Abstract
Ectorea stella Marquardt et C.E.Wetzel, gen. et sp. nov., a cruciform 'araphid' diatom is proposed from Quaternary deposits of the Colônia basin, Southeast Brazil, based on light and scanning electron microscopy observations. Type material of the morphologically most similar species Fragilaria inflatissima Hustedt was also examined and a new combination for the taxon is proposed as well. The new genus diagnostic features include valves strongly inflated transapically, presence of a wide hyaline sternum bordered by spines, inconspicuous striae composed of rounded areolae without volae or rotae and restricted to mantle or to the marginal valve face area, girdle composed of at least one open, narrow, non-perforated band, and the non-fimbriated valvocopula. We further call attention to the lack of structures that are usually observed in araphid diatom representatives, such as the apical pore fields, rimoportula, and mantle silica plaques along the valve mantle edge. Differentiation between species includes valve dimensions and morphology. Furthermore, Ectorea stella sp. nov. has valve face composed of a flat sternum with short marginal striae, opposite to the rough non striated sternum of Ectorea inflatissima, comb. nov. Regarding ecology, the new genus occurs in acidic oligotrophic environments. While E. inflatissima occurred in large oligotrophic rivers from the Amazon basin, the new species E. stella occurrence suggests a peat bog formation round the lake, and may indicate an increased lake productivity, probably in response to the peatland development in the catchment area.