TREMARIN, P.I., FREIRE, E.G., ALGARTE, V.M., LUDWIG, T. Acanthoceras and Urosolenia species (Diatomeae) in subtropical reservoirs from South Brazil: Ultrastructure, distribution and autoecology.http://dx
A new planktonic species of Urosolenia is described from Southern Brazilian reservoirs. Urosolenia obesa sp. nov. was found in several studied samples and the unique set of features led us to propose it as new and to compare their morphology with similar species found in the literature, as Rhizosolenia naui, R. eriensis var. pusilla and Urosolenia parva. Urosolenia obesa differs from the other species mainly by sub-cylindrical frustules, conical valves, calyptra straight, positioned in right to oblique angle in relation to pervalvar axis, ornamented by longitudinal ribs and ending in two teeth and one ligula. Probably, the new species has a wider geographic distribution, since the small size and slightly silicified frustules make it difficult to visualize them by light microscopy analysis of samples.
The species originally described from brackish waters of the Venetian Lagoon as Nitzschia persuadens is a diatom rarely cited in the literature since its proposition and it is here recorded for the first time in a freshwater environment in South America. Morphological features of this species, such valve slightly panduriform, with a longitudinal straight fold of the valve face, poroidal areolae, and strongly eccentric raphe system clearly assign this species to Tryblionella, and the transfer was made. Here we present new observations on the frustule morphology and comparisons with related species. Light and scanning electron microscopy data of Tryblionella persuadens comb. nov. from Cachoeira River, Northeastern Brazil are documented.
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