New and interesting diatoms from Tibet. II. Description of two new species of monoraphid diatoms

Light (LM) and scanning electron microscopy (SEM) observations were used to describe two new species of the freshwater monoraphid genus Crenotia Wojtal. Both species, Crenotia distincta, sp. nov. and Crenotia oblonga, sp. nov. have a unique stria structure, bi- to multiseriate terminating near the axial area. Internally, these terminal areolae have C-shaped openings that are occluded by a tapering flap, a feature unique to Crenotia species in China. The two species are easily distinguished from each other and from other members of the genus in both LM (size and valve outline) and SEM stria structure. The bi- to multiseriate nature of the striae suggests an affinity of this genus with Planothidium, but further phylogenetic analyses are required before the phylogenetic position of this genus is settled. Verified records of Crenotia are currently known from Europe and Asia, although species included in the genus by Wojtal have also been reported from North Africa and North America. The genus was originally described from springs but seems to have a wider ecological distribution.