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Abstract
Ultrastructural observations of one previously misidentified freshwater species of a Cocconeis (Bacillariophyceae) from the Crozet Archipelago, Indian Sector of the Southern Ocean, are presented. Cocconeis crozetensis sp. nov. possesses small valves (apical axis: 10–13 μm; transapical axis: 6.7–8.4 μm). The main frustule features that distinguish the proposed new species are: (1) the sternum valve (SV) areolae with an external vola and the internal vela, (2) the submarginal area of the raphe-sternum valve, and (3) the morphology of valvocopula and fimbriae of the SV. Possible morphological relationships with several other small Cocconeis, such as C. neodiminuta, C. neothumensis, C. placentula var. pseudolineata and C. pseudothumensis, as well as its morphological similarities with placentuloid Cocconeis are discussed. Reliable identification of C. crozetensis sp. nov. under light microscopy can prove difficult for less-experienced diatomologists and ecologists, and the use of electron microscopy proves to be unavoidable for its correct identification.
Acknowledgements
This survey was made possible with the logistic and financial support of the Institut Polaire Français – Paul-Emile Victor (IPEV) in the frame of the Terrestrial Ecology program 136 (Yves Frenot & Marc Lebouvier). O.E.R. was supported by the Spanish Research Council (CSIC) and the European Union Program Synthesis of Systematics Resources (synthesys). Additional funding for B.V.V. was provided by the Science Foundation (Flanders, Belgium). Pierre Compère corrected the Latin diagnosis. Mr. Sven Bellanger prepared Fig. 1. C. Riaux-Gobin and one anonymous reviewer are greatly acknowledged for their contributions in correcting and improving this work.