Observations on Ceratoperidinium (Dinophyceae)

Abstract Until now, the rare dinoflagellate genus Ceratoperidinium Margalef has been recorded only from the Mediterranean Sea. For the first time, photomicrographs (bright field, Nomarski and epifluorescence) are reported from Lugol-fixed samples collected from the Sulu and Celebes Seas and the western Equatorial Pacific Ocean. The specimens showed high variability in the relative size of the flexible extensions. Several specimens corresponded to the type species, C. yeye, and lacked the apical extension. Other specimens showed an apical extension of variable size that corresponded to the description of C. mediterraneum. This taxon is considered to be a morphological variety of C. yeye on the basis of the high interspecimen variability in the length of the extensions; specimens intermediate between C. yeye and C. mediterraneum occur where both forms coexist. The ventral view is proposed (confirmed by DAPI staining) to be that with the nucleus located in the left side of the cell. Thecal plates were not observed in specimens stained with Fluorescent Brightener 28. Consequently, the placement of this genus in the order Peridiniales on the basis of the initial description from a single cell should be reconsidered.