Observations and typification of diatoms of the order Rhopalodiales (Bacillariophyta) in the Josef Pantocsek collection, Hungarian Natural History Museum. I. Epithemia species from Élesd

As part of revisionary studies of the diatom order Rhopalodiales, in this work, we are initiating a review of the species described by Josef Pantocsek, including the typification of his species. Pantocsek presented 5 new genera and over 280 species of diatoms, 2 of the genus Epithemia, from a locality listed as Élesd, now part of Romania. We present the first light and scanning electron micrographs of Epithemia bihariensis Pantocsek and designate a lectotype for this species. By virtue of its highly biarcuate raphe system that almost reaches the dorsal margin at the centre of the valve, Epithemia bihariensis is assigned to the E. sorex group. Its ecology, as a marine species, and some ultrastructural features, such as segment-like frustules and the raphe contained in a narrow keel, suggest the retention of some ancestral features in the Rhopalodiales. A second species presented by Pantocsek, E. costata, is shown to be a superfluous name, as is the name E. pantocsekites Van Landingham. The Miocene epoch, which is the earliest period for which we currently have verified specimens of the Rhopalodiales, was apparently a time of morphological diversification of this taxon.