Pellucidodinium psammophilum gen. & sp. nov. and Nusuttodinium desymbiontum sp. nov. (Dinophyceae), two novel heterotrophs closely related to kleptochloroplastidic dinoflagellates

Abstract

:Nusuttodinium spp. use ingested cryptomonad chloroplasts as kleptochloroplasts but form a sister group to Spiniferodinium spp., which are typical photosynthetic dinoflagellates. Our survey of the diversity of Nusuttodinium-related dinoflagellates resulted in the discovery of two colourless dinoflagellates, referred to as DAI (dinoflagellate collected from Aininkappu) and DIS (dinoflagellate collected from Ishikari). Cells of DAI possess a right-handed cingulum, an apical groove connecting with the sulcal extension at a right angle and nuclear chambers. Cells of DIS have a projection on their epicone encircled by a counterclockwise-directed apical groove and lack nuclear chambers. Cells of DAI digest cryptomonads directly, and DIS never ingests cryptomonads, making both species nonkleptochloroplastidic. Phylogenetic analyses showed that DIS is a member of the Nusuttodinium clade; whereas, DAI is a sister of the clade, and the photosynthetic genus Spiniferodinium is positioned at the base of these dinoflagellates. Based on a unique combination of features, including a unique shape to the apical groove, a right-handed cingulum, nuclear chambers and lack of a chloroplast, we describe DAI as Pellucidodinium psammophilum gen. & sp. nov. Based on a projection on the epicone, a counterclockwise-directed apical groove and the lack of nuclear chambers, we describe DIS as Nusuttodinium desymbiontum sp. nov. despite its inability to display kleptochloroplastidy. The phylogenetic position of P. psammophilum, together with its shared presence of nuclear chambers with Spiniferodinium, implies that it represents an evolutionary intermediate prior to the acquisition of kleptochloroplastidy; N. desymbiontum appears to have lost this competence secondarily.