Morphology and molecular phylogeny of a widely distributed but little-known sand-dwelling phototrophic dinoflagellate, Coutea sabulosa gen. & sp. nov. (Dinophyceae, Alveolata)

ABSTRACT A new thecate, photosynthetic, sand-dwelling marine dinoflagellate, Coutea sabulosa gen. & sp. nov., observed in various locations from temperate to subtropical areas, is described based on detailed morphological and molecular data of material from Germany and Kuwait. Cells of C. sabulosa are oval, small (14.5–28.3 µm long and 11.1–18.0 µm wide), dorsoventrally compressed, and show a conspicuous apical hook projection pointing to the right. The epitheca is smaller than the hypotheca and the cingulum is ascending, about 3× its width. The thecal plate pattern is unusual and interpreted as APC, 4ʹ, 3a, 7ʹʹ, 5c, 4s, 6ʹʹʹ, 2ʹʹʹʹ. The APC comprises a narrow Po plate with a slit opening, located on the right-dorsal side, and it is covered by a projection of the first apical plate. Morphologically, the plate pattern has some affinities with Amphidiniella sedentaria, a sand-dwelling dinoflagellate species of roughly the same size and gross outline. However, the two taxa differ from each other in shape, size of epitheca and organization of the APC. They possess the same number of apical, precingular, postcingular and antapical plates but their relative sizes, shapes and especially the arrangement differs. Molecular phylogeny inferred from concatenated ribosomal genes reveals that C. sabulosa forms a well supported clade in the core dinoflagellates, but it is not related to any other existing taxa and diverges widely from A. sedentaria. From the present study, this new taxon appears very atypical among dinoflagellates, and further studies will be necessary to resolve its evolutionary position.