Shionodiscus karianus sp. nov. (Thalassiosirales, Thalassiosiraceae), a new planktonic diatom from the Kara Sea and notes on some morphological characters of Shionodiscus taxa

Abstract

The genus Shionodiscus (Thalassiosirales, Thalassiosiraceae) includes species that have strutted processes with long inward but reduced outward extensions, a labiate process typically located on the valve face, distant from the margin. Shionodiscus species inhabit the marine environment, and the genus includes both living and fossil species. In the course of our study of plankton samples from the Kara Sea, we found specimens belonging to Shionodiscus. Based on LM, SEM, and TEM investigations, a new species, Shionodiscus karianus sp. nov., is described. This species is distinguished from others in the genus based on areola densities, as well as the fine structure and location of the rimoportula and the central fultoportula and the ultrastructure of the areolae and cingulum. In this paper, we provide a morphological description of this taxon as well as a comparison with similar taxa. Previous records of Shionodiscus species in the Russian Arctic seas are discussed. Finally, we summarize and evaluate information on the important morphological characters, such as rimoportula position and fultoportula structure, for Shionodiscus.

Keywords:

• Shionodiscus
• Thalassiosirales
• diatoms
• morphology
• taxonomy
• Arctic seas
• Russia

Acknowledgments

The work of A.A. Georgiev and M.A. Gololobova was carried out as part of the Scientific Project of the State Order of the Government of Russian Federation to Lomonosov Moscow State University (No. 121032300080-0). SEM studies were carried out at the Shared Research Facility ‘Electron microscopy in life sciences’ at Moscow State University (Unique Equipment ‘Three-dimensional electron microscopy and spectroscopy’). TEM studies were carried out at Electron microscopy laboratory of Moscow State University Biology Faculty. The authors thank the Lomonosov Moscow State University Marine Research Center for the obtain plankton samples. The authors would like to thank Dr Rinat Gogorev (Komarov Botanical Institute, Russia) for sharing information and Dr Russell Shiel (The University of Adelaide, Australia) for linguistic corrections in the earlier draft. We are grateful to two anonymous reviewers for constructive and helpful comments.

Disclosure statement

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

Notes

1 Some Thalassiosira species that show features of Shionodiscus have not yet been formally transferred to the latter.

2 According to Nikolaev & Harwood (2002, p. 11), foramina can be occluded by a thin membrane.

3 We do not include this taxon in Table 1 because we are sure that it was a misidentification.