The Dinoflagellate Gonyaulax fragilis Is ‘the Wrong Man’ of the Dirty Seas, and Reinstatement of Steiniella Within the Protoceratiaceae (Dinophyceae)

The production of mucilage aggregates is commonly associated with diatoms, but the harmful events known as ‘mare sporco’ or dirty seas have been attributed to the dinoflagellate Gonyaulax fragilis or G. hyalina. The synonymy of these taxa has been debated for decades. We report observations of G. fragilis from the Mediterranean Sea, and Atlantic and Indian Oceans, along with its SSU- and LSU rRNA gene and ITS region sequences from cells of the open Indian Ocean. The rDNA/ITS sequences are distantly related to those identified as G. fragilis from the Mediterranean Sea and New Zealand involved in dirty sea events. Unequivocally, G. fragilis is not the culprit of the mucilage events. Gonyaulax fragilis clusters with full support alongside with Schuettiella mitra, forming a sister group to the benthic genus Carinadinium, as an earlier branching lineage with the Protoceratiaceae (Ceratocorys, Pentaplacodinium, Protoceratium). A single anterior intercalary plate (1a) characterizes these genera, while the Gonyaulacaceae possess 2a. The genus Steiniella, first described for G. fragilis and S. mitra, has historically been synonymized with Gonyaulax. We reinstate Steiniella for these two species, and S. inflata, placing Schuettiella as a junior synonym. The species responsible of the mucilage events is attributed to G. hyalina.