Morphology of Brachidinium capitatum F.J.R. Taylor (Brachidiniales, Dinophyceae) collected from the western Pacific Ocean

This is a first report of the genus Brachidinium F.J.R. Taylor from the Pacific Ocean. Of the 17 specimens of B. capitatum reported here, 12 were collected from the vicinity of the Kuroshio in May (2 specimens) and July (10 specimens), 3 from the western equatorial Pacific Ocean, one from the Sulu Sea, and one from Tanabe Bay, Japan. The last-mentioned specimen was observed live. For the first time, the flagella and the sulcus of a member of the order Brachidiniales A.R. Loeblich III ex Sournia are depicted in photomicrographs. The ventral view corresponds to that seen when the position of the nucleus is in the left side of the cell. In several specimens (confirmed by DAPI-staining) showed a secondary nucleus located in the opposite side of the dinokaryon nucleus. In the live specimen, the sulcus was visible and the lateral extensions were observed to be moveable.