Bennettella ceticola (Nelson ex Bennett) Holmes on the skin of Franciscana dolphin (Pontoporia blainvillei) of the Argentinean Sea: an emendation of the generic description

Abstract

The presence of epizoic diatoms on the skin of a variety of large marine vertebrates, such as whales and dolphins, has been often reported in the scientific literature. The first observations of an algal growth over on the skin of cetaceans were probably made around 1920. Later studies showed the presence of a new species, Cocconeis ceticola, on skin samples. Morphological features of this species led to the transference of C. ceticola, together with related forms, to the new genus Bennettella Holmes.

Here, we report the occurrence of a diatom film of Bennettella ceticola on the skin of the Franciscana dolphin (Pontoporia blainvillei), obtained from bycatch in fishermen’s gillnets at Samborombon Bay, Argentina, in April 2005. For comparison the holotype of B. ceticola, deposited in the Natural History Museum (London, U.K.) dated 1920 and labelled as Cocconeis ceticola was examined. Detailed analysis of the fine structure of B. ceticola shows that it mostly matches the original description. However, the external raphe ending is not bifurcated (as originally described), and has only one simple, parallel sided slit and polar fissures hidden by a triangular flange. The triangular flange is the main diagnostic feature distinguishing Bennettella from Epipellis Holmes and Cocconeis Ehrenberg, allowing us to propose an emended description of Bennettella. The taxonomic affinities of B. ceticola with related genera, such as Cocconeis and Epipellis, are discussed. The present study constitutes the first report of B. ceticola as an epizoic diatom of a cetacean species in waters of the Argentinean Sea.

Keywords:

• marine epizoic diatoms
• cetaceans
• Bennettella
• taxonomy
• Southwestern Atlantic Ocean

Acknowledgements

We thank Drs L. Hector, J. P. Kociolek, G. Campana and L. Mauco, for providing pertinent bibliographic references and data with this work. We extend our gratitude to Dra. N. Maidana, for her valuable help on Laboratorio de Diatomeas Continentales, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires – CONICET. Laboratorio de Limnología de la Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina. Also our thankfulness to the local artisanal fishermen from Samborombon Bay whose cooperation made this research possible, to P. Sarmiento for her technical assistance with SEM work in the Service of the Museum of the La Plata, Argentina, and to Dr. H. Isbert Perlender for his help with the map. Oscar E. Romero was supported by the German Science Foundation. Mr Edgley Cesar (Curator, Diatoms, Natural History Museum, London, U.K.) is acknowledged for the loan of the type material.

Disclosure statement

No potential conflict of interest was reported by the authors.