Erythropsidinium (Gymnodiniales, Dinophyceae) in the Pacific Ocean, a unique dinoflagellate with an ocelloid and a piston

The distribution and morphology of the dinoflagellate Erythropsidinium (=Erythropsis) was studied in the vicinity of the Kuroshio and Oyashio Currents, the Philippine, Celebes, Sulu and South China Seas, western and central equatorial and southeast Pacific Ocean. Ninety-four specimens were observed, most of them collected from depths of less than 90 m. The highest abundance (15 cells L−1) was recorded in the north Philippine Sea in May (32°N, 138°E, 30-m depth). Twenty-four specimens were found in a station in the offshore Perú-Chile Current (31°52′S, 91°24′W). The transition regions between open warm waters and productive currents or upwellings seem to favour the abundance of Erythropsidinium. Specimens with duplicate pistons, with two protuberant ocelloids, and specimens with a piston that attains up to 20 times the body length are illustrated for the first time. All the specimens have been ascribed to the type species, Erythropsidinium agile, until stable taxonomical criteria are established for the species diagnosis. Despite the complexity of its organelles, the ocelloid and piston, the competitiveness of Erythropsidinium in the pelagic ecosystem seems to be low.