Thalassiosira rotula, a heterotypic synonym of Thalassiosira gravida: morphological evidence

Abstract

Colonies that could be identified as Thalassiosira rotula, others that could be identified as Thalassiosira gravida and colonies with a mixture of the valve structures of these two species were found coexisting in the same samples from Piedras Coloradas (40°50′46″S, 65°06′18″W). Net samples were collected from surface water at several stations in the northern area of San Matías Gulf in the Río Negro Province, Argentina, from April 1998 to May 2000 and from March 2006 to April 2007. Untreated and cleaned diatom samples were examined using light and scanning electron microscopy. The differential features used to distinguish T. rotula and T. gravida were discussed and refuted with morphological evidence. Based on this analysis, both taxa are assumed to be conspecific by sharing fultoportulae pattern and morphology of the cingulum. Thus, the name of the species must be T. gravida by the principle of priority. A revision of the original material of T. gravida from Baffin Bay was carried out with light microscopy. The original figure 14 was designated as lectotype and the slide no. 64 of the Tempère and Peragallo Collection (2nd edition) curated at the Muséum National d'Histoire Naturelle in Paris was designated as epitype.

Keywords:

• Thalassiosira gravida
• Thalassiosira rotula
• lectotype
• epitype
• morphological analysis

Acknowledgements

The authors wish to thank Regine Jahn, Frithjof Sterrenburg, David Mann and Richard Crawford for helpful discussion on nomenclatural issues, Sergei Genkal for assistance with some selected papers by Russian authors, curators and contacts of Diatom Collections of the Swedish Museum of Natural History, Muséum National d'Histoire Naturelle, Alfred Wegener Institute for Polar- and Marine Research, National Botanic Garden of Belgium, Royal Botanic Garden in Edinburgh for searching for type material, and two anonymous reviewers for their valuable comments. We also would like to thank. Cecilia Castaños and Pablo Sacco for helping us with the sampling. The electron microscopy was done in the Servicio de Microscopía Electrónica of the Facultad de Ciencias Naturales y Museo. The research was supported by grants from the CONICET, PIP 5312/06 and from the UNLP 11/N 516.