Molecular phylogeny and morphology of Torquentidium gen. et comb. nov. for Cochlodinium convolutum and allied species (Ceratoperidiniaceae, Dinophyceae)

Abstract

Although the genus Pseliodinium within the family Ceratoperidiniaceae includes Ceratoperidinium falcatum, Cochlodinium cf. convolutum, C. cf. helix and unidentified Cochlodinium species, it is in need of reclassification because of the morphological differences and lack of morphological details of the species within the genus. A Cochlodinium-like species was isolated from a Korean coastal area and examined by light and scanning electron microscopy, as well as by the analysis of nuclear-encoded small subunit (SSU) and large subunit (LSU) rDNA. The Korean isolate was morphologically characterized by cellular torsion, and outer rows consisting of small rectangular and polygonal vesicles were visible along the sides of the cingulum. The apical structure complex (ASC) formed a complete circle surrounding the cell apex, consisting of three parallel rows of vesicles. In the ASC, the upper row was sometimes hidden and very small knobs were present on the central row. Morphological characteristics separated the Korean isolate from Ce. margalefii, Pseliodinium fusus(=Ce. falcatum), Kirithra asteri and Gymnodinium species (Gymnodinium sp. 1 and sp. 2) within the family Ceratoperidiniaceae. However, the morphological characteristics coincided with those of the previously recorded C. convolutum, C. cf. helix and other Cochlodinium species within the same family. Phylogeny based on SSU and LSU rDNA sequences revealed that the Korean isolate forms a clade independent from P. fusus, although they have high sequence similarity. Based on the morphological and phylogenetic analyses, we propose the new genus Torquentidium gen. nov. and a new combination for C. cf. helix and the Korean isolate Torquentidium convolutum erected within the family Ceratoperidiniaceae.