Shionodiscus gaarderae sp. nov. (Thalassiosirales, Thalassiosiraceae), a bloom-producing diatom from the southwestern Atlantic Ocean, and emendation of Shionodiscus bioculatus var. bioculatus

Abstract

The recently established diatom genus Shionodiscus is characterized as possessing a labiate process on the valve face and strutted processes with long internal and reduced, or no, external extensions. Many Thalassiosira species with these features were transferred to this new genus, as well as some with short internal, strutted process extensions. Examination of samples from the Argentine continental shelf and slope waters, and from the Beagle Channel, revealed the presence of a small centric diatom that formed an extensive bloom in slope waters during spring 2005 and 2006. Analysis by light and electron microscopy revealed high similarity to specimens previously referred as Thalassiosira bioculata var. raripora. This name was never effectively published; nevertheless, the name has been adopted and observations referring to it have been reported on several occasions. Here we trace the usage of the (nomenclaturally invalid) name Thalassiosira bioculata var. raripora in the literature, and formally describe the species as Shionodiscus gaarderae, based on our observations and comparison with previous reports. A morphological comparison of this and similar taxa is also provided. In addition, we offer an emended description of S. bioculatus var. bioculatus from Ostenfeld material sampled from the ‘Färöer Island Naströ Fjord Plankton (16.9.1902)’, held in the Hustedt collection. Finally, we propose the transfer of Thalassiosira rosulata to Shionodiscus.

Keywords:

• Thalassiosira bioculata
• Thalassiosira bioculata var. raripora
• Shionodiscus rosulatus
• spring bloom
• Argentine Sea

Acknowledgements

We would like to express our gratitude towards Dr G. Hasle for confirming the new species S. gaarderae and for providing some of her own micrographs of this species (Figs 5, 9 in this paper). We also acknowledge: Drs G. Fryxell and A. Prasad who always generously enriched us with their positive suggestions and kindly responded to our questions; Friedel Hinz for her valuable support with the Hustedt Collection (AWI, Bremerhaven, Germany); Dr A. Alverson for clarify some questions about the genus Shionodiscus and Dr A. Piola for his useful oceanographic comments. Also, Patricia Sarmiento provided technical assistance with SEM work in the Service of the Museo de La Plata, Argentina. We extend our gratitude to the crew of the ‘ARA Puerto Deseado’ (GEF–1, 3 cruises). Three anonymous reviewers are acknowledged for their helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Bánk Beszteri http://orcid.org/0000-0002-6852-1588

Additional information

Funding

The financial support was provided by CONICET [grant number GEF-PNUD ARG 02/18], [grant number PIP 01734], and project UCAR-UNLP in the Beagle Channel.