Fryxell, G.A.2010-02-152010-02-151975http://hdl.handle.net/1969.3/23975189 p., DissertationCultures of marine phytoplankton have increasing value in morphological and taxonomic studies. Fifteen species of Thalassiosira have been studied from culture and field samples in both light and scanning electron microscopes, revealing consistent patterns that may be in identification and taxonomic placement. Process patterns are considered good diagnostic characters, especially the patterns of strutted and labiate processes. The position of the strutted process inside or outside radial rows of areolae on the face of the valve is suggested to be of potential taxonomic value. The presence of spines is noted on a few species. The newly observed occluded process is found on three of the species discussed in detail: T. lundiana, T. tubifera, and T. australis. Distributional data are considered in placing the diatoms in ecological categories. Suggested taxonomic grouping within the genus are based on the nature and placement of processes and patterns of areolae. Species discussed include: T. oestrupii, T. symmetrica, T. punctifera, T. elsayedii, T. eccentrica, T. lundiana, T. tubifera, T. rotula, T. fluviatilis, T. gracilis, T. tumida, T. australis, and T. gravida.diatomsphytoplanktonalgaeThalassiosira sp.plant morphologytaxonomyecological distributionbiological speciationBook