Ultrastructure of three species of Surirella (Bacillariophyta) from Lake Qinghai, China, with descriptions of two new species.

Three Surirella species found at the same locality in Lake Qinghai, northwestern China, are studied using light and scanning electron microscope observations. Two species are proposed as new to science and named S. ectorii sp. nov. and S. qinghainensis sp. nov. The third species is identified as S. brightwellii W. Smith. Both S. brightwellii and S. qinghainensis have valves with an ovate outline and a broadly rounded headpole and cuneate footpole, whereas S. ectorii has valves with a nearly elliptical outline and an almost isopolar headpole and footpole. Both S. ectorii and S. qinghainensis produce a marginal row of costae on the wall of the raphe canal, whereas S. brightwellii does not possess this feature. This study provides further insights into the diversity of endemic diatom species inhabiting the ancient Lake Qinghai and illustrates the variability of valve ultrastructure in the genus Surirella.