Karthickia verestigmata gen. et sp. nov. - an interesting diatom with frustular morphology similar to several different cymbelloid diatom genera

Light and scanning electron microscope observations are presented for Karthickia verestigmata gen. et sp. nov. The taxon is described from Laos and Vietnam. This diatom has features that would suggest similarities with Cymbopleura, Cymbella and Oricymba. The new taxon is characterised by the presence of a single external stigma opening that has two elongated slit-like openings internally, residing within two longer central striae. These slit-like furrows occupied one-third of stria length near the central area. The presence of a stigma suggests a relationship of this species with genera such as like Cymbella and Oricymba, and the single external opening with two internal openings is similar to that in Oricymba. Internally, areolae are covered by tectulla that are not typical for Cymbopleura but known in species of Cymbella as well as Gomphonema. The morphological features of this unique taxon lead us to conclude that it is best accommodated in a new genus.