A new freshwater diatom genus Trialacinia gen. nov. (Naviculaceae: Bacillariophyta) from Guangxi Autonomous Region, China

A new genus and species of freshwater diatoms from the Guangxi Autonomous region of southern China were studied with light and scanning electron microscopy. The newly proposed genus has several features that assign it to the Naviculaceae, including symmetry about the apical, transapical and pervalvar axis, slit-like areolae that are occluded internally by fine hymenes, hook-like external distal raphe ends and the presence of an internal auxillary rib bordering the raphe sternum. These features also suggest a strong morphological similarity with the genus Navicula. The new genus and species, however, have several external flaps of silica on the valve face and apex that give the raphe a bifurcate appearance, a feature not found in any Navicula species and more reminiscent of the genus Neidium. Also present is a hooded structure on the auxillary rib that covers the central nodule and expanded central area on both sides of the raphe, on one side resembling a forked expanded fascia. These features of the exterior and interior of the valve are not seen in other Navicula species, or in other genera within the family. The proposed new genus and species, Trialacinia guangxiana joins other diatom genera and species being endemic from the Guangxi Autonomous region of China.