Fragilaria shirshovii sp. nov.-A New Species of Araphid Diatoms (Bacillariophyta, Fragilariophyceae) from the Gulf of Ob (Kara Sea, Arctic)

A new species, Fragilaria shirshovii sp. nov., is described on the basis of molecular and morphological investigations. Cells were isolated from the surface levels of desalinated water masses in the zone of mixing river and marine waters in the Gulf of Ob. The morphology of this species is analyzed with light microscopy (LM) and scanning electron microscopy (SEM). The valves of F. shirshovii sp. nov. are fusiform to almost linear. The frustules are linked together in the central part, forming double comb-shaped colonies. The axial area is narrow and linear, with a distinct rounded or rectangular fascia in the center. Ghost striae are present on the central area. Areolae are not discernible in LM. Apical pore fields are composed of small pores and closed papillary outgrowths. The lips of the rimoportula are well pronounced and the striae are uniseriate. Phylogenetic analysis based on partials 18S rRNA and rbcL genes infers the species F. shirshovii sp. nov. as a member of Fragilariaceae. The species most resembling F. shirshovii sp. nov. are F. crotonensis, F. pararumpens, F. bidens and F. perminuta. The differences between F. shirshovii sp. nov. and close taxa are discussed. This work is a pioneer investigation of Fragilariaceae taxa from the freshwater ecosystems of the Siberian Arctic using a combination of morphological and molecular tools.