Notes on the genus Nupela (Bacillariophyceae) including the description of a new species, Nupela scissura sp nov and an expanded description of Nupela paludigena

Two species of the diatom genus Nupela are reported from freshwater lakes situated along the Atlantic Coastal Plain of North Carolina, USA. One of the species, N. scissura sp. nov., is described as new and the description of the other, Nupela paludigena (Scherer) Lange-Bertalot, is expanded to include a full suite of ultrastructural characters. Nupela scissura is a heterovalvar taxon with one valve having a fully developed raphe identical in structure to those found on other Nupela species. The other valve lacks a true raphe, but presents one to several elongated slits in the apical portion of the sternum. The true identity of the slits, whether they represent a highly reduced raphe, a rudimentary raphe, or neither is unknown. In addition, both valves of a single N. scissura frustule differ in the structure of the axial and central areas. The structure of the areolae and details of the raphe clearly place this species in Nupela. Nupela paludigena (Scherer) Lange-Bertalot was originally described in the genus Anomoeoneis from acidic and humic localities from the south-eastern part of the Atlantic Coastal Plain and later transferred to Nupela. Although this species has rarely been reported since its description, our findings indicate that it is a common component of the floras in the Carolina bays of North Carolina. The characteristics currently used to circumscribe taxa within the genus Nupela are discussed in light of published work and our own observations.