A new gelatinous colony-forming Thalassiosira minicosmica sp. nov. (Bacillariophyta) from Korean coastal waters and a consideration of the Thalassiosira subtilis group

Abstract

A new, convex-valved Thalassiosira species, T. minicosmica, was observed from Korean coastal waters between 6 May 2009 and 6 March 2014. Thalassiosira minicosmica was characterized by: (1) gelatinous colony formation by mucilage threads extruded from the fultoportulae, (2) eccentric arrangement of the areolae, (3) almost occluded foramina, (4) a short external tube of marginal fultoportulae, and (5) a single rimoportula (with a remarkably long external tube) between marginal fultoportulae. Similar species, such as T. minuscula, T. diporocyclus and T. subtilis, were compared with T. minicosmica, and their several shared characters, such as the convex valve, foramen structure and an externally larger rimoportula than fultoportula, are diagnostic for the Thalassiosira subtilis group, rather than the gelatinous colony-forming feature. Based on the morphological similarities, we recognize the Thalassiosira subtilis group including seven Thalassiosira species.

Keywords:

• colony form
• Korea
• new species
• Thalassiosira minicosmica
• Thalassiosira subtilis

Acknowledgements

We are thankful to Bánk Beszteri and two anonymous reviewers for their constructive comments. We would also like to thank Eileen J. Cox for English editing and constructive comments.

Additional information

Funding

This work was supported by a grant from the National Institute of Biological Resources (NIBR No. 20140441815-00) and by the Ministry of Environment of the Republic of Korea (#416-111-008, Development of biosensor technology using microalgal resources of The Eco-Innovation Project in 2014).