First record of a raphid diatom species Plagiolemma distortum Nezan (Naviculales, Bacillariophyceae) from the East China Sea and Korean coastal areas

Abstract

A new recorded diatom, Plagiolemma distortum was isolated from plankton samples from the East China Sea and Korean coastal areas. The species was characterized by light and scanning electron microscopy of laboratory cultures, as well as small subu nit (SSU) rDNA gene and chloroplast - encoded rbcL gene sequences . Cells have an unusual and complex shape, single or in pairs, contain some yellow- brown plastids and a variable number of refractive granules. In addition, a novel capsule stage containing motile cell was observed. The valves are strongly vaulted, with undulating margins. The girdle is plain, and the raphe is strongly sigmoid. Molecular phylogenetic analyses of multigene sequences (SSU+rbcL) revealed that the sequences of Plagiolemma distortum formed an indiependent clade nested within the Plagiotropi daceae. Phylogenetic analysis based on SSU rDNA gene sequences indicated that the clade of Plagiolemma distortum was most closely related to Plagiotropis species, and the Plagiotropidaceae clade was sister to the Pleurosigmataceae clade.