A new Brachysira species from mountain lakes in northern Italy and Corsica

Abstract

A faintly heteropolar Brachysira species, with an acutely rounded headpole and a base pole which is sometimes slightly protracted, found in two lakes in northern Italy and Corsica, is described and named Brachysira chiaruccii sp. nov. This proposed new species can be differentiated from similar species by recognizable characters or character combinations: valve outline and symmetry, shape of the apices and of the central area, striation density, size, anchor-shaped terminal raphe endings (SEM feature), ecology. Brachysira chiaruccii sp. nov. is so far known to colonize oligotrophic, circumneutral, sufficiently buffered, moderately low conductivity mountain lakes, whilst the typical habitat of the most similar (North American) heteropolar Brachysira species (B. ocalanensis) is dystrophic, very low alkalinity and pH environments. The description is based on SEM and LM micrographs which document the full spectrum of shape variability along the size diminution series (including girdle views), plastid arrangement and morphology, and ecological preferences, in particular along the pH-alkalinity gradient.

Keywords:

• new species
• Brachysira
• Brachysira chiaruccii
• mountain lakes
• Lombardy
• Corsica
• reference sites
• biodiversity
• pH-alkalinity gradient

Acknowledgements

MUSE – Museo delle Scienze (Trento) for making available its facilities (SEM etc.) to study the new Brachysira species. Center for Electronic Microscopy (ARPA Lombardia – Settore Laboratori – U.O. Laboratorio di Milano) for its support in taking SEM images of the new species from L. Ganna. The survey in L. Ninu was funded within the programme ‘For the sustainable management of mountain lakes in Corsica’. We are grateful to the Environment Office of Corsica (OEC), particularly divers, for sampling L. Ninu. We thank Eurofins Hydrobiologie France (Maxéville, France) for the possibility to analyze in detail this species. We thank Edgley Cesar (NHM London) and Nélida Abarca (BGBM Berlin) for kind assistance during the deposition of the isotype slides in the diatom collections of the mentioned institutions, and Wolf-Henning Kusber for the Phycobank registration. We thank Diatom Research EiC Eileen Cox and an anonymous Reviewer for important observations that allowed us to substantially improve the new species description.

Disclosure statement

No potential conflict of interest was reported by the author(s).