Thalassiosirales (Diatomeae) of the Guaraguacu river, littoral basin, Parana State, Brazil

(Thalassiosirales (Diatomeae) of the Guaraguacu river, littoral basin, Parana State, Brazil). The floristic inventory of Thalassiosirales from Guaraguacu river was based on planktonic and periphytic samples collected at six sampling stations throughout the river, considering a salinity gradient. A total of 28 species were identified with 19 included in Thalassiosiraceae family. Among the diatoms recorded, 85,7% were marine/estuarine and 14,3% were continental species. Cyclotella atomus Hustedt, C. choctawhatcheeana Prasad, Thalassiocyclus lucens (Hustedt) Hakansson & Mahood, Thalassiosira minima Gaarder, T. prochkinae Makarova, T. pseudonana Haste & Heimdal, T. tealata Takano, T. tenera Proschkina-Lavrenko and Thalassiosira sp. were the nine new records for the State of the Parana. Identification keys, taxonomic descriptions, measurements, MO and MEV illustrations complement the study.