Paralia kawasumii sp. nov., a new fossil Paralia species with an elliptical valve from upper Holocene coastal sediments of the central Ise Plain, central Japan

Abstract

A new fossil diatom species, Paralia kawasumii Sato sp. nov., has been found in upper Holocene coastal sediments of the central Ise Plain, central Japan. Detailed examination by light and scanning electron microscopy showed that P. kawasumii is a straight, chain-forming diatom characterized by double heterovalvy and spathulate linking spines. Like P. elliptica Garcia, its valve face is elliptical and undulate, and parallel and anastomosing ridges and grooves are present on sibling valve faces. Both species together comprise the ‘Paralia elliptica group’. However, P. kawasumii is considered a separate species from P. elliptica because of morphological differences in the structure and position of the rimoportulae and in the densities of fenestrae and of slits on the cingulum. Rimoportulae of P. kawasumii are perpendicular to the striae and distributed just below the overhanging mantle edge. Fenestrae and slits on the cingulum of P. kawasumii are more densely distributed than in P. elliptica. Paralia kawasumii is associated with loose sandy bottoms in intertidal areas (tidal flats to shallow outer bay environments). It is possible that P. kawasumii is an extant species, although no living cells have been found in surface sediments in Japan. If this were the case, P. kawasumii would be the fifth extant Paralia species in Japan.

Keywords:

• Paralia
• coastal sediment
• fossil marine diatom
• Holocene
• Japan

Acknowledgements

We are deeply grateful to Dr. Hiroyuki Tanaka of Maebashi Diatom Institute, Dr. Toshikazu Goto of Kindai University, Dr. Yukio Yanagisawa of the Geological Survey of Japan, Advanced Industrial Science and Technology, and Dr. Susumu Konno of Marine Works Japan, Ltd. for constructive advice and comments during taxonomic discussions. We also express our gratitude to Dr. Tatsunori Kawasumi, late of Ritsumeikan University, with the cherished desire for providing us the opportunity to investigate alluvium in the study area and supporting the field survey. We appreciate two anonymous reviewers for constructive comments and suggestions.

Disclosure statement

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

Additional information

Funding

This work was supported by a Grant-in-Aid for Scientific Research C (No. 25370925) and a Grant-in-Aid for Young Scientists B (No. 15K16282) from the Japan Society for the Promotion of Science.