Ultrastructure of four Surirella taxa (Bacillariophyceae) from Qinghai Province, northwest China, with reference to the characteristics of portulae

During our investigations on the freshwater diatoms from Qinghai Province, China, four sympatric Surirella taxa belonging to the group Pinnatae were analysed. Based on morphological observations derived from light and scanning electron microscopy, three of these four taxa were identified as: S. minuta, S. lacrimula, and S. brebissonii var. kuetzingii. The fourth taxon is described as Surirella liubingii sp. nov., a new species with a unique combination of characteristics. These include the distribution pattern of its costa-stria bundles (CSBs) alternating with its over-fibula costae (OFCs), which is formed by the distinctly elevated CSBs on the valve face, mostly composed of three costae, and OFCs with a remarkedly lower position. Other characteristics include the presence of robust fibulae extending to the valve midline, the presence of only one portula between two adjacent fibulae, and a pseudoseptum extending internally from the valve margin. From the observations on these four Surirella taxa, we described and discussed two types of fibula (one in which the fibula nearly reaches the valve midline and one with short fibula) and two types of portula morphology (one with only one portula between two adjacent fibulae and the other with 2-4 portulae between two adjacent fibulae).

Automated summary

During investigations on freshwater diatoms in Qinghai Province, China, four Surirella species were studied. Three of these species were identified as S. minuta, S. lacrimula, and S. brebissonii var. kuetzingii based on morphological observations using light and scanning electron microscopy. A new species, Surirella liubingii sp. nov., was also described, characterized by its unique distribution pattern of costa-stria bundles and over-fibula costae, the presence of robust fibulae and a pseudoseptum internally, and the presence of only one portula between two adjacent fibulae.