a group without clear affiliations within the Dinophyceae. The lack of identifiable features linking Dodgeum to existing groups, together with its genetic distinctiveness, supports its status as an independent genus with uncertain taxonomic position at the class level. This study highlights the gaps in our knowledge of dinoflagellate systematics, and underscores the importance of integrating morphological and molecular approaches in revealing hidden dinoflagellate diversity and solving phylogenetic problems.
Ruíz-García et al. (Sat,) studied this question.