Two new freshwater species of Surirella (Bacillariophyta) from the Wuling Mountains, China

Two sympatric Surirella species found at the same specific locality in the Wuling Mountains of China are documented with light and scanning electron microscope. Both species are new to science and named S.wufluminensis sp. nov. and S.suiningensis sp. nov. Surirellawufluminensis has large frustules that are either clockwise or counterclockwise twisted when viewed with the light microscope, and possesses distinctive fibulae, mound-like outgrowths on the valve surface throughout, raised longitudinal ridges on both sides of the raphe, and two helictoglossa-like processes at one apex internally. Surirellasuiningensis has narrowly ovate valve outline, distinctive fibulae, troughs alternating with crests from pole to pole, and two helictoglossa-like processes at one apex internally. These two species do not produce costae on the valve surface in contrast to many species in Surirella. This study provides a further two examples of the wide range of morphological diversity in the genus Surirella.