Two new periphytic Eunotia species from the neotropical Amazonian ‘black waters’, with a type analysis of E. braunii

Abstract

Two new diatom species, Eunotia emedii and Eunotia kayaporum, are described from the Negro River hydrographical basin (Amazon), Brazil. Both species were found growing on submerged leaves in a ‘black water’ affluent characterized by low nutrient concentrations, absence of suspended matter, low pH and high concentrations of humic compounds. Eunotia emedii is similar to E. punctastriata concerning the apparent absence of striae on the valve surface and similar to E. winsboroughae in valve outlines and dimensions, although both species clearly differ by their ultrastructure. Eunotia kayaporum is a typical eunotioid form with bi-undulated dorsal margins; however, a unique character is the angled, non-smoothened inflation at the dorsal valve side, with the deeper central concavity readily observed with light microscopy almost forming a ‘V’. The morphologically most similar species is E. braunii originally described from the Amazon whose type material is here compared using scanning electron microscopy. Eunotia kayaporum is mainly distinguished by its more acute and deeper central concavity and narrowly produced apices. The three discussed species completely lack the rimoportulae structure.

Keywords:

• Negro River
• Eunotia
• South America
• Brazil

Acknowledgements

Financial support for this work was provided by FINEP (Financiadora de Estudos e Projetos, Ministério da Ciência e Tecnologia, Governo Federal, Brazil), FAPESP- ‘Fundação de Amparo à Pesquisa do Estado de São Paulo’ for PhD grant (Process n° 07/51360-6) to CEW and CNPq, Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grant 305072/2009-9 to DCB). We would like to thank Eduardo A. Lobo (Universidade de Santa Cruz do Sul) and José A. Gomes (Instituto Nacional de Pesquisas da Amazônia) for the opportunity to participate in the ‘Pixúna’ Expedition across the Negro River hydrographical basin. We are grateful to Friedel Hinz (Hustedt Collection, Alfred-Wegener-Institut, Bremerhaven, Germany) for providing F. Hustedt type material. CEW also thanks the Centre de Recherche Public - Gabriel Lippmann (Belvaux, Luxembourg) for support. We thank Karen Serieyssol for kindly revising the manuscript.