Morpho-molecular characterization of diatom Skeletonema pseudocostatum (Thalassiosirales, Bacillariophyta) from the Korean coast = 규조류 Skeletonema pseudocostatum Medlin(Thalassiosirales, Bacillariohyta)의 형태적 특징과 분자계통학적 위치

Abstract

Morphology of a strain of unspecified Skeletonema species established from Korean coast was examined by light, fluorescence and scanning electron microscopy, and SSU (small subunit) and LSU (large subunit) rDNA of the strain were also sequenced. The specimen was characterized by solitary or short chains, and each cell contained 1-2 chloroplasts. The valve face was slightly convex, and the terminal fultoportula processes (TFPPs) were open and showed narrow distal ends that could be truncated or spiny with claw-like protrusions. The basal part of the TFPPs was tubular and oblique to the cell axis. The intercalary fultoportula processes (IFPPs) were also narrow, completely open, and joined in a 1 : 1 junction. Occasionally, one IFPP was connected with two opposing IFPPs. The morphological features of the specimen were identical to those of Skeletonema pseudocostatum. Molecular phylogeny based on SSU rDNA revealed that the Korean strain is nested within a clade comprising S. pseudocostatum and S. tropicum. However, based on D1-D2 LSU rDNA sequences, a clade including S. pseudocostatum and a Korean strain was separated from the S. tropicum clade. This indicates that the Korean strain can be identified as S. pseudocostatum. This species represents the first record from Korean coastal waters.