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 characterised by cellular torsion, cingulum with 1.25 turns and sulcus with 0.25 turn, and a hemispherical hypocone. The nucleus was curved, and sausage-shaped, and there were small, 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 formed a complete circle surrounding the cell apex, consisting of three parallel rows of vesicles; and that the outer rows, composed of small vesicles, were 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, confirmed that the species was closely related to T. convolutum within the family Ceratoperidiniaceae. However, the species was distinct from T. convolutum by differences in cingulum and sulcus turn numbers, shape of hypocone in dorsal view and size. Based on morphological and phylogenetic analyses, we propose Torquentidium flavescens comb. nov. nested within the family Ceratoperidiniaceae. ⓒ 2020, ⓒ 2020 International Phycological Society.