Ostreopsis cf. siamensis and Ostreopsis cf. ovata from the Atlantic Iberian Peninsula: Morphological and phylogenetic characterization

• Provide new molecular data about existing strains in the Atlantic Iberian Peninsula.
• Found two sizes of thecal pores in O. cf. siamensis and one in O. cf. ovata.
• O. cf. siamensis had 11–18 thecal pores per 100 μm2 and 11–15 in O. cf. ovata.
• Provide a morphometric table with most of the data available in bibliography.
• Field isolates presented larger cell sizes than cultured ones.

Individuals of Ostreopsis, a genus containing potentially toxic species which affects human health, were collected during summer-autumn 2010 and 2011 from 17 sites located along the Atlantic coast of the Iberian Peninsula, a temperate area which during summer presents contrasting seawater temperatures. Ostreopsis cells were obtained by shaking macroalgae collected from rocky-shore areas bordering accessible beaches. Isolated strains and field samples were analyzed for morphological and phylogenetic characterization where sequences of the ITS1-5.8S-ITS2 region of the rDNA delineated two different species fitting Ostreopsis cf. ovata and Ostreopsis cf. siamensis. By means of calcofluor staining and scanning electron microscopy, it was observed that field samples of both species exhibited a wide and overlapping range of dorsoventral as well as width values. Those cells presented 11–18 pores/100 μm2 and were also similar concerning plates shape and size. The main differential feature between the two species was the presence of two sizes of thecal pores (0.07–0.13 μm and 0.15–0.39 μm) in Ostreopsis cf. siamensis and one size (0.24–0.56 μm) in Ostreopsis cf. ovata. A comparison of field vs. cultured cells indicated that field isolates presented larger cells than in culture.