Colonial planktonic Eunotia (Bacillariophyceae) from Brazilian Amazon: Taxonomy and biogeographical considerations on the E. asterionelloides species complex

Abstract

Colonial planktonic diatoms representative of the genus Eunotia Ehrenberg are common in phytoplankton assemblages from oligotrophic pristine rivers and streams in the Amazon hydrographical basin. A taxonomic account on E. asterionelloides and related species revealed the presence of four unknown taxa, which are formally described here. E. loboi sp. nov., E. gomesii sp. nov., E. tukanorum sp. nov., and E. waimiriorum sp. nov. differ from all described Eunotia species by their typical colonial life strategy, cell dimensions, striae density, short raphe, overall shape and ultrastructural features. E. tukanorum is the most common species found in the Negro River while E. loboi, E. gomesii and E. waimiriorum are representative of the Branco River, a tributary of the Negro River, which has marked different limnological features. In the light microscope, all South American species closely resemble E. zasuminensis, originally described from Europe (Poland) and commonly reported from the Northern hemisphere. E. asterionelloides was originally described from the Tapajos River in the lower Amazon and to date has not been found in the Negro nor Branco rivers. Given the small differences between these colonial planktonic forms, the global diversity of this species complex has almost certainly been underestimated.