Psammodinium inclinatum gen. nov. et comb. nov. (=Thecadinium inclinatum Balech) is the closest relative to the toxic dinoflagellate genera Gambierdiscus and Fukuyoa

11 pages, 8 figures, 1 table, supplementary data https://doi.org/10.1016/j.hal.2019.04.001The heterotrophic sand-dwelling dinoflagellate Thecadinium inclinatum has been re-examined by light and scanning electron microscopy in order to resolve the discrepancies on its plate pattern from the literature, and to obtain its phylogenetic information single-cell PCR technique has been used. The comparison of morphological and molecular information available for other Thecadinium species confirms the genus is polyphyletic and T. inclinatum seems not related to other representatives of the genus sensu lato. Thus, a new genus and combination for the species, Psammodinium inclinatum gen. nov., comb. nov. is proposed. Cells are heterotrophic and strongly laterally flattened, with sulcal pocket. The revised tabulation is: APC 3' 7” 7c 7s? 5”' 1p 2”” with a long-shank fishhook-shaped apical pore and descending cingulum. The cingulum inclines ventrally and declines on the right lateral side producing an asymmetrical epitheca. The epitheca is much smaller than the hypotheca. The phylogenetic results showed a strong relationship with the autotrophic epiphytic genera Gambierdiscus and Fukuyoa, being closely related with the latter. The Gambierdiscus species typically have a tropical and sub-tropical distribution and produce ciguatoxins, causing thousands of intoxications every year by consumption of contaminated fish. Fukuyoa representatives have a wider distribution including warm and temperate waters, and it has been demonstrated that they are also able to produce ciguatoxins, even though at lower amounts. P. inclinatum, which potential toxicity remains to be determined, represents an interesting independent evolutionary branch that resulted in the loss of chloroplasts, the strong lateral compression and the adaptation to sandy habitats in temperate and cold watersA.R. was funded by a “Senckenberg Taxonomy Grant, 2017”, and a DAAD “Research Stays for University Academics and Scientists, 2018, Grant 91644317”Peer Reviewe