The paper presents a dichotomous key and a comparative table summarizing dimension data and diagnostic characteristics of seventeen Thalassiosira species (diatoms) commonly found in Lagoa dos Patos estuary and the coastal adjacent area (~32° S and 52° W). For all studied species, optic microscope illustrations and comments on significant morphological features are provided, together with scanning electron microscopy images.
phytoplankton; taxonomy; ultra-structure