MORPHOLOGICAL STUDIES OF THALASSIOSIRA SPECIES WITH LINEAR AREOLA ARRAY FROM CHINA'S COASTAL WATERS

Morphology and pattern of areola on the valve are key taxonomic characteristics for Thalassiosira species. Linear areola array only occurred in a few Thalassiosira taxa and most of these species are transferred from the genus Coscinodiscus after a large number of marginal fultoportulae were observed under electron microscopy. These species are very similar under light microscopy thus electron microscopy is strongly recommended for accurate identification. Previous reports about Thalassiosira species with linear areola array from China's coast were rare, and almost no EM photos are available. In order to characterize the species diversity and distribution of the genus Thalassiosira along Chinese coastal waters, water samples have been collected from some locations. Thalassiosira specimens within these samples, as well as several clonal strains isolated from natural samples, were studied by electron microscopy. Six Thalassiosira species with linear areola array were observed and they were T. densannula Hasle & Fryxell, T. exigua Fryxell & Hasle, T. lineata Jous? T. nanolineata (Mann) Fryxell & Hasle, T. nodulolineata (Hendey) Hasle & Fryxell and T. tenera Proschkina-Lavrenko. Four of them were newly recorded species for China, T. densannula, T. lineata, T. nanolineata and T. nodulolineata. The detailed morphological description, habits and ecological distribution of these species were given in this paper. Simultaneously, the taxonomic comparison among resembling species were made. The variations of areola, including their morphology and pattern, were discussed and their taxonomic significance should be re-analyzed in conjunction with the usage of other modern techniques.