Abstract
Two new species of Tryblionella are described occurring both in epiphytic and microphytobenthic communities from Patos Lagoon salt marshes, Rio Grande do Sul, southern Brazil. Tryblionella confusa can be misidentified as T. debilis, since the examination under light microscopy provides few characters, besides that, the later species shows a wide amplitude of characters in the literature interfering in the identification. On the other hand, Tryblionella ornata exhibits more distinguishable features in light microscopy observation, which are reinforced by its singular pattern of ornamentation visible under scanning electron microscopy. The species were observed in all sites and periods studied, undergoing a wide range of salinity and pH. No preference of substrate was observed.