Pentapharsodinium ocelliferum sp. nov. (Ensiculiferaceae, Dinophyceae), a novel armored dinoflagellate with an eyespot from the Philippines

An eyespot-bearing armored dinoflagellate from the Philippines is described as a novel Pentapharsodinium species based on distinct cellular morphology, thecal plate tabulation, and phylogenetic position inferred from ITS and LSU rDNA sequences. Cells were ovoid to teardrop-shaped, with an episome slightly larger than the hyposome. An eyespot was present in the sulcal region, and the nucleus was located centrally to posteriorly. The plate tabulation Po, cp, X, 4′, 3a, 7′′, 5c, 5s, 5′′′, 2′′′′, with a spine on plate C1, was consistent with Pentapharsodinium , although variation occurred in the number of postcingular and antapical plates. Both a round apical pore plate with a shallow indentation forming a V-shaped concavity and a rectangular X-plate were flanked by ridges of plates 2′ and 4′. Plate 7′′ was isodiametric, and plate Sa was small. Pentapharsodinium ocelliferum sp. nov. can be distinguished by the presence of an eyespot and distinctive thecal plate features, including a reduced Sa plate, an isodiametric 7′′ plate, and characteristic features of the apical pore. Temporary cysts were common, while resting cysts with smooth, thick walls were rare in culture. The new species was positioned within the Pentapharsodinium clade, with P. imariense as its closest relative in the ITS phylogeny.