Reclassification of Gyrodinium flavescens Kofoid & Swezy as Torquentidium flavescens comb. nov. (Ceratoperidiniaceae, Dinophyceae), based on morphology and phylogeny

Abstract

A Cochlodinium-like species was isolated from the Korean coast and examined by light microscopy and scanning electron microscopy (SEM). The species was characterized by cellular torsion, cingulum with 1.25 turn and sulcus with 0.25 turn, and a hemispherical hypocone. The nucleus was curved sausage-shaped, and there were small and dark grains distributed at the cell periphery, which were also reported in the original description of Gyrodinium flavescens by Kofoid & Swezy (1921). SEM observations revealed that the apical structure complex of the species forms a complete circle surrounding the cell apex, consisting of three parallel rows of vesicles, and that the outer rows composed of small vesicles are visible along the sides of cingulum. These morphological features were identical to those of Torquentidium convolutum. Phylogeny based on small subunit and large subunit rDNA sequences also confirmed that the species is closely related to T. convolutum within the family Ceratoperidiniaceae. However, the species was distinguished from T. convolutum by differences in cingulum and sulcus turn numbers, shape of hypocone in dorsal view and size. Based on the morphological and phylogenetic analyses, we propose the new combination Torquentidium flavescens nested within the family Ceratoperidiniaceae.