Psammothidium elnatanianum sp. nov. (Achnanthidiaceae, Bacillariophyta) a new diatom species found in Holocene sediments (Meghalayan Age) of the Xingu River, Eastern Amazon

An unknown species of Psammothidium (Achnanthidiaceae) was found in core sediment (similar to 4000 cal yr BP) collected from Xingu ria, located in eastern Amazon Basin (Brazilian Amazon). The detailed morphology of the new species was examined and described using light (LM) and scanning electron (SEM) microscopy. The new species described here is mainly characterized by small valve dimensions, an irregular and expanded central area in rapheless valve (RLV) clearly visible in LM. Under SEM observations, the new species show slightly radiate striae with rectangular to rounded areolae present both on the surface and the valve mantle. Morphology and ecology of the new species is compared to those already described for the genus. Moreover, information about core chronology and the co-occurrence of other diatom species in the sample are also provided.