Ultrastructure of Tryblionella qinghainensis sp. nov., T. apiculata and T. levidensis (Bacillariophyta) from Lake Qinghai (China), with reference to the marginal ridge

Three Tryblionella species found at the same locality in Lake Qinghai, the largest inland saline water lake of China, are studied by using light and scanning electron microscope. One species is proposed as new to science and named Tryblionella qinghainensis sp. nov. The other two species are identified as T. apiculata W. Gregory and T. levidensis W. Smith. Tryblionella qinghainensis sp. nov. is characterized by its linear-lanceolate valve outline, broad axial sternum, a stria density to fibula density ratio of ca. 1.9:1, alveolate striae, and a simple standing lamella-like marginal ridge unperforated. Several ultrastructural details for T. apiculata and T. levidensis are revealed for the first time, especially the ultrastructure of their marginal ridges. The structure and shape of the marginal ridge in these three Tryblionella species are different, and the ultrastructure at the junction between the marginal ridge and the distal mantle can also vary for each individual species. The ultrastructure of the marginal ridge and distal mantle may be used as important diagnostic characters for the species of the genus Tryblionella.