Chaetoceros atlanticusvar.koreanusvar. nov. (Bacillariophyta) from the East Sea of Korea and closely related taxa: insight into the ultrastructure of the setae

Chaetoceros atlanticus var. koreanus, a new variety of C. atlanticus, was collected from the East Sea of Korea on 20 August 2013. Its morphological characteristics were examined from wild material, and the new variety was compared with three closely related taxa, C. atlanticus var. atlanticus, C. atlanticus var. neapolitanus and C. atlanticus var. skeleton. The new taxon belongs to the subgenus Chaetoceros, which is characterized by numerous granular chloroplasts in the setae as well as the body of the cell and a rimoportula on each valve, and to the section Atlantica, which is characterized by a long tubular external rimoportula at the centre of each valve, terminal and intercalary setae differing in length and direction, and wide hexagonal apertures. Chaetoceros atlanticus var. koreanus shares its general morphological characteristics with three closely related species, but has rows of small poroids forming a grid pattern, a tetragonal cross-section, and perpendicular costae on the setae. These features...