Skeletonema is a common and word-wide distributed diatom genus and is a very common red-tide organism in coastal waters.However, morphological identification of Skeletonema species is usually difficult and Skeletonema has been considered as a cryptic diatom genus that many studies have to use the commonly used name S.costatum when a correct identification of this cryptic taxon is impossible.Recent studies have showed the high species diversity of Skeletonema.But the species diversity of Skeletonema in China seas keeps poorly known.Correct identification of Skeletonema species will facilitate the further studies on this important diatom genus.