Ultrastructure and distribution of Urosolenia obesa sp. nov. (Rhizosoleniaceae, Diatomeae) in reservoirs from southern Brazil

Abstract

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.