Study of the type material of two Platessa Lange-Bertalot species (formerly Cocconeis brevicostata Hust. and Cocconeis cataractarum Hust. (Bacillariophyta)

Abstract

After their original description in the late 1930s by F. Hustedt, Cocconeis brevicostata Hust. and Cocconeis cataractarum Hust. have rarely been cited and illustrated. In the early 2000s, both taxa were transferred to Platessa Lange-Bertalot. At the time, no study of the type material was presented. In order to clarify the ultrastructure of these two taxa and their correct assignment to Platessa, their type material held at the Hustedt Diatom Study Centre (Alfred-Wegener-Institute, Bremerhaven, Germany) was studied under light and electron microscopy. Observations on the frustule morphology and morphometric data for each taxon are provided. Frustule features of Platessa brevicostata (Hust.) Lange-Bertalot and Platessa cataractarum (Hust.) Lange-Bertalot (type material) match those of Platessa and their transfer was correct. The following frustule features distinguish between the two taxa: valve outline, raphe structure, stria type and density, and the presence of tiny marginal areolae (poroids).

Keywords:

• benthic diatoms
• Cocconeis
• Hustedt
• Platessa
• taxonomy
• type material

Acknowledgements

Friedel Hinz and Sarah Olischläger (Hustedt Diatom Study Centre, Alfred-Wegener-Institute, Bremerhaven, Germany) are acknowledged for their assistance with the use of light and electron microscopes, and their help with the search for material and literature. Two anonymous reviewers are acknowledged for their thorough reviews. I thank Diatom Research Associate Editor. Mark Edlund, and Editor in Chief, Eileen J. Cox. for their editorial help. Partial financial support from the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author.