The biogeography and morphological variability of Gomphonema and Gomphosphenia species are still poorly known in Brazil. Due to the secretion of mucilage by the apical pore fields, Gomphonema is a common genus in periphytic algal communities, being well represented in richness and density. Studied samples were removed from Potamogeton polygonus Chamess. & Schltdl. and Egeria densa Planch. gathered in Maurício river, Fazenda Rio Grande, Paraná State. Twenty taxa were identified. Eleven species of Gomphonema and the genus Gomphosphenia were first recorded in the state of Paraná. In addition, the results of ultrastructural observations were presented. Variability in valve outline and ultrastructural details warrant further attempts to clarify the taxonomy of closely related species, such as: G. gracile and Gomphonema sp.5, G. contraturris and G. salae, G. capitatum and G. laticollum.
diatoms; taxonomy; ultrastructure; lotic system