Two new species of Cymbella (Bacillariophyceae) from China, with comments on their valve dimensions

Abstract

Two new species of Cymbella, Cymbella stigmacentralis sp. nov. and C. compactiformis sp. nov., are described. Both C. stigmacentralis and C. compactiformis have a wide size range, with distinctive valve outlines that change markedly from the largest to the smallest. They also occasionally show one or two stigmoid-like pores on their dorsal (secondary) side. Cymbella stigmacentralis and C. compactiformis share features of the apical pore field: a complete area which is not divided by the distal raphe fissure; round foramina arranged in parallel; each pervalvar row of foramina covered internally by an undulate flap-like silica strip. Based on the characteristics of these two new species that lack a constant valve outline, and their fine morphological structures, it is worth studying species of Cymbella more intensively.

Keywords:

• apical pore field
• stigmoid
• taxonomy
• ultrastructure
• Wuling Mountains

Acknowledgments

The authors are grateful to Dr Xin Yang of Huaihua University for help with SEM operation and photography, to two anonymous reviewers and the editor for their careful comments and revisions, to Xiaoyan Jiang, Jingjing Xu, Yongda Ou and Su Li for assistance in the field.

Disclosure statement

No potential conflict of interest was reported by the author(s).

ORCID

David M. Williams http://orcid.org/0000-0002-0584-307X

Additional information

Funding

This research was supported by the National Natural Science Foundation of China [grant number 31760051], Natural Science Foundation of Hunan Province [grant number 2018JJ2311].