Revision of Amphorotia curvata Williams & Reid (Bacillariophyta) from the Pearl River delta, China

The genus Amphorotia Williams & Reid (2006) was established to accommodate a group of diatoms formerly allocated to Eunotia Ehrenberg. The new genus was shown to display a distinct biogeographical distribution. To increase the knowledge of this genus, especially in China, a taxonomic investigation of Amphorotia in the Pearl River delta area was undertaken using borehole materials. This paper reports and describes specimens of an uncommon species of Amphorotia extracted from sediment samples using a special concentration technique. Morphological data derived from both light (LM) and scanning electron microscopy (SEM) are used to characterise the specimens. Based on these observations, an emended description of a species formerly reported from the same region, Amphorotia curvata Williams & Reid, is provided and its neotype is established. The new Pearl River specimens are all attributed to A. curvata and this species is compared to other Amphorotia species from China, Southeast Asia and Lake Baikal. It is similar to the Siberian taxon Amphorotia lacusbaikali (Skvortzov) Williams & Reid when observed with LM, but can be distinguished by ultrastructural details (SEM). Amphorotia is clearly monophyletic and the new features of A. curvata are used to suggest links with Amphorotia species from East Asian regions.