Gonyaulax hyalina and G. fragilis (Dinoflagellata), two taxa associated with ‘mare sporco’, indicate the same species.

Aggregates of mucilaginous material have been at times observed in coastal and oceanic sea waters. In the Adriatic Sea (Mediterranean Sea), these events have been known since the 18th century as 'mare sporco' (= dirty sea), and in recent years, they have been associated with the dinoflagellate Gonyaulax fragilis; whereas, in New Zealand mucilage events were linked to Gonyaulax hyalina. In summer 2012, during a 'mare sporco' event in the Gulf of Naples (Mediterranean Sea), numerous cells of a species tentatively identified as Gonyaulax hyalina were detected in the mucilaginous aggregates. Since the boundary between G. fragilis and G. hyalina was not clear, we compared a strain isolated from the Gulf of Naples in 2012 with two strains from the Adriatic Sea and New Zealand waters, the latter two identified as G. fragilis and G. hyalina, respectively. Detailed light microscopy and scanning electron microscopy observations of the three strains showed that all shared the same thecal plate pattern and morphological features. Partial small subunit and large subunit rDNA regions of the three strains were identical. Based on these results and on a revision of the taxonomic history of the two taxa, we propose that G. fragilis and G. hyalina are the same species. Gonyaulax fragilis was described as Steiniella fragilis by Schutt in 1895 and transferred to G. fragilis by Kofoid in 1911. Gonyaulax hyalina was described a few years later by Ostenfeld and Schmidt in 1901. Thus, the name G. fragilis has priority, while G. hyalina is to be considered a synonym.