Gonyaulacalean tabulation revisited using plate homology and plate overlap, with emphasis on the ventral area (Dinophyceae)

We propose a standardization of the gonyaulacalean (Dinophyceae) Kofoidian plate tabulation using plate homology and overlap patterns, on the basis of a new morphological study of species belonging to 17 genera previously classified in the order Gonyaulacales: Acanthogonyaulax, Alexandrium, Amphidoma, Azadinium, Ceratium, Ceratocorys, Cladopyxis, Cribroperidinium, Fragilidium, Gonyaulax, Heterodinium, Lingulodinium, Paleophalacroma, Peridiniella, Spiraulax, Triadinium and Tripos. The plate immediately left of the flagellar pore is reinterpreted as a sulcal plate rather than its more conventional interpretation as a postcingular plate. With this new perspective the studied genera fall into two groups: 1) genera with only five Kofoidian postcingular plates (Acanthogonyaulax, Alexandrium, Ceratocorys, Cribroperidinium, Gonyaulax, Lingulodinium, Spiraulax and Triadinium) or six postcingular plates (Fragilidium); 2) genera with six Kofoidian postcingular plates, as well as differences in episomal plate patterns (Amphidoma, Azadinium, Cladopyxis, Heterodinium, Paleophalacroma and Peridiniella). The former are here considered true gonyaulacaleans, whilst the latter need further study for a more appropriate phylogenetic placement, and are here informally called non-gonyaulacaleans. In these non-gonyaulacalean genera, the first posterior intercalary plate overlaps the first postcingular plate/anterior left sulcal plate, but is always overlapped by the second postcingular homologue plate (a plate in similar position) demonstrating that the first plate of the postcingular series is not homologous in the two groups. Additionally, the identical overlapping pattern shows that the anterior left sulcal plate (Ssa) in gonyaulacaleans with five postcingular plates is the same plate as the first postcingular plate in gonyaulacaleans with six postcingular plates. Kofoidian definitions of posterior intercalary plates as well as antapical plates remain the same and are applied here. The Kofoidian hyposomal plate formula for gonyaulacaleans would then be 5–6''', 2p, 1''''.