Abstract
Sand samples collected from three freshwater and brackish sandy beaches in Southern Brazil have revealed the presence of a new hyaline araphid diatom belonging to a new genus. The new genus, Rimoneis M.Garcia, is characterized by the presence of two slits at each apex, a wide sternum, small areolae occluded by hymenes, striae with internal openings in a cavity, valve edge with simple spines or a ridge, the absence of rimoportulae, and plain open bands. Two species belong to the new genus : the type species Rimoneis M.Garcia sp. nov. from Southern Brazil and Rimoneis densestriata (Hust.) M.Garcia comb. nov. from Java (Asia). Rimoneis is ecologically and morphologically different from the marine hyaline diatoms Pravifusus, Hyaloneis (both without areolae), Synedropsis and from freshwater fragilarioid genera such as Pseudostaurosira, Pseudostaurosiropsis and Synedrella (distinct in colony formation, areolae occluded by volae and simple striae with internal openings).
