Two new Staurosirella species (Staurosiraceae, Bacillariophyta) observed in an historic Rabenhorst sample

Abstract

During a survey of some exsiccata samples from Rabenhorst’s Die Algen Sachen’s und Europa’s, two Staurosirella taxa that could not be identified using the currently available literature were observed in a sample from the Swiss Alps, collected in 1863 CE. The two taxa occurred together with a large population of S. neopinnata and were studied using detailed light and scanning electron microscopy. Based on the obtained observations on their morphology, and after comparing both taxa with all currently known Staurosirella and some Staurosira species, both are described as new. Staurosirella coutelasiana Van de Vijver sp. nov. is characterized in having a linear-lanceolate to lanceolate, isopolar valve outline with small apical pore fields on both apices. The second new species, S. minutissima Van de Vijver sp. nov., is a small-celled Staurosirella species and possesses short lineolae, an almost flat valve surface and small apical pore fields. Both species are extensively illustrated and discussed. Their ecological preferences are derived from the associated diatom flora in the sample and point to oligotrophic, calcium-carbonate rich, oligosaprobic conditions.